Short-circuit protection device of flyback converter

Abstract

The invention relates to a short-circuit protection device of a flyback converter, which samples a first voltage or a second voltage through a first sampling comparison module and a second sampling comparison module, and compares the first voltage or the second voltage with a first reference voltage and a second reference voltage respectively, so that short circuit of a main winding of a flyback transformer can be found. And when the main circuit voltage is short-circuited, a first control signal or a second control signal is generated, and then the flyback converter is controlled to enter a protection working mode through the first control signal or the second control signal, so that the flyback converter can be protected.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of flyback converter, more particularly, to a short circuit protection device of flyback converter. BACKGROUND

[0002] The common short circuit protection of flyback converter is over-current detection and feedback protection on secondary side. The main scheme is that the output current is monitored by over-current detection circuit through sampling resistor in series on secondary side, and once over-current, the fault signal is fed back to primary side controller to force the controller to close power switch tube. However, the defect of such short circuit protection is that it cannot detect transformer winding short circuit. When primary or secondary winding inter-turn short circuit occurs inside the transformer, the inductance and coupling characteristics will change sharply, but the secondary side may still have voltage output, or the output current does not reach the over-current protection threshold. At this time, the traditional over-current protection circuit on secondary side cannot recognize this fatal hidden fault at all. SUMMARY

[0003] The technical problem to be solved by the present application is to provide a short circuit protection device of flyback converter which can detect and protect the main winding short circuit of transformer, aiming at the above defects of prior art.

[0004] The technical scheme adopted by the present application to solve the technical problem is that a short circuit protection device of flyback converter is constructed, the flyback converter comprises a flyback transformer and a main switch tube, the flyback transformer comprises a primary winding, a secondary winding and a power supply winding, the short circuit protection device comprises a first sampling comparison module, a second sampling comparison module and a control module; The first sampling comparison module is used for sampling a first voltage of the power supply winding, and generating a first control signal based on the short circuit result identified by using the first voltage and a first reference voltage; The second sampling comparison module is used for sampling a second voltage of the power supply winding, and generating a second control signal based on the short circuit result identified by using the second voltage and a second reference voltage; The control module controls the flyback converter to enter a protection working mode based on the first control signal or the second control signal.

[0005] In the short circuit protection device of flyback converter, the first sampling comparison module comprises a first rectifier diode, a second rectifier diode, a first sampling resistor, a second sampling resistor, a first filter capacitor and a first comparison unit; An anode of the first rectifier diode is connected to a same name end of the power supply winding, a cathode of the first rectifier diode is connected to a first end of the first filter capacitor and a first end of the first sampling resistor; a cathode of the second rectifier diode is connected to a different name end of the power supply winding, an anode of the second rectifier diode is connected to a second end of the first filter capacitor, a second end of the first sampling resistor is connected to a first end of the second sampling resistor and a first input end of the first comparison unit, a second end of the second sampling resistor, a second end of the first filter capacitor and a second input end of the first comparison unit are grounded, and an output end of the first comparison unit outputs the first control signal; The first sampling comparison module is configured to sample a first voltage of the power supply winding and generate a first control signal based on a short circuit result identified by using the first voltage and a first reference voltage, and includes: The first sampling resistor and the second sampling resistor are configured to sample the first voltage, the first rectifier diode is configured to rectify the first voltage, and the first sampling resistor, the second sampling resistor and the first filter capacitor are configured to simultaneously perform low-pass filtering on the first voltage; The first comparison unit is configured to compare the first voltage with the first reference voltage, and output the first control signal when the first voltage is greater than the first reference voltage.

[0006] In the short circuit protection device of the flyback converter, the first reference voltage Vp21=Vp2*1.15, where Vp2=-Vinmax / n2, Vinmax is a maximum input voltage of the flyback converter, and n2 is a turns ratio of the primary winding to the power supply winding. A time constant T1 of the low-pass filtering is T1=C7*(R6+R7)<(1 / fsw*Dmax) / 10, where C7 represents a capacitance value of the first filter capacitor, R6 represents a resistance value of the first sampling resistor, R7 represents a resistance value of the second sampling resistor, fsw represents a switching frequency of the flyback converter, and Dmax represents a maximum duty cycle of the flyback converter.

