ABSTRACT
A switched-mode power supply (switching-mode power
supply, SMPS, or simply switcher) is an electronic power supply that
incorporates a switching regulator in order to be highly efficient in
the conversion of electrical power. Like other types of power supplies,
an SMPS transfers power from a source like the electrical power grid to
a load (e.g., a personal computer) while converting voltage and
current characteristics. An SMPS is usually employed to efficiently
provide a regulated output voltage, typically at a level different from
the input voltage. Unlike a linear power supply, the pass transistor of a
switching mode supply continually switches between low-dissipation
full-on and full-off states and spends very little time in the high
dissipation transitions (which minimizes wasted energy). Ideally, a
switched-mode power supply dissipates no power. Voltage regulation is
achieved by varying the ratio of on-to-off time. In contrast, a linear
power supply regulates the output voltage by continually dissipating
power in the pass transistor.
This higher power conversion efficiency is an important advantage of a switched-mode power supply. Switched-mode power supplies may also be substantially smaller and lighter than a linear supply. Switching regulators are used as replacements for the linear regulators when higher efficiency, smaller size or lighter weight are required. They are, however, more complicated, their switching currents can cause electrical noise problems if not carefully suppressed, and simple designs may have a poor power factor. 1.INTRODUCTION A linear regulator provides the desired output voltage by dissipating excess power in ohmic losses (e.g., in a resistor or in the collector–emitter region of a pass transistor in its active mode). A linear regulator regulates either output voltage or current by dissipating the excess electric power in the form of ,heat and hence its maximum power efficiency is voltage-out/voltage-in since the volt difference is wasted. In contrast, a switched-mode power supply regulates either output voltage or current by switching ideal storage elements, like inductor and capacitor, into and out of different electrical configurations. Ideal switching elements (e.g., transistors operated outside of their active mode) have no resistance when "closed" and carry no current when "open", and so the converters can theoretically operate with 100% efficiency (i.e., all input power is delivered to the load; no power is wasted as dissipated heat). For example, if a DC source, an inductor, a switch, and the corresponding electrical ground are placed in series and the switch is driven by a square wave the peak-to-peak voltage of the waveform measured across the switch can exceed the input voltage from the DC source. This is because the inductor responds to changes in current by inducing its own voltage to counter the change in current, and this voltage adds to the source voltage while the switch is open. If a diode-and-capacitor combination is placed in parallel to the switch, the peak voltage can be stored in the capacitor, and the capacitor can be used as a DC source with an output voltage greater than the DC voltage driving the circuit. This boost converter acts like a step up transformer for DC signals. A buck boost converter works in a similar manner, but yields an output voltage which is opposite in polarity to the input voltage. Other buck circuits exist to boost the average output current with a reduction of voltage. In an SMPS, the output current flow depends on the input power signal, the storage elements and circuit topologies used, and also on the pattern used (e.g., pulse width modulation with an adjustable duty cycle) to drive the switching elements. Typically, the spectral density of these switching waveforms has energy concentrated at relatively high frequencies. As such, switching transients, like , ripple introduced onto the output waveforms can be filtered with small LC filters. THEORY OF OPERATION Fig 1 Block diagram of a mains operated AC/DC SMPS with output voltage regulation Fig1.1 AC, half-wave and full-wave rectified signal If the SMPS has an AC input, then the first stage is to convert the input to DC. This is called rectification.The rectifier circuit can be configured as a voltage doubler by the addition of a switch operated either manually or automatically. This is a feature of larger supplies to permit operation from nominally 120 V or 240 V supplies. The rectifier produces an unregulated DC voltage which is then sent to a large filter capacitor. The current drawn from the mains supply by this rectifier circuit occurs in short pulses around the AC voltage peaks. These pulses have significant high frequency energy which reduces the power factor. Special control techniques can be employed by the SMPS to force the average input current to follow the sinusoidal shape of the AC input voltage, correcting the power factor. An SMPS with a DC input does not require this stage. An SMPS designed for AC input can often be run from a DC supply (for230 V AC this would be 330 V DC), as the DC passes through the rectifier stage unchanged. It's however advisable to consult the manual before trying this, though most supplies are quite capable of such operation even though nothing is mentioned in the documentation. However, this type of use may be harmful to the rectifier stage as it will only use half of diodes in the rectifier for the full load. This may result in overheating of these components, and cause them to fail prematurely. If an input range switch is used, the rectifier stage is usually configured to operate as voltage doubler when operating on the low voltage (~120 V AC) range and as a straight rectifier when operating on the high voltage (~240 V AC) range. If an input range switch is not used, then a full-wave rectifier is usually used and the downstream inverter stage is simply designed to be flexible enough to accept the wide range of DC voltages that will be produced by the rectifier stage. In higher-power SMPSs, some form of automatic range switching may be used. Inverter stage This section refers to the block marked chopper in the block diagram. The inverter stage converts DC, whether directly from the input or from the rectifier stage described above, to AC by running it through a power oscillator, whose output transformer is very small with few windings at a frequency of tens or hundreds of kilohertzThe frequency is usually chosen to be above 20 kHz, to make it inaudible to humans. The output voltage is optically coupled to the input and thus very tightly controlled. The switching is implemented as a multistage (to achieve high gain) mosfet amplifier. MOSFETs are a type of transistor with a low on- andresistance a high current-handling capacity. Voltage converter and output rectifier If the output is required to be isolated from the input, as is usually the case in mains power supplies, the inverted AC is used to drive the primary winding of a high-frequency transformer. This converts the voltage up or down to the required output level on its secondary winding. The output transformer in the block diagram serves this purpose. If a DC output is required, the AC output from the transformer is rectified. For output voltages above ten volts or so, ordinary silicon diodes are commonly used. For lower voltages, schottky diodes are commonly used as the rectifier elements; they have the advantages of faster recovery times than silicon diodes (allowing low-loss operation at higher frequencies) and a lower voltage drop when conducting. For even lower output voltages, MOSFETs may be used as synchronous rectifiers compared to Schottky diodes, these have even lower conducting state voltage drops. The rectified output is then smoothed by a filter consisting of inductors and capacitors switching frequencies, components with lower capacitance and inductance are needed. Simpler, non-isolated power supplies contain an inductor instead of a transformer. This type includes boost converter , buck converter and the buck boost converter. These belong to the simplest class of single input, single