CN212752140U - Flyback switching power supply and synchronous rectification drive circuit thereof - Google Patents
Flyback switching power supply and synchronous rectification drive circuit thereof Download PDFInfo
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- CN212752140U CN212752140U CN202021725243.9U CN202021725243U CN212752140U CN 212752140 U CN212752140 U CN 212752140U CN 202021725243 U CN202021725243 U CN 202021725243U CN 212752140 U CN212752140 U CN 212752140U
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Abstract
The utility model discloses a flyback switching power supply and synchronous rectification drive circuit thereof, this circuit includes: the turn-off time detection circuit is used for determining a start-stop result of synchronous rectification and a turn-off time detection result of simultaneous turn-off of the primary side and the secondary side according to the detection voltage output by the synchronous rectification detection voltage output end; the synchronous rectification start-stop controller is used for generating a corresponding synchronous rectification driving signal according to a start-stop result; the driver is used for controlling the on and off of the synchronous rectification controllable switch in the secondary winding side circuit according to the off time detection result and the synchronous rectification driving signal; the utility model discloses utilize turn-off time detection circuitry to detect the turn-off time that former secondary was turn-offed simultaneously, make the driver can shield synchronous rectification in this turn-off time and start the synchronous rectification drive signal of stopping the controller output, reduce the false turn-on situation of the controllable switch of synchronous rectification in the Toff period, avoid the phenomenon of former secondary intercommunication of transformer, improve the security of flyback switching power supply.
Description
Technical Field
The utility model relates to a power electronic technology field, in particular to flyback switching power supply and synchronous rectification drive circuit thereof.
Background
The secondary side rectification scheme of the prior flyback switching power supply has two types: one is passive, i.e. using diodes; another is to use a synchronous rectification controllable switch (as shown in fig. 1 and 2) such as a power transistor, and a synchronous rectification controller (as a synchronous rectification driving chip in fig. 1 and 2) is required to drive the synchronous rectification controllable switch. In certain power application occasions, the synchronous rectification by using the synchronous rectification controllable switch has the characteristics of low power consumption and high system efficiency. Therefore, the temperature characteristic of the whole flyback switching power supply system is also superior.
In the prior art, in a conventional single-voltage output flyback switching power supply system, synchronous rectification works in a DCM (discontinuous conduction mode), and after demagnetization of a secondary winding of a transformer is finished, ringing in a Toff period (an original secondary simultaneous turn-off period) is a sine wave, as shown in fig. 3. However, in a system with multiple voltages and multiple current outputs, such as a recently-emerging USB PD (USB Power Delivery) and a fast charging Power supply system, in a light load or no-load state, a waveform of a Toff period after the demagnetization of a secondary winding of a transformer is a square wave or a trapezoidal wave like a Tonp period (primary side on time period) and a Tons period (secondary side on time period), as shown in fig. 4. At the moment, the synchronous rectification controller in the prior art is easy to open the synchronous rectification controllable switch by mistake, and excitation inductance oscillation is aggravated after the synchronous rectification controller is opened by mistake, so that the synchronous rectification controller continues to be opened by mistake at high frequency; once the primary controllable switch is switched on, the primary side and the secondary side of the transformer are communicated with each other, and then the synchronous rectification controllable switch of the secondary side is damaged or the explosion machine is caused.
Therefore, how to provide a synchronous rectification driving circuit of a flyback switching power supply is a problem which needs to be solved urgently nowadays, so as to reduce the false turn-on condition of a synchronous rectification controllable switch in a Toff period, avoid the phenomenon of the intercommunication of the primary side and the secondary side of a transformer, and improve the use safety of the flyback switching power supply.
SUMMERY OF THE UTILITY MODEL
The utility model aims at providing a flyback switching power supply and synchronous rectification drive circuit thereof to reduce the false turn-on situation of the controllable switch of synchronous rectification in the Toff period, avoid appearing the former limit of transformer and the phenomenon of vice limit intercommunication, improve the safety in utilization of flyback switching power supply.