[0007] In the short circuit protection device of the flyback converter, the second sampling comparison module includes a third rectifier diode, a fourth rectifier diode, a third sampling resistor, a fourth sampling resistor, a second filter capacitor and a second comparison unit. An anode of the third rectifier diode is connected to a different name end of the power supply winding, a cathode of the third rectifier diode is connected to a first end of the second filter capacitor and a first end of the third sampling resistor; a cathode of the fourth rectifier diode is connected to a same name end of the power supply winding, an anode of the fourth rectifier diode is connected to a second end of the second filter capacitor, a second end of the third sampling resistor is connected to a first end of the fourth sampling resistor and a first input end of the second comparison unit, a second end of the fourth sampling resistor, the second end of the second filter capacitor and a second input end of the second comparison unit are grounded, and an output end of the second comparison unit outputs the second control signal; The second sampling comparison module is used for sampling a second voltage of the power supply winding, and generating a second control signal based on a short circuit result identified by using the second voltage and a second reference voltage, and comprises The third sampling resistor and the fourth sampling resistor are used for sampling the second voltage, the second rectifier diode is used for rectifying the second voltage, and the third sampling resistor, the fourth sampling resistor and the second filter capacitor are used for simultaneously performing low-pass filtering on the second voltage. The second comparison unit is used for comparing the second voltage with the second reference voltage, and when the second voltage is greater than the second reference voltage, the second comparison unit outputs the second control signal.

[0008] In the short circuit protection device of the flyback converter, the second reference voltage Vp23=Vp22*1.15; wherein Vp2_2=Vout*n3, Vout is an output voltage of the flyback converter, and n3 is a turn ratio of the power supply winding to the secondary winding. A time constant T2 of the low-pass filtering is C6*(R4+R5)<(1 / fsw*(1-Dmax)) / 10; wherein C6 represents a capacitance value of the second filter capacitor, R4 represents a resistance value of the third sampling resistor, R5 represents a resistance value of the fourth sampling resistor, fsw represents a switching frequency of the flyback converter, and Dmax represents a maximum duty cycle of the flyback converter.

[0009] In the short circuit protection device of the flyback converter, the control module controls the flyback converter to enter a protection working mode based on the first control signal, and comprises: The control module judges that a main winding short circuit occurs and an input voltage of the flyback converter is a maximum value based on the first control signal, and limits a maximum value of a current flowing through the main switch tube of the flyback converter when the main switch tube is next turned on to control the flyback converter to enter a pulse cross-cycle modulation mode.

[0010] In the short-circuit protection device of the flyback converter, the control module controls the flyback converter to enter a protection working mode based on the second control signal, including: The control module judges that the main winding short circuit occurs but the input voltage of the flyback converter is not the maximum value based on the second control signal, judges the occurrence time of the main winding short circuit, and controls the maximum value of the current flowing through the main switch tube next time the main switch tube is turned on based on the occurrence time to control the flyback converter to enter a pulse cross-cycle modulation mode. When the main winding short circuit occurs at the turn-on time of the main switch tube, the second control signal can be detected at the turn-off time of the main switch tube.

[0011] In the short-circuit protection device of the flyback converter, the control module further judges the output winding short circuit or the supply winding short circuit of the flyback converter based on a third control signal, and controls the flyback converter to enter a hiccup mode.

[0012] In the short-circuit protection device of the flyback converter, the secondary winding and the supply winding are common; The flyback transformer further includes a magnetic core, a first insulation layer and a second insulation layer; The primary winding includes a first primary sub-winding and a second primary sub-winding; The first primary sub-winding is wound on the magnetic core, the first insulation layer is arranged outside the first primary sub-winding, and the secondary winding and the supply winding are wound side by side on the first insulation layer; The second insulation layer is arranged outside the secondary winding and the supply winding, and the second primary sub-winding is wound on the second insulation layer; The winding of the first primary sub-winding is aligned with the winding of the first primary sub-winding, and the winding of the secondary winding and the winding of the supply winding are staggered with the winding of the first primary sub-winding and the winding of the first primary sub-winding.

[0013] In the short-circuit protection device of the flyback converter, the secondary winding and the supply winding are not common; The primary winding includes a first primary sub-winding and a second primary sub-winding; The first primary sub-winding is wound on the magnetic core, and the first insulation layer is arranged outside the first primary sub-winding; The secondary winding and the supply winding are wound on the first insulation layer, and the secondary winding is located above the supply winding or the secondary winding is located below the supply winding; The second insulation layer is arranged outside the secondary side winding and the power supply winding, and the second primary side sub-winding is wound on the second insulation layer. The first primary side sub-winding and the winding alignment of the first primary side sub-winding.

