TWI460976B - Flyback power supply with lossless snubber - Google Patents

Description

Flyback power supply with lossless cushioning circuit

The present invention relates to a flyback power supply, and more particularly to a flyback power supply as an auxiliary power supply and a lossless cushioning circuit having a lossless cushioning circuit and facilitating the addition of multiple sets of power output.

In recent years, with the popularization and vigorous development of electronic technology, various portable electronic devices have sprung up. However, the power supply is an indispensable component of the electronic device but is rather bulky and difficult to mount on the board. As a result, Switch Mode Power Supplies (SMPS), which excels in weight, size and efficiency, has become one of the top choices for power suppliers.

In general, all types of converters can be used to implement switching power supplies, such as: half-bridge converters, full-bridge converters, push-pull converters ( Push-pull converter), flyback converter or forward converter... and so on. In the case of the power supply as an auxiliary power supply, in order to be electrically isolated from the power line and to facilitate the provision of multiple sets of outputs, both the flyback converter and the forward converter are suitable for use in the auxiliary power supply than other converters. However, since the winding structure of the internal transformer is in any case brought about leakage inductance, the flyback converter has a problem that the conversion efficiency is low and the voltage surge passes through the power transistor switch.

In view of this, some manufacturers have proposed to use the RC clamp circuit to absorb the energy stored in the leakage inductance and suppress the spike, and use the LC clamp circuit to improve the conversion efficiency. However, in this way, the reverse recovery effect of the diode is not considered, resulting in oscillation of the surge voltage during the switching. In addition, it has been proposed to reduce the switching loss (or switching loss) by using the RCD cushioning circuit to recover the energy in the leakage inductance. As shown in Figure 1, the first figure is a mutual interaction with the switch. A schematic diagram of a flyback converter of a parallel RCD snubber circuit, wherein the RCD snubber circuit 10 and the power transistor switch 20 are connected in parallel to transfer switching losses to the RCD snubber circuit 10, and since the circuits are passive components The composition is low, so the cost is relatively low. However, the loss of the resistor due to the "Fig. 1" method.

In summary, it can be seen that the prior art has long had problems of switching loss and low conversion efficiency, so it is necessary to propose an improved technical means to solve this problem.

In view of the problems of the prior art, the present invention discloses a flyback power supply with a lossless cushioning circuit.

The flyback power supply with the lossless cushioning circuit disclosed in the present invention comprises: a flyback converter, a lossless cushioning circuit and a plurality of power output terminals. The flyback converter includes a main transformer, a power transistor switch, a first output diode, a first output capacitor, and a first load, and a primary side loop of the main transformer includes an input power source and a power transistor switch. And the circuit of the secondary side of the main transformer includes a first output diode, a first output capacitor, and a first load to form a first power output.

Then, the lossless cushioning circuit is electrically connected to the flyback converter, the lossless cushioning circuit includes a return transformer, and the primary side of the return transformer transmits the cushioning diode, the first returning diode, and The cushioning capacitor is electrically connected to the power transistor switch, and the secondary side of the return transformer is transmitted through the plurality of second return diodes and the returning power The first power source output is electrically connected, wherein the cushioning diode and the cushioning capacitor are connected in series, and the cushioning diode and the cushioning capacitor are connected in parallel with each other to connect the power transistor switch.

The power supply disclosed in the present invention is as above, and the difference from the prior art is that the present invention is through a recovery transformer, a cushioning diode, a first returning diode, a second returning diode, a returning inductance, and a cushioning The capacitor forms a lossless snubber circuit, and electrically connects the lossless snubber circuit to the flyback converter to recover the energy of the leakage inductance of the main transformer and reduce the parasitic capacitance of the diode and the leakage inductance of the main transformer The resulting shock.

Through the above technical means, the present invention can achieve the technical effect of reducing switching loss and improving conversion efficiency.

The embodiments of the present invention will be described in detail below with reference to the drawings and embodiments, so that the application of the technical means to solve the technical problems and achieve the technical effects can be fully understood and implemented.

Before describing the flyback power supply with the lossless cushioning circuit disclosed in the present invention, the nouns defined by the present invention are described. The return transformer, the return diode and the return inductance of the present invention are respectively Refers to the transformer coupled to the output energy recovery circuit, and the diode and inductor in the output energy recovery circuit. The output energy recovery circuit can restore the energy of the leakage inductance of the main transformer, and will later make the electrical connection with the pattern. Detailed description.