output converters which use one inductor and one active switch. The buck converter reduces the input voltage in direct proportion to the ratio of conductive time to the total switching period, called the duty cycle. For example an ideal buck converter with a 10 V input operating at a 50% duty cycle will produce an average output voltage of 5 V. A feedback control loop is employed to regulate the output voltage by varying the duty cycle to compensate for variations in input voltage. The output voltage of a boost converter is always greater than the input voltage and the buck-boost output voltage is inverted but can be greater than, equal to, or less than the magnitude of its input voltage. There are many variations and extensions to this class of converters but these three form the basis of almost all isolated and non-isolated DC to DC converters. By adding a second inductor the cuk and SEPIC converters can be implemented, or, by adding additional active switches, various bridge converters can be realised. Other types of SMPSs use a capacitor voltage diode Instead of inductors and transformers. These are mostly used for generating high voltages at low currents Cockcroft woltan generator. The low voltage variant is called charge pump. Regulation A feedback circuit monitors the output voltage and compares it with a reference voltage, which shown in the block diagram serves this purpose. Depending on design/safety requirements, the controller may contain an isolation mechanism (such as opto couplers) to isolate it from the DC output. Switching supplies in computers, TVs and VCRs have these opto-couplers to tightly control the output voltage. Open-loop regulators do not have a feedback circuit. Instead, they rely on feeding a constant voltage to the input of the transformer or inductor, and assume that the output will be correct. Regulated designs compensate for the impedence of the transformer or coil. Monopolar designs also compensate for the magnetic hysteresis of the core. The feedback circuit needs power to run before it can generate power, so an additional non-switching power-supply for stand-by is added. Transformer design SMPS transformers run at high frequency. Most of the cost savings (and space savings) in off-line power supplies come from the fact that a high frequency transformer is much smaller than the 50/60 Hz transformers formerly used. There are additional design tradeoffs. The higher the switching frequency, the lower the amount of energy that needs to be stored intermediately during the time of a single switching cycle. Because this energy is stored in form of magnetic energy in the transformer core material (like ferrite), less of such material is needed. However, higher frequency also means more energy lost during transitions of the switching semiconductor. Furthermore, much more attention to the physical layout of the circuit board is required, and the amount of electromagnetic interference will be more pronounced. Core losses increase at higher frequencies. Cores use ferrite material which has a low loss at the high frequencies and high flux densities used. The laminated iron cores of lower-frequency (<400 Hz) transformers would be unacceptably lossy at switching frequencies of a few kilohertz. Copper loss At low frequencies such the line frequency of 50 or 60 Hz), designers can usually ignore the skin effect. For these frequencies, the skin effect is only significant when the conductors are large, more than 0.3 inches (7.6 mm) in diameter. Switching power supplies must pay more attention to the skin effect because it is a source of power loss. At 500 kHz, the skin depth in copper is about 0.003 inches (0.076 mm) – a dimension smaller than the typical wires used in a power supply. The effective resistance of conductors increases, because current concentrates near the surface of the conductor and the inner portion carries less current than at low frequencies. The skin effect is exacerbated by the harmonics present in the high speed pwm switching waveforms. The appropriate skin depth is not just the depth at the fundamental, but also the skin depths at the harmonics. In addition to the skin effect, there is also a proximity effect, which is another source of power loss. Power factor Simple off-line switched mode power supplies incorporate a simple full-wave rectifier connected to a large energy storing capacitor. Such SMPSs draw current from the AC line in short pulses when the mains instantaneous voltage exceeds the voltage across this capacitor. During the remaining portion of the AC cycle the capacitor provides energy to the power supply. As a result, the input current of such basic switched mode power supplies has high harmonic content and relatively low power factor. This creates extra load on utility lines, increases heating of building wiring, the utility transformers, and standard AC electric motors, and may cause stability problems in some applications such as in emergency generator systems or aircraft generators. Harmonics can be removed by filtering, but the filters are expensive.Distortion cannot be corrected by addition of a single linear component. 2.BLOCK DIAGRAM A conventional SMPS must implement PFC if it draws more than 75 watts from the AC Mains. The PFC circuitry draws input current in phase with the input voltage, and theTotal Harmonic Distortion (THD) of the input current should be less than 5% at full load. The PFC provides a fixed DC high-output voltage, which needs to be converted to a lower Direct Current (DC) output voltage and isolated with an input mains supply.Figure 2 shows a high-level block diagram of the SMPS AC/DC Reference Design. .The SMPS AC/DC Reference Design operates on universal input voltage and produces multiple DC output voltages. The front-end PFC Boost circuit converts universal AC input voltage to 420 VDC bus voltage. The Phase-Shift Zero Voltage Transition (ZVT) circuit produces 12 VDC output voltage from a 420 VDC bus. The Phase-Shift ZVT converter also provides output voltage isolation from the input AC mains. The Multi-Phase Synchronous Buck converter produces 3.3 VDC @ 69 Amps from the 12 VDC bus. The Single-Phase Buck converter produces 5 VDC @ 23 Amps from the 12 VDC bus. The following sections in this chapter provide an overview and background of the main power conversion blocks implemented in the SMPS AC/DC Reference Design. FIGURE.2 HIGH-LEVEL SMPS AC/DC REFERENCE DESIGN BLOCK DIAGRAM FIG 3 .DETAILED SMPS AC/DC REFERENCE DESIGN BLOCK DIAGRAM Power Factor Correction (PFC) Most power conversion applications consist of an AC-to-DC conversion stage immediately following the AC source. The DC output obtained after rectification is subsequently used for further stages. Current pulses with high peak amplitude are drawn from a rectified voltage source with sine wave input and capacitive filtering.Regardless of the load connected to the system, the current drawn is discontinuous and of short duration. Because many applications demand a DC voltage source, a rectifier with a capacitive filter is necessary. However, this results in discontinuous, short duration current spikes. Overview and background information Two factors that provide a quantitative measure of the power quality in an electrical system are Power Factor (PF) and Total Harmonic Distortion (THD). The amount of useful power being consumed by an electrical system is predominantly decided by the PF of the system. To understand PF, it is important to know that power has two components: • Working (or Active Power) Working Power is the power that is actually consumed and registered on the electric meter at the consumer's location. Working power is expressed in kilowatts (kW), which register as kilowatt hour (kWh) on an electric meter. • Reactive Power Reactive Power is required to maintain and sustain the electromagnetic field associated with the industrial inductive loads such as induction motors driving pumps or fans, welding machines and many more. Reactive Power is measured in kilovolt ampere reactive (kVAR) units. The total required power capacity, including Working Power and Reactive Power, is known as Apparent