In order to solve the above technical problem, the utility model provides a flyback switching power supply's synchronous rectification drive circuit, include:
the turn-off time detection circuit is used for determining a start-stop result of synchronous rectification and a turn-off time detection result of simultaneous turn-off of an original secondary side according to a detection voltage output by a synchronous rectification detection voltage output end in a secondary side winding side circuit of a transformer in the flyback switching power supply;
the synchronous rectification start-stop controller is used for generating a corresponding synchronous rectification driving signal according to the start-stop result;
and the driver is used for controlling the on and off of the synchronous rectification controllable switch in the secondary winding side circuit according to the off time detection result and the synchronous rectification driving signal.
Optionally, the off-time detection circuit includes:
the synchronous rectification control and characteristic quantity detector is used for generating a synchronous rectification control signal corresponding to the start-stop result and the period or frequency of a preset characteristic quantity according to the detection voltage; the synchronous rectification control signal is a synchronous rectification on signal or a synchronous rectification off signal, the preset characteristic quantity is a characteristic quantity corresponding to the detection voltage within the turn-off time of the primary side and the secondary side which are simultaneously turned off, the input end of the synchronous rectification control and characteristic quantity detector is connected with the output end of the synchronous rectification detection voltage, the first output end of the synchronous rectification control and characteristic quantity detector is connected with the input end of the synchronous rectification start-stop controller, and the second output end of the synchronous rectification control and characteristic quantity detector is connected with the first input end of the comparator;
the comparator is used for comparing the period or the frequency of the preset characteristic quantity with a reference value to obtain a comparison result; the reference value is a reference period corresponding to the period of the preset characteristic quantity or a reference frequency corresponding to the frequency of the preset characteristic quantity, a second input end of the comparator is connected with an output end of the reference value, and an output end of the comparator is connected with an input end of the shielding time generator;
the shielding time generator is used for generating a shielding control signal corresponding to the turn-off time detection result according to the comparison result; the shielding control signal is a shielding time signal or a non-shielding time signal, and the output end of the shielding time generator is connected with the first input end of the driver.
Optionally, the synchronous rectification control and characteristic quantity detector includes:
a synchronous rectification control signal detector for generating the synchronous rectification control signal according to the detection voltage; the input end of the synchronous rectification control signal detector is connected with the synchronous rectification detection voltage output end, and the output end of the synchronous rectification control signal detector is connected with the input end of the synchronous rectification start-stop controller;
the detection voltage waveform judger is used for judging whether the voltage is in the turn-off time or not according to the detection voltage; the input end of the detected voltage waveform judger is connected with the synchronous rectification detected voltage output end, and the output end of the detected voltage waveform judger is connected with the first input end of the characteristic quantity detector;
the characteristic quantity detector is used for detecting the period or the frequency of the preset characteristic quantity within the turn-off time according to the judgment result of the detection voltage waveform judger; the second input end of the characteristic quantity detector is connected with the synchronous rectification detection voltage output end, and the output end of the characteristic quantity detector is connected with the first input end of the comparator.
Optionally, an input end of the turn-off time detection circuit is connected to a first end of a secondary winding of the transformer; and the first end of the secondary winding of the transformer is grounded through the synchronous rectification controllable switch.
Optionally, an input end of the turn-off time detection circuit is connected to a second end of the synchronous rectification controllable switch; the first end of the secondary winding of the transformer is grounded, the second end of the secondary winding of the transformer is connected with the first end of the synchronous rectification controllable switch, and the second end of the synchronous rectification controllable switch is used as the output end of the flyback switching power supply.
The utility model also provides a flyback switching power supply, include: the synchronous rectification control circuit comprises a transformer, a primary side controllable switch, a synchronous rectification controllable switch, a capacitor and a synchronous rectification controller; the synchronous rectification controller comprises the synchronous rectification driving circuit of the flyback switching power supply;
the first end of the primary winding of the transformer is used for being connected with the input end of a power supply, and the second end of the primary winding of the transformer is grounded through the primary controllable switch; the first end of the secondary winding of the transformer and the negative electrode of the capacitor are connected with the common end of the capacitor and grounded, and the second end of the secondary winding of the transformer and the positive electrode of the capacitor are connected with the common end of the capacitor and used as the output end of the flyback switching power supply;
the first end of the secondary winding of the transformer is connected with the negative electrode of the capacitor through the synchronous rectification controllable switch, the input end of the synchronous rectification controller is connected with the first end of the secondary winding of the transformer, and the output end of the synchronous rectification controller is connected with the control end of the synchronous rectification controllable switch; or the second end of the secondary winding of the transformer is connected with the positive electrode of the capacitor through the synchronous rectification controllable switch, the input end of the synchronous rectification controller is connected with the positive electrode of the capacitor, and the output end of the synchronous rectification controller is connected with the control end of the synchronous rectification controllable switch.
