KR20090125321A - Driving circuit of synchronous rectifier for flyback converter - Google Patents

Abstract

PURPOSE: A synchronous rectifier driver circuit for a flyback converter is provided to simplify a structure of a secondary side rectification circuit of the flyback converter by driving a secondary side synchronous rectifier without receiving information about voltage from a first side of the flyback converter. CONSTITUTION: A synchronization pulse generating circuit(201) includes a synchronization resistance(Rsync) and a synchronization diode(Dsync). The synchronization pulse generating circuit generates a synchronization pulse signal for synchronizing a start time of a synchronous rectifier(SR). A turn-on driving voltage generation unit(202) applies synchronous rectifier driving currents to a gate terminal of the synchronous rectifier. A turn-off driving voltage discharge unit(203) discharges voltage, charged in the gate of the synchronous rectifier, to earth.

Description

Synchronous Rectifier Drive Circuit for Flyback Converter {DRIVING CIRCUIT OF SYNCHRONOUS RECTIFIER FOR FLYBACK CONVERTER}

The present invention relates to a synchronous rectifier driving circuit for a flyback converter. In particular, the secondary-side synchronous rectifier of the flyback converter can be driven using a synchronization pulse signal generated based on the voltage level of the transformer secondary coil of the flyback converter. The present invention relates to a synchronous rectifier driving circuit for a flyback converter.

Recently, a flyback converter is widely used in many electrical, electronic and communication equipments such as notebooks and PCs, which has the advantage of miniaturization of power circuits and low manufacturing costs.

However, as the power capacity increases with the recent increase in the performance of electrical, electronic, and communication equipment, as shown in FIG. 1, the voltage of the rectifying diode is used in the power structure using the rectifying diode as the secondary side rectifier of the flyback converter. The drop loss is large, which causes a problem that the efficiency of the entire power supply circuit is lowered.

In order to solve the above problems, conventionally, as shown in FIG. 2, a power efficient synchronous rectifier is devised and used as a secondary side rectifier of a flyback converter.

2 is an internal circuit diagram of a flyback converter using a conventional synchronous rectifier as a secondary side rectifier, and a flyback converter using a synchronous rectifier as a secondary side rectifier is a power semiconductor switch (MOSFET) Q ₁ switching by a pulse width modulation method. The winding ratio of the primary coil (L ₁ ), the primary coil (L ₁ ), and the secondary coil (L ₂ ) to which the input voltage (V _in ) is applied by switching the power semiconductor switch (MOSFET) Q ₁ . 2, the transformer consisting of a secondary coil included in the primary coil to the number of turns / first secondary coil voltage is converted to the number of turns) in the coil _{(L 1) (L 2)} , the synchronous rectifier drive circuit of (L ₂₎ (T ), And a synchronous rectifier (SR) and an output capacitor (C _o ).

As described above, in the conventional flyback converter using the synchronous rectifier as the secondary side rectifier, when the power semiconductor switch (MOSFET) Q ₁ is turned on, the primary side current i ₁ flows to the primary coil of the transformer T. The primary side voltage V _in equal to the input voltage V _in is applied to L ₁ ). At this time, the secondary synchronous rectifier SR is turned off by the driving circuit.

On the other hand, if the power semiconductor switch (MOSFET) (Q ₁₎ is turned off via a transformer (T) is the energy of the primary coil (L ₁₎ is guided to the secondary coil (L ₂₎ the secondary current (i ₂₎ flows is transferred to the output capacitor (C _o), at the same time, the primary coil (L ₁₎ energy is a secondary coil (L ₃₎ is a synchronous rectifier rectifying operation is received secondary-side synchronous rectifier (SR) is supplied to the driving power induced in the Done.

However, in the synchronous rectifier driving circuit of the conventional flyback converter, as described above, additional coils must be additionally installed in the synchronous rectifier driving circuit in the transformer T of the flyback converter, which not only complicates the structure of the transformer. In addition, the circuit for the synchronous rectifier (SR) power semiconductor switch (MOSFET) drive is also complicated to increase the number of devices, thereby increasing the area of the printed circuit board has a problem that the manufacturing cost increases.