The following is a description of the flyback power supply with the lossless cushioning circuit of the present invention. Please refer to "2A" and "2B", "2A" and "2B". The circuit diagram of the flyback power supply with the lossless cushioning circuit of the present invention, wherein "FIG. 2A" is a circuit schematic of the flyback converter 100 with the lossless cushioning circuit 200, comprising: the main transformer 110 ( T _{r 1} ), power transistor switch 120 ( M ₁ ), first output diode 130 ( D _o ), first output capacitor 140 ( C _o ), and first load 150 ( R ₁ ). The primary side of the main transformer 110 includes an input power supply 160 ( V _i ) and a power transistor switch 120, and the secondary side of the main transformer 110 includes a first output diode 130, a first output capacitor 140, and The first load 150 forms a first power output 170, and the first output capacitor 140 ( C _o ) and the first load 150 ( R ₁ ) are connected in parallel with each other. So far, the components and their constituent circuits are conventional flyback converters that do not have the lossless cushioning circuit 200. Since this is a conventional technique, it will not be described here.

Next, in the portion of the lossless snubber circuit 200, the recovery transformer 210 ( T _{r 2} ), the cushioning diode 220 ( D ₁ ), the first return diode 230 ( D ₂ ), and the cushioning A capacitor 240 ( C ₁ ), a plurality of second return diodes 250 ( D ₃ , D ₄ ), and a return inductor 260 ( L _o ). The cushioning diode 220 ( D ₁ ) and the cushioning capacitor 240 ( C ₁ ) are connected in series with each other, and the cushioning diode 220 ( D ₁ ) and the cushioning capacitor 240 ( C ₁ ) connected in series are connected in parallel with each other. The crystal switch 120 ( M ₁ ) has a flywheel diode 121 and an equivalent capacitor 122 connected in parallel with the power transistor switch 120 ( M ₁ ). The lossless snubber circuit 200 is electrically connected to the primary side and the secondary side winding of the main transformer 110 to form a flyback converter 100 having a lossless snubber circuit 200. In particular, the primary side of the main transformer 110 has an equivalent magnetizing inductance 111 ( L _{m 11} ) and an equivalent leakage inductance 112 ( L _{K 11} ), and its electrical connection can be regarded as the primary side of the main transformer 110. After being connected in parallel with the equivalent magnetizing inductance 111 ( L _{m 11} ), it is electrically connected to the equivalent leakage inductance 112 ( L _{K 11} ). In addition, the primary side of the recovery transformer 210 also has an equivalent excitation inductance 211 ( L _{m 21} ) and an equivalent leakage inductance 212 ( L _{K 21} ), and the electrical connection manner can be regarded as the primary side of the return transformer 210 and the equivalent. The magnetizing inductances 211 ( L _{m 21} ) are connected in parallel to each other and then electrically connected to the equivalent leakage inductance 212 ( L _{K 21} ).

As described above, if the flyback converter 100 having the lossless snubber circuit has a plurality of outputs, the second output diode 271 and the second output capacitor 272 can be utilized as illustrated in FIG. 2B. The second load 273 constitutes a second power output 270, and the second power output 270 is electrically connected to the secondary side of the main transformer 110. In particular, the present invention does not limit the number of second power output ends 270. In other words, a plurality of second power output ends 270 may be present at the same time, and each of the second power output ends 270 includes a second The output diode 271 and the second output capacitor 272 and the second load 273 connected in parallel are electrically connected to the secondary side of the main transformer 110. When there is a second power output 270, the flyback power supply of the present invention having the lossless cushioning circuit 200 has two power output (ie, the first power output 170 and the second power output 270); When there are two second power output ends 270, the flyback power supply of the present invention having the lossless cushioning circuit 200 has three power output outputs (ie, the first power output 170 and the two second power outputs) 270) and so on. In actual implementation, if there is only the first power output terminal 170 and no second power output terminal 270, it is a single output power supply as illustrated in "FIG. 2A".

The lossless snubber circuit 200 includes a return transformer 210. The primary side of the return transformer 210 is electrically connected to the power transistor switch 120 through the snubber diode 220, the first return diode 230, and the snubber capacitor 240. The secondary side of the recovery transformer 210 is electrically connected to the first power output terminal 170 through a plurality of second return diodes and a return inductor.

