Abstract:
Provided is apparatus and a method for driving synchronous rectifiers, which relate to the field of power supplies for communications. The apparatus includes: detection circuits, wherein each of the detection circuits is configured to detect drain and source voltages of one of synchronous rectifiers to obtain a detection signal for indicating a current direction in the one of the synchronous rectifiers; an isolated driving circuit, configured to generate isolated driving signals for driving the synchronous rectifiers according to the detection signals output by the detection circuits; and the synchronous rectifiers, configured to synchronously rectify input signals from a main transformer by using the isolated driving signals. The present disclosure can obtain the isolated driving signals of the synchronous rectifiers simply and effectively, and has a superior protective feature in case of shoot-through and other abnormalities.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to the field of power supplies for communications, and in particular to a driving apparatus for LLC resonant converter synchronous rectifier and a relevant driving method. 
       BACKGROUND 
       [0002]    In order to meet high-efficiency and high-power density requirements, a resonant converter is widely applied to a Direct Current (DC)-DC power converter. However, due to the fact that a secondary-side rectification diode may cause a quite high conduction loss, a circuit composed of rectification diodes is replaced by a rectifier circuit composed of transistors, and the rectifier circuit is applied to the resonant converter. Compared with a conversion circuit adopting the rectification diodes, the circuit adopting the transistors for rectification can reduce a power loss. A conventional synchronous rectifier control method is as follows: 
         [0003]    1, a current flowing through a secondary-side synchronous rectifier parasitic diode is detected by using a current transformer, a synchronous rectifier is turned on when it is detected that the current flows, however, due to the fact that the current transformer has parasitic inductance, a current signal and a turn-on signal are likely to delay, and the current transformer is likely to be interfered, thereby increasing the cost and the size; and 
         [0004]    2, a control signal of the synchronous rectifier is the same as or different from that of a main power mosfet, and a driving signal of a synchronous driving tube, serving as a control signal of the synchronous rectifier, is relatively easy to obtain, but when the synchronous rectifier works in a discontinuous current mode, the control signal of the synchronous rectifier is relatively difficult to acquire, and if a signal which is the same as or different from that of the main power mosfet is directly adopted, the problems of reverse current flowing and the like will be caused so as to seriously affect the working of the circuit. 
       SUMMARY 
       [0005]    An embodiment of the present disclosure is intended to provide apparatus and a  method for driving synchronous rectifiers, which may better solve the problem how to obtain isolated driving signals of the synchronous rectifiers simply and effectively. 
         [0006]    According to one aspect of the embodiment of the present disclosure, apparatus for driving synchronous rectifiers is provided, which may include: 
         [0007]    detection circuits configured to detect drain and source voltages of the synchronous rectifiers to obtain detection signals for indicating current directions in the synchronous rectifiers; 
         [0008]    an isolated driving circuit configured to generate isolated driving signals for driving the synchronous rectifiers according to the detection signals output by the detection circuits; and 
         [0009]    the synchronous rectifiers configured to synchronously rectify input signals from a main transformer by using the isolated driving signals. 
         [0010]    Preferably, the apparatus may include two synchronous rectifiers, each of the two synchronous rectifiers being connected to a secondary winding of the main transformer and one of the detection circuits. 
         [0011]    Preferably, the isolated driving circuit may include two push-pull circuits and an isolated driving transformer, wherein 
         [0012]    an input end of each of the two push-pull circuits may be connected to one of the detection circuits; and 
         [0013]    a primary winding of the isolated driving transformer may be connected to output ends of the two push-pull circuits, and each of two secondary windings of the isolated driving transformer may be connected to a gate and source of one of synchronous rectifiers. 
         [0014]    Preferably, the apparatus may include a full-bridge rectifier circuit formed by four synchronous rectifiers, input ends of the full-bridge rectifier circuit may be connected to the secondary windings of the main transformer, and a synchronous rectifier, of which the source is grounded, in the two synchronous rectifiers in each input branch circuit of the full-bridge rectifier circuit may be connected to one of the detection circuits. 
         [0015]    Preferably, the isolated driving circuit may include two push-pull circuits and an isolated driving transformer, wherein 
         [0016]    an input end of each of the two push-pull circuits may be connected to the one of the detection circuit; and 
         [0017]    a primary winding of the isolated driving transformer may be connected to output  ends of the two push-pull circuits, and each of four secondary windings of the isolated driving transformer may be connected to a gate and source of the one of the synchronous rectifier. 