The utility model provides a flyback switching power supply's synchronous rectification drive circuit, include: the turn-off time detection circuit is used for determining a start-stop result of synchronous rectification and a turn-off time detection result of simultaneous turn-off of an original secondary side according to a detection voltage output by a synchronous rectification detection voltage output end in a secondary side winding side circuit of a transformer in the flyback switching power supply; the synchronous rectification start-stop controller is used for generating a corresponding synchronous rectification driving signal according to a start-stop result; the driver is used for controlling the on and off of the synchronous rectification controllable switch in the secondary winding side circuit according to the off time detection result and the synchronous rectification driving signal;
it can be seen that, the utility model discloses utilize turn-off time detection circuitry to detect the turn-off time that former secondary was turn-offed simultaneously to make the driver can shield the synchronous rectification drive signal that synchronous rectification started and stopped the controller output in this turn-off time, reduce the false turn-on general situation of the controllable switch of synchronous rectification in the Toff period, avoid appearing the former limit of transformer and the phenomenon of secondary intercommunication, improve the safety in utilization of flyback switching power supply. Furthermore, the utility model also provides a flyback switching power supply has above-mentioned beneficial effect equally.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required to be used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
Fig. 1 is a schematic circuit diagram of a High Side application of a synchronous rectification controllable switch in a flyback switching power supply in the prior art;
fig. 2 is a schematic circuit diagram of a Low Side application of a synchronous rectification controllable switch in a flyback switching power supply in the prior art;
fig. 3 is a schematic diagram of a characteristic waveform of a VDET pin of a synchronous rectification driving chip relative to GND in a conventional single-voltage flyback switching power supply;
fig. 4 is a schematic diagram of a characteristic waveform of a VDET pin of a synchronous rectification driving chip relative to GND during no-load or light-load operation in a flyback switching power supply in the prior art;
fig. 5 is a schematic structural diagram of a synchronous rectification driving circuit of a flyback switching power supply according to an embodiment of the present invention;
fig. 6 is a schematic structural diagram of a synchronous rectification control and characteristic quantity detector according to an embodiment of the present invention.
Detailed Description
The core of the utility model is to provide
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative work belong to the protection scope of the present invention.
Referring to fig. 5, fig. 5 is a schematic structural diagram of a synchronous rectification driving circuit of a flyback switching power supply according to an embodiment of the present invention. The circuit may include:
the turn-off time detection circuit 11 is used for determining a start-stop result of synchronous rectification and a turn-off time detection result of simultaneous turn-off of an original secondary side according to a detection voltage output by a synchronous rectification detection voltage output end in a secondary side winding side circuit of a transformer in the flyback switching power supply;
the synchronous rectification start-stop controller 12 is used for generating a corresponding synchronous rectification driving signal according to a start-stop result;
and the driver 13 is used for controlling the on and off of the synchronous rectification controllable switch in the secondary winding side circuit according to the off time detection result and the synchronous rectification driving signal.
It can be understood that the synchronous rectification driving circuit of the flyback switching power supply provided in this embodiment may be a circuit for controlling on and off of a synchronous rectification controllable switch (such as a MOS transistor) in a secondary winding side circuit of the flyback switching power supply, that is, a circuit in a synchronous rectification controller (such as the synchronous rectification driving chip in fig. 1 and fig. 2) that drives the synchronous rectification controllable switch.
Specifically, the off-time detection circuit 11 in this embodiment may determine a start-stop result (normal synchronous rectification on or off) of synchronous rectification and an off-time (Toff time) detection result of simultaneous turn-off of the primary and secondary sides according to a detection Voltage (VDET) output by a synchronous rectification detection voltage output end (such as a VDET end in fig. 1 and fig. 2) in a secondary winding side circuit of a transformer in the flyback switching power supply. The start-stop result of the synchronous rectification may be a result of determining whether to perform normal synchronous rectification in the prior art according to the input detection voltage by the off-time detection circuit 11; the detection result of the turn-off time when the original secondary side is turned off at the same time may be the detection result of whether the turn-off time detection circuit 11 determines the turn-off time when the original secondary side is turned off at the same time according to the input detection voltage.