The following description will be made in the following manner in conjunction with "3rd figure", such as " 3 is a circuit diagram of a flyback five-output power supply with a lossless cushioning circuit according to the present invention. As mentioned above, the present invention does not limit the number of second power output terminals 270. Taking five outputs as an example, that is, as shown in FIG. 3, the first power output terminal 170 is combined with the four second power output ends 270 to implement a flyback five-output power supply with a lossless cushioning circuit. 100a. The second power output terminal 270 adjacent to the first power output terminal 170 can be adjusted to the circuit connection mode illustrated in FIG. 3 based on the convenience of circuit wiring.

For the sake of convenience, the seven operating modes (Mode 1 to Mode 7) of this circuit are described below with reference to the circuit of "Phase 2A" to "4G". Fig. 5 (i.e., a waveform diagram of the power supply of the present invention in each mode) illustrates the waveform changes of current and voltage of key elements in each mode. Please refer to "4A" first, and "4A" is the power supply to which the present invention is applied in mode one ( t ₀ Schematic diagram of the operation of t < t ₁ ). When t = t ₀ , the power transistor switch 120 ( M ₁ ) is turned on, at which time the leakage inductance current I _{LK 11 of the} main transformer 110 ( T _{r 1} ) is smaller than the excitation current I _{Lm 11} , the main transformer 110 ( T _{r 1)} continuously through a first output diode 130 (D _o) transfer energy to a first load 150 (R _o). During this time interval, the terminal voltage of the equivalent leakage inductance 112 ( L _{K 11} ) rises to "( V _i + V _o / N )", causing the current I _{LK 11} to increase rapidly, but at this time, the current I _{Lm 11} It is linearly falling. In addition, once the power transistor switch 120 ( M ₁ ) is turned ON, the voltage of the buffer capacitor 240 ( C ₁ ) terminal V _{C 1} is directly applied to the primary winding of the return transformer 210 ( T _{r 2} ), so that A return diode 230 ( D ₂ ) and a second return diode 250 ( D ₃ ) are forward biased, so the energy stored in the cushioning capacitor 240 ( C ₁ ) is transferred via the return inductor 260 ( L _o ) To the output.

Please refer to "Fig. 4B", "Fig. 4B" is the power supply to which the present invention is applied in mode 2 ( t ₁ Schematic diagram of the operation of t < t ₂ ). At t ₁ , when I _{LK 11} is equal to I _{Lm 11} , the first output diode 130 ( D _o ) is reverse biased. During this time interval, I _{Lm 11} increases linearly and main transformer 110 ( T _{r 1} ) stores energy, while cushioning capacitor 240 ( C ₁ ) keeps releasing its energy, which will pass through first return diode 230 ( D ₂ ), the transformer 210 ( T _{r 2} ), the second return diode 250 ( D ₃ ), and the return inductor 260 ( L _o ) to the first load 150 ( R _o ).

Please refer to "4C" and "4C" for the power supply to which the present invention is applied in mode 3 ( t ₂ Schematic diagram of the operation of t < t ₃ ). When this mode is started after the energy stored in the cushioning capacitor 240 ( C ₁ ) is completely released, the cushioning diode 220 ( D ₁ ) and the second returning diode 250 ( D ₄ ) will become forward biased. The second return diode 250 ( D ₃ ) is reverse biased, in which case the magnetization energy stored in the return transformer 210 ( T _{r 2} ) passes through the cushioning diode 220 ( D ₁ ) and the first return dipole The body 230 ( D ₂ ) is in a freewheeling state, and the energy stored in the recovery inductor 260 ( L _o ) is transmitted to the first load 150 ( R _o ) via the second return diode 250 ( D ₄ ). In this mode, the main transformer 110 ( T _{r 1} ) is in the energy storage phase and the exciting current I _{Lm 11} rises linearly.

Please refer to "4D", "4D" is the power supply to which the present invention is applied in mode 4 ( t ₃ Schematic diagram of the operation of t < t ₄ ). When t = t ₃ , the power transistor switch 120 ( M ₁ ) is turned off, and the inductor current I _{Lm 11} is kept continuous through the equivalent capacitor 122 ( C _{M 1} ) and the cushioning capacitor 240 ( C ₁ ). Since the cushioning capacitor 240 ( C ₁ ) is larger than the equivalent capacitor 122 ( C _{M 1} ), the voltage of the power transistor switch 120 ( M ₁ ) terminal is smoothly increased from “0” to “( V _i + V _o / N )). ". Therefore, the power transistor switch 120 ( M ₁ ) operates in a Zero-Voltage Transition (ZVT). The cushioning diode 220 ( D ₁ ), the first returning diode 230 ( D ₂ ), and the second returning diode 250 ( D ₄ ) continue to pass through the equivalent magnetizing inductance 211 ( L _m21 ) and the returning inductance 260 ( L _o ) is maintained in the freewheeling state.

