Active clamp forward converter with pre-bias start-up function and control method thereof

Abstract

The present invention discloses an active clamp forward converter with a pre-bias start function and a control method thereof. A first self-driving circuit and a second self-driving circuit are respectively arranged at the control ends of a rectifier switch tube M3 and a rectifier switch tube M4. In the initial startup stage, the first self-driving circuit makes the rectifier switch tube M3 non-conductive, and the second self-driving circuit makes the rectifier switch tube M4 non-conductive, so that the output residual voltage will not be discharged to the ground through the rectifier switch tube M3 or the rectifier switch tube M4, thereby effectively avoiding the rectifier switch tube from being damaged due to excessive discharge current, and improving the reliability and stability of the entire circuit.

Description

Technical Field

[0001] The present invention belongs to the field of power electronics, and more specifically, relates to an active clamp forward converter with a pre-bias start function and a control method thereof. Background Art

[0002] like Figure 1 The figure shows an active clamp forward converter of the prior art. Under the control signal, the main switch tube M1 and the embedded switch tube are alternately turned on and off to realize the conversion of electric energy. The embedded capacitor C1 is used to absorb the peak voltage generated by the leakage inductance of the transformer to protect the main switch tube M1. The energy storage inductor L3 is the output inductor, which is used for energy storage and filtering to make the output current smoother. The output capacitor C3 filters the output voltage to further reduce the ripple of the output voltage. The resistor R0 is a load resistor, which is used to connect the load to obtain a stable output voltage.

[0003] When the control signal turns on the main switch tube M1, the input voltage Vin is applied to the primary winding of the transformer T, the current in the primary winding rises linearly, and the transformer stores energy. At this time, the secondary winding induces a voltage, the rectifier switch tube M3 is turned on, the energy storage inductor L3 starts to store energy, and the output capacitor C3 starts to charge.

[0004] When the main switch tube M1 is turned off, since the magnetic flux of the transformer cannot change suddenly, the secondary winding will induce a reverse voltage. At this time, the rectifier switch tube M4 is turned on, and the energy stored in the energy storage inductor L3 is released through the rectifier switch tube M4, and continues to supply power to the load and the output capacitor C3 to maintain the stability of the output voltage.

[0005] In actual use, if the power is turned on again shortly after being turned off, there will be residual voltage at the secondary output end, which will damage the rectifier switch tube and affect the reliability and stability of the entire circuit. Summary of the invention

[0006] In view of the above defects or improvement needs of the prior art, the present invention provides an active clamp forward converter with a pre-bias startup function, the purpose of which is that in the initial startup stage, the first self-driving circuit makes the rectifier switch tube M3 non-conductive, and the second self-driving circuit makes the rectifier switch tube M4 non-conductive, so that the output residual voltage will not be discharged to the ground through the rectifier switch tube M3 or the rectifier switch tube M4, effectively avoiding the situation where the rectifier switch tube is damaged due to excessive discharge current, and improving the reliability and stability of the entire circuit, thereby solving the technical problem that when starting up, the residual voltage will be discharged to the ground through the rectifier switch tube M3 or the rectifier switch tube M4, and if the discharge current is too large, the rectifier switch tube will be damaged, affecting the reliability and stability of the entire switching power supply.

[0007] To achieve the above object, according to one aspect of the present invention, an active clamp forward converter with a pre-bias start-up function is provided, comprising: a transformer T, the transformer T comprising a primary winding L1 and a secondary winding L2, a main switch tube M1 and a clamp switch tube M2 are arranged on the side of the primary winding L1; wherein the main switch tube M1 and the clamp switch tube M2 are alternately turned on to convert an input voltage into an output voltage;

[0008] One end of the secondary winding L2 is connected to one end of the energy storage inductor L3, and the other end of the energy storage inductor L3 is used to connect to the load; one end of the secondary winding L2 is also connected to one end of the rectifier switch tube M4, and the other end of the rectifier switch tube M4 is grounded; the other end of the secondary winding L2 is connected to one end of the rectifier switch tube M3, and the other end of the rectifier switch tube M3 is grounded; a first self-driving circuit is also provided between one end of the secondary winding L2 and the control end of the rectifier switch tube M3; a second self-driving circuit is also provided between the other end of the secondary winding L2 and the control end of the rectifier switch tube M4;

[0009] When the output voltage is lower than a preset value, the first self-driving circuit is used to turn the rectifier switch tube M3 off, and the second self-driving circuit is used to turn the rectifier switch tube M4 off; when the output voltage is greater than or equal to the preset value, the first self-driving circuit is used to selectively turn on the rectifier switch tube M3 according to the voltage condition at one end of the secondary winding L2; the second self-driving circuit is used to selectively turn on the rectifier switch tube M4 according to the voltage condition at the other end of the secondary winding L2.