That is to say, the purpose of this embodiment may be to determine, by the off-time detection circuit 11, whether the current time is at an off-time (e.g., Toff time in fig. 4) when the primary controllable switch (e.g., M12 in fig. 1 and 2) of the primary winding side circuit and the synchronous rectification controllable switch (e.g., M16 in fig. 1 and 2) of the secondary winding side circuit of the transformer in the flyback switching power supply are turned off at the same time according to the input detection voltage, so that when the current time is at the Toff time, the driver 13 may ignore the synchronous rectification driving signal output by the synchronous rectification start-stop controller 12, and turn off the synchronous rectification controllable switch, thereby reducing the false on-off condition of the synchronous rectification controllable switch in the Toff time period, avoiding the phenomenon of the mutual connection between the primary side and the secondary side of the transformer, and improving the safety of the flyback switching power supply.
Specifically, for the specific circuit structure of the OFF-time detecting circuit 11 in this embodiment, that is, the specific manner in which the OFF-time detecting circuit 11 determines the start-stop result of the synchronous rectification and the OFF-time detecting result of the simultaneous turn-OFF of the primary side and the secondary side according to the input detection voltage can be set by a designer according to a practical scene and a user requirement, for example, the OFF-time detecting circuit 11 can adopt the same or similar manner as the synchronous rectification control signal detector 101 (i.e., VDET ON/OFF detector) in the prior art, and determine the start-stop result of the synchronous rectification according to the input detection voltage to output a corresponding synchronous rectification control signal, that is, a synchronous rectification ON signal (ON signal) or a synchronous rectification OFF signal (OFF signal), to the synchronous rectification start-stop controller 12. The turn-off time detection circuit 11 may also determine the turn-off time detection result of the simultaneous turn-off of the primary and secondary sides by detecting a characteristic quantity (i.e., a preset characteristic quantity) corresponding to the input detection voltage, and as long as the turn-off time detection circuit 11 can determine the start-stop result of the synchronous rectification and the turn-off time detection result of the simultaneous turn-off of the primary and secondary sides by using the input detection voltage, this embodiment does not limit this.
Correspondingly, for the specific manner in which the off-time detection circuit 11 determines the off-time detection result of the primary and secondary sides being turned off simultaneously by using the preset characteristic quantity corresponding to the input detection voltage in this embodiment, the specific manner may be set by a designer, and if the preset characteristic quantity is the characteristic quantity corresponding to the detection voltage within the off-time (Toff time) of the primary and secondary sides of the flyback switching power supply being turned off simultaneously, the off-time detection circuit 11 may determine whether the current time is in the Toff time by using the frequency or the period of the preset characteristic quantity; as shown in fig. 5, the off-time detection circuit 11 may include: a synchronous rectification control and characteristic quantity detector 111, configured to generate a synchronous rectification control signal and a cycle or frequency (Tcycle signal) of a preset characteristic quantity corresponding to a start-stop result according to the detected voltage; the synchronous rectification control signal is a synchronous rectification ON signal (ON signal) or a synchronous rectification OFF signal (OFF signal), and the preset characteristic quantity is a characteristic quantity corresponding to the detection voltage within the turn-OFF time of the synchronous rectification controllable switch; a comparator 112 for comparing the period or frequency of the preset feature quantity with a reference value (Tref) to obtain a comparison result (Y _ CMP signal); the reference value is a reference period corresponding to the period of the preset characteristic quantity or a reference frequency corresponding to the frequency of the preset characteristic quantity; a masking time generator 113, configured to generate a masking control signal corresponding to the off-time detection result according to the comparison result; the mask control signal is a mask time signal (Tblank signal) or a non-mask time signal.