Power, expressed in kilovolt ampere (kVA) units.Power Factor is a parameter that gives the amount of working power used by any system in terms of the total apparent power INPUT CURRENT WAVEFORM WITH AND WITHOUT PFC Figure 4 .shows a block diagram of the AC-to-DC converter stage, which converts the Ac These waveforms illustrate that PFC can improve the input current drawn from themains supply and reduce the DC bus voltage ripple. The objective of PFC is to make the input to a power supply look like a simple resistor. The PFC circuitry provides apower factor that is nearly equal to unity with very low current THD (< 5%) input voltage to a DC voltage and maintains sinusoidal input current at a high input P Factor. The input rectifier converts the alternating voltage at power frequency into unidirectional voltage. This rectified voltage is fed to the chopper circuit to produce a smooth and constant DC output voltage to the load. The chopper circuit is controlled by the PWM switching pulses generated by the dsPIC DSC device, based on three measured feedback signals: • Rectified input voltage • DC bus current • DC bus voltage FIGURE 5. BLOCK DIAGRAM OF THE COMPONENTS FOR POWER FACTOR CORRECTION PFC TOPOLOGIES The Power Factor can be achieved with various basic topologies such as Buck, Boost and Buck/Boost. Buck PFC Circuit In a Buck PFC circuit, the output DC voltage is less than the input rectified voltage Large filters are needed to suppress switching ripples and this circuit produces considerable Power Factor improvement. The switch (MOSFET) is rated to VIN in this case. Figure 1-5 shows the circuit for the Buck PFC stage. Figure 1-6 shows the Buck PFC input current shape. FIGURE 6 .BUCK PFC FIGURE 7. BUCK PFC INPUT CURRENT SHAPE Boost PFC Circuit The Boost converter produces a voltage higher than the input rectified voltage; therefore, the switch (MOSFET) rating should be rated higher than VOUT. Figure 1-7 shows the circuit for the Boost PFC stage. Figure 1-8 shows the Boost PFC input current shape. FIGURE 8. BOOST PFC 8.1 Boost PFC in current shape Buck/Boost PFC Circuit In the Buck/Boost PFC circuit, the output DC voltage may be either less or greater than the input rectified voltage. High Power Factor can be achieved in this case. The switch (MOSFET) is rated to (VIN + VOUT). Figure 1-9 shows the circuit for the Buck/Boost PFC stage. Figure 1-10 shows the Boost PFC input current shape. FIGURE 9. BUCK/BOOST PFC FIGURE 10. BUCK/BOOST PFC INPUT CURRENT SHAPE Regardless of the input line voltage and output load variations, input current drawn by the Buck converter and the Buck/Boost converter is always discontinuous. However, when the Boost converter operates in Continuous Conduction mode, the current drawn from the input voltage source is always continuous and smooth as shown in Figure 1-8. This feature makes the Boost converter an ideal choice for the Power Factor Correction (PFC) application. In PFC, the input current drawn by the converter should be continuous and smooth enough to meet Total Harmonic Distortion (THD) specifications for the input current (ITHD) such that it is close to unity. In addition, input current should follow the input sinusoidal voltage waveform to meet displacement factor such that it is close to unity. Phase-Shift ZVT Converter A Full-Bridge converter is a transformer isolated Buck converter. The basic schematic and switching waveform is shown in Figure 1-11. The transformer primary is connected between the two legs formed by switches Q1,Q2 and Q4,Q3. Switches Q1,Q2 and Q4, Q3 create a pulsating AC voltage at the transformer primary. The transformer is used to step down the pulsating primary voltage, as well as to provide isolation between the input voltage source and the output voltage VOUT. A Full-Bridge converter configuration retains the voltage properties of the Half-Bridge topology, and the current properties ofpush-pull topology. The diagonal switch pairs, Q1,Q3 and Q4,Q2, are switched alternately at the selected switching period. Since the maximum voltage stress across any switch is VIN, and with the complete utilization of magnetic core and copper, this combination makes the Full-Bridge converter an ideal choice for high input voltage, high-power range SMPS applications. In the Full-Bridge converter, four switches are used, thereby increasing the amount of switching device loss. The conduction loss of a MOSFET can be reduced by using a MOSFET with a low RDS(ON) rating. Switching losses can be reduced by using Zero Voltage Transition (ZVT), Zero Current Switching (ZCS), or both techniques. At high power output and high input voltage, the ZVT technique is preferred for the MOSFET. In a Phase-Shift ZVT converter, the output is controlled by varying the phase of switch Q4 with respect to Q1.In this topology, the parasitic output capacitor of the MOSFETs, and the leakageinductance of the switching transformer, are used as a resonant tank circuit to achieve zero voltage across the MOSFET at the turn-on transition. There are two major differences in the operation of a Phase-Shift ZVT and simple Full-Bridge topology. In a Phase-Shift ZVT converter, the gate drive of both diagonal switches is phase shifted. In addition, both halves of the bridge switch network are driven through the complementary gate pulse with a fixed 50% duty cycle. The phase difference between the two half-bridge switching network gate drives control the power flow from primary to secondary, which results in the effective duty cycle. Power is transferred to the secondary only when the diagonal switches are ON. If the top or bottom switches of both legs are ON simultaneously, zero voltage is applied across the transformer primary. Therefore, no power is transferred to the secondary during this period. When the appropriate diagonal switch is turned OFF, primary current flows through the output capacitor of the respective MOSFETs causing switch drain voltage to move toward to the opposite input voltage rail. This creates zero voltage across the MOSFET to be turned ON next, which creates zero voltage switching when it turns ON. This is possible when enough circulating current is provided by the inductive storage energy to charge and discharge the output capacitor of the respective MOSFETs. Figure 1-12 shows the gate pulse required, and the voltage and current waveform across the switch and transformer. The operation of the Phase-Shift ZVT can be divided into different time intervals.Assuming that the transformer was delivering the power to the load, the current flowing through primary is IPK, and the diagonal switch Q1,Q3 was ON, at t = t0, the switch Q3 is turned OFF as shown in Figure TIME INTERVALS • Interval1: t0 < t < t1 Switch Q3 is turned OFF, beginning the resonant transition of the right leg. Primary current is maintained constant by the resonant inductor LLK. The primary current charges the output capacitor of switch Q3 (COSS3) to the input voltage VIN, which results in the output capacitance of Q4 (COSS4) being discharged to zero potential. This creates zero potential across switch Q4 prior to turn-on, resulting in zero voltage switching. During this transition period, the transformer primary voltage decreases from VIN to zero, and the primary no longer supplies power to the output. Inductive energy stored in the output inductor, and zero voltage across the primary, cause both output MOSFETs to share the load current equally. • Interval2: t1 < t < t2 After charging COSS3 to VIN, the primary current starts flowing through the body diode of Q4. Q4 can then be turned on any time after t1 and have a zero voltage turn-on transition. • Interval3: t2 < t < t3 At t = t2, Q1 was turned OFF and the primary was maintained by the resonant inductor LLK. In addition, at t = t2, IP is slightly less than the primary peak current IPK because of finite losses. The primary resonant current charges the output capacitor of switch Q1 (COSS1) to input voltage VIN, which discharges the output capacitor of Q2 (COSS2) to zero potential, thus preparing for zero voltage turn-on for switch Q2. During this transition, the primary current decays to zero. ZVS of the