Please refer to "4E" and "4E" for the power supply to which the present invention is applied in mode 5 ( t ₄ Schematic diagram of the operation of t < t ₅ ). At t ₄ , the voltage at the terminal of the cushioning capacitor 240 ( C ₁ ) reaches "( V _i + V _o / N )", which causes the first output diode 130 ( D _o ) to be forward biased. Thus, the energy stored in main transformer 110 (T _{r 1)} can be released to a first load 150 (R _o) via the first output diode 130 (D _o), while the current I _{Lm 11} also decreases linearly, while equivalent The magnetizing inductance 211 ( L _m21 ) and the returning inductance 260 ( L _o ) are maintained in the flywheel state.

Please refer to "4F" and "4F" for the power supply to which the present invention is applied in mode 6 ( t ₅ Schematic diagram of the operation of t < t ₆ ). When the energy stored in the recovery inductor 260 ( L _o ) is completely released to the first load 150 ( R _o ), the mode 6 is activated, and the second return diode 250 ( D ₄ ) is reverse biased, and at this time only the main transformer 110 (T _{r 1)} supplying energy to a first load 150 (R _o) via the first output diode 130 (D _o).

Please refer to "4G" and "4G" for applying the power supply of the present invention in mode seven ( t ₆ Schematic diagram of the operation of t < t ₇ ). At t ₆ , the energy stored in the equivalent magnetizing inductance 211 ( L _m21 ) is reset to “0” and the cushioning diode 220 ( D ₁ ) and the first returning diode 230 ( D ₂ ) are turned off ( Off). The current I _{Lm 11} continues to release energy to the first load 150 ( R _o ) and decreases linearly. When the power transistor switch 120 ( M ₁ ) is turned on at the end of mode seven, a new switching cycle will begin.

In summary, it can be seen that the difference between the present invention and the prior art is that the recovery transformer 210, the cushioning diode 220, the first returning diode 230, the second returning diode 250, the returning inductance 260, and the cushioning are transmitted. The capacitor 240 forms a lossless snubber circuit 200 and electrically connects the lossless snubber circuit 200 to the flyback converter for recovery The energy of the leakage inductance of the main transformer 110 and the oscillation caused by the parasitic capacitance of the diode and the leakage inductance of the main transformer 110 can solve the problems of the prior art by the technical means, thereby achieving the reduction of the switching loss. And the technical effect of improving conversion efficiency.

While the present invention has been described above in the foregoing embodiments, it is not intended to limit the invention, and the invention may be modified and modified without departing from the spirit and scope of the invention. The scope of patent protection shall be subject to the definition of the scope of the patent application attached to this specification.

10‧‧‧RCD cushioning circuit

20‧‧‧Power transistor switch

100‧‧‧Return-to-speed converter with lossless cushioning circuit

110‧‧‧ main transformer

111‧‧‧Equivalent magnetizing inductance

112‧‧‧Equivalent leakage inductance

120‧‧‧Power transistor switch

121‧‧‧Flywheel diode

122‧‧‧ equivalent capacitance

130‧‧‧First output diode

140‧‧‧First output capacitor

150‧‧‧First load

160‧‧‧Input power supply

170‧‧‧First power output

200‧‧‧ lossless cushioning circuit

210‧‧‧Restoring transformer

211‧‧‧ equivalent magnetizing inductance

212‧‧‧Equivalent leakage inductance

220‧‧‧ cushioning diode

230‧‧‧First Responsive Diode

240‧‧‧ cushioning capacitor

250‧‧‧Secondary return diode

260‧‧‧Responsive inductance

270‧‧‧second power output

271‧‧‧Second output diode

272‧‧‧second output capacitor

273‧‧‧second load

FIG. 1 is a schematic diagram of a conventional flyback converter having an RCD snubber circuit in parallel with a switch.

2A and 2B are circuit diagrams showing a flyback power supply with a lossless cushioning circuit of the present invention.

FIG. 3 is a schematic circuit diagram of a flyback five-output power supply with a lossless cushioning circuit according to the present invention.