[0014] The short circuit protection device of the flyback converter of the present application can find that the primary winding of the flyback transformer has a short circuit by sampling the first voltage or the second voltage through the first sampling comparison module and the second sampling comparison module, comparing the first voltage or the second voltage with the first reference voltage and the second reference voltage respectively, and generating the first control signal or the second control signal when the primary winding has a short circuit, and then controlling the flyback converter to enter the protection working mode through the first control signal or the second control signal, so that the flyback converter can be protected. BRIEF DESCRIPTION OF DRAWINGS

[0015] The present application will be further described below in conjunction with the drawings and embodiments, wherein: Figure 1 is a principle block diagram of a preferred embodiment of the short circuit protection device of the flyback converter of the present application; Figure 2 is a circuit diagram of a preferred embodiment of the short circuit protection device of the flyback converter of the present application; Figure 3 is a circuit diagram of another preferred embodiment of the short circuit protection device of the flyback converter of the present application; Figure 4 is a perspective view of a first preferred embodiment of the flyback transformer of the flyback converter of the present application; Figure 5 is a sectional view of the first preferred embodiment of the flyback transformer of the flyback converter of the present application; Figure 6 is a perspective view of a second preferred embodiment of the flyback transformer of the flyback converter of the present application; Figure 7 is a sectional view of the second preferred embodiment of the flyback transformer of the flyback converter of the present application. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical solutions and advantages of the present application more clear, the present application will be further described below in conjunction with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application, and are not used to limit the present application.

[0017] Figure 1 is a principle block diagram of a preferred embodiment of the short circuit protection device of the flyback converter of the present application. As Figure 1 shown, the short circuit protection device of the flyback converter of the present application is applicable to any known flyback converter in the art. In the preferred embodiment of the present application, the short circuit protection device of the flyback converter of the present application is combined withFigure 2 It can be known that the flyback converter comprises a flyback transformer and a main switch Q1, the flyback transformer comprises a primary winding P1, a secondary winding S1 and a supply winding P2. Figure 1 As shown, the short-circuit protection device comprises a first sampling comparison module 100, a second sampling comparison module 200 and a control module 300. The first sampling comparison module 100 is used for sampling a first voltage of the supply winding P2, and generating a first control signal based on a short-circuit result identified by using the first voltage and a first reference voltage; the second sampling comparison module 200 is used for sampling a second voltage of the supply winding P2, and generating a second control signal based on a short-circuit result identified by using the second voltage and a second reference voltage. The control module 300 controls the flyback converter to enter a protection working mode based on the first control signal or the second control signal.

[0018] The short-circuit protection device of the flyback converter of the present application can find that the main circuit winding of the flyback transformer is short-circuited by sampling the first voltage or the second voltage by the first sampling comparison module and the second sampling comparison module, and comparing the first voltage or the second voltage with the first reference voltage and the second reference voltage respectively, and can generate the first control signal or the second control signal when the main circuit voltage is short-circuited, and then control the flyback converter to enter the protection working mode by the first control signal or the second control signal, so as to protect the flyback converter.

[0019] Figure 2 is a circuit diagram of a preferred embodiment of the short-circuit protection device of the flyback converter of the present application. As shown, Figure 2As shown, the flyback converter can include a flyback transformer, a main switch Q1, a control chip U1, resistors R1-R3, diodes D1-D4, capacitors C1-C3, output capacitors C4 and C5. The flyback transformer includes a primary winding P1, a secondary winding S1, and a supply winding P2. The AC input terminal Vin is connected to the first end of the capacitor C1, the first end of the resistor R1, the first end of the capacitor C2, and the like-named end of the primary winding P1, and the second end of the capacitor C1 is grounded. The second end of the resistor R1 and the second end of the capacitor C2 are connected to the cathode of the diode D1, the different-named end of the primary winding P1 and the anode of the diode D1 are connected to the drain of the main switch Q1, the source of the main switch Q1 is grounded through the resistor R2, and at the same time the source of the main switch Q1 is connected to the Cs terminal of the control chip U1 through the resistor R3, and the Gate terminal of the control chip U1 is connected to the gate of the main switch Q1 to output a control signal to the main switch Q1. The anode of the diode D2 is connected to the different-named end of the secondary winding S1, and the cathode is connected to the power output terminal Vout+, the like-named end of the secondary winding S1 is connected to the power output terminal Vout-, and the capacitor C4 is connected between the power output terminal Vout+ and the power output terminal Vout-. The anode of the diode D3 is connected to the different-named end of the supply winding P2, and the cathode is connected to the supply output terminal Vcc, the like-named end of the supply winding P2 is grounded GND, and the capacitor C4 is connected between the supply output terminal Vcc and the ground GND. The cathode of the diode D4 is connected to the like-named end of the supply winding P2, and the anode is grounded GND. The secondary winding S1 and the supply winding P2 can share a common ground or not.