         [0018]    Preferably, each of the detection circuits may include: 
         [0019]    a comparison circuit, an input end thereof being connected to a drain and source of the one of the synchronous rectifiers; and 
         [0020]    an amplification circuit, an input end thereof being connected to the comparison circuit, an output end thereof being connected to one of the two push-pull circuits. 
         [0021]    Preferably, the comparison circuit may include a first comparison branch circuit and a second comparison branch circuit, and one end of the first comparison branch circuit and one end of the second comparison branch circuit may be connected to an auxiliary power supply via a first resistor, wherein 
         [0022]    the first comparison branch circuit may include: 
         [0023]    a first triode, a base and collector thereof being connected to the drain of the one of the synchronous rectifiers; 
         [0024]    a first diode, a cathode thereof being connected to an emitter of the first triode, an anode thereof being connected to the first resistor; 
         [0025]    the second comparison branch circuit may include: 
         [0026]    a second triode, a base thereof being connected to the source of the one of the synchronous rectifiers, a collector thereof being connected to the amplification circuit; and 
         [0027]    a second diode, a cathode thereof being connected to an emitter of the second triode, an anode thereof being connected to the first resistor. 
         [0028]    According to another aspect of the embodiment of the present disclosure, a method for driving synchronous rectifiers is provided, which may include that: 
         [0029]    detection signals for indicating current directions in the synchronous rectifiers are obtained respectively by detecting drain and source voltages of the synchronous rectifiers; 
         [0030]    isolated driving signals for driving the synchronous rectifiers are generated according to the obtained detection signals; and 
         [0031]    input signals from a main transformer are synchronously rectified by using the isolated driving signals. 
         [0032]    Preferably, the step that the detection signals for indicating the current directions in the synchronous rectifiers are obtained may include that:  
         [0033]    the drain and source voltages of each of the synchronous rectifiers are compared by using a comparison circuit; and 
         [0034]    an output of the comparison circuit is amplified by using an amplification circuit to obtain the detection signal for indicating the current direction in the each of the synchronous rectifiers. 
         [0035]    Preferably, the step that the isolated driving signals for driving the synchronous rectifiers are generated may include that: 
         [0036]    the detection signals are output to an isolated driving transformer in a push-pull way by using a push-pull circuit, in order that the isolated driving transformer generates the isolated driving signals for driving the synchronous rectifiers. 
         [0037]    Compared with the traditional art, the embodiment of the present disclosure has beneficial effects as follows. 
         [0038]    The embodiment of the present disclosure can obtain the isolated driving signals of the synchronous rectifier simply and effectively, and has a superior protective feature in case of shoot-through and other abnormalities. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0039]      FIG. 1  is a block diagram of apparatus for driving synchronous rectifiers provided by an embodiment of the present disclosure; 
           [0040]      FIG. 2  is a principal block diagram of a method for driving synchronous rectifiers provided by an embodiment of the present disclosure; 
           [0041]      FIG. 3  is a circuit principle diagram of synchronous rectifier driving apparatus provided by an embodiment of the present disclosure; 
           [0042]      FIG. 4  is a first circuit principle diagram of a detection circuit provided by an embodiment of the present disclosure; 
           [0043]      FIG. 5  is a second circuit principle diagram of a detection circuit provided by an embodiment of the present disclosure; and 
           [0044]      FIG. 6  is a principle diagram of a full-bridge synchronous rectifier circuit provided by an embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0045]    The preferred embodiments of the present disclosure are described below with reference to the drawings in detail. It should be understood that the preferred embodiments described below are only intended to describe and explain the present  disclosure, and do not limit the present disclosure. 
         [0046]      FIG. 1  is a block diagram of apparatus for driving synchronous rectifiers provided by an embodiment of the present disclosure. As shown in  FIG. 1 , the apparatus includes detection circuits, an isolated driving circuit, synchronous rectifiers and a main transformer. each detection circuit detects drain and source voltages of one of the synchronous rectifiers to obtain a detection signal for indicating a current direction in the one of the synchronous rectifiers; the isolated driving circuit generates isolated driving signals for driving the synchronous rectifiers according to the detection signals output by the detection circuits; and the synchronous rectifiers synchronously rectifies input signals from the main transformer by using the isolated driving signal. 
         [0047]    Preferably, the main transformer of the apparatus is provided with two secondary windings. 