The present invention has been made to solve the above-described problem, by detecting the voltage level of the secondary coil (L ₂ ) of the flyback converter transformer to generate a synchronization pulse signal according to the detected voltage level, the generated synchronization pulse signal An object of the present invention is to provide a synchronous rectifier driving circuit for a flyback converter capable of driving a flyback converter secondary side synchronous rectifier by controlling a photocoupler of a low turn-on driving voltage generator and a transistor of a turn-off driving voltage discharge part.

Another object of the present invention is to provide a synchronous rectifier driving circuit for a flyback converter which simplifies the synchronous rectifier driving circuit and reduces manufacturing costs.

The synchronous rectifier driving circuit for a flyback converter according to an embodiment of the present invention for achieving the above object is composed of a synchronous resistor and a synchronous diode to generate a synchronization pulse signal for synchronizing the driving time of the synchronous rectifier, When the voltage level applied to the synchronous diode is higher than the diode turn-on voltage according to the voltage level of the back converter secondary coil, the synchronous diode is turned on to generate a negative logic synchronization pulse signal, and the flyback converter secondary coil A synchronous pulse generating circuit unit for generating a positive logic synchronous pulse signal by turning off the synchronous diode when the voltage level applied to the synchronous diode is lower than the diode turn-on voltage according to the voltage level of the synchronous diode; A turn-on driving voltage generation unit which is turned on based on a negative logic synchronization pulse signal applied from the synchronization pulse generation circuit unit and applies a synchronous rectifier driving current to a gate terminal of the synchronous rectifier; And a turn-off driving voltage discharge unit that is turned on based on a positive logic synchronization pulse signal applied from the synchronization pulse generation circuit unit and discharges a voltage charged in the gate of the synchronous rectifier to ground.

Further, the synchronous pulse generating circuit portion is configured by connecting one terminal of the synchronous resistor and the anode terminal of the synchronous diode in series, and the other end of the synchronous resistor not connected to the synchronous diode is connected to a synchronous rectifier driving power supply. The cathode terminal of the synchronous diode is preferably connected in common to one terminal of the transformer secondary coil of the flyback converter and the drain terminal of the synchronous rectifier.

The turn-on driving voltage generator includes a first resistor, a second resistor, and a photo coupler, wherein one terminal of the first resistor and one terminal of the second resistor are the synchronous resistors of the synchronous pulse generator. The other end of the first resistor is connected to the anode terminal of the photodiode on the primary side of the photocoupler, and the cathode terminal of the photodiode on the primary side of the photocoupler is connected to the synchronous rectifier driving power supply. The other end of the second resistor is connected to the collector terminal of the phototransistor on the photocoupler secondary side in common with the synchronous resistance of the pulse generating circuit portion and the series connection point of the synchronous diode. The terminal terminal is preferably connected to the gate terminal of the synchronous rectifier.

The turn-off driving voltage discharge unit may include a base resistor and a transistor, and one terminal of the base resistor may include a synchronous resistor of the synchronous pulse generating circuit unit together with a cathode terminal of the photocoupler photodiode of the turn-on driving voltage generator. And the other end of the base resistor are connected to the base terminal of the transistor, and the collector terminal of the transistor is coupled with the emitter terminal of the phototransistor on the photocoupler secondary side. It is preferable that it is commonly connected to the gate terminal of the rectifier, and the emitter terminal of the transistor is connected to ground.

According to the synchronous rectifier driving circuit for the flyback converter of the present invention, the secondary side of the flyback converter to which the synchronous rectifier is applied by allowing the secondary rectifier to be driven without receiving voltage information from the primary side of the flyback converter. The structure of the rectifier circuit can be simplified more.

In addition, the manufacturing cost can be reduced by implementing the synchronous rectifier driving circuit for the flyback converter using a minimum number of components.