[0020] The common protection working modes of flyback converter include pulse skipping modulation (PSM) mode, cycle-by-cycle protection (CBC) mode and burst mode (BM). The cycle-by-cycle protection mode cannot be applied to long-term short circuit, and the fault recovery of burst mode is slow and cannot limit the current peak value of the main switch. In the preferred embodiment, the pulse skipping modulation mode is selected as the protection working mode. The pulse skipping modulation mode is usually used in the very light load condition of the flyback converter, and the current peak value of the main switch is further limited to achieve high-efficiency control. Generally, when the voltage of the COMP pin of the control chip of the flyback converter, such as UCC28C45 of TI, is lower than 1.4V, the pulse skipping modulation mode is entered In combination Figures 1-2It can be known that the short-circuit protection device comprises a first sampling comparison module 100, a second sampling comparison module 200 and a control module 300. The first sampling comparison module 100 is used for sampling a first voltage of the power supply winding P2, and generating a first control signal based on a short-circuit result identified by using the first voltage and a first reference voltage; the second sampling comparison module 200 is used for sampling a second voltage of the power supply winding P2, and generating a second control signal based on a short-circuit result identified by using the second voltage and a second reference voltage. The control module 300 controls the flyback converter to enter a protection working mode based on the first control signal or the second control signal.

[0021] As shown in Figure 2 The first sampling comparison module 100 comprises a rectifier diode D7, a rectifier diode D8, a sampling resistor R6, a sampling resistor R7, a filter capacitor C7 and a first comparison unit TL2. Figure 2 In the preferred embodiment shown in

[0022] An anode of the rectifier diode D7 is connected to a same name end of the power supply winding P2, a cathode is connected to a first end of the filter capacitor C7 and a first end of the sampling resistor R6; a cathode of the rectifier diode D8 is connected to a different name end of the power supply winding P2, a cathode is connected to a second end of the filter capacitor C7 and a second end of the sampling resistor R7; a second end of the sampling resistor R6 is connected to a first end of the sampling resistor R7 and a first input end of the first comparison unit TL2, a second end of the sampling resistor R7, the filter capacitor C7 and a second input end of the first comparison unit TL2 are grounded, and an output end of the first comparison unit outputs the first control signal. The sampling resistor R6 and the sampling resistor R7 are used for sampling the first voltage, the rectifier diodes D7 and D8 are used for rectifying the first voltage, and the sampling resistor R6, the sampling resistor R7 and the filter capacitor C7 are used for simultaneously low-pass filtering the first voltage; the first comparison unit TL2 is used for comparing the first voltage with the first reference voltage, and when the first voltage is greater than the first reference voltage, the first comparison unit is turned on to output the first control signal. The first reference voltage Vp21 = Vp2 * 1.15, wherein Vp2 = -Vinmax / n2, Vinmax is a maximum input voltage of the flyback converter, and n2 is a turns ratio of the primary winding P1 to the power supply winding P2; a time constant T1 of the low-pass filtering is C7*(R6+R7)<(1 / fsw*Dmax) / 10, wherein C7 represents a capacitance value of the filter capacitor C7, R6 represents a resistance value of the sampling resistor R6, R7 represents a resistance value of the sampling resistor R7, fsw represents a switching frequency of the flyback converter, and Dmax represents a maximum duty cycle of the flyback converter.

[0023] As shown in Figure 2 The second sampling comparison module 200 includes a rectifier diode D5, a rectifier diode D6, a sampling resistor R4, a sampling resistor R5, a filter capacitor C6 and a second comparison unit TL1; in Figure 2In the preferred embodiment shown, the second comparison unit selects a device with a saturation on-voltage less than 1.4V, such as a precision programmable reference voltage source TL432 produced by Texas Instruments. The anode of the rectifier diode D5 is connected to the non-identical end of the power supply winding P2, the cathode is connected to the first end of the filter capacitor C6 and the first end of the sampling resistor R4; the cathode of the rectifier diode D6 is connected to the identical end of the power supply winding P2, the anode is connected to the second end of the filter capacitor C6 and the second end of the sampling resistor R5, the second end of the sampling resistor R4 is connected to the first end of the sampling resistor R5 and the first input end of the second comparison unit, the second end of the sampling resistor R5, the second end of the filter capacitor C6 and the second input end of the second comparison unit TL1 are grounded, and the output end of the second comparison unit TL1 outputs the second control signal. The sampling resistors R4 and R5 are used to sample the second voltage, the rectifier diodes D5 and D6 are used to rectify the second voltage, and the sampling resistors R4, R5 and the filter capacitor C6 are used to simultaneously low-pass filter the second voltage; the second comparison unit is used to compare the second voltage with the second reference voltage, and when the second voltage is greater than the second reference voltage, the second comparison unit is turned on to output the second control signal.

[0024] The second reference voltage Vp23=Vp22*1.15; wherein Vp2_2=Vout*n3, Vout is the output voltage of the flyback converter, and n3 is the turns ratio of the power supply winding P2 to the secondary winding S1; the time constant T2 of the low-pass filter is C6*(R4+R5)<(1 / fsw*(1-Dmax)) / 10; wherein C6 represents the capacitance value of the filter capacitor C6, R4 represents the resistance value of the sampling resistor R4, and R5 represents the resistance value of the sampling resistor R5; fsw represents the switching frequency of the flyback converter, and Dmax represents the maximum duty cycle of the flyback converter.

