TW385593B - Forward type electric power transformer - Google Patents

Abstract

This present invention relates to a forward power transformer, particularly a power transformer that only requires semiconductor switch component having low voltage specification before being applied for transforming high input voltage, which mainly includes a semiconductor component, transformer coils and a basic circuit unit formed by coupled capacitors and diodes. Through the design of connecting plural basic circuits in series so as to allow each semiconductor switch components to take an input voltage only with 2/M times that of voltage ( M is represented the total number of semiconductor switch component ) to reduce cost. Also each basic circuit units is provided with filtering wave and storing up energy effect therein. Furthermore, electromagnetic interference will be reduced and raising transformation efficiency will be improved.

Description

A7 B7 Printed by the Ministry of Economic Affairs, Standards Bureau, and Consumer Cooperatives V. Description of the invention (The invention is a forward power converter, which is mainly made by connecting multiple identical basic circuit units in series to each other. The electric house that the switching element withstands is only 2 / M of the input voltage ... is the total number of semiconductor switch reads) 'formation — a type of semiconductor switching element that only requires low voltage specifications can be applied to high input voltage occasions. The most troublesome in the design of high-frequency power converters with high input voltage (440VAC or 600VDC or more) is that it is not easy to find semiconductor switches (transistors) components that can withstand high electricity. Although the semiconductor market now has up to 1-side MOSFET or 1-bit insulated gate transistor IGBT Unsulated Gate Bipolar Transist is available. However, in order to ensure that the semiconductor element can operate in a safe area (Operation Area, S0A), it must be used such as half-bridge, full-bridge or The circuit architecture of the multi-semiconductor switch design, such as the double-switch forward type, enables each semiconductor switch to withstand approximately double the input voltage value. However, in actual design, it is necessary to consider the voltage surge derived from the unavoidable leakage inductance of the transformer winding. Below, you need to use a semiconductor element that can withstand 1.2 times the input voltage. The first figure shows the curve of the input voltage (V i η) and the source / drain withstand voltage of the semiconductor switching element under different architectures of the power converter application. In the figure, push-pull is used. Under the direction and BI FF C architecture, the semiconductor switch element withstands dust at twice the input voltage. The semiconductor switching element using the FI yback architecture has a voltage of approximately 1_ About 3 times, when using 2-Switch Forward, Half-Bridge, Full Bridge, and 2SBIFFC type, the paper standard of semiconductor switching elements applies to Chinese national standards (CNS) A4 specification (210X297 mm)! Ice coat-(Please read the notes on the back before 4 :, write this page)-order-come-Spring A7 A7 Printed by the Consumers' Cooperative of the Central Standards Bureau of the Ministry of Economic Affairs ¾ _________ Β7 V. Description of the Invention (ν) Withstand voltage of about i times the input voltage. In addition, when using the latest 3-level mi-ZVS architecture, the withstand voltage of semiconductor switches is about 0.5 times of the input voltage. So 'from the curve of the first figure can Under the latest 3 Level PWM-ZVS technology, when the input voltage is 2000v, the withstand voltage of the semiconductor switching element is still as high as 1000v. In terms of the current M0SFET element products, it is the withstand voltage If the input voltage is higher, it cannot be used, and the higher the withstand voltage of the MGSFET element, the larger the on-resistance (Rds (〇n)), resulting in an increase in conduction loss and a large increase in exchange loss due to the high voltage. (It is proportional to the square of the voltage when the _τ switching element is turned off.) 'Can't meet the requirements of high efficiency. Although the insulated gate transistor (IGBT) can withstand 12 voltage, but it is limited by the current when the element is turned off. Delay (Current with i _ phenomenon can only work in the lower operating frequency range of tens of GHz, so the design of power converters is difficult to meet the requirements of high power density and small size. Therefore, it is currently available on the market In terms of semiconductor withstand voltage regulations, in the application of input voltages below v, semiconductor devices with higher on-resistance can still be used, and suffer from the problem of low efficiency. Applications (such as the shaded area in the figure), there are no ready-made semiconductor components available. Therefore, based on the fact that the current component withstand voltage is not further advanced, it is impossible to produce a power converter with a high input voltage. Therefore, it is necessary to find other solutions. (8) Therefore, the inventor has considered a power converter architecture in which a plurality of basic circuit units are connected in series, so that each semiconductor switching element of each basic circuit unit presents each other. The type of series connection, this makes each semiconductor switch L__ 4 This paper size applies to China National Standard (CNS) A4 specifications (Please read the precautions on the back before filling this page)

A7 B7 V. Description of the invention (The input voltage is shared evenly, so the specifications of the input voltage can be seen.