Hereinafter, a synchronous rectifier driving circuit for a flyback converter according to an exemplary embodiment of the present invention will be described in detail with reference to the accompanying drawings. In the following description of the present invention, detailed descriptions of related well-known technologies or configurations will be omitted when it is determined that the detailed description of the present invention may unnecessarily obscure the subject matter of the present invention. Terms to be described later are terms defined in consideration of functions in the present invention, and may be changed according to intentions or customs of users or operators. Therefore, the definition should be made based on the contents throughout the specification.

First, the synchronous rectifier according to the present invention uses a rectifier diode as a secondary rectifier in order to reduce the power loss due to the voltage drop of the secondary rectifier diode in the prior art power semiconductor switch having a small conduction resistance instead of the rectifier diode (Preferably, it refers to a rectifier that reduces power loss by using a metal oxide semiconductor field effect transistor (MOSFET).

3 is a schematic circuit diagram of a flyback converter to which a synchronous rectifier driving circuit according to the present invention is applied.

As shown in FIG. 3, the flyback converter to which the synchronous rectifier driving circuit according to the present invention is applied comprises a primary circuit and a secondary circuit of a transformer T, and the primary circuit includes a pulse width modulation ( Power semiconductor switch (MOSFET) (Q ₁ ) and power semiconductor switch (MOSFET) (Q ₁ ) operating according to the pulse width modulation (PWM) signal by the PWM circuit to the primary coil (L ₁₎ ) And the primary coil of the transformer T to guide the secondary side with the winding ratio of the secondary coil (L ₂ ) (= number of turns of the secondary coil (L ₂ ) / number of turns of the primary coil (L ₁ )) L ₁ ), and the secondary circuit 10 includes a synchronous rectifier SR and an output capacitor C _o connected to the secondary coil L _{2 and the} secondary coil L ₂ of the transformer T. And a synchronous rectifier driving circuit 20 for a flyback converter according to the present invention for driving the synchronous rectifier SR.

4 is a synchronous rectifier driving circuit for a flyback converter according to the present invention, and includes a synchronous pulse generating circuit unit 201, a turn-on driving voltage generating unit 202, and a turn-off driving voltage discharge unit 203.

In such configuration, the synchronous pulse generating circuit 201 is the anode terminal of the synchronous diode (D _sync) and one terminal of the synchronous resistance (R _sync) connected in series and configured, that is not connected to the synchronous diode (D _sync) The other end of the synchronous resistor (R _sync ) is connected to the synchronous rectifier driving power supply (V _drv ), and the cathode terminal of the synchronous diode (D _sync ) is connected to one terminal of the transformer secondary coil (L ₂ ) of the flyback converter and the synchronous rectifier ( It is commonly connected to the drain terminal of SR.

)에서 음(-)논 리의 동기화펄스신호가 발생되고, 플라이백 컨버터 2차측 코일(L₂)에 전류가 흐르지 않게 되는 경우에는 플라이백 컨버터 2차측 코일(L₂)의 전압레벨에 따라 동기다이오드(D_sync)에 걸리는 전압레벨이 다이오드 턴온 전압보다 낮게 되며, 이러한 경우에는 동기다이오드(D_sync)가 턴오프되어 동기화펄스신호를 발생시키는 동기저항(R_sync)과 동기다이오드(D_sync)의 직렬연결 접속점(

)에서 양(+)논리의 동기화펄스신호가 발생된다.The sync pulse generating circuit unit 201 having the above-described configuration generates a sync pulse signal for synchronizing the driving time of the synchronous rectifier SR, but when a current flows in the flyback converter secondary coil L ₂ . According to the voltage level of the flyback converter secondary coil L ₂ , the voltage level applied to the sync diode D _sync is higher than the diode turn-on voltage. In this case, the sync diode D _sync is turned on to generate a sync pulse signal. Series connection point of _sync resistor (R _sync ) and sync diode (D _sync )

) Synchronous diode in accordance with the voltage level, the flyback converter, the secondary coil (L ₂₎ if no non-Li, and the synchronized pulse signal is generated, the flyback converter 2 current to the primary coil (L ₂₎ flow -) negative (in The voltage level applied to (D _sync ) becomes lower than the diode turn-on voltage. In this case, the sync resistor (R _sync ) and the sync diode (D _sync ) in which the _sync diode (D _sync ) is turned off to generate a sync pulse signal are generated. Connection point

), A positive logic pulse signal is generated.