That is, the input terminal of the synchronous rectification control and characteristic quantity detector 111 is connected to the synchronous rectification detection voltage output terminal in the secondary winding side circuit of the transformer in the flyback switching power supply as the input terminal of the OFF time detection circuit 11, and the synchronous rectification control and characteristic quantity detector 111 not only can generate a synchronous rectification control signal (ON/OFF) corresponding to the start-stop result of synchronous rectification by using the input detection Voltage (VDET), that is, the first output terminal of the synchronous rectification control and characteristic quantity detector 111 can be connected to the input terminal of the synchronous rectification start-stop controller 12 as the first output terminal of the OFF time detection circuit 11; the period or the frequency of a preset characteristic quantity corresponding to the VDET can be detected and is marked as Tcycle; a second output terminal of the synchronous rectification control and feature quantity detector 111 is connected to a first input terminal of the comparator 112, a second input terminal of the comparator 112 is connected to an output terminal of the reference value (Tref), and the comparator 112 may compare the received Tcycle and Tref to generate a comparison result (Y _ CMP); the output terminal of the comparator 112 is connected to the input terminal of the mask time generator 113, and the mask time generator 113 can determine whether to generate the mask time signal (Tblank) according to Y _ CMP; the output terminal of the masking time generator 113 is connected to the first input terminal of the driver 13 as the second output terminal of the off time detection circuit 11, if the masking time generator 113 generates Tblank, the driver 13 masks the synchronous rectification driving signal (Drv _ In) output by the synchronous rectification start/stop controller 12 when receiving Tblank, and the signal output by the output terminal (Gate terminal) of the driver 13 turns off the synchronous rectification controllable switch (M16); on the contrary, if Tblank is not generated by the mask time generator 113, the driver 13 normally receives the Drv _ In signal.
Specifically, the specific selection of the preset feature quantity corresponding to the detection Voltage (VDET) detected by the synchronous rectification control and feature quantity detector 111 can be set by a designer according to practical scenarios and user requirements, for example, the preset feature quantity can be a determined synchronous rectification ON-signal (ON-signal) or synchronous rectification OFF-signal (OFF-signal), or a feature quantity corresponding to the synchronous rectification ON-signal or synchronous rectification OFF-signal, or a feature signal that the integral of the detection Voltage (VDET) and the first preset voltage is greater than a first threshold, a feature signal that the integral of the detection voltage and the second preset voltage is less than a second threshold, a feature signal that the slope of the detection voltage is greater than a first slope threshold, a feature signal that the slope of the detection voltage is less than a second slope threshold, a feature signal that the detection voltage is greater than a first level threshold, or a feature signal that the detection voltage is less than a second level threshold, etc., as long as the preset characteristic quantity is a characteristic quantity corresponding to the detected voltage within the turn-off time (e.g., Toff time in fig. 4) when the primary controllable switch (e.g., M12 in fig. 1 and 2) of the primary winding side circuit of the transformer and the synchronous rectification controllable switch (e.g., M16 in fig. 1 and 2) of the secondary winding side circuit of the flyback switching power supply are turned off at the same time, it can be determined whether the current time is at the Toff time by using the preset characteristic quantity, which is not limited in this embodiment.
Correspondingly, for the specific circuit structure of the synchronous rectification control and characteristic quantity detector 111, the specific circuit structure may be set by a designer, as shown in fig. 6, the synchronous rectification control and characteristic quantity detector 111 may include: a synchronous rectification control signal detector 101 (i.e., VDET ON/OFF detector) for generating a synchronous rectification control signal (ON/OFF) based ON the detection voltage; a detected voltage waveform determiner 102 (i.e., VDET waveform determiner) for determining whether or not it is in the off-time based on the detected voltage; a characteristic amount detector 103 for detecting a cycle or frequency (type) of a preset characteristic amount within the off-time, based on the determination result (Y _ Wave) of the detected voltage waveform determiner 102. That is to say, the input end of the synchronous rectification control signal detector 101 may be connected to the synchronous rectification detection voltage output end in the secondary winding side circuit, and the output end of the synchronous rectification control signal detector 101 may be connected to the input end of the synchronous rectification start-stop controller 12, and is configured to generate a synchronous rectification control signal corresponding to the start-stop result of synchronous rectification according to the input detection voltage and output the synchronous