[0010] Furthermore, one end of the primary winding L1 is connected to the positive electrode of the input power supply, the other end of the primary winding L1 is connected to one end of the main switch tube M1, and the other end of the main switch tube M1 is grounded; the other end of the primary winding L1 is also connected to one end of the clamping capacitor C1, the other end of the clamping capacitor C1 is connected to one end of the clamping switch tube M2, and the other end of the clamping switch tube M2 is connected to the negative electrode of the input power supply.

[0011] Further, the first self-driving circuit includes a first switch unit and a second switch unit, the control end of the first switch unit is connected to the other end of the energy storage inductor L3, one end of the first switch unit is connected to the control end of the second switch unit, and the other end of the first switch unit is grounded;

[0012] One end of the second switch unit is connected to one end of the secondary winding L2 , and the other end of the second switch unit is connected to the control end of the rectifier switch tube M3 .

[0013] Further, the first switch unit includes a transistor Q1 and a transistor Q2, the base of the transistor Q1 serves as a control end of the first switch unit, the collector of the transistor Q1 is connected to the base of the transistor Q2, and the emitter of the transistor Q1 is grounded;

[0014] The base of the transistor Q2 serves as the control end of the second switch unit, the emitter of the transistor Q2 is connected to one end of the secondary winding L2, and the collector of the transistor Q2 is connected to the control end of the rectifier switch tube M3.

[0015] Furthermore, the transistor Q1 is an NPN transistor, and the transistor Q2 is a PNP transistor.

[0016] Further, the second self-driving circuit includes a third switch unit and a fourth switch unit, the control end of the third switch unit is connected to the other end of the energy storage inductor L3, one end of the third switch unit is connected to the control end of the fourth switch unit, and the other end of the third switch unit is grounded;

[0017] One end of the fourth switch unit is connected to the other end of the secondary winding L2 , and the other end of the fourth switch unit is connected to the control end of the rectifier switch tube M4 .

[0018] Further, the third switch unit includes a transistor Q3 and a transistor Q4, the base of the transistor Q3 serves as a control end of the third switch unit, the collector of the transistor Q3 is connected to the base of the transistor Q4, and the emitter of the transistor Q3 is grounded;

[0019] The base of the transistor Q4 serves as the control end of the fourth switch unit, the emitter of the transistor Q4 is connected to the other end of the secondary winding L2, and the collector of the transistor Q4 is connected to the control end of the rectifier switch tube M4.

[0020] Furthermore, the transistor Q3 is an NPN transistor, and the transistor Q4 is a PNP transistor.

[0021] Furthermore, the main switch tube M1, the clamp switch tube M2, the rectifier switch tube M3 and the rectifier switch tube M4 are all MOS tubes.

[0022] According to another aspect of the present invention, a control method for an active clamp forward converter with a pre-bias start-up function is provided, comprising:

[0023] Controlling the main switch tube M1 and the clamp switch tube M2 to be turned on alternately to convert the input voltage into an output voltage;

[0024] When the output voltage is lower than a preset value, the first self-driving circuit turns the rectifier switch tube M3 off, and the second self-driving circuit turns the rectifier switch tube M4 off, so as to prevent the residual voltage at the secondary output end from discharging to the ground through the rectifier switch tube M3 or the rectifier switch tube M4;

[0025] When the output voltage is greater than or equal to a preset value, the first self-driving circuit causes the rectifier switch tube M3 to be selectively turned on according to the voltage condition at one end of the secondary winding L2; the second self-driving circuit causes the rectifier switch tube M4 to be selectively turned on according to the voltage condition at the other end of the secondary winding L2.

[0026] In general, the above technical scheme conceived by the present invention has the following beneficial effects compared with the prior art: a first self-driving circuit and a second self-driving circuit are respectively arranged at the control ends of the rectifier switch tube M3 and the rectifier switch tube M4. In the initial startup stage, the first self-driving circuit makes the rectifier switch tube M3 non-conductive, and the second self-driving circuit makes the rectifier switch tube M4 non-conductive, and the output residual voltage will not be discharged to the ground through the rectifier switch tube M3 or the rectifier switch tube M4, thereby effectively avoiding the rectifier switch tube from being damaged due to excessive discharge current, and improving the reliability and stability of the entire circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a circuit structure schematic diagram of an active clamp forward converter in the prior art;