)에 공통으로 접속된다.Meanwhile, the turn-on driving voltage generator 202 includes a first resistor R ₁ , a second resistor R ₂ , and a photo coupler U _on , and one terminal and the second terminal of the first resistor R ₁ . One end of the resistor R ₂ is commonly connected to the synchronous rectifier driving power supply V _drv together with the other end of the synchronous pulse generating circuit unit 201, the synchronous resistor R _sync , and the other end of the first resistor R ₁ is The photocoupler U _on is connected to the anode terminal of the photodiode _{on the} primary side, and the cathode terminal of the photodiode on the primary side of the photocoupler U _on is synchronized with the sync resistor R _sync of the sync pulse generating circuit section 201 and the sync diode. Series connection point of (D _sync )

) Are commonly connected.

Further, the photo-coupler (U _on) the collector terminal of the phototransistor of the secondary side is connected to the other end of the second resistor (R _2), photo-coupler (U _on) second emitter terminal of the primary side phototransistor is synchronous rectifier (SR Is connected to the gate terminal.

The turn-on driving voltage generator 202 having the above-described configuration has a negative logic synchronization applied from the sync pulse generator circuit 201 when the _sync diode D _{sync of the} sync pulse generator circuit 201 is turned on. According to the pulse signal, the photodiode and the phototransistor of the photocoupler U _on are turned on to apply the synchronous rectifier driving current to the gate terminal of the synchronous rectifier SR.

)에 공통으로 접속되고, 베이스저항(R_b)의 타단은 트랜지스터(TR_off)의 베이스 단자에 접속되며, 트랜지스터(TR_off)의 컬렉터 단자는 포토커플러(U_on) 2차측의 광트랜지스터의 에미터 단자와 함께 동기정류기(SR)의 게이트 단자에 공통으로 접속되고, 트랜지스터(TR_off)의 에미터 단자는 접지에 접속된다.On the other hand, the turn-off driving voltage discharge unit 203 is composed of a base resistor (R _b ) and a transistor (TR _off ), one terminal of the base resistor (R _b ) is a photocoupler ( U _on ) A series connection point of the sync resistor R _sync of the sync pulse generating circuit unit 201 and the sync diode D _sync together with the cathode terminal of the photodiode (

) Are connected in common to the base resistor (R _b) of the other end of the transistor (TR _off) for being connected to the base terminal, a collector terminal of the transistor (TR _off) is photo-coupler (U _on) the emitter of the photo transistor of the secondary side The terminal is connected to the gate terminal of the synchronous rectifier SR together with the emitter terminal, and the emitter terminal of the transistor TR _off is connected to the ground.

The turn-off driving voltage discharge unit 203 having such a configuration synchronizes the positive logic applied from the sync pulse generation circuit unit 201 when the _sync diode D _sync of the sync pulse generation circuit unit 201 is turned off. The transistor TR _off is turned on according to the pulse signal to discharge the voltage charged in the gate of the synchronous rectifier SR to ground.

As described above, the synchronous rectifier driving power source V _drv may be used as a driving power source of the synchronous rectifier driving circuit 20 shown in FIG. 4 and connected to the positive terminal of the flyback converter output voltage _Vo . In the transformer T, a separate driving power source may be formed and connected to the auxiliary coil and the rectifier diode, or may be connected to a separate driving power source supplied from an external circuit of the flyback converter.

5 is a diagram illustrating a theoretical operation waveform of a synchronous rectifier driving circuit for a flyback converter according to the present invention.

In FIG. 5, the waveform of V _GS1 represents a theoretical waveform of the gate-source voltage applied to the gate terminal of the primary power semiconductor switch (MOSFET) Q ₁ through pulse width modulation, and i ₁ is a power semiconductor switch (MOSFET). (Q ₁ ) shows the theoretical waveform of the linearly increasing primary current when turned on in response to the pulse width modulation signal.