rectification control signal to the synchronous rectification start-stop controller 12; the input end of the detected voltage waveform judger 102 may be connected to the synchronous rectification detected voltage output end in the secondary winding side circuit, and the output end of the detected voltage waveform judger 102 may be connected to the first input end of the characteristic quantity detector 103, and is configured to judge the off-time (Toff-time) at the current time according to the input VDET, so as to obtain Y _ Wave; a second input terminal of the characteristic quantity detector 103 may be connected to the synchronous rectification detection voltage output terminal in the secondary winding side circuit, and an output terminal of the characteristic quantity detector 103 may be connected to an input terminal of the comparator 112, for detecting a period or frequency of a preset characteristic quantity corresponding to VDET during Toff time based on Y _ Wave and VDET. That is, after the detected voltage waveform determiner 102 determines that the Toff time has elapsed, the synchronous rectification control and feature amount detector 111 detects the cycle or frequency (Tcycle) of the preset feature amount corresponding to VDET during the Toff time by the feature amount detector 103, and determines whether the Toff time has ended by comparing the received Tcycle with Tref (reference value) by the comparator 112. Similarly, the preset feature amount corresponding to the VDET includes, but not only includes, the following options: a synchronous rectified ON signal (ON signal), a synchronous rectified OFF signal (OFF signal), some characteristic quantity associated with ON/OFF, an integral of VDET with some voltage difference greater or less than some threshold, a slope of VDET greater or less than some threshold slope, or a VDET level greater or less than some level voltage, etc. As long as the synchronous rectification control and characteristic quantity detector 111 can determine the start-stop result of the synchronous rectification and the period or frequency of the preset characteristic value corresponding to the detection voltage within the turn-off time of the simultaneous turn-off of the primary side and the secondary side according to the input detection voltage, this embodiment does not limit this.
It should be noted that in this embodiment, the input terminal of the off-time detection circuit 11 may be connected to the synchronous rectification detection voltage output terminal in the secondary winding side circuit of the transformer in the flyback switching power supply. As for the specific selection of the synchronous rectification detection voltage output end in the secondary winding Side circuit of the transformer in the flyback switching power supply, which is connected to the input end of the off time detection circuit 11 in this embodiment, the specific selection may be set by a designer, for example, the specific selection may be set according to the specific setting of the synchronous rectification controllable switch in the flyback switching power supply, as shown in fig. 2 and 5, when the synchronous rectification controllable switch is applied to the Low Side of the flyback switching power supply, the input end of the off time detection circuit 11 is connected to the first end of the secondary winding (20-2 in fig. 5) of the transformer (20 in fig. 2 and 5) in the flyback switching power supply; the first end of the secondary winding of the transformer is grounded through the synchronous rectification controllable switch. As shown in fig. 3, when the synchronous rectification controllable switch is applied to a High Side of the flyback switching power supply, the input terminal of the off-time detection circuit 11 is connected to the second terminal of the synchronous rectification controllable switch; the first end of the secondary winding of the transformer is grounded, the second end of the secondary winding of the transformer is connected with the first end of the synchronous rectification controllable switch, and the second end of the synchronous rectification controllable switch is used as the output end of the flyback switching power supply (VOUT in fig. 3).
It is understood that the input terminal of the synchronous rectification start-stop controller 12 in this embodiment may be connected to the first output terminal of the off-time detection circuit 11, and the output terminal of the synchronous rectification start-stop controller 12 may be connected to the second input terminal of the driver 13, and is configured to output a control signal (i.e., a synchronous rectification driving signal) corresponding to synchronous rectification to the driver 13 according to a signal (such as the above-mentioned synchronous rectification control signal) corresponding to the start-stop result of synchronous rectification output by the off-time detection circuit 11.
Specifically, for the specific structure of the synchronous rectification start-stop controller 12 in this embodiment, that is, the specific manner in which the synchronous rectification start-stop controller 12 generates the corresponding synchronous rectification driving signal according to the start-stop result, may be set by a designer according to a practical scene and a user requirement, and if the method can be implemented in the same or similar manner as the method for controlling the synchronous rectification start-stop or turn-on control device in the prior art, this embodiment does not limit this.