[0025] In the preferred embodiment of the present application, the control module 300 can be realized by a program built-in in the control chip U1, or by a separate control chip. The following is described by taking the case of being built-in in the control chip U1. The Comp end of the control chip U1 receives the first control signal, judges that the primary winding short circuit occurs and the input voltage of the flyback converter is the maximum value based on the first control signal, generates a control signal for controlling the main switch Q1, and outputs the control signal from the Gate end, thereby limiting the maximum value of the current flowing through the main switch Q1 of the flyback converter when it is turned on next time to control the flyback converter to enter the pulse cross-cycle modulation mode.

[0026] The Comp terminal of the control chip U1 receives the second control signal, judges that the main winding short circuit occurs but the input voltage of the flyback converter is not the maximum value based on the first human control signal, judges the occurrence time of the main winding short circuit, and controls the control signal of the main switch Q1 based on the occurrence time, outputs the control signal from the Gate terminal of the main switch Q1, so as to control the maximum value of the current flowing through the main switch Q1 at the next opening time of the main switch Q1 to control the flyback converter to enter the pulse cross-cycle modulation mode; wherein the second control signal can be detected at the closing time of the main switch Q1 when the main winding short circuit occurs at the opening time of the main switch Q1.

[0027] When the main winding short circuit occurs and the input voltage Vin of the flyback converter is at the maximum value, this is also the condition under which the main switch Q1 is stressed the most. When the main switch Q1 is opened, the voltage on the supply winding P2 is Vp2=-Vinmax / n2; wherein n2 is the turn ratio of the primary winding P1 and the supply winding P2. At this time, the protection voltage (i.e. the first reference voltage) Vp21=Vp2*1.15 is designed. At this time, the sampling resistor R6, the sampling resistor R7, and the filter capacitor C7 constitute a low-pass filter, and the time constant of the low-pass filter is set to T1=C7*(R6+R7)<(1 / fsw*Dmax) / 10, wherein C7 represents the capacitance value of the filter capacitor C7, R6 represents the resistance value of the sampling resistor R6, R7 represents the resistance value of the sampling resistor R7; fsw represents the switching frequency of the flyback converter, and Dmax represents the maximum duty cycle of the flyback converter.

[0028] The whole protection path is: the main switch Q1 is opened— the voltage of the supply winding P2 exceeds Vp2_1— the first comparison unit TL2 (precision programmable reference voltage source TL432) is saturated and turned on— the control chip U1 limits the maximum value of the current flowing through the main switch Q1 at the next opening time— the control chip controls the flyback converter to enter the pulse cross-cycle modulation mode. The advantage is that the excitation inductance energy storage stage has been intercepted; the stress of the main switch can be further reduced, and the flyback converter entering the pulse cross-cycle modulation mode can also be applicable to long-term short circuit.

[0029] When the main winding short circuit and the input voltage Vin of the flyback converter is not at the maximum value, the voltage on the supply winding P2 is Vp2_2=Vout*n3 when the main switch Q1 is off; where n3 is the turns ratio of the supply winding P2 and the secondary winding S1. At this time, the protection voltage Vp2-3=Vp22*1.15 is designed. It should also be noted that the sampling resistor R4, the sampling resistor R5, and the filter capacitor C6 constitute a low-pass filter, and the time constant of the low-pass filter is set to T2=C6*(R4+R5)<(1 / fsw*(1-Dmax)) / 10, where C6 represents the capacitance value of the filter capacitor C6, R4 represents the resistance value of the sampling resistor R4, R5 represents the resistance value of the sampling resistor R5; fsw represents the switching frequency of the flyback converter, and Dmax represents the maximum duty cycle of the flyback converter.

[0030] The entire protection path is divided into two cases. Case 1: the main winding short circuit occurs when the main switch Q1 is off - the voltage on the supply winding P2 exceeds Vp2 3 - the second comparison unit TL2 (precision programmable reference voltage source TL432) is saturated and turned on - the control chip U1 limits the maximum current flowing through the main switch Q1 when it is turned on next time - the control chip controls the flyback converter to enter the pulse cross-cycle modulation mode - only when the main switch Q1 is turned on. Case 2: the main winding short circuit occurs when the main switch Q1 is on - the voltage on the supply winding P2 exceeds Vp2_3 during the period when the main switch Q1 is off - the second comparison unit TL2 (precision programmable reference voltage source TL432) is saturated and turned on - the control chip U1 limits the maximum current flowing through the main switch Q1 when it is turned on next time - the control chip controls the flyback converter to enter the pulse cross-cycle modulation mode. This propagation path is obviously slower when the main switch Q1 is turned on. However, this path is triggered only when the input voltage is low, which is not the worst case.