= The number of modules, which only requires low-voltage semiconductors to produce electric converters that still input voltage. J The main purpose of the present invention is to provide a forward-type power converter. Multiple basic circuits are connected in series with each other, so that the withstand voltage of each semiconductor element is only 2 of the wheel-in voltage. If the number of semiconductor switching elements is only one-fourth of the input voltage of the body switching element, and the number of conductor switching elements is i 6, the withstanding voltage of each semiconductor switching element is reduced to only one per person- Input voltage, therefore, if you want to meet the ancient input voltage specifications, you only need to change the number of basic circuit units accordingly: that is, easy to solve, to overcome the shortage of semiconductor switching elements. A second object of the present invention is to provide a forward power converter, which can appropriately reduce the semiconductor-component specifications under the above-mentioned structure, and can produce a 嶋 ET device with low dust resistance and low on-resistance, so as to achieve cost reduction and high power density. With high conversion efficiency. The Consumers ’Cooperative of the Central Standards Bureau of the Ministry of Economic Affairs of the present invention aims to provide a forward power converter, in which each basic circuit unit includes two clamped diodes, two semiconductor switching elements, The staggered coupling capacitor and a transformer (including four primary coils and a secondary coil) constitute a double-switch forward filtering power conversion module, and are connected in series through multiple modules, and the transformer part is integrated into a single unit. According to the type, it is a multi-switch integrated power converter. It is a further object of the present invention to provide a forward power converter, which has both the effect of reducing conduction loss and exchange loss, since it makes low L_____5 paper size suitable for financial compensation (CNS) Λ4 · __ (2 丨0 > &297;-Printed A7 by the Consumer Cooperatives of the Central Government Bureau of the Ministry of Economic Affairs ---------- B7 V. Description of the invention (\ |) ~ ~ Semiconductor components with voltage specifications, The on-resistance is reduced, and the filter circuit formed by the leakage inductance of the transformer and the staggered coupling capacitance (equivalent to the effect of the input filter) can improve the input current waveform to a non-pulse type and reduce unnecessary harmonics, making the input current The reduction of the root-mean-square value of the electrode reduces the overall conduction loss, and because the terminal voltage of the semiconductor switching element has been reduced to one-Mth of the input voltage, compared with a single high-voltage electronic switch, the exchange loss can also be reduced to the input voltage. One-third of M. In addition, the circuit parasitic element also forms a lossless snubber circuit to avoid the surge voltage generated by the semiconductor switching element and the clamping diode, and the leakage energy storage. And recycling also improves the efficiency of the power converter. In order to allow your reviewers to further understand the structure, characteristics and other purposes of the present invention, the detailed description is attached with the drawings. (1) Schematic part: The first figure: It is a curve diagram of the withstand voltage and wheel-in voltage of a semiconductor element. The second diagram is a schematic structural diagram of a multi-module series connection of the present invention. The second A diagram is a circuit diagram of an embodiment of the present invention in which four semiconductor switching elements are connected in series. Figure 2B is the voltage or current waveform diagram of the relevant position in Figure 3a. Figure 4A to E: is the equivalent circuit diagram of each operation period in Figure 3a. Figure 5 is the third A Figure 6 shows the waveform of the terminal voltage of each semiconductor switching element. Figure 6 is the waveform of the interleaving coupling capacitor and clamp diode of Figure 3A. Figure 7: Figure 7 is the semiconductor switch of Figure 3A. Gate / Source and Input Electricity _ _ 6} A4W7l0X297 ^ t)-(Please read the notes on the back before writing this page) Install ',? Τ • II In A7 B7 Staff Consumer Cooperatives, Central Standards Bureau, Ministry of Economic Affairs Printed 5. Description of invention (waveform diagram of γ stream. ： It is the power efficiency curve of the voltage of the person in the third round of Figure A. (II) Part of the figure: (τ) Transformer (1 η, Gan ^ 10) Basic circuit unit CC1) ~ (C4) Interleaving coupling capacitor ( DC) ~ (DV) clamp diode (s1) ~ (S4) semiconductor switching element (LP1) ~ (lP6) primary coil 1S1) secondary coil ⑺ 丄) (D2) diode ( L) Inductor (C) Filtering capacitor ⑴ Load resistance (Vin) Input voltage (L 1 η) Parasitic inductance-as shown in the second figure, it is formed as a kind of transformer The output of the coil (LSI) is rectified and filtered by the diode (di) (D2), inductor (L), filter, and wave capacitor (c, ^ e), and then used by the load resistor (R), and the transformer ^ ^ The primary end of Wen Jian steals I Γ) is connected in series with multiple basic circuit units (1 β〇 ,,, flat I 1 0) of the same structure. Each basic circuit is 10 U in four sets with the same number of turns and points. Primary coils (LP1) to (LP4) placed at four corners, two semiconductor switching elements (s 1) (s 2) connected in series and in series with two of the primary windings (LP1) (LP2), two Clamp diode D v) (D c) and two interleaved light-capacitance capacitors (C1) (C2) connected to four primary coils (Lp 1) to (Lp): ^ This circuit unit (i 〇 The upper τ terminal of) is connected in series with each other and then connected to the input voltage. This paper size is Lai Jia Guan Guan (CNS) Α4 listen (2! Gx297 money). (Please read the precautions on the back before filling this page)-installed.