         [0048]    The apparatus includes two synchronous rectifiers, each being connected to the corresponding secondary winding of the main transformer and a detection circuit. At this time, the isolated driving circuit comprises two push-pull circuits and an isolated driving transformer, an input end of each of the two push-pull circuits is connected to a detection circuit, a primary winding of the isolated driving transformer is connected to output ends of the two push-pull circuits, and each of two secondary windings of the isolated driving transformer is connected to a gate and source of the corresponding synchronous rectifier. 
         [0049]    Preferably, the main transformer of the apparatus is provided with a primary winding. 
         [0050]    The apparatus comprises a full-bridge rectifier circuit formed by four synchronous rectifiers, input ends of the full-bridge rectifier circuit are connected to the secondary windings of the main transformer, and the synchronous rectifier, of which the sound is grounded, in the two synchronous rectifiers of each input branch circuit is connected to a detection circuit. At this time, the isolated driving circuit comprises two push-pull circuits and an isolated driving transformer, an input end of each of the two push-pull circuits is connected to a detection circuit, a primary winding of the isolated driving transformer is connected to output ends of the two push-pull circuits, and each of four secondary windings of the isolated driving transformer is connected to a gate and source of a synchronous rectifier. 
         [0051]    The detection circuit includes: 
         [0052]    a comparison circuit, an input end thereof being connected to a drain and source  of the synchronous rectifier; and 
         [0053]    an amplification circuit, an input end thereof being connected to the comparison circuit, an output end thereof being connected to the two push-pull circuits. 
         [0054]    Preferably, the comparison circuit includes a first comparison branch circuit and a second comparison branch circuit, and one end of the first comparison branch circuit and one end of the second comparison branch circuit are connected to an auxiliary power supply via a first resistor, wherein 
         [0055]    the first comparison branch circuit includes: 
         [0056]    a first triode, a base and collector thereof being connected to the drain of the synchronous rectifier; 
         [0057]    a first diode, a cathode thereof being connected to an emitter of the first triode, an anode thereof being connected to the first resistor; 
         [0058]    the second comparison branch circuit includes: 
         [0059]    a second triode, a base thereof being connected to the source of the synchronous rectifier, a collector thereof being connected to the amplification circuit; and 
         [0060]    a second diode, a cathode thereof being connected to an emitter of the second triode, an anode thereof being connected to the first resistor. 
         [0061]      FIG. 2  is a principal block diagram of a method for driving synchronous rectifiers provided by an embodiment of the present disclosure. As shown in  FIG. 2 , the method includes the steps as follows. 
         [0062]    Step  201 : drain and source voltages of each synchronous rectifier are detected to obtain a detection signal for indicating a current direction in the synchronous rectifier. 
         [0063]    The step that the detection signal for indicating the current direction in the synchronous rectifier is obtained includes that: the drain and source voltages of the synchronous rectifier are compared by using a comparison circuit; and an output of the comparison circuit is amplified by using an amplification circuit to obtain the detection signal for indicating the current direction in the synchronous rectifier. 
         [0064]    Step  202 : an isolated driving signal for driving the synchronous rectifier is generated according to the obtained detection signal. 
         [0065]    The step that the isolated driving signal for driving the synchronous rectifier is generated includes that: the detection signal is output to an isolated driving transformer in a push-pull way by using a push-pull circuit, in order that the isolated  driving transformer generates the isolated driving signal for driving the synchronous rectifier. 
         [0066]    Step  203 : an input signal from a main transformer is synchronously rectified by using the isolated driving signal. 
         [0067]      FIG. 3  is a circuit principle diagram of synchronous rectifier driving apparatus provided by an embodiment of the present disclosure. As shown in  FIG. 3 , the apparatus includes comparison circuits, amplification circuits and an isolated driving circuit, wherein the comparison circuits compare the magnitudes of source and drain voltages of a synchronous rectifier Metal Oxide Semiconductor (MOS) tube respectively, the amplification circuits amplify signals obtained by comparison to obtain detection signals respectively, and the isolated driving circuit generates an isolated driving signal according to the detection signals, and provides the isolated driving signal for gates and sources of a first synchronous rectifier SR 1  and a second synchronous rectifier SR 2 . The direction of a current flowing through the synchronous rectifier MOS tube can be judged by detecting the source and drain voltages of the synchronous rectifier MOS tube, so that corresponding driving signals of the first synchronous rectifier SR 1  and the second synchronous rectifier SR 2  are generated. 