의 파형은 동기펄스발생회로부(201)의 동기저항(R_sync)와 동기다이오드 (D_sync)의 직렬연결 접속점(

)에서 발생되는 전압파형을 나타내며, V_GSS의 파형은 동기정류기(SR)의 게이트 단자에 인가되는 게이트-소스 전압의 이론적 파형이다.The waveform of V ₁ represents the voltage applied to the primary coil L ₁ of the transformer T,

The waveform of is the series connection point of the sync resistor R _sync of the sync pulse generating circuit unit 201 and the sync diode D _sync (

The waveform of V _GSS is a theoretical waveform of the gate-source voltage applied to the gate terminal of the synchronous rectifier SR.

i ₂ represents the theoretical waveform of the secondary side current which decreases linearly when the synchronous rectifier SR is turned on by the turn-on driving voltage generator 202, and V ₂ represents the secondary coil L ₂ of the transformer T. Is the theoretical waveform of the induced voltage.

Hereinafter, an operating state of the synchronous rectifier driving circuit for a flyback converter according to the present invention will be described with reference to FIG. 4.

First, when the power semiconductor switch (MOSFET) Q ₁ operating in response to the pulse width modulation signal by the primary side pulse width modulation (PWM) circuit of the flyback converter is turned on, the primary side current When (i ₁ ) flows so that a primary side voltage equal to the input voltage V _in is applied to the primary coil L ₁ of the transformer T, and the power semiconductor switch (MOSFET) Q ₁ is turned off, through the transformer (T) is the energy of the primary coil (L ₁₎ is guided to the secondary coil (L ₂₎ to flow the secondary current (i _2).

As described above, the primary side voltage is 2 by the operation of the power semiconductor switch (MOSFET) Q _{1 which} is turned on or off in response to the pulse width modulated signal by the primary side pulse width modulated (PWM) circuit of the flyback converter. When induced with the difference voltage, a voltage V _AK as shown in Equation 1 is applied between the anode and the cathode terminal of the sync diode D _sync of the sync pulse generating circuit unit 201.

In Equation 1, V _drv is a synchronous rectifier driving voltage, V _o is an output voltage, and I _sync is a synchronous current flowing through a synchronous resistor R _sync and a sync diode D _sync of the synchronous pulse generating circuit unit 201. I _sync = (V _drv -V _o + V ₂ -V _AK ) / R _sync , where R _sync I _sync is the voltage drop that follows Ohm's law shown in the _sync resistance (R _sync ).

In addition, since the voltage drop (R _sync I _sync ) of the synchronous rectifier driving voltage (V _drv ), the output voltage (V _o ), and the synchronous resistor (R _sync ) in Equation 1 may be regarded as a constant voltage or almost constant voltage, _If the voltage of V _drv -R _sync I _sync -V _o in Equation 1 is defined as a constant voltage K [V], Equation 1 may be re-expressed as in Equation 2 below.

)의 전압은 (V_o-V₂)+V_{AK ,on}가 된다.As can be seen from Equation 2, the primary power is controlled by an operation of a power semiconductor switch (MOSFET) Q _{1 that} is turned on or off in response to a pulse width modulation signal by a primary pulse width modulation (PWM) circuit of a flyback converter. As the energy of the coil L ₁ is induced to the secondary coil L ₂ , the secondary voltage V ₂ is changed to change the voltage V _AK between the anode of the synchronous diode D _sync and the cathode terminal. . At this time, the power semiconductor switch (MOSFET) (Q ₁₎ is turned is turned off via a transformer (T) is the energy of the primary coil (L ₁₎ is guided to the secondary coil (L ₂₎ the secondary current (i ₂₎ , synchronous diode (D _sync) on is larger than the turn-on voltage (V _{AK, on)} of a voltage (V _AK) is synchronized diode (D _sync) between the anode and cathode terminal synchronous diode (D _sync) when the flow is turned on, which Due to this, the series connection point of the sync resistor R _sync of the sync pulse generating circuit unit 201 and the sync diode D _sync (

) Voltage becomes (V _o -V ₂ ) + V _{AK , on} .