It should be noted that, in this embodiment, a first input terminal of the driver 13 may be connected to a second output terminal of the off-time detection circuit 11, a second input terminal of the driver 13 may be connected to an output terminal of the synchronous rectification start-stop controller 12, and an output terminal of the driver 13 may be connected to a control terminal of the synchronous rectification controllable switch, and is configured to control the synchronous rectification controllable switch in the secondary winding side circuit to turn on and off according to the off-time detection result and the synchronous rectification driving signal. When the off time detection result is the off time (Toff time), the driver 13 may shield the synchronous rectification driving signal, and control the synchronous rectification controllable switch to turn off; when the off-time detection result is a non-off time (such as a Tons or a Tonp time), the driver 13 may control the synchronous rectification controllable switch to be turned on and off according to the synchronous rectification driving signal.
In this embodiment, the embodiment of the utility model provides an utilize turn-off time that turn-off time detection circuitry 11 detected former secondary and turn-offs simultaneously to make driver 13 can shield the synchronous rectification drive signal that synchronous rectification started and stopped controller 12 outputs in this turn-off time, reduce the false turn-on situation of the controllable switch of synchronous rectification in the Toff period, avoid appearing the former limit of transformer and the phenomenon of secondary intercommunication, improve the safety in utilization of flyback switching power supply.
Furthermore, the embodiment of the utility model provides a flyback switching power supply is still provided, include: the synchronous rectification control circuit comprises a transformer, a primary side controllable switch, a synchronous rectification controllable switch, a capacitor and a synchronous rectification controller; the synchronous rectification controller comprises a synchronous rectification driving circuit of the flyback switching power supply provided by the embodiment;
the first end of the primary winding of the transformer is used for being connected with the input end of the power supply, and the second end of the primary winding of the transformer is grounded through the primary controllable switch; the first end of the secondary winding of the transformer and the cathode of the capacitor are connected with the common end of the capacitor and grounded, and the second end of the secondary winding of the transformer and the anode of the capacitor are connected with the common end of the capacitor and used as the output end of the flyback switching power supply;
the first end of the secondary winding of the transformer is connected with the negative electrode of the capacitor through the synchronous rectification controllable switch, the input end of the synchronous rectification controller is connected with the first end of the secondary winding of the transformer, and the output end of the synchronous rectification controller is connected with the control end of the synchronous rectification controllable switch; or the second end of the secondary winding of the transformer is connected with the positive electrode of the capacitor through the synchronous rectification controllable switch, the input end of the synchronous rectification controller is connected with the positive electrode of the capacitor, and the output end of the synchronous rectification controller is connected with the control end of the synchronous rectification controllable switch.
It is further noted that, in the present specification, relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
It is right above the utility model provides a flyback switching power supply and synchronous rectification drive circuit thereof introduces in detail. The principles and embodiments of the present invention have been explained herein using specific examples, and the above descriptions of the embodiments are only used to help understand the method and its core ideas of the present invention. It should be noted that, for those skilled in the art, without departing from the principle of the present invention, the present invention can be further modified and modified, and such modifications and modifications also fall within the protection scope of the appended claims.
Claims (6)
1. A synchronous rectification drive circuit of a flyback switching power supply is characterized by comprising:
the turn-off time detection circuit is used for determining a start-stop result of synchronous rectification and a turn-off time detection result of simultaneous turn-off of an original secondary side according to a detection voltage output by a synchronous rectification detection voltage output end in a secondary side winding side circuit of a transformer in the flyback switching power supply;
the synchronous rectification start-stop controller is used for generating a corresponding synchronous rectification driving signal according to the start-stop result;
and the driver is used for controlling the on and off of the synchronous rectification controllable switch in the secondary winding side circuit according to the off time detection result and the synchronous rectification driving signal.
2. The synchronous rectification driving circuit of the flyback switching power supply as claimed in claim 1, wherein the off-time detection circuit comprises:
the synchronous rectification control and characteristic quantity detector is used for generating a synchronous rectification control signal corresponding to the start-stop result and the period or frequency of a preset characteristic quantity according to the detection voltage; the synchronous rectification control signal is a synchronous rectification on signal or a synchronous rectification off signal, the preset characteristic quantity is a characteristic quantity corresponding to the detection voltage within the turn-off time of the primary side and the secondary side which are simultaneously turned off, the input end of the synchronous rectification control and characteristic quantity detector is connected with the output end of the synchronous rectification detection voltage, the first output end of the synchronous rectification control and characteristic quantity detector is connected with the input end of the synchronous rectification start-stop controller, and the second output end of the synchronous rectification control and characteristic quantity detector is connected with the first input end of the comparator;
the comparator is used for comparing the period or the frequency of the preset characteristic quantity with a reference value to obtain a comparison result; the reference value is a reference period corresponding to the period of the preset characteristic quantity or a reference frequency corresponding to the frequency of the preset characteristic quantity, a second input end of the comparator is connected with an output end of the reference value, and an output end of the comparator is connected with an input end of the shielding time generator;
the shielding time generator is used for generating a shielding control signal corresponding to the turn-off time detection result according to the comparison result; the shielding control signal is a shielding time signal or a non-shielding time signal, and the output end of the shielding time generator is connected with the first input end of the driver.