         [0068]    Specifically, the first synchronous rectifier SR 1  and the second synchronous rectifier SR 2  perform respective half-wave rectification on a secondary side of the main transformer, and the comparison circuits and amplification circuits of the first synchronous rectifier SR 1  and the second synchronous rectifier SR 2  are identical. The comparison circuits are configured to compare the source and drain voltages of the first synchronous rectifier SR 1  and the second synchronous rectifier SR 2  respectively, and the comparison circuits corresponding to the first synchronous rectifier SR 1  and the second synchronous rectifier SR 2  are identical. The amplification circuits are configured to amplify signals generated by the comparison circuits of the first synchronous rectifier SR 1  and the second synchronous rectifier SR 2  to obtain detection signals, and the amplification circuits corresponding to the first synchronous rectifier SR 1  and the second synchronous rectifier SR 2  are identical. The isolated driving circuit is configured to output the detection signals generated by the amplification circuits of the first synchronous rectifier SR 1  and the second synchronous rectifier SR 2  in a push-pull way, and then the detection signals are input into first and second pins of a primary side of an isolated driving transformer T 1 , and two secondary windings of the isolated driving transformer perform isolated  driving on gates and sources of the corresponding first synchronous rectifier SR 1  and the corresponding second synchronous rectifier SR 2  according to a phase relationship respectively. 
         [0069]    Each comparison circuit includes two triodes and two diodes. As shown in  FIG. 4  or  FIG. 5 , a base and collector of a triode T 1  are connected and then coupled to a drain of a synchronous rectifier MOS tube SR, an emitter of the triode T 1  is connected to a cathode of a diode D 1 , a base of a triode T 2  is coupled to a source of the synchronous rectifier MOS tube SR, a collector of the triode T 2  is coupled to an input end of the corresponding amplification circuit, an emitter of the triode T 2  is connected to a cathode of a diode D 2 , and anodes of the diode D 1  and the diode D 2  are coupled to an auxiliary power supply via a resistor R 1 . 
         [0070]    Each amplification circuit includes a triode, a diode and a resistor. As shown in  FIG. 4 , an emitter of a triode T 3  is connected to a source of the synchronous rectifier MOS tube SR, a base of the triode T 3  and an anode of a diode D 3  are each connected to an output end of the corresponding comparison circuit, and a collector of the triode T 3  is connected to a cathode of the diode D 3  and is connected to the auxiliary power supply V cc  via a resistor R 2 . Or, each amplification circuit includes three triodes, a diode and a resistor. As shown in  FIG. 5 , an emitter of a triode T 3  is connected to a source of the synchronous rectifier MOS tube SR, a base of the triode T 3  and an anode of a diode D 3  are connected to an output end of the corresponding comparison circuit respectively, a collector of the triode T 3  and a cathode of the diode D 3  are connected to a collector of a triode T 4  respectively, a base of the triode T 4  is connected to a base of a triode T 5  and a collector of the triode T 5  respectively and is connected to the source of the synchronous rectifier MOS tube SR via a resistor R 2 , and an emitter of the triode T 4  and an emitter of the triode T 4  are connected to the auxiliary power supply V cc . 
         [0071]    The isolated driving circuit includes two integrated driving chips and an isolated driving transformer, an input end of each integrated driving chip is coupled to an output end of the corresponding amplification circuit, an output end of the integrated driving chip corresponding to the first synchronous rectifier SR 1  is coupled to a first pin of the isolated driving transformer T 1 , an output end of the integrated driving chip corresponding to the second synchronous rectifier SR 2  is coupled to a second pin of the isolated driving transformer T 1 , third and fourth pins of the isolated driving transformer T 1  are connected to the gate and source of the first synchronous rectifier  SR 1  respectively, and sixth and fifth pins of the isolated driving transformer T 1  are connected to the gate and source of the second synchronous rectifier SR 2  respectively. Or, the isolated driving circuit includes two push-pull circuits and an isolated driving transformer, a triode VT 7  and a triode VT 8  corresponding to the first synchronous rectifier SR 1  form a push-pull circuit, bases of the triode VT 7  and the triode VT 8  are coupled to the output end of the amplification circuit corresponding to the first synchronous rectifier SR 1  respectively, and emitters of the triode VT 7  and the triode VT 8  are coupled to a first pin of the isolated driving transformer T 1 ; and a triode VT 9  and a triode VT 10  corresponding to the second synchronous rectifier SR 2  form another push-pull circuit, bases of the triode VT 9  and the triode VT 10  are coupled to the output end of the amplification circuit corresponding to the second synchronous rectifier SR 2 , emitters of the triode VT 9  and the triode VT 10  are coupled to a second pin of the isolated driving transformer T 1 , third and fourth pins of the isolated driving transformer T 1  are connected to the gate and source of the first synchronous rectifier SR 1  respectively, and sixth and fifth pins of the isolated driving transformer T 1  are connected to the gate and source of the second synchronous rectifier SR 2  respectively. 