)의 전압은 동기정류기 구동전압(V_drv)이 된다.Then, when the power semiconductor switch (MOSFET) Q ₁ is turned on so that the secondary side current i ₂ does not flow in the secondary coil L ₂ , the voltage V between the anode of the synchronous diode D _sync and the cathode terminal. _AK) is smaller than the turn-on voltage (V _{AK, on)} of the synchronous diode (D _sync), the synchronization diode (D _sync) is turned off, this synchronous resistance because of the synchronous pulse generating circuit (201) (R _sync) and Serial connection point of synchronous diode (D _sync )

) Is the synchronous rectifier driving voltage (V _drv ).

)의 전압이 (V_o- V₂)+V_AK,on과 같이 되어 동기다이오드(D_sync)가 턴온될 때 동작한다. 동기펄스발생회로부(201)의 동기저항(R_sync)과 동기다이오드(D_sync)의 직렬연결 접속점(

)의 전압이 (V_o-V₂)+V_{AK ,on}과 같이 되어 동기다이오드(D_sync)가 턴온 되면, 동기정류기 구동전원(V_drv)으로부터 제1저항(R₁)을 통하여 동기전류(I_sync)가 흐르게 되고, 포토커플러(U_on)의 광다이오드는 턴온 되며, 이것은 다시 포토커플러(U_on)의 광트랜지스터를 턴온시킨다.On the other hand, the turn-on driving voltage generator 202 is a series connection connection point of the sync resistor (R _sync ) and the sync diode (D _sync ) of the _sync pulse generating circuit unit 201 (

) Voltage (V _o of - is as V ₂₎ + V _{AK, on} and operates when the sync diode (D _sync) turned on. Series connection point of the sync resistor R _sync and the sync diode D _sync of the _sync pulse generating circuit unit 201 (

) Is equal to (V _o -V ₂ ) + V _{AK , on,} and the synchronous diode (D _sync ) is turned on, the synchronous current (A 1) from the synchronous rectifier driving power supply (V _drv ) through the first resistor (R ₁ ). I _sync ) flows and the photodiode of the photocoupler U _on is turned on, which in turn turns on the phototransistor of the photocoupler U _on .

Then, the synchronous rectifier driving current flows from the driving power supply V _drv of the synchronous rectifier SR through the phototransistor of the photocoupler U _on through the second resistor R ₂ , and the gate of the synchronous rectifier SR The synchronous rectifier SR is turned on by charging the voltage between the source terminals to the turn-on driving voltage.

At this time, since the current does not flow to the base resistor R _b of the turn-off driving voltage discharge unit 203, the transistor TR _off is turned off, and the voltage between the charged gate and the source terminal of the synchronous rectifier SR is It is not discharged.

)의 전압이 동기정류기 구동전압(V_drv)이 될 때 동작한다.On the other hand, the turn-off driving voltage discharge unit 203 is a series connection connection point of the synchronous resistor (R _sync ) and the synchronous diode (D _sync ) of the synchronous pulse generating circuit unit 201 (

It operates when the voltage of) becomes the synchronous rectifier driving voltage (V _drv ).

)의 전압이 동기정류기 구동전압(V_drv)이 되면 베이스저항(R_b)으로 전류가 흐르게 되고, 이것은 트랜지스터(TR_off)를 턴온시킨다. 그러면, 턴온구동전압발생부(202)에 의해 충전되어 있던 동기정류기(SR)의 게이트와 소스 단자 사이의 턴온구동전압을 접지로 방전시키게 되고, 동기정류기(SR)을 턴오프하게 된다.Series connection point of the sync resistor R _sync and the sync diode D _sync of the _sync pulse generating circuit unit 201 (

When the voltage of) becomes the synchronous rectifier driving voltage V _drv , current flows to the base resistor R _b , which turns on the transistor TR _off . Then, the turn-on driving voltage between the gate and the source terminal of the synchronous rectifier SR charged by the turn-on driving voltage generator 202 is discharged to ground, thereby turning off the synchronous rectifier SR.

In this case, since the photodiode of the photocoupler U _on is turned off and does not turn on the phototransistor of the photocoupler U _on , the turn-on driving voltage generation unit 202 is formed between the gate and the source terminal of the synchronous rectifier SR. The voltage at is not charged.