left leg switches depending on the energy stored in the resonant inductor,Conduction losses in the primary switches and the losses in the transformer winding. Since the left leg transition depends on leakage energy stored in the transformer, it may require an external series inductor if the stored leakage energy is not enough for ZVS. When Q2 is then turned ON in the next interval, voltage VIN is applied across the primary in the reverse direction. • Interval: t3 < t < t4 The two diagonal switches Q4, Q2 are ON, applying full input voltage across the primary. During this period, the magnetizing current, plus the reflected secondary current into the primary, flows through the switch. The exact diagonal switch-on time depends on the input voltage, the transformer turns ratio and the output voltage. After the switch-on time period of the diagonal switch, Q4 is turned OFF.One switching cycle is completed when the switch Q4 is turned OFF. The primary current charges COSS4 to a potential of input voltage VIN, and discharges COSS3 to zero potential, thereby enabling ZVS for switch Q3. The identical analysis is required for the next half cycle. In the Phase-Shift ZVT converter shown in Figure 1-11, the maximum transition time occurs for the left leg at minimum load current and maximum input voltage, and minimum transition time occurs for the right leg at maximum load current and minimum input voltage. Therefore, Marathon series of Switch Mode Power The output voltage is measured using the analog input AN1. The analog comparator input CMP1A is connected to the output of the current transformer. The output voltage is controlled by varying the duty cycle of PWM4.The PWM4 pair is operated in Complementary mode with dead time. The switching frequency is approximately 500 kHz. The duty cycle is controlled directly by the built-in Cycle-by-Cycle Current-Limit mode and the analog comparator.When the current-sense signal at the input of the analog comparator exceeds the programmed comparator threshold, the PWM output is immediately terminated for the remainder of the PWM cycle.The Single-Phase Buck Converter circuitry is designed to operate in continuous conduction mode at load currents greater than approximately 3A. If the Single-Phase Buck Converter is operated in Discontinuous Conduction mode, the freewheeling MOSFET is disabled through software. At no load and light load current (< 3A), the PWM output may enter a “burst” mode. This is caused by a low demand for load current by the converter in this range load current. The voltage control loop is executed in the Multi-Phase Buck Converter MULTI-PHASE BUCK CONVERTER CONTROL SCHEME Voltage mode control is used for controlling the output of the Multi-Phase Buck Converter on the SMPS AC/DC Reference Design. As shown in Figure 3-11, the scheme only implements a single control loop The output voltage is compared with the reference and results in a voltage error, which is fed as an input to the voltage error compensator. The output of the voltage error compensator modifies the duty cycle of all phases of the Multi-Phase Buck Converter. The voltage error compensator is implemented as a PID function that is implemented in the ADC ISR. The Multi-Phase converter comprises of three individual phases, but the output is controlled by a single duty cycle that identically drives the three phases. The PWM drive signals for each phase are phase shifted by 120 degrees using the built-in PWM phase-shifting feature available on the dsPIC33FJ16GS504. The PWM drive signals for the Multi-Phase Buck Converter are shown in Figure. FIGURE 13:MULTIPHASE BUCK CONVERTER Features of SMPS high efficiency High reliability Low temperature rise Built in EMI filter Compact size, light weight Rugged heavy duty enclosure Short Circuit protection, Overload / Over voltage protection 100% Full load burn-in tested Over Temperature Protection Parallel /Redundancy operation is Possible APPLICATIONS OF SMPS Smps are desined with unique state of art current mode pwm technology to obtain precise regulated output voltage at rated power.this smps are specifically uses in Indian power line conditions. Due to exahastive range these smps are great in demand in Wide spectrum of industries Instrumentation office automation Telecom Medical Electronics Railways Fire alarm systems Control panels Research institute Process industries Engineering industries etc., INPUT AND OUTPUT ELECTRICAL SPECIFICATIONS SYSTEM SPECIFICATIONS This reference design describes the design of an off-line Switch Mode Power Supply (SMPS) design using an SMPS dsPIC® DSC (dsPIC33FJ16GS504).The SMPS AC/DC Reference Design works with universal input voltage range and produces three output voltages (12V, 3.3V and 5V). The continuous output rating of the reference design is 300 Watts. This reference design is based on a modular structure having three major block sets as shown in Figure 1-1. Figure 1-2 shows a more detailed block diagram with all functional blocks as implemented on the SMPS AC/DC Reference Design. The Power Factor Circuit (PFC) converts the universal AC input voltage to constant high-voltage DC, and maintains the sinusoidal input current at high power factor. The Phase-Shift Zero Voltage Transition circuit converts high-voltage DC to intermediate low-voltage DC with isolation from the input AC mains, at high efficiency. The Multi-Phase Synchronous and Single-Phase Synchronous Buck circuit converts intermediate low-voltage DC to very low-voltage DC at high current at high efficiency.The input and output specifications are as follows: • Input: - Input voltage: 85 VAC-265 VAC - Input frequency: 45 Hz-65 Hz • Outputs (individually loaded): - Output voltage 1 (Vo1) = 12V - Output load 1 (Io1) = 0A-30A - Output voltage 2 (Vo2) = 3.3V - Output load 2 (Io2) = 0A-69A - Output voltage 3 (Vo3) = 5V - Output load 3 (Io3) = 0A-23A • Outputs (simultaneously loaded): - Output voltage 2 (Vo2) = 3.3V - Output load 2 (Io2) = 0A-56A - Output voltage 3 (Vo3) = 5V - Output load 3 (Io3) = 0A-23A 3.LOCATION OF FUNCTIONAL BLOCK WITH RESPECT ISOLATION BARRIER CONCLUTION The main advantage of this method is greater efficiency because the switching transistor dissipates little power when it is outside of its active region (i.e., when the transistor acts like a switch and either has a negligible voltage drop across it or a negligible current through it). Other advantages include smaller size and lighter weight (from the elimination of low frequency transformers which have a high weight) and lower heat generation due to higher efficiency. REFERENCES This section provides the list of references used throughout this document. • Herfurth, M., “Active Harmonic Filtering for Line Rectifiers of Higher Output Power”,Siemens Components XXI (1986), No. 1, pp. 9 - 13. • Zhou, C.and Jovanovic, M.M., “Design Trade-offs in Continuous Current-Mode • Controlled Boost Power-Factor Correction Circuits”, Proceedings of HFPC '92, May 1992,pp. 209 - 219. • Chen, W, Lee, F. C., Jovanovic, M. M., and Sabate, J. A., “A Comparative Study of a Class of Full Bridge Zero-Voltage-Switched PWM Converters”. • Frank, W., Dahlquist, F., Kapels, H., Schmitt, M., and Deboy, G., “Compensation MOSFETs with Fast Body Diode - Benefits in Performance and Reliability in ZVS . Proceedings of IPECSA, the International Power Electronics Component Systems • Snelling, E.C., “Soft Ferrites. Properties and Applications”, 2nd Edition, Butterworths, London, UK, 1988. • Jongsma, J., “High-Frequency Ferrite Power Transformer and Choke Design - Part 3 Transformer Winding Design”, N. V. Philips, September 1982. • Dowell, P. L., “Effects of Eddy Currents in Transformer Windings”, Proceedings of the IEE, Vol. 113, No. 8, August 1966, pp. 1387 - 1394. • McLyman, C. W. T., “Transformer and Inductor Design Handbook”, 3rd edition, Marcel Dekker Inc., New York, USA, 2004. • “MOSFETs Move in on Low Voltage Rectification”, MOSPOWER Applications Handbook, Siliconix, 1984, pp. 5-69 - 5-86. • Kutkut, N. H., Divan, D. M., and Gascoigne, R. W., “An Improved Full-Bridge Zero-Voltage-Switching PWM Converter Using a Two-Inductor Rectifier”, IEEE Transactions on Industry Applications, Vol. 31, No. 1, January/February 1995, pp. 119 - 126 • Alivio, G., Ambrus, J., McDonald, T., and Dowling, R., “Maximizing the Effectiveness of your SMD Assemblies”, Application Note AN-994, International Rectifier. • Wei, J. and Lee, F. C., “An Output Impedance-based Design of Voltage Regulator Output Capacitors for High Slew-rate Load Current Transients”, Proceedings of APEC 2004, pp. 304 - 310. • “12 W Input Universal CV Adapter”, Power Integrations Design Idea DI-91, January 2006