[0031] In the preferred embodiment of the present application, the control module 300 further judges the output winding short circuit or the supply winding P2 short circuit of the flyback converter based on the third control signal, and controls the flyback converter to enter the hiccup mode. When the supply winding is short circuited, the flyback converter will eventually enter the hiccup mode because the output voltage VCC of the supply winding P2 has no power, at which time the protection of the flyback converter can be realized by the parameters of the output capacitor C5 and the soft start circuit of the control chip U1. When the main circuit output capacitor is short circuited, the conduction path of the entire protection is consistent with the case of the supply winding short circuit, and the hiccup protection is finally entered, at which time the protection of the flyback converter can be realized by the parameters of the output capacitor C5 and the soft start circuit of the control chip U1. When the supply output capacitor is short circuited, the flyback converter will eventually enter the hiccup mode because VCC has no power, at which time the protection of the flyback converter can be realized by the parameters of the output capacitor C5 and the soft start circuit of the control chip U1. Those skilled in the art know various parameter adjustment methods, which will not be repeated here.

[0032] Figure 3 is a circuit diagram of another preferred embodiment of the short circuit protection device of the flyback converter of the present application. In Figure 3 the preferred embodiment shown, the principle is the same as Figure 2 , and the difference is only in the implementation of the first comparison unit and the second comparison unit. Only the difference will be described as follows.

[0033] In Figure 3 the preferred embodiment shown, the first comparison unit and the second comparison unit are implemented by comparators. As Figure 3 shown, the first comparison unit includes a first comparator U3, the first input end of the first comparator U3 is connected to the midpoint of the sampling resistor R6 and the sampling resistor R7, the second input end is connected to the first reference voltage Ref2, the output end outputs the first control signal, and the power supply end is connected to the reference voltage Vref and the ground end is grounded. Similarly, the second comparison unit includes a second comparator U2, the first input end of the second comparator U2 is connected to the midpoint of the sampling resistor R4 and the sampling resistor R5, the second input end is connected to the second reference voltage Ref1, the output end outputs the second control signal, and the power supply end is connected to the reference voltage Vref and the ground end is grounded. The first comparator and the second comparator output the first control signal and the second control signal based on the comparison result of the sampling voltage and the reference voltage. The first control signal and the second control signal are preferably low-level effective.

[0034] Figure 4 is a perspective view of the first preferred embodiment of the flyback transformer of the flyback converter of the present application; Figure 5 is a sectional view of the first preferred embodiment of the flyback transformer of the flyback converter of the present application. InFigures 4-5 In the preferred embodiment shown, the leakage inductance can be reduced by designing the winding of the flyback transformer. Figures 4-5 In the preferred embodiment shown, the secondary winding S1 and the power supply winding P2 are grounded. The flyback transformer further comprises a magnetic core 10, a first insulation layer 20 and a second insulation layer 30; the primary winding P1 comprises a first primary sub-winding P11 and a second primary sub-winding P12; the first primary sub-winding P11 is wound on the magnetic core 10, the first insulation layer 20 is arranged outside the first primary sub-winding P11, the secondary winding S1 and the power supply winding P2 are wound side by side on the first insulation layer 20; the second insulation layer 30 is arranged outside the secondary winding S1 and the power supply winding P2, the second primary sub-winding P12 is wound on the second insulation layer 30; the winding of the first primary sub-winding P11 and the first primary sub-winding P11 are aligned, the winding of the secondary winding S1 and the power supply winding P2 are staggered with the winding of the first primary sub-winding P11 and the first primary sub-winding P11. In this preferred embodiment, the winding of the main winding and the power supply winding are arranged side by side, and are wound as a "wire", the leakage inductance between the three windings is small, and the structure is magnetic core-primary sub-winding-insulation layer-(secondary winding / power supply winding)-insulation layer-primary sub-winding-insulation layer.

[0035] Figure 6 is a perspective view of a second preferred embodiment of the flyback transformer of the flyback converter of the present application; Figure 7 is a sectional view of a second preferred embodiment of the flyback transformer of the flyback converter of the present application. In the preferred embodiment shown, the leakage inductance can be reduced by designing the winding of the flyback transformer. Figures 6-7 In the preferred embodiment shown, the leakage inductance can be reduced by designing the winding of the flyback transformer. Figures 6-7 In the preferred embodiment shown, the secondary winding S1 and the power supply winding P2 are not grounded; the flyback transformer further comprises a magnetic core 10, a first insulation layer 20 and a second insulation layer 30; the primary winding P1 comprises a first primary sub-winding P11 and a second primary sub-winding P12; the first primary sub-winding P11 is wound on the magnetic core 10, the first insulation layer 20 is arranged outside the first primary sub-winding P11, the secondary winding S1 and the power supply winding P2 are wound on the first insulation layer 20; the secondary winding S1 and the power supply winding P2 are wound on the first insulation layer 20. As Figure 6As shown, in the preferred embodiment, the secondary winding S1 is located above the power supply winding P2, that is, the secondary winding S1 is wound first, and then the power supply winding P2 is wound. The second insulation layer 30 is arranged outside the secondary winding S1 and the power supply winding P2, and the second primary winding P12 is wound on the second insulation layer 30; the first primary winding P11 and the winding of the first primary winding P11 are aligned.