[0028] Figure 2 This is a schematic diagram of the circuit structure of a first active clamp forward converter with a pre-bias start-up function provided by an embodiment of the present invention;

[0029] Figure 3 is a circuit structure diagram of a second active clamp forward converter with a pre-bias start-up function provided by an embodiment of the present invention;

[0030] Figure 4 is a schematic diagram of the circuit structure of a third active clamp forward converter with a pre-bias start-up function provided by an embodiment of the present invention;

[0031] Figure 5 is a schematic diagram of the circuit structure of a fourth active clamp forward converter with a pre-bias start-up function provided by an embodiment of the present invention;

[0032] Figure 6 It is a flow chart of a control method of an active clamp forward converter with a pre-bias start-up function provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0034] Unless the context requires otherwise, throughout the specification and claims, the term "including" is to be interpreted as open inclusion, that is, "including, but not limited to". In the description of the specification, the terms "one embodiment", "some embodiments", "exemplary embodiments", "examples", "specific examples" or "some examples" and the like are intended to indicate that specific features, structures, materials or characteristics associated with the embodiment or example are included in at least one embodiment or example of the present disclosure. The schematic representation of the above terms does not necessarily refer to the same embodiment or example. In addition, the specific features, structures, materials or characteristics may be included in any one or more embodiments or examples in any appropriate manner, that is, although they may be carried in the embodiments or examples of the above terms due to reasons such as the order and position of appearance, it is not limited to that they can be carried in combination by one embodiment or example.

[0035] In the description of the present invention, the terms "first" and "second" are used only for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Thus, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the embodiments of the present disclosure, unless otherwise specified, the meaning of "multiple" is two or more. In addition, for example, the same type of nouns may be described as two independent individuals by adding "A" and "B" at the end. In this case, the corresponding features defined as "A" and "B" are only used to distinguish the same type of individuals for description purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features.

[0036] In the description of the present invention, the expression "A and / or B" (where A and B are used to formally represent specific characteristic contents) will be involved, and the corresponding expressions include the following three combinations: only A, only B, and a combination of A and B.

[0037] As used herein, "about," "substantially," or "approximately" includes the stated value and an average value that is within an acceptable range of deviation from the particular value as determined by one of ordinary skill in the art taking into account the measurements in question and the errors associated with the measurement of the particular quantity (i.e., the limitations of the measurement system).

[0038] In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0039] Embodiment 1:

[0040] Figure 1 The active clamp forward converter provided has a duty cycle of the primary circuit that increases slowly when it is turned on. When the duty is small, the energy transmitted from the transformer to the secondary circuit is small, resulting in a small and discontinuous output inductor current. At this time, the residual voltage at the secondary output end will discharge to the ground through the rectifier switch tube M3 or the rectifier switch tube M4. If the discharge current is too large, the rectifier switch tube will be damaged, affecting the reliability and stability of the entire circuit.

[0041] In order to prevent the residual voltage at the secondary output terminal from discharging to the ground through the rectifier switch tube M3 or the rectifier switch tube M4 and damaging the rectifier switch tube, this embodiment provides an active clamp forward converter with a pre-bias start function.

[0042] like Figure 2 As shown, the active clamp forward converter with pre-bias start-up function includes: a transformer T, the transformer T includes a primary winding L1 and a secondary winding L2, and a main switch tube M1 and a clamp switch tube M2 are arranged on the side of the primary winding L1; wherein the main switch tube M1 and the clamp switch tube M2 are alternately turned on to convert the input voltage into the output voltage.

[0043] One end of the secondary winding L2 is connected to one end of the energy storage inductor L3, and the other end of the energy storage inductor L3 is used to connect to the load; one end of the secondary winding L2 is also connected to one end of the rectifier switch tube M4, and the other end of the rectifier switch tube M4 is grounded; the other end of the secondary winding L2 is connected to one end of the rectifier switch tube M3, and the other end of the rectifier switch tube M3 is grounded.

[0044] The energy storage inductor L3 is used for energy storage and filtering to make the output current smoother. The rectifier switch tube M3 and the rectifier switch tube M4 are used to alternately conduct and perform rectification. R0 is a load and is used to obtain a stable output voltage.

[0045] A first self-driving circuit is further provided between one end of the secondary winding L2 and the control end of the rectifier switch tube M3 ; a second self-driving circuit is further provided between the other end of the secondary winding L2 and the control end of the rectifier switch tube M4 .