This higher power conversion efficiency is an important advantage of a switched-mode power supply. Switched-mode power supplies may also be substantially smaller and lighter than a linear supply. Switching regulators are used as replacements for the linear regulators when higher efficiency, smaller size or lighter weight are required. They are, however, more complicated, their switching currents can cause electrical noise problems if not carefully suppressed, and simple designs may have a poor power factor. 1.INTRODUCTION A linear regulator provides the desired output voltage by dissipating excess power in ohmic losses (e.g., in a resistor or in the collector–emitter region of a pass transistor in its active mode). A linear regulator regulates either output voltage or current by dissipating the excess electric power in the form of ,heat and hence its maximum power efficiency is voltage-out/voltage-in since the volt difference is wasted. In contrast, a switched-mode power supply regulates either output voltage or current by switching ideal storage elements, like inductor and capacitor, into and out of different electrical configurations. Ideal switching elements (e.g., transistors operated outside of their active mode) have no resistance when "closed" and carry no current when "open", and so the converters can theoretically operate with 100% efficiency (i.e., all input power is delivered to the load; no power is wasted as dissipated heat). For example, if a DC source, an inductor, a switch, and the corresponding electrical ground are placed in series and the switch is driven by a square wave the peak-to-peak voltage of the waveform measured across the switch can exceed the input voltage from the DC source. This is because the inductor responds to changes in current by inducing its own voltage to counter the change in current, and this voltage adds to the source voltage while the switch is open. If a diode-and-capacitor combination is placed in parallel to the switch, the peak voltage can be stored in the capacitor, and the capacitor can be used as a DC source with an output voltage greater than the DC voltage driving the circuit. This boost converter acts like a step up transformer for DC signals. A buck boost converter works in a similar manner, but yields an output voltage which is opposite in polarity to the input voltage. Other buck circuits exist to boost the average output current with a reduction of voltage. In an SMPS, the output current flow depends on the input power signal, the storage elements and circuit topologies used, and also on the pattern used (e.g., pulse width modulation with an adjustable duty cycle) to drive the switching elements. Typically, the spectral density of these switching waveforms has energy concentrated at relatively high frequencies. As such, switching transients, like , ripple introduced onto the output waveforms can be filtered with small LC filters. THEORY OF OPERATION Fig 1 Block diagram of a mains operated AC/DC SMPS with output voltage regulation Fig1.1 AC, half-wave and full-wave rectified signal If the SMPS has an AC input, then the first stage is to convert the input to DC. This is called rectification.The rectifier circuit can be configured as a voltage doubler by the addition of a switch operated either manually or automatically. This is a feature of larger supplies to permit operation from nominally 120 V or 240 V supplies. The rectifier produces an unregulated DC voltage which is then sent to a large filter capacitor. The current drawn from the mains supply by this rectifier circuit occurs in short pulses around the AC voltage peaks. These pulses have significant high frequency energy which reduces the power factor. Special control techniques can be employed by the SMPS to force the average input current to follow the sinusoidal shape of the AC input voltage, correcting the power factor. An SMPS with a DC input does not require this stage. An SMPS designed for AC input can often be run from a DC supply (for230 V AC this would be 330 V DC), as the DC passes through the rectifier stage unchanged. It's however advisable to consult the manual before trying this, though most supplies are quite capable of such operation even though nothing is mentioned in the documentation. However, this type of use may be harmful to the rectifier stage as it will only use half of diodes in the rectifier for the full load. This may result in overheating of these components, and cause them to fail prematurely. If an input range switch is used, the rectifier stage is usually configured to operate as voltage doubler when operating on the low voltage (~120 V AC) range and as a straight rectifier when operating on the high voltage (~240 V AC) range. If an input range switch is not used, then a full-wave rectifier is usually used and the downstream inverter stage is simply designed to be flexible enough to accept the wide range of DC voltages that will be produced by the rectifier stage. In higher-power SMPSs, some form of automatic range switching may be used. Inverter stage This section refers to the block marked chopper in the block diagram. The inverter stage converts DC, whether directly from the input or from the rectifier stage described above, to AC by running it through a power oscillator, whose output transformer is very small with few windings at a frequency of tens or hundreds of kilohertzThe frequency is usually chosen to be above 20 kHz, to make it inaudible to humans. The output voltage is optically coupled to the input and thus very tightly controlled. The switching is implemented as a multistage (to achieve high gain) mosfet amplifier. MOSFETs are a type of transistor with a low on- andresistance a high current-handling capacity. Voltage converter and output rectifier If the output is required to be isolated from the input, as is usually the case in mains power supplies, the inverted AC is used to drive the primary winding of a high-frequency transformer. This converts the voltage up or down to the required output level on its secondary winding. The output transformer in the block diagram serves this purpose. If a DC output is required, the AC output from the transformer is rectified. For output voltages above ten volts or so, ordinary silicon diodes are commonly used. For lower voltages, schottky diodes are commonly used as the rectifier elements; they have the advantages of faster recovery times than silicon diodes (allowing low-loss operation at higher frequencies) and a lower voltage drop when conducting. For even lower output voltages, MOSFETs may be used as synchronous rectifiers compared to Schottky diodes, these have even lower conducting state voltage drops. The rectified output is then smoothed by a filter consisting of inductors and capacitors switching frequencies, components with lower capacitance and inductance are needed. Simpler, non-isolated power supplies contain an inductor instead of a transformer. This type includes boost converter , buck converter and the buck boost converter. These belong to the simplest class of single input, single output converters which use one inductor and one active switch. The buck converter reduces the input voltage in direct proportion to the ratio of conductive time to the total switching period, called the duty cycle. For example an ideal buck converter with a 10 V input operating at a 50% duty cycle will produce an average output voltage of 5 V. A feedback control loop is employed to regulate the output voltage by varying the duty cycle to compensate for variations in input voltage. The output voltage of a boost converter is always greater than the input