1. A7 printed by the Consumer Cooperatives of the Central Standards Bureau of the Ministry of Economic Affairs --------------- --- Β7 V. Description of the invention ~ '… η) connection can form a complete multi-switch Type of forward power converter. Each of the aforementioned basic circuit units (10) is connected in series with each other. If the total number of semiconductor switching elements used is M, each semiconductor switching element is averagely input into the electrical house, so that each semiconductor switching element The withstand voltage is 2 / M times the input voltage. In this way, in the case of high input voltage, the low-voltage-resistant bile ET can still be used to achieve the effect of reducing costs. As shown in the first A diagram, the power converter forming four semiconductor switching elements is used as an example to explain the working principle of the present invention. On the left side of the third A diagram, the above and the next two sets of basic circuit units are constituted and connected in series. Connected, including four semiconductor switching elements (S work) ~ (S4), four clamp two. Polar body (DV1) (DV2) (DC1) (DC2), four parent error coupling capacitors (ci) ~ (C4) is composed of a transformer (T). The transformer (D) is integrated with six sets of primary coils (L ρ 1) to (L ρ 6) and a primary line _ (L si), and the turns ratio is i. : 2 • 1.. 2: 1: N (the number of turns 2 is the combination of the adjacent primary coils representing the upper and lower basic circuit units), and the parasitic inductance (Li η) on the input power side is given by The equivalent inductor formed by the leakage inductance of the transformer and the stray inductance generated between the input source and the primary coils of the transformer, and the secondary coil (l S 1) of the transformer (T) is rectified with the same diode And the AC / DC conversion circuit used to supply the load resistance (R) through LC filtering. Switching element gate / source (V GS) voltage, source / drain voltage of each semiconductor switching element (This paper size applies to China National Standard (CNS) A4 specification (210X297)) Packing 1 (read the precautions on the back first Rewrite this page) '11Industry Consumer Cooperatives of the Central Standards Bureau of the Ministry of Economic Affairs, A7-~~ ----- B7 V. Description of the Invention ^ ^--V DS1 4), input current (j 土 n), Current / voltage (I DC1-2) (v dCi_2) waveform of clamp diode (〇〇1 \ (DC 2), μ + γ- 'of each interleaving coupling capacitance (Ci) ~ (C4), 丄 J 1 U 4 J (voltage / current) (I C1-4) and the current waveforms of the six primary coils (B p 1) to 6 (6), in the third semiconductor switch element:… / and the pole voltage The (terminal voltage) waveform shows the maximum input voltage value of each switching element is only one-half of the input voltage value. Although the effect of significantly reducing the voltage cannot be achieved in this example, it is applied to more semiconductor switching elements. It has the two-pole effect of linearly reducing the terminal voltage of each switching element. The output chirp inductance (L) is assumed to be large enough to make the output end inductance as a current source, and the staggered coupling capacitance (c .1) (C 4) is also assumed to be large enough to be regarded as a voltage source. : When entering the stable working state, as indicated in the third B diagram, there are five working modes in one exchange cycle (Ding 0 ~ τ4). For this, refer to the equivalent circuit description in the fourth A to E diagram. Of it. As shown in FIG. 4A, it shows the operating state during τ 0 ~ τ 丄. In this state, the source voltage (V DS) of the gate of each semiconductor switching element as shown in FIG. During the period, a high potential is displayed, so that the four semiconductor switching elements (s 1) to (S 4) are turned on at the same time, so they are represented by short-circuit lines in the drawing. At this time, the forward diode of the secondary side of the transformer (τ) ( D 1) is turned on, and the flywheel diode (D 2) is turned off (represented by short circuit and open circuit respectively). For the primary circuit of the transformer) ~ (LP 6), in addition to forming the main current circuit __; ___ 9 Paper size General Chinese National Ginseng Marking (CMS) A4 specification (21〇χ 297 ^ ％) — " " " " — ---------. 装 — (Please read the note on the back first Matters again _4 · 'write this page)