[0046] In actual use, the main switch tube M1 and the clamp switch tube M2 are controlled to be turned on alternately to achieve power conversion. In the initial startup stage, in order to prevent the residual voltage at the secondary output end from discharging to the ground through the rectifier switch tube M3 or the rectifier switch tube M4 and damaging the rectifier switch tube, when the output voltage is lower than a preset reference, the rectifier switch tube M3 and the rectifier switch tube M4 are disconnected.

[0047] In actual use, when the output voltage is lower than a preset value, the first self-driving circuit is used to put the rectifier switch tube M3 in an off state, and the second self-driving circuit is used to put the rectifier switch tube M4 in an off state.

[0048] When the output voltage is lower than the preset value, when the duty is small, the energy transmitted from the transformer to the secondary circuit is small, resulting in a small and discontinuous output inductor current. At this time, the residual voltage at the secondary output end will be discharged to the ground through the rectifier switch tube M3 or the rectifier switch tube M4. In order to avoid this problem, the rectifier switch tube M3 and the rectifier switch tube M4 are both in the disconnected state, which can avoid damage to the rectifier switch tube M3 or the rectifier switch tube M4.

[0049] In this case, the rectification is performed by relying on the body diode of the rectifying switch tube M3 or the rectifying switch tube M4. Due to the unidirectional conduction characteristic of the diode, the output residual voltage will not be discharged to the ground.

[0050] When the output voltage is greater than or equal to a preset value, the first self-driving circuit is used to selectively turn on the rectifier switch tube M3 according to the voltage condition at one end of the secondary winding L2; the second self-driving circuit is used to selectively turn on the rectifier switch tube M4 according to the voltage condition at the other end of the secondary winding L2, wherein the rectifier switch tube M3 and the rectifier switch tube M4 are alternately turned on to rectify the voltage.

[0051] In this case, the branch between the rectifier switch tube M3 and the secondary winding L2 is in a conducting state, and the branch between the rectifier switch tube M4 and the secondary winding L2 is also in a conducting state. Whether the rectifier switch tube M3 and the rectifier switch tube M4 are turned on depends on the voltage of the secondary winding L2. Because the voltage of the secondary winding L2 is a square wave, the rectifier switch tube M3 and the rectifier switch tube M4 are turned on alternately to perform rectification.

[0052] The preset value can be 90% to 100% of the input voltage. When the output voltage reaches 90%-100% of the input voltage, the primary duty value is large, the output inductor current is large and continuous, and the output voltage will not discharge to the ground through the rectifier switch tube, and will not damage the rectifier switch tube, thereby ensuring the stability of the output voltage and facilitating the normal operation of the load.

[0053] In one embodiment, one end of the primary winding L1 is connected to the positive electrode of the input power supply, the other end of the primary winding L1 is connected to one end of the main switch tube M1, and the other end of the main switch tube M1 is grounded; the other end of the primary winding L1 is also connected to one end of the clamping capacitor C1, the other end of the clamping capacitor C1 is connected to one end of the clamping switch tube M2, and the other end of the clamping switch tube M2 is connected to the negative electrode of the input power supply.

[0054] In one embodiment, input capacitor C2 is provided at both ends of the input power supply to filter the input power supply and reduce the ripple of the input voltage. Both ends of the load R0 are connected to output capacitor C3 to further reduce the ripple of the output voltage.

[0055] In one embodiment, Figure 3 As shown, the first self-driving circuit includes a first switch unit and a second switch unit, the control end (i.e., S1) of the first switch unit is connected to the other end (i.e., Vout+) of the energy storage inductor L3, one end of the first switch unit is connected to the control end (i.e., S2) of the second switch unit, and the other end of the first switch unit is grounded. One end of the second switch unit is connected to one end of the secondary winding L2, and the other end of the second switch unit is connected to the control end of the rectifier switch tube M3.

[0056] In one embodiment, Figure 4 As shown, the first switch unit includes a transistor Q1 and a transistor Q2, the base of the transistor Q1 serves as the control end of the first switch unit, the collector of the transistor Q1 is connected to the base of the transistor Q2, and the emitter of the transistor Q1 is grounded. Specifically, the base of the transistor Q1 is connected to one end of a resistor R1 and one end of a resistor R2, the other end of the resistor R1 is connected to the other end of the energy storage inductor L3 (i.e., Vout+), and the other end of the resistor R2 is grounded. The resistor R1 is used for current limiting, and the resistor R2 is used to prevent the transistor Q1 from being mis-conducted. See Figure 5 , a diode Z3 can also be used to prevent the transistor Q1 from being mis-conducted. The specific connection method is that the base of the transistor Q1 is connected to the positive electrode of the diode Z3, the negative electrode of the diode Z3 is connected to one end of the resistor R1, and the other end of the resistor R1 is connected to the other end of the energy storage inductor L3 (that is, Vout+).