The synchronous rectifier driving circuit for the flyback converter of the present invention is not limited to the above-described embodiment and can be modified in various ways within the scope of the technical idea of the present invention.

1 is an internal circuit diagram of a flyback converter using a conventional rectifier diode as a secondary rectifier.

2 is an internal circuit diagram of a flyback converter using a conventional synchronous rectifier as a secondary rectifier.

3 is an overall conceptual circuit diagram of a flyback converter to which a synchronous rectifier driving circuit according to the present invention is applied;

4 is a synchronous rectifier driving circuit diagram for a flyback converter according to the present invention.

5 is a view showing a theoretical operating waveform of a synchronous rectifier driving circuit for a flyback converter according to the present invention;

*** Explanation of symbols for the main parts of the drawing ***

10. secondary circuit of the flyback converter, 20. synchronous rectifier driving circuit,

201.Synchronous pulse generating circuit section, 202. Turn-on driving voltage generating section,

203. Turn-on driving voltage discharge unit

Claims (4)

It is composed of a synchronous resistor and a synchronous diode to generate a synchronous pulse signal for synchronizing the driving time of the synchronous rectifier, but when the voltage level applied to the synchronous diode is higher than the diode turn-on voltage according to the voltage level of the secondary coil of the flyback converter. The synchronous diode is turned on to generate a negative logic synchronization pulse signal, and when the voltage level applied to the synchronous diode is lower than the diode turn-on voltage according to the voltage level of the flyback converter secondary coil, the synchronous diode is turned on. A synchronization pulse generation circuit section for turning off to generate a positive logic synchronization pulse signal; A turn-on driving voltage generation unit which is turned on based on a negative logic synchronization pulse signal applied from the synchronization pulse generation circuit unit and applies a synchronous rectifier driving current to a gate terminal of the synchronous rectifier; And a turn-off driving voltage discharge unit which is turned on based on a positive logic synchronization pulse signal applied from the synchronization pulse generating circuit unit and discharges a voltage charged in the gate of the synchronous rectifier to ground. Rectifier driving circuit. The synchronizing pulse generating circuit unit according to claim 1, One terminal of the synchronous resistor and an anode terminal of the synchronous diode are connected in series, and the other end of the synchronous resistor which is not connected to the synchronous diode is connected to a synchronous rectifier driving power supply, and the cathode terminal of the synchronous diode is a flyback converter. A synchronous rectifier drive circuit for a flyback converter, characterized in that it is commonly connected to one terminal of the transformer secondary coil and the drain terminal of the synchronous rectifier. The method of claim 1, wherein the turn-on driving voltage generator, And a first resistor, a second resistor, and a photo coupler, one terminal of the first resistor and one terminal of the second resistor being connected to the synchronous rectifier driving power supply together with the other end of the synchronous resistor of the synchronous pulse generating circuit part. The other end of the first resistor is connected to the anode terminal of the photodiode on the primary side of the photocoupler, and the cathode terminal of the photodiode on the primary side of the photocoupler is connected to the synchronous resistor and the synchronous diode of the Is connected in common to a series connection point of the second coupler, the other end of the second resistor is connected to the collector terminal of the phototransistor secondary side, and the emitter terminal of the photocoupler secondary side phototransistor is a gate terminal of the synchronous rectifier. A synchronous rectifier driving circuit for a flyback converter, characterized in that connected to. The method of claim 1, wherein the turn-off driving voltage discharge unit, A base resistor and a transistor are provided, and one terminal of the base resistor is commonly connected to the synchronous resistance of the synchronous pulse generating circuit part and the series connection point of the synchronous diode together with the cathode terminal of the photocoupler photodiode of the turn-on driving voltage generation part. The other end of the base resistor is connected to the base terminal of the transistor, the collector terminal of the transistor is commonly connected to the gate terminal of the synchronous rectifier together with the emitter terminal of the phototransistor on the photocoupler secondary side, And the emitter terminal of the transistor is connected to ground.

Images