—S Printed by the Consumer Cooperatives of the Central Bureau of Standards of the Ministry of Economic Affairs A7 B7 V. Invention Description u) —— (LP1 si S2 LP2 S3-S4-LP3, in addition to three additional current loops, S a-S1-S2 -LP2—S3_S4—C4—Lp5 C2_LP4_Lpi si_ S2 and C30-S4-LP3-LP6, return the energy stored in each of the interleaved light capacitors (c 1) to C 4) to the load (R) side and span The electrical house of the clamp-pole body (DC1) (DC2) parasitic capacitance (CDC1) (C DC2) will rise to the input electrostatic dust (vin) 'in this cycle and remain fixed. _ During the period T1 to D2: as shown in Figure 4B and Figure 32, at time T1, to turn off the trigger signal of each semiconductor switching element, so that each switching element (s1) ~ (S4 ) Cut off (indicated by the stray capacitance forming an open circuit in the drawing), the current reflected by the inductor (L) of the output side of the transformer to the primary side of the transformer, and for the switch (: S 1): stray capacitors shaped by) to (s 4) are linearly charged. When the total voltage of each switching element (S 1) to (s 4) rises to the input voltage (V i η), it follows The directional diode (D1) is turned off, and the flywheel diode (D 2) is turned on. This cycle continues to the end of τ 2 until each of the interleaved coupling capacitors (C i) to (c 4) is completely discharged, and / After the fourth, fifth, and sixth primary coils (L p 4) to (lp 6), the current is reduced to zero. & During the period T2 ~ T3: For cooperation, see Figure 3 and Figure 4C, the input voltage (vin) is interleaved by Lin-hpKupsn LP3 and Lin-LP4-C2-LP2-C3-LP6 Coupling capacitors (ς 1) to (C4) are charged. Due to the winding polarity of the transformer (T), the two coils LP1-LP5-LP3 and LP6-LP2-LP4 on the primary side of the transformer apply the Chinese national standard on this paper ( CNS) Α4 size (2 丨 0 × 297mm) (Please read the precautions on the back first, and then go to this page) -------------- Approve clothes --- ^ ---- 1Τ ------ A7 B7 V. Description of the invention (price) — The voltage sum is zero, although the parasitic inductance (L i η) is not substantially connected to each of the interleaved light valleys (C1) ~ (C4) However, at this time, an equivalent LC filter is formed at the input by a series-parallel combination. This wave filter can reduce the input current ripple, and at the same time, across the interleaved coupling capacitors (c 丄) ~ (C4) The instantaneous voltage value is only one-half of the input voltage and has only a small amount of ripple. When the clamping diode (D c 1) (DC 2) is turned on, the semiconductor switching element source / drain is turned on. Voltage (V Ds) is clamped At half the input voltage, at the same time, the other two clamp diodes (DV1) (D.V2) are turned on to ensure that the voltage on the second and fourth semiconductor switching elements (S2) (S4) is limited At the end of the second and fourth interleaving capacitors (C2) (C4), VDS1 = VC1 + VC2-VDS2 = VC1 = 0.5Vin and VDS3 = VC3 + VC4 ~ VDS4 = VC3 = 0.5Vin, that is, The voltage applied to each switching element is equal to half the input voltage. During T3 ~ T4: as shown in Figures 3b and 4d, the clamp diode (D c 丄) (D c 2) is turned off at time T 3 and the source of each switching element / Drain voltage (VD s) is gradually reduced. Printed by the Consumers' Cooperative of the Central Standards Bureau of the Ministry of Economic Affairs. ----------------- (Please read the precautions on the back before filling this page), and clamp The terminal voltage of the diode (DC1) (DC2) slowly rises to half of the input voltage. During the period from T4 to Ding0: the total terminal voltage of the four semiconductor switching elements (s χ) ~ (s 4) can be matched to the input voltage (Vin) (that is, each The terminal voltage of the switching element is only the input voltage, and it maintains this voltage value. When the TO point arrives, the aforementioned cycle is recycled. __ 11 This: Paper is again applicable to China's national regulations ((2 Yang) Eight Days ^ (21〇 > < 297 Gongchu) I ~ ---- Printed by the Consumers Cooperative of the Central Standards Bureau of the Ministry of Economic Affairs A7 ~~~ --------- B7 V. Description of the invention (V) ~~ Each of the aforementioned staggered coupling capacitors (Cl) ~ (C4) has the following functions: 1 When the circuit is in a steady state, each staggered capacitor is equivalent to a voltage source (the voltage value is the input voltage) Half), when turned off, the total voltage value of the four switching elements is doubled by the staggered coupling capacitor and the clamped diode box. Therefore, it is similar to providing a reset on the transformer (T) Voltage (V t), this reset voltage = VDS-Vin = Vin, in order to make the iron core completely reset Due to high current collapse), the maximum duty cycle should be limited to less than 50%. 2 · When each switching element is turned off, the staggered coupling capacitor will additionally provide a current loop, LP1-C1-LP5-C4-LP3, LP4 -C2-LP2-C3-LP6 to avoid the interruption of the input current (jin), forming a semiconductor cut-off shock absorber 'for storing leakage energy. 3 · Capacitor and parasitic inductance (lin) constitute a __domain input wave filter , Can make the input current form a non-pulse type, with the effect of suppressing harmonic production ^, reducing the current root-mean-square value and reducing ripples. 4. The parent-fault coupling capacitor provides the storage and release of leakage inductance energy in each cycle. Function to improve the efficiency of the converter. To demonstrate the practical effect of the multi-switch architecture of the present invention, the input voltage specification is 360 ~ 400 volts, the output voltage is 5 volts, and the wheel output power is _ watts. The operating frequency is set to Ηζ, the transformer's resistance ratio is 20: 40: 20: 20: 40: 20: 3 (effective turns ratio is 80: 3), each semiconductor switching element uses an IRF644 with a voltage resistance of 250 volts, and a magic instrument (D 丄) Use _Q45 'of staggered capacitors ^ The value is 22 micrometers. __________12 ^ The paper size is applicable to the Chinese National Standard (CNS) A4 specification (__ ----------- (Please read the precautions on the back before writing this page)