voltage and the buck-boost output voltage is inverted but can be greater than, equal to, or less than the magnitude of its input voltage. There are many variations and extensions to this class of converters but these three form the basis of almost all isolated and non-isolated DC to DC converters. By adding a second inductor the cuk and SEPIC converters can be implemented, or, by adding additional active switches, various bridge converters can be realised. Other types of SMPSs use a capacitor voltage diode Instead of inductors and transformers. These are mostly used for generating high voltages at low currents Cockcroft woltan generator. The low voltage variant is called charge pump. Regulation A feedback circuit monitors the output voltage and compares it with a reference voltage, which shown in the block diagram serves this purpose. Depending on design/safety requirements, the controller may contain an isolation mechanism (such as opto couplers) to isolate it from the DC output. Switching supplies in computers, TVs and VCRs have these opto-couplers to tightly control the output voltage. Open-loop regulators do not have a feedback circuit. Instead, they rely on feeding a constant voltage to the input of the transformer or inductor, and assume that the output will be correct. Regulated designs compensate for the impedence of the transformer or coil. Monopolar designs also compensate for the magnetic hysteresis of the core. The feedback circuit needs power to run before it can generate power, so an additional non-switching power-supply for stand-by is added. Transformer design SMPS transformers run at high frequency. Most of the cost savings (and space savings) in off-line power supplies come from the fact that a high frequency transformer is much smaller than the 50/60 Hz transformers formerly used. There are additional design tradeoffs. The higher the switching frequency, the lower the amount of energy that needs to be stored intermediately during the time of a single switching cycle. Because this energy is stored in form of magnetic energy in the transformer core material (like ferrite), less of such material is needed. However, higher frequency also means more energy lost during transitions of the switching semiconductor. Furthermore, much more attention to the physical layout of the circuit board is required, and the amount of electromagnetic interference will be more pronounced. Core losses increase at higher frequencies. Cores use ferrite material which has a low loss at the high frequencies and high flux densities used. The laminated iron cores of lower-frequency (<400 Hz) transformers would be unacceptably lossy at switching frequencies of a few kilohertz. Copper loss At low frequencies such the line frequency of 50 or 60 Hz), designers can usually ignore the skin effect. For these frequencies, the skin effect is only significant when the conductors are large, more than 0.3 inches (7.6 mm) in diameter. Switching power supplies must pay more attention to the skin effect because it is a source of power loss. At 500 kHz, the skin depth in copper is about 0.003 inches (0.076 mm) – a dimension smaller than the typical wires used in a power supply. The effective resistance of conductors increases, because current concentrates near the surface of the conductor and the inner portion carries less current than at low frequencies. The skin effect is exacerbated by the harmonics present in the high speed pwm switching waveforms. The appropriate skin depth is not just the depth at the fundamental, but also the skin depths at the harmonics. In addition to the skin effect, there is also a proximity effect, which is another source of power loss. Power factor Simple off-line switched mode power supplies incorporate a simple full-wave rectifier connected to a large energy storing capacitor. Such SMPSs draw current from the AC line in short pulses when the mains instantaneous voltage exceeds the voltage across this capacitor. During the remaining portion of the AC cycle the capacitor provides energy to the power supply. As a result, the input current of such basic switched mode power supplies has high harmonic content and relatively low power factor. This creates extra load on utility lines, increases heating of building wiring, the utility transformers, and standard AC electric motors, and may cause stability problems in some applications such as in emergency generator systems or aircraft generators. Harmonics can be removed by filtering, but the filters are expensive.Distortion cannot be corrected by addition of a single linear component. 2.BLOCK DIAGRAM A conventional SMPS must implement PFC if it draws more than 75 watts from the AC Mains. The PFC circuitry draws input current in phase with the input voltage, and theTotal Harmonic Distortion (THD) of the input current should be less than 5% at full load. The PFC provides a fixed DC high-output voltage, which needs to be converted to a lower Direct Current (DC) output voltage and isolated with an input mains supply.Figure 2 shows a high-level block diagram of the SMPS AC/DC Reference Design. .The SMPS AC/DC Reference Design operates on universal input voltage and produces multiple DC output voltages. The front-end PFC Boost circuit converts universal AC input voltage to 420 VDC bus voltage. The Phase-Shift Zero Voltage Transition (ZVT) circuit produces 12 VDC output voltage from a 420 VDC bus. The Phase-Shift ZVT converter also provides output voltage isolation from the input AC mains. The Multi-Phase Synchronous Buck converter produces 3.3 VDC @ 69 Amps from the 12 VDC bus. The Single-Phase Buck converter produces 5 VDC @ 23 Amps from the 12 VDC bus. The following sections in this chapter provide an overview and background of the main power conversion blocks implemented in the SMPS AC/DC Reference Design. FIGURE.2 HIGH-LEVEL SMPS AC/DC REFERENCE DESIGN BLOCK DIAGRAM FIG 3 .DETAILED SMPS AC/DC REFERENCE DESIGN BLOCK DIAGRAM Power Factor Correction (PFC) Most power conversion applications consist of an AC-to-DC conversion stage immediately following the AC source. The DC output obtained after rectification is subsequently used for further stages. Current pulses with high peak amplitude are drawn from a rectified voltage source with sine wave input and capacitive filtering.Regardless of the load connected to the system, the current drawn is discontinuous and of short duration. Because many applications demand a DC voltage source, a rectifier with a capacitive filter is necessary. However, this results in discontinuous, short duration current spikes. Overview and background information Two factors that provide a quantitative measure of the power quality in an electrical system are Power Factor (PF) and Total Harmonic Distortion (THD). The amount of useful power being consumed by an electrical system is predominantly decided by the PF of the system. To understand PF, it is important to know that power has two components: • Working (or Active Power) Working Power is the power that is actually consumed and registered on the electric meter at the consumer's location. Working power is expressed in kilowatts (kW), which register as kilowatt hour (kWh) on an electric meter. • Reactive Power Reactive Power is required to maintain and sustain the electromagnetic field associated with the industrial inductive loads such as induction motors driving pumps or fans, welding machines and many more. Reactive Power is measured in kilovolt ampere reactive (kVAR) units. The total required power capacity, including Working Power and Reactive Power, is known as Apparent Power, expressed in kilovolt ampere (kVA) units.Power Factor is a parameter that gives the amount of working power used by any system in terms of the total apparent power INPUT CURRENT WAVEFORM WITH AND WITHOUT PFC Figure 4 .shows a block diagram of the AC-to-DC converter stage, which converts the Ac These waveforms illustrate that PFC can improve the input current drawn from themains supply and reduce the DC bus voltage ripple. The objective of PFC is to make the input to a power supply look like a simple resistor. The PFC circuitry provides apower