         [0072]    Preferably, the apparatus further includes a first parasitic diode connected between the drain and source of the first synchronous rectifier SRI, an anode of the first parasitic diode is connected to the source of the first synchronous rectifier SR 1 , and a cathode of the first parasitic diode is connected to the drain of the first synchronous rectifier SR 1 . The apparatus further includes a second parasitic diode connected between the drain and source of the second synchronous rectifier SR 2 , an anode of the second parasitic diode is connected to the source of the second synchronous rectifier SR 2 , and a cathode of the second parasitic diode is connected to the drain of the second synchronous rectifier SR 2 . The apparatus further includes a capacitor, one end of the capacitor is connected to a centre tap of the secondary winding of the main transformer, and the other end of the capacitor is connected to the source of the first synchronous rectifier SR 1  and the source of the second synchronous rectifier SR 2  respectively. 
         [0073]    As mentioned above, the input ends of the each comparison circuit of the apparatus for driving the synchronous rectifier are coupled to the source and drain of the synchronous rectifier MOS tube, and the output end of the each comparison circuit is coupled to the input end of the amplification circuit; the output end of the  amplification circuit is coupled to the input end of the isolated driving circuit; and outputs of the secondary side of the isolated driving transformer of the isolated driving circuit are coupled to the gates and sources of the first synchronous rectifier SR 1  and the second synchronous rectifier SR 2  respectively. The comparison circuits are configured to compare the source and drain voltages of the synchronous rectifier MOS tube, preferably, a circuit composed of an accurately-matched triode pair and an accurately-matched high-voltage diode pair is adopted, and a result reflects the direction of the current flowing through the synchronous rectifier MOS tube. The amplification circuit amplify the signal output by the comparison circuit. The isolated driving circuit is configured to generate an isolated driving signal according to an amplification result, and transmit the isolated driving signal to the gates and sources of the first synchronous rectifier SR 1  and the second synchronous rectifier SR 2 . 
         [0074]      FIG. 4  is a first circuit principle diagram of a detection circuit provided by an embodiment of the present disclosure. As shown in  FIG. 4 , the detection circuit includes a comparison circuit and an amplification circuit. 
         [0075]    The comparison circuit includes a triode T 1 , a triode T 2 , a diode D 1  and a diode D 2 . A base and collector of the triode T 1  are connected to a drain of a synchronous rectifier MOS tube SR, a base of the triode T 2  is connected to a source of the synchronous rectifier MOS tube SR, an emitter of the triode T 1  is connected to a cathode of the diode D 1 , an emitter of the triode T 2  is connected to a cathode of the diode D 2 , anodes of the diode D 1  and the diode D 2  are connected to an auxiliary power supply V cc  via a resistor R 1 , and a collector of the triode T 2  and a base of the triode T 3  are connected to an anode of the diode D 3 . 
         [0076]    The amplification circuit includes a triode T 3 , a diode D 3  and a resistor R 2 . An emitter of the triode T 3  is connected to the source of the synchronous rectifier MOS tube SR, a base of the triode T 3  and an anode of the diode D 3  are connected to the collector of the triode T 2 , and a collector of the triode T 3  is connected to a cathode of the diode D 3  and is connected to the auxiliary power supply V cc  via the resistor R 2 . 
         [0077]    The circuit composed of the accurately-matched triode pair Ti and T 2  and the accurately-matched high-voltage diode pair D 1  and D 2  compares the drain and source voltages of the synchronous rectifier MOS tube SR, and transmits a signal obtained by comparison to the amplification circuit composed of the triode T 3 , the diode D 3  and the resistor R 2 , the signal is amplified and then is transmitted to the isolated driving circuit, and an isolated driving signal is generated by the isolated  driving circuit and then is transmitted to a gate of the synchronous rectifier MOS tube SR. 