Figure 4A is a diagram showing the application of the power supply of the present invention in mode one ( t ₀ Schematic diagram of the operation of t < t ₁ ).

Figure 4B is a diagram showing the application of the power supply of the present invention to mode 2 ( t ₁ Schematic diagram of the operation of t < t ₂ ).

Figure 4C is a diagram showing the application of the power supply of the present invention in mode three ( t ₂ Schematic diagram of the operation of t < t ₃ ).

Figure 4D is a power supply to which the present invention is applied in mode four ( t ₃ Schematic diagram of the operation of t < t ₄ ).

Figure 4E is a diagram showing the application of the power supply of the present invention in mode 5 ( t ₄ Schematic diagram of the operation of t < t ₅ ).

Figure 4F is a power supply to which the present invention is applied in mode six ( t ₅ Schematic diagram of the operation of t < t ₆ ).

Figure 4G is a diagram showing the application of the power supply of the present invention in mode seven ( t ₆ Schematic diagram of the operation of t < t ₇ ).

Fig. 5 is a waveform diagram showing the power supply of the present invention in each mode.

100‧‧‧Return-to-speed converter with lossless cushioning circuit

110‧‧‧ main transformer

111‧‧‧Equivalent magnetizing inductance

112‧‧‧Equivalent leakage inductance

120‧‧‧Power transistor switch

121‧‧‧Flywheel diode

122‧‧‧ equivalent capacitance

130‧‧‧First output diode

140‧‧‧First output capacitor

150‧‧‧First load

160‧‧‧Input power supply

170‧‧‧First power output

200‧‧‧ lossless cushioning circuit

210‧‧‧Restoring transformer

211‧‧‧ equivalent magnetizing inductance

212‧‧‧Equivalent leakage inductance

220‧‧‧ cushioning diode

230‧‧‧First Responsive Diode

240‧‧‧ cushioning capacitor

250‧‧‧Secondary return diode

260‧‧‧Responsive inductance

Claims (9)

A flyback power supply with a lossless cushioning circuit, comprising: a flyback converter, the flyback converter comprising a main transformer, a power transistor switch, a first output diode, a first output capacitor and a first load, wherein a loop of the primary side of the main transformer includes an input power source and the power transistor switch, and a circuit of the secondary side of the main transformer includes the first output diode, The first output capacitor and the first load form a first power output terminal; and a lossless cushioning circuit for electrically connecting the flyback converter, the lossless cushioning circuit includes a return transformer, The primary side of the recovery transformer is electrically connected to the power transistor switch through a cushioning diode, a first returning diode and a cushioning capacitor, and the secondary side of the returning transformer is transmitted through the plurality of second returning poles The body and a returning inductor are electrically connected to the first power output end, wherein the cushioning diode and the cushioning capacitor are connected in series with each other, and the cushioning diode connected in series with the damping capacitor is connected in parallel with the cushioning capacitor turn off. The flyback power supply device with the lossless cushioning circuit of claim 1, wherein the power supply further comprises a plurality of second power output ends, each of the second power output ends comprises a first The second output diode and a second output capacitor and a second load connected in parallel are electrically connected to the secondary side of the main transformer. The flyback power supply with a lossless cushioning circuit according to claim 1, wherein the primary side of the main transformer has an equivalent magnetizing inductance and an equivalent leakage inductance. The flyback type power with the lossless cushioning circuit as described in item 3 of the patent application scope a source supply, wherein a primary side of the main transformer and the equivalent magnetizing inductance are connected in parallel with each other and electrically connected to the equivalent leakage inductance. The flyback power supply with a lossless cushioning circuit as described in claim 1, wherein the primary side of the return transformer has an equivalent magnetizing inductance and an equivalent leakage inductance. The flyback power supply with a lossless cushioning circuit according to claim 5, wherein the primary side of the return transformer and the equivalent magnetizing inductance are connected in parallel with each other, and are electrically connected to the equivalent leakage inductance. . The flyback power supply with a lossless cushioning circuit according to claim 6, wherein the equivalent leakage inductance is connected in series with the first returning diode, the equivalent magnetizing inductance and the cushioning The diodes are connected in parallel with each other. The flyback power supply with a lossless cushioning circuit as described in claim 1, wherein the power transistor switch has a flywheel diode and an equivalent capacitor connected in parallel. The flyback power supply with a lossless cushioning circuit according to claim 1, wherein the first output capacitor and the first load are connected in parallel with each other.