factor that is nearly equal to unity with very low current THD (< 5%) input voltage to a DC voltage and maintains sinusoidal input current at a high input P Factor. The input rectifier converts the alternating voltage at power frequency into unidirectional voltage. This rectified voltage is fed to the chopper circuit to produce a smooth and constant DC output voltage to the load. The chopper circuit is controlled by the PWM switching pulses generated by the dsPIC DSC device, based on three measured feedback signals: • Rectified input voltage • DC bus current • DC bus voltage FIGURE 5. BLOCK DIAGRAM OF THE COMPONENTS FOR POWER FACTOR CORRECTION PFC TOPOLOGIES The Power Factor can be achieved with various basic topologies such as Buck, Boost and Buck/Boost. Buck PFC Circuit In a Buck PFC circuit, the output DC voltage is less than the input rectified voltage Large filters are needed to suppress switching ripples and this circuit produces considerable Power Factor improvement. The switch (MOSFET) is rated to VIN in this case. Figure 1-5 shows the circuit for the Buck PFC stage. Figure 1-6 shows the Buck PFC input current shape. FIGURE 6 .BUCK PFC FIGURE 7. BUCK PFC INPUT CURRENT SHAPE Boost PFC Circuit The Boost converter produces a voltage higher than the input rectified voltage; therefore, the switch (MOSFET) rating should be rated higher than VOUT. Figure 1-7 shows the circuit for the Boost PFC stage. Figure 1-8 shows the Boost PFC input current shape. FIGURE 8. BOOST PFC 8.1 Boost PFC in current shape Buck/Boost PFC Circuit In the Buck/Boost PFC circuit, the output DC voltage may be either less or greater than the input rectified voltage. High Power Factor can be achieved in this case. The switch (MOSFET) is rated to (VIN + VOUT). Figure 1-9 shows the circuit for the Buck/Boost PFC stage. Figure 1-10 shows the Boost PFC input current shape. FIGURE 9. BUCK/BOOST PFC FIGURE 10. BUCK/BOOST PFC INPUT CURRENT SHAPE Regardless of the input line voltage and output load variations, input current drawn by the Buck converter and the Buck/Boost converter is always discontinuous. However, when the Boost converter operates in Continuous Conduction mode, the current drawn from the input voltage source is always continuous and smooth as shown in Figure 1-8. This feature makes the Boost converter an ideal choice for the Power Factor Correction (PFC) application. In PFC, the input current drawn by the converter should be continuous and smooth enough to meet Total Harmonic Distortion (THD) specifications for the input current (ITHD) such that it is close to unity. In addition, input current should follow the input sinusoidal voltage waveform to meet displacement factor such that it is close to unity. Phase-Shift ZVT Converter A Full-Bridge converter is a transformer isolated Buck converter. The basic schematic and switching waveform is shown in Figure 1-11. The transformer primary is connected between the two legs formed by switches Q1,Q2 and Q4,Q3. Switches Q1,Q2 and Q4, Q3 create a pulsating AC voltage at the transformer primary. The transformer is used to step down the pulsating primary voltage, as well as to provide isolation between the input voltage source and the output voltage VOUT. A Full-Bridge converter configuration retains the voltage properties of the Half-Bridge topology, and the current properties ofpush-pull topology. The diagonal switch pairs, Q1,Q3 and Q4,Q2, are switched alternately at the selected switching period. Since the maximum voltage stress across any switch is VIN, and with the complete utilization of magnetic core and copper, this combination makes the Full-Bridge converter an ideal choice for high input voltage, high-power range SMPS applications. In the Full-Bridge converter, four switches are used, thereby increasing the amount of switching device loss. The conduction loss of a MOSFET can be reduced by using a MOSFET with a low RDS(ON) rating. Switching losses can be reduced by using Zero Voltage Transition (ZVT), Zero Current Switching (ZCS), or both techniques. At high power output and high input voltage, the ZVT technique is preferred for the MOSFET. In a Phase-Shift ZVT converter, the output is controlled by varying the phase of switch Q4 with respect to Q1.In this topology, the parasitic output capacitor of the MOSFETs, and the leakageinductance of the switching transformer, are used as a resonant tank circuit to achieve zero voltage across the MOSFET at the turn-on transition. There are two major differences in the operation of a Phase-Shift ZVT and simple Full-Bridge topology. In a Phase-Shift ZVT converter, the gate drive of both diagonal switches is phase shifted. In addition, both halves of the bridge switch network are driven through the complementary gate pulse with a fixed 50% duty cycle. The phase difference between the two half-bridge switching network gate drives control the power flow from primary to secondary, which results in the effective duty cycle. Power is transferred to the secondary only when the diagonal switches are ON. If the top or bottom switches of both legs are ON simultaneously, zero voltage is applied across the transformer primary. Therefore, no power is transferred to the secondary during this period. When the appropriate diagonal switch is turned OFF, primary current flows through the output capacitor of the respective MOSFETs causing switch drain voltage to move toward to the opposite input voltage rail. This creates zero voltage across the MOSFET to be turned ON next, which creates zero voltage switching when it turns ON. This is possible when enough circulating current is provided by the inductive storage energy to charge and discharge the output capacitor of the respective MOSFETs. Figure 1-12 shows the gate pulse required, and the voltage and current waveform across the switch and transformer. The operation of the Phase-Shift ZVT can be divided into different time intervals.Assuming that the transformer was delivering the power to the load, the current flowing through primary is IPK, and the diagonal switch Q1,Q3 was ON, at t = t0, the switch Q3 is turned OFF as shown in Figure TIME INTERVALS • Interval1: t0 < t < t1 Switch Q3 is turned OFF, beginning the resonant transition of the right leg. Primary current is maintained constant by the resonant inductor LLK. The primary current charges the output capacitor of switch Q3 (COSS3) to the input voltage VIN, which results in the output capacitance of Q4 (COSS4) being discharged to zero potential. This creates zero potential across switch Q4 prior to turn-on, resulting in zero voltage switching. During this transition period, the transformer primary voltage decreases from VIN to zero, and the primary no longer supplies power to the output. Inductive energy stored in the output inductor, and zero voltage across the primary, cause both output MOSFETs to share the load current equally. • Interval2: t1 < t < t2 After charging COSS3 to VIN, the primary current starts flowing through the body diode of Q4. Q4 can then be turned on any time after t1 and have a zero voltage turn-on transition. • Interval3: t2 < t < t3 At t = t2, Q1 was turned OFF and the primary was maintained by the resonant inductor LLK. In addition, at t = t2, IP is slightly less than the primary peak current IPK because of finite losses. The primary resonant current charges the output capacitor of switch Q1 (COSS1) to input voltage VIN, which discharges the output capacitor of Q2 (COSS2) to zero potential, thus preparing for zero voltage turn-on for switch Q2. During this transition, the primary current decays to zero. ZVS of the left leg switches depending on the energy stored in the resonant inductor,Conduction losses in the primary switches and the losses in the transformer winding. Since the left leg transition depends on leakage energy stored in the transformer, it may require an external series inductor if the stored leakage energy is not enough for ZVS. When Q2 is then turned ON in the next interval, voltage VIN is applied across the primary in the reverse direction. • Interval: t3 < t < t4 The two diagonal switches Q4, Q2 are ON, applying full input voltage across the