         [0078]      FIG. 5  is a second circuit principle diagram of a detection circuit provided by an embodiment of the present disclosure. The difference between the detection circuits shown by  FIG. 5  and  FIG. 4  is the amplification circuit. As shown in  FIG. 5 , the amplification circuit includes a triode T 3 , a triode T 4 , a triode T 5 , a diode D 3  and a resistor R 2 . An emitter of the triode T 3  is connected to the source of the synchronous rectifier MOS tube SR, a base of the triode T 3  and an anode of the diode D 3  are connected to the collector of the triode T 2  respectively, a collector of the triode T 3  and a cathode of the diode D 3  are connected to a collector of the triode T 4 , a base of the triode T 4  is connected to a base of the triode T 5  and a collector of the triode T 5  respectively and is connected to the source of the synchronous rectifier MOS tube SR via the resistor R 2 , and an emitter of the triode T 4  and an emitter of the triode T 5  are connected to the auxiliary power supply V cc . 
         [0079]      FIG. 6  is a principle diagram of a full-bridge synchronous rectifier circuit provided by an embodiment of the present disclosure. The difference between the circuits shown by  FIG. 6  and  FIG. 3  is as follows. In the embodiment, a secondary side of a main transformer T 2  is a single winding, the full-bridge synchronous rectifier circuit is composed of four synchronous rectifiers SR 1 , SR 2 , SR 3  and SR 4 , and the isolated driving transformer is provided with four secondary windings for driving the four synchronous rectifiers respectively. As shown in  FIG. 6 , in the embodiment, double tubes SR 1  and SR 2  form comparison circuits and amplification circuits, an input end of the full-bridge synchronous rectifier circuit is connected to the single winding of the secondary side of the main transformer T 2 , the drain and source voltages of the two synchronous rectifiers SR 1  and SR 2  on one of input branch circuits are compared by using the comparison circuits respectively, and comparison results are amplified by using the amplification circuits to obtain two detection signals corresponding to the synchronous rectifiers SR 1  and SR 2  respectively. The detection signal corresponding to the synchronous rectifier SR 1  is output to a push-pull circuit composed of VT 7  and VT 8 , the detection signal corresponding to the synchronous rectifier SR 2  is output to a push-pull circuit composed of VT 9  and VT 10 , and outputs of the two push-pull circuits are connected to first and second pins of a primary winding of the isolated driving transformer respectively. The secondary side of the isolated driving transformer adopts four windings. According to polarity situations of primary and  secondary sides, third and fourth pins of the isolated driving transformer T 1  are connected to the gate and source of the synchronous rectifier SR 1  respectively, sixth and fifth pins of the isolated driving transformer T 1  are connected to the gate and source of the synchronous rectifier SR 2  respectively, tenth and ninth pins of the isolated driving transformer T 1  are connected to the gate and source of the synchronous rectifier SR 3  respectively, and seventh and eighth pins of the isolated driving transformer T 1  are connected to the gate and source of the synchronous rectifier SR 4  respectively. 
         [0080]    The circuits shown in  FIG. 4  or  FIG. 5  may be selected as the comparison circuit and the amplification circuit. 
         [0081]    Preferably, the apparatus further includes four parasitic diodes, each parasitic diode is connected to the corresponding synchronous rectifier, an anode of each parasitic diode is connected to a source of the corresponding synchronous rectifier, and a cathode of this parasitic diode is connected to a drain of this synchronous rectifier. The apparatus further includes a capacitor, one end of the capacitor is connected to drains of the synchronous rectifiers SR 3  and SR 4  respectively, and the other end of the capacitor is connected to sources of the synchronous rectifiers SR 1  and SR 2  respectively. 
         [0082]    As mentioned above, in the embodiment of the present disclosure, the direction of the current flowing through the synchronous rectifier is judged by detecting the source and drain voltages of the synchronous rectifier, so that the isolated driving signal of the corresponding synchronous rectifier is generated, thereby acquiring the isolated driving signals of the synchronous rectifier more simply and effectively. 
         [0083]    Although the present disclosure is described above in detail, the present disclosure is not limited thereto. Those skilled in the art can make various modifications according to the principle of the present disclosure. Thus, the modifications made according to the principle of the present disclosure shall fall within the protection scope of the present disclosure. 
       INDUSTRIAL APPLICABILITY 
       [0084]    As mentioned above, the apparatus and method for driving the synchronous rectifier provided by the embodiment of the present disclosure have the beneficial effects as follows. In the embodiment of the present disclosure, the direction of the current flowing through the synchronous rectifier is judged by detecting the source  and drain voltages of the synchronous rectifier, so that the isolated driving signal of the corresponding synchronous rectifier is generated, thereby acquiring the isolated driving signal of the synchronous rectifier more simply and effectively.