3. The synchronous rectification driving circuit of the flyback switching power supply as claimed in claim 2, wherein the synchronous rectification control and characteristic quantity detector comprises:
a synchronous rectification control signal detector for generating the synchronous rectification control signal according to the detection voltage; the input end of the synchronous rectification control signal detector is connected with the synchronous rectification detection voltage output end, and the output end of the synchronous rectification control signal detector is connected with the input end of the synchronous rectification start-stop controller;
the detection voltage waveform judger is used for judging whether the voltage is in the turn-off time or not according to the detection voltage; the input end of the detected voltage waveform judger is connected with the synchronous rectification detected voltage output end, and the output end of the detected voltage waveform judger is connected with the first input end of the characteristic quantity detector;
the characteristic quantity detector is used for detecting the period or the frequency of the preset characteristic quantity within the turn-off time according to the judgment result of the detection voltage waveform judger; the second input end of the characteristic quantity detector is connected with the synchronous rectification detection voltage output end, and the output end of the characteristic quantity detector is connected with the first input end of the comparator.
4. The synchronous rectification driving circuit of the flyback switching power supply as claimed in claim 1, wherein an input terminal of the off-time detection circuit is connected to a first terminal of a secondary winding of the transformer; and the first end of the secondary winding of the transformer is grounded through the synchronous rectification controllable switch.
5. The synchronous rectification driving circuit of the flyback switching power supply as claimed in claim 1, wherein an input terminal of the off-time detection circuit is connected to a second terminal of the synchronous rectification controllable switch; the first end of the secondary winding of the transformer is grounded, the second end of the secondary winding of the transformer is connected with the first end of the synchronous rectification controllable switch, and the second end of the synchronous rectification controllable switch is used as the output end of the flyback switching power supply.
6. A flyback switching power supply, comprising: the synchronous rectification control circuit comprises a transformer, a primary side controllable switch, a synchronous rectification controllable switch, a capacitor and a synchronous rectification controller; wherein the synchronous rectification controller comprises a synchronous rectification driving circuit of the flyback switching power supply according to any one of claims 1 to 5;
the first end of the primary winding of the transformer is used for being connected with the input end of a power supply, and the second end of the primary winding of the transformer is grounded through the primary controllable switch; the first end of the secondary winding of the transformer and the negative electrode of the capacitor are connected with the common end of the capacitor and grounded, and the second end of the secondary winding of the transformer and the positive electrode of the capacitor are connected with the common end of the capacitor and used as the output end of the flyback switching power supply;
the first end of the secondary winding of the transformer is connected with the negative electrode of the capacitor through the synchronous rectification controllable switch, the input end of the synchronous rectification controller is connected with the first end of the secondary winding of the transformer, and the output end of the synchronous rectification controller is connected with the control end of the synchronous rectification controllable switch; or the second end of the secondary winding of the transformer is connected with the positive electrode of the capacitor through the synchronous rectification controllable switch, the input end of the synchronous rectification controller is connected with the positive electrode of the capacitor, and the output end of the synchronous rectification controller is connected with the control end of the synchronous rectification controllable switch.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113507215A (en) * | 2021-06-21 | 2021-10-15 | 艾科微电子(深圳)有限公司 | Synchronous rectification control device, power supply and synchronous rectification control method |
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| CN113507215A (en) * | 2021-06-21 | 2021-10-15 | 艾科微电子(深圳)有限公司 | Synchronous rectification control device, power supply and synchronous rectification control method |
| CN113507215B (en) * | 2021-06-21 | 2022-09-20 | 艾科微电子(深圳)有限公司 | Synchronous rectification control device, power supply and synchronous rectification control method |
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