[0036] In the preferred embodiment, the primary winding and the power supply winding are divided into several equal parts, and then wound alternately in one layer of primary winding and one layer of power supply winding. The leakage inductance between the three windings is slightly larger, and the structure is magnetic core - half primary winding - insulation layer - 1 / 2 position secondary winding -> insulation layer - 1 / 2 position winding power supply winding -> insulation layer - primary winding. The design uses close interleaving winding, and according to this winding method, the primary leakage inductance can be lower than 0.5% of the excitation inductance, and the leakage inductance of the power supply winding and the primary winding is lower than 0.5%.

[0037] In another preferred embodiment of the present application, the secondary winding S1 can also be designed to be located below the power supply winding P2, that is, the power supply winding P2 is wound first, and then the secondary winding S1 is wound.

[0038] The present application can achieve protection of self-winding short circuit and long-term short circuit of the output port by detecting the level state of the secondary winding, controlling the leakage inductance of the transformer and selecting the working mode of the flyback transformer. In the case of self-winding short circuit, the propagation path of the protection is faster, and the reliability is higher.

[0039] Although the present application is described by specific embodiments, those skilled in the art should understand that various modifications and equivalent substitutions can be made to the present application without departing from the scope of the present application. In addition, various modifications can be made to the present application for specific situations or materials without departing from the scope of the present application. Therefore, the present application is not limited to the disclosed specific embodiments, but should include all embodiments falling within the scope of the claims of the present application.

[0040] The above is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent substitution and improvement made within the spirit and principles of the present application shall be included in the protection scope of the present application. The above is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent substitution and improvement made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A short-circuit protection device for a flyback converter, the flyback converter comprising a flyback transformer and a main switching transistor, the flyback transformer comprising a primary winding, a secondary winding, and a power supply winding, characterized in that, The short-circuit protection device includes a first sampling comparison module, a second sampling comparison module, and a control module; The first sampling comparison module is used to sample the first voltage of the power supply winding and generate a first control signal based on the short circuit result identified using the first voltage and the first reference voltage; The second sampling comparison module is used to sample the second voltage of the power supply winding and generate a second control signal based on the short circuit result identified using the second voltage and the second reference voltage; The control module controls the flyback converter to enter the protection mode based on the first control signal or the second control signal.

2. The short-circuit protection device for a flyback converter according to claim 1, characterized in that, The first sampling comparison module includes a first rectifier diode, a second rectifier diode, a first sampling resistor, a second sampling resistor, a first filter capacitor, and a first comparison unit; The anode of the first rectifier diode is connected to the same-name terminal of the power supply winding, and the cathode is connected to the first terminal of the first filter capacitor and the first terminal of the first sampling resistor; the cathode of the second rectifier diode is connected to the opposite-name terminal of the power supply winding, and the anode is connected to the second terminal of the first filter capacitor; the second terminal of the first sampling resistor is connected to the first terminal of the second sampling resistor and the first input terminal of the first comparison unit; the second terminal of the second sampling resistor, the second terminal of the first filter capacitor, and the second input terminal of the first comparison unit are grounded; the output terminal of the first comparison unit outputs the first control signal. The first sampling comparison module is used to sample the first voltage of the power supply winding and generate a first control signal based on the short-circuit result identified using the first voltage and the first reference voltage, including: The first sampling resistor and the second sampling resistor are used to sample the first voltage, the first rectifier diode is used to rectify the first voltage, and the first sampling resistor, the second sampling resistor and the first filter capacitor are used to low-pass filter the first voltage. The first comparator unit is used to compare the first voltage with the first reference voltage. When the first voltage is greater than the first reference voltage, the first comparator unit outputs the first control signal.

3. The short-circuit protection device for a flyback converter according to claim 2, characterized in that, The first reference voltage Vp21 = Vp2 * 1.15, where Vp2 = -Vinmax / n2, Vinmax is the maximum input voltage of the flyback converter, and n2 is the turns ratio of the primary winding to the power supply winding; The time constant of the low-pass filter is T1 = C7 * (R6 + R7) < (1 / fsw * Dmax) / 10, where C7 represents the capacitance value of the first filter capacitor, R6 represents the resistance value of the first sampling resistor, R7 represents the resistance value of the second sampling resistor; fsw represents the switching frequency of the flyback converter, and Dmax represents the maximum duty cycle of the flyback converter.