, 1T. Lu. Printed by the Consumer Cooperatives of the Central Standards Bureau of the Ministry of Economic Affairs A7-一 ______ B7 V. Description of the invention (\ 丨) Fara, stray parasitic inductance is used as the input filter inductance, and the primary coil of the transformer is AWG26. Wire, the secondary coil is wound with copper foil, and the power converter is made with the same structure as the second A picture. The input voltage is 400 volts, the output voltage is 5 volts, and the output current is 丨 〇A. The measurement formula under the conditions is shown in the fifth figure, which shows the source / drain voltage variation waveforms of each semiconductor switching element (S 1) to (S 4). In this figure, each switching element is roughly turned on and off at the same time. Cut off, and the highest voltage is only half of the input voltage (200 volts), and because the leakage inductance energy of the transformer has been effectively used as a built-in damping circuit, therefore, the traditional forward direction is not generated in the voltage waveform. Voltage surge problem caused by the power conversion circuit, and the on-resistance of the 250-volt MOSFET used in this example is ι.12 ohm (0.28 * 4), which is also the same as the conventional dual switch architecture. 500 volts with an on resistance of 1.7 ohms (〇.85 * 2) MMOSFET or using a single switch architecture with a withstand voltage of 800 volts and an on-resistance of 3ohm MMOSFET. Compared with the MOSSFET with a resistance of 3 ohms, the conduction loss in this example is at least 50%. Reduce, the conversion efficiency must have the effect of appropriate improvement. Before each semiconductor switching element is turned on, the voltage drop across the semiconductor switching element is 1/4 of the input voltage, and the switching loss during conduction can be expressed as follows: 4 * l / 2 * CS * VdS2 = 4 * l / 2 * CS * (Vin / 4) 2 = l / 4 * (l / 2 * cS * Vin 2) < Therefore, the parent of the forward power converter architecture using this example with a single semiconductor switching element type is used The exchange loss can be reduced to only 1/4 households. ___ 13 1 This paper size applies to China National Standard (CNS) A4 specifications (2〗 Ox: 297 feet) ------- ^----------- install-(Please read first (Notes on the back then fill out this page)