primary. During this period, the magnetizing current, plus the reflected secondary current into the primary, flows through the switch. The exact diagonal switch-on time depends on the input voltage, the transformer turns ratio and the output voltage. After the switch-on time period of the diagonal switch, Q4 is turned OFF.One switching cycle is completed when the switch Q4 is turned OFF. The primary current charges COSS4 to a potential of input voltage VIN, and discharges COSS3 to zero potential, thereby enabling ZVS for switch Q3. The identical analysis is required for the next half cycle. In the Phase-Shift ZVT converter shown in Figure 1-11, the maximum transition time occurs for the left leg at minimum load current and maximum input voltage, and minimum transition time occurs for the right leg at maximum load current and minimum input voltage. Therefore, Marathon series of Switch Mode Power The output voltage is measured using the analog input AN1. The analog comparator input CMP1A is connected to the output of the current transformer. The output voltage is controlled by varying the duty cycle of PWM4.The PWM4 pair is operated in Complementary mode with dead time. The switching frequency is approximately 500 kHz. The duty cycle is controlled directly by the built-in Cycle-by-Cycle Current-Limit mode and the analog comparator.When the current-sense signal at the input of the analog comparator exceeds the programmed comparator threshold, the PWM output is immediately terminated for the remainder of the PWM cycle.The Single-Phase Buck Converter circuitry is designed to operate in continuous conduction mode at load currents greater than approximately 3A. If the Single-Phase Buck Converter is operated in Discontinuous Conduction mode, the freewheeling MOSFET is disabled through software. At no load and light load current (< 3A), the PWM output may enter a “burst” mode. This is caused by a low demand for load current by the converter in this range load current. The voltage control loop is executed in the Multi-Phase Buck Converter MULTI-PHASE BUCK CONVERTER CONTROL SCHEME Voltage mode control is used for controlling the output of the Multi-Phase Buck Converter on the SMPS AC/DC Reference Design. As shown in Figure 3-11, the scheme only implements a single control loop The output voltage is compared with the reference and results in a voltage error, which is fed as an input to the voltage error compensator. The output of the voltage error compensator modifies the duty cycle of all phases of the Multi-Phase Buck Converter. The voltage error compensator is implemented as a PID function that is implemented in the ADC ISR. The Multi-Phase converter comprises of three individual phases, but the output is controlled by a single duty cycle that identically drives the three phases. The PWM drive signals for each phase are phase shifted by 120 degrees using the built-in PWM phase-shifting feature available on the dsPIC33FJ16GS504. The PWM drive signals for the Multi-Phase Buck Converter are shown in Figure. FIGURE 13:MULTIPHASE BUCK CONVERTER Features of SMPS high efficiency High reliability Low temperature rise Built in EMI filter Compact size, light weight Rugged heavy duty enclosure Short Circuit protection, Overload / Over voltage protection 100% Full load burn-in tested Over Temperature Protection Parallel /Redundancy operation is Possible APPLICATIONS OF SMPS Smps are desined with unique state of art current mode pwm technology to obtain precise regulated output voltage at rated power.this smps are specifically uses in Indian power line conditions. Due to exahastive range these smps are great in demand in Wide spectrum of industries Instrumentation office automation Telecom Medical Electronics Railways Fire alarm systems Control panels Research institute Process industries Engineering industries etc., INPUT AND OUTPUT ELECTRICAL SPECIFICATIONS SYSTEM SPECIFICATIONS This reference design describes the design of an off-line Switch Mode Power Supply (SMPS) design using an SMPS dsPIC® DSC (dsPIC33FJ16GS504).The SMPS AC/DC Reference Design works with universal input voltage range and produces three output voltages (12V, 3.3V and 5V). The continuous output rating of the reference design is 300 Watts. This reference design is based on a modular structure having three major block sets as shown in Figure 1-1. Figure 1-2 shows a more detailed block diagram with all functional blocks as implemented on the SMPS AC/DC Reference Design. The Power Factor Circuit (PFC) converts the universal AC input voltage to constant high-voltage DC, and maintains the sinusoidal input current at high power factor. The Phase-Shift Zero Voltage Transition circuit converts high-voltage DC to intermediate low-voltage DC with isolation from the input AC mains, at high efficiency. The Multi-Phase Synchronous and Single-Phase Synchronous Buck circuit converts intermediate low-voltage DC to very low-voltage DC at high current at high efficiency.The input and output specifications are as follows: • Input: - Input voltage: 85 VAC-265 VAC - Input frequency: 45 Hz-65 Hz • Outputs (individually loaded): - Output voltage 1 (Vo1) = 12V - Output load 1 (Io1) = 0A-30A - Output voltage 2 (Vo2) = 3.3V - Output load 2 (Io2) = 0A-69A - Output voltage 3 (Vo3) = 5V - Output load 3 (Io3) = 0A-23A • Outputs (simultaneously loaded): - Output voltage 2 (Vo2) = 3.3V - Output load 2 (Io2) = 0A-56A - Output voltage 3 (Vo3) = 5V - Output load 3 (Io3) = 0A-23A 3.LOCATION OF FUNCTIONAL BLOCK WITH RESPECT ISOLATION BARRIER CONCLUTION The main advantage of this method is greater efficiency because the switching transistor dissipates little power when it is outside of its active region (i.e., when the transistor acts like a switch and either has a negligible voltage drop across it or a negligible current through it). Other advantages include smaller size and lighter weight (from the elimination of low frequency transformers which have a high weight) and lower heat generation due to higher efficiency. REFERENCES This section provides the list of references used throughout this document. • Herfurth, M., “Active Harmonic Filtering for Line Rectifiers of Higher Output Power”,Siemens Components XXI (1986), No. 1, pp. 9 - 13. • Zhou, C.and Jovanovic, M.M., “Design Trade-offs in Continuous Current-Mode • Controlled Boost Power-Factor Correction Circuits”, Proceedings of HFPC '92, May 1992,pp. 209 - 219. • Chen, W, Lee, F. C., Jovanovic, M. M., and Sabate, J. A., “A Comparative Study of a Class of Full Bridge Zero-Voltage-Switched PWM Converters”. • Frank, W., Dahlquist, F., Kapels, H., Schmitt, M., and Deboy, G., “Compensation MOSFETs with Fast Body Diode - Benefits in Performance and Reliability in ZVS . Proceedings of IPECSA, the International Power Electronics Component Systems • Snelling, E.C., “Soft Ferrites. Properties and Applications”, 2nd Edition, Butterworths, London, UK, 1988. • Jongsma, J., “High-Frequency Ferrite Power Transformer and Choke Design - Part 3 Transformer Winding Design”, N. V. Philips, September 1982. • Dowell, P. L., “Effects of Eddy Currents in Transformer Windings”, Proceedings of the IEE, Vol. 113, No. 8, August 1966, pp. 1387 - 1394. • McLyman, C. W. T., “Transformer and Inductor Design Handbook”, 3rd edition, Marcel Dekker Inc., New York, USA, 2004. • “MOSFETs Move in on Low Voltage Rectification”, MOSPOWER Applications Handbook, Siliconix, 1984, pp. 5-69 - 5-86. • Kutkut, N. H., Divan, D. M., and Gascoigne, R. W., “An Improved Full-Bridge Zero-Voltage-Switching PWM Converter Using a Two-Inductor Rectifier”, IEEE Transactions on Industry Applications, Vol. 31, No. 1, January/February 1995, pp. 119 - 126 • Alivio, G., Ambrus, J., McDonald, T., and Dowling, R., “Maximizing the Effectiveness of your SMD Assemblies”, Application Note AN-994, International Rectifier. • Wei, J. and Lee, F. C., “An Output Impedance-based Design of Voltage Regulator Output Capacitors for High Slew-rate Load Current Transients”, Proceedings of APEC 2004, pp. 304 - 310. • “12 W Input Universal CV Adapter”, Power Integrations Design Idea DI-91, January 2006
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