4. The short-circuit protection device for a flyback converter according to any one of claims 2 to 3, characterized in that, The second sampling comparison module includes a third rectifier diode, a fourth rectifier diode, a third sampling resistor, a fourth sampling resistor, a second filter capacitor, and a second comparison unit; The anode of the third rectifier diode is connected to the opposite terminal of the power supply winding, and the cathode is connected to the first terminal of the second filter capacitor and the first terminal of the third sampling resistor; the cathode of the fourth rectifier diode is connected to the same terminal of the power supply winding, and the anode is connected to the second terminal of the second filter capacitor; the second terminal of the third sampling resistor is connected to the first terminal of the fourth sampling resistor and the first input terminal of the second comparison unit; the second terminal of the fourth sampling resistor, the second terminal of the second filter capacitor, and the second input terminal of the second comparison unit are grounded; the output terminal of the second comparison unit outputs the second control signal. The second sampling comparison module is used to sample the second voltage of the power supply winding and generate a second control signal based on the short-circuit result identified using the second voltage and the second reference voltage, including... The third sampling resistor and the fourth sampling resistor are used to sample the second voltage, the second rectifier diode is used to rectify the second voltage, and the third sampling resistor, the fourth sampling resistor, and the second filter capacitor are used simultaneously for low-pass filtering of the second voltage; The second comparator unit is used to compare the second voltage with the second reference voltage. When the second voltage is greater than the second reference voltage, the second comparator unit outputs the second control signal.

5. The short-circuit protection device for a flyback converter according to claim 4, characterized in that, The second reference voltage Vp23 = Vp22 * 1.15; where Vp2_2 = Vout * n3, Vout is the output voltage of the flyback converter, and n3 is the turns ratio of the power supply winding to the secondary winding; The time constant T2 of the low-pass filter is T2 = C6*(R4+R5)<(1 / fsw*(1-Dmax)) / 10; where C6 represents the capacitance value of the second filter capacitor, R4 represents the resistance value of the third sampling resistor, R5 represents the resistance value of the fourth sampling resistor; fsw represents the switching frequency of the flyback converter, and Dmax represents the maximum duty cycle of the flyback converter.

6. The short-circuit protection device for a flyback converter according to claim 4, characterized in that, The control module controls the flyback converter to enter a protection mode based on the first control signal, including: The control module determines, based on the first control signal, that a short circuit has occurred in the main winding and that the input voltage of the flyback converter is at its maximum value. It then limits the maximum current flowing through the flyback converter when the main switch is turned on again to control the flyback converter to enter the pulse cross-cycle modulation mode.

7. The short-circuit protection device for a flyback converter according to claim 4, characterized in that, The control module controls the flyback converter to enter a protection mode based on the second control signal, including: The control module determines, based on the second control signal, that a short circuit has occurred in the main winding but the input voltage of the flyback converter is not at its maximum value, and determines the occurrence time of the short circuit in the main winding. Based on the occurrence time, it controls the maximum value of the current flowing through the main switch of the flyback converter when it is turned on next time, so as to control the flyback converter to enter the pulse cross-cycle modulation mode. When the short circuit in the main winding occurs during the turn-on time of the main switch, the second control signal can only be detected during the turn-off time of the main switch.

8. The short-circuit protection device for a flyback converter according to any one of claims 1 to 3, characterized in that, The control module further determines whether the output winding or the power supply winding of the flyback converter is short-circuited based on the third control signal, and controls the flyback converter to enter the hiccup mode.

9. The short-circuit protection device for a flyback converter according to any one of claims 1 to 3, characterized in that, The secondary winding and the power supply winding share a common ground; The flyback transformer further includes a magnetic core, a first insulating layer, and a second insulating layer; The primary winding includes a first primary sub-winding and a second primary winding; The first primary winding is wound on the magnetic core, the first insulating layer is disposed on the outside of the first primary winding, and the secondary winding and the power supply winding are wound side by side on the first insulating layer; The second insulating layer is disposed on the outside of the secondary winding and the power supply winding, and the second primary winding is wound on the second insulating layer; The windings of the first primary winding and the first primary winding are aligned, while the windings of the secondary winding and the power supply winding are offset from the windings of the first primary winding and the first primary winding.

10. The short-circuit protection device for a flyback converter according to any one of claims 1 to 3, characterized in that, The secondary winding and the power supply winding do not share a common ground; The primary winding includes a first primary sub-winding and a second primary winding; The first primary winding is wound on the magnetic core, and the first insulating layer is disposed on the outside of the first primary winding; The secondary winding and the power supply winding are wound on the first insulation layer, with the secondary winding located above the power supply winding or below the power supply winding. The second insulating layer is disposed on the outside of the secondary winding and the power supply winding, and the second primary winding is wound on the second insulating layer; The first primary winding and the first primary winding are aligned.

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