, 1T • I -I I-I--1 A7

A7 Printed by the Consumers' Cooperative of the Central Standards Bureau of the Ministry of Economic Affairs I. Description of the invention The components are staggered, such as capacitors, clamped two poles, etc. The first and second groups are the switching elements =: = = voltage waveform, Trinity Bit diode (DCJ core :, (C1) ~ (C4) and the corresponding voltage waveform of the interleaved capacitor (C1) ~ core, the voltage of each (C4) is the same as the _ voltage during the entire exchange cycle Source, its voltage is kept at half of the input voltage and the terminal diode of the clamped diode (DC1) (DC2) is doubled

The “inrush voltage” shows the relative waveform of the gate / source signal (VGS) of the switching element and the input current (1 1 η) in the seventh figure. In the figure, the wheel current is 150 亳 -tj- j, γ, γ- Penwoman (DC), which has a ripple of 75 milliamps, and because the internal input of the present invention is equivalently formed, the current is in a non-pulse type, this; ^ to confirm the foregoing Speaking of words, the first figure shows the power efficiency curves under different input voltage states. At low input voltage (360V) and 1/4 load, the maximum efficiency can reach 89 · 2%, even at full load (20Α ), The efficiency is still more than 80%. Therefore, according to the foregoing description, it can be known that the structure of the multi-switch forward power converter provided by the present invention can not only increase the number of basic circuit units and make it applicable to high input voltage applications, but can also use low withstand voltage. In addition to the effect of reducing the cost of semiconductor switching elements, and because of its internal basic circuit units, the equivalent terrain is more equivalent. Chengmei ’s input chirp function < reduces the harmonic content of the input current and achieves the characteristics of reducing electromagnetic interference. With the internal staggered coupling capacitors and clamping diodes, how to effectively reduce the voltage surge? 4. The work of hanging all the switching elements and the machine with iron core reset 14 This paper size is applicable to China National Standard (CNS) A4 specifications (2 Sichuan > < 297 mm) ---- r-^ ---- ^ !! (Please read the notes on the back first. 4! Written book I)

Order mI-, ———!-I

I-II

• I-1- II A7 B7 V. Description of the invention (A) Yes, since it is truly novel and meets the input voltage field used in the industry, it is applicable to Takamatsu according to the law; please: convert to electric power Device, should meet the requirements for patent application, 爰 (Please read the note on the back first # Fill this page)

Printed by the Consumer Cooperatives of the Central Bureau of Standards of the Ministry of Economic Affairs

This paper size applies to China National Standard (CNS) Α4 specification (210 × 297 mm)

Claims (1)

Patent application scope A8 B8 C8 D8 Printed by the Consumer Cooperatives of the Central Standards Bureau of the Ministry of Economic Affairs1. A forward power converter, including: at least one set of basic circuit units containing two series-connected switching elements, rain staggered light-weight capacitors, Two clamped diodes and four sets of transformer primary coils located at the upper and lower ends of the switching element and one end of the clamped diodes; the primary stage wave network is a secondary coil of the transformer. The pole body, flywheel diode body, filter inductor, and filter capacitor form a rectifier and filter circuit. By connecting more than one set of basic circuit units to each other, the switching elements can share the input voltage evenly, reducing the The switching element withstands the voltage value. 2. The forward power converter described in item 丄 of the patent application range, wherein the voltage shared by each switching element is 2 / M times the input voltage, and M is the total number of switching elements. 3. The forward power converter according to item 1 or 2 of the scope of patent application, wherein two interleaving coupling capacitors of the basic circuit unit are bridged between four primary loops. 4. The forward power converter as described in item 1 and scope of the patent application, wherein the four primary coils of the transformer are the same number of turns. ° --------- t .—— (Read the first and then read the notes on the back, then fill out this page) Order Each paper size applies the Chinese National Standard (CNS) Λ4 specification (210X297 mm)