[0057] The base of the transistor Q2 serves as the control end of the second switch unit, the emitter of the transistor Q2 is connected to one end of the secondary winding L2, and the collector of the transistor Q2 is connected to the control end of the rectifier switch tube M3. Specifically, the collector of the transistor Q1 is connected in series with the resistor R3 and then connected to the base of the transistor Q2, the emitter of the transistor Q2 is connected in series with the resistor R4 and then connected to one end of the secondary winding L2, the collector of the transistor Q2 is also connected to one end of the resistor R5, and the other end of the resistor R5 is grounded. The diode Z1 is connected in series at both ends of the resistor R5, and the diode Z1 can be a unidirectional transient voltage suppression diode.

[0058] In one embodiment, the transistor Q1 is an NPN transistor, and the transistor Q2 is a PNP transistor.

[0059] In one embodiment, Figure 3 As shown, the second self-driving circuit includes a third switch unit and a fourth switch unit, the control end (i.e., S3) of the third switch unit is connected to the other end of the energy storage inductor L3, one end of the third switch unit is connected to the control end (i.e., S4) of the fourth switch unit, and the other end of the third switch unit is grounded; one end of the fourth switch unit is connected to the other end of the secondary winding L2, and the other end of the fourth switch unit is connected to the control end of the rectifier switch tube M4.

[0060] In one embodiment, Figure 4 As shown, the third switch unit includes a transistor Q3 and a transistor Q4, the base of the transistor Q3 serves as the control end of the third switch unit, the collector of the transistor Q3 is connected to the base of the transistor Q4, and the emitter of the transistor Q3 is grounded; specifically, the base of the transistor Q3 is connected to one end of a resistor R6 and one end of a resistor R7, the other end of the resistor R6 is connected to the other end of the energy storage inductor L3 (i.e., Vout+), and the other end of the resistor R7 is grounded. The resistor R6 is used for current limiting, and the resistor R7 is used to prevent the transistor Q3 from being mis-conducted.

[0061] The base of the transistor Q4 serves as the control end of the fourth switch unit, the emitter of the transistor Q4 is connected to the other end of the secondary winding L2, and the collector of the transistor Q4 is connected to the control end of the rectifier switch tube M4. Specifically, the collector of the transistor Q3 is connected in series with the resistor R8 and then connected to the base of the transistor Q4, and the emitter of the transistor Q4 is connected in series with the resistor R9 and then connected to the other end of the secondary winding L2. The collector of the transistor Q4 is also connected to one end of the resistor R10, and the other end of the resistor R10 is grounded. The diode Z2 is connected in series at both ends of the resistor R10, and the diode Z2 can be a unidirectional transient voltage suppression diode.

[0062] In one embodiment, the transistor Q3 is an NPN transistor, and the transistor Q4 is a PNP transistor.

[0063] In one embodiment, the main switch tube M1, the clamp switch tube M2, the rectifier switch tube M3 and the rectifier switch tube M4 are all metal-oxide-semiconductor field-effect transistors (MOSFET), where MOSFET is abbreviated as MOS. That is, the main switch tube M1, the clamp switch tube M2, the rectifier switch tube M3 and the rectifier switch tube M4 are all MOS tubes.

[0064] In this embodiment, a first self-driving circuit and a second self-driving circuit are respectively arranged at the control ends of the rectifier switch tube M3 and the rectifier switch tube M4. In the initial startup stage, the first self-driving circuit makes the rectifier switch tube M3 non-conductive, and the second self-driving circuit makes the rectifier switch tube M4 non-conductive, so that the output residual voltage will not be discharged to the ground through the rectifier switch tube M3 or the rectifier switch tube M4, thereby effectively avoiding the rectifier switch tube from being damaged due to excessive discharge current, thereby improving the reliability and stability of the entire circuit.

[0065] Embodiment 2:

[0066] Based on the active clamp forward converter with pre-bias start-up function provided in the above-mentioned embodiment 1, this embodiment provides a control method of the active clamp forward converter, including:

[0067] Step 101: Control the main switch tube M1 and the clamp switch tube M2 to be turned on alternately to convert the input voltage into the output voltage.

[0068] In one embodiment, the main switch tube M1 and the clamp switch tube M2 may be controlled by a control module to be turned on alternately.

[0069] In one embodiment, the main switch tube M1 and the clamp switch tube M2 are both MOS tubes.

[0070] Step 102: When the output voltage is lower than a preset value, the first self-driving circuit turns the rectifier switch tube M3 into an off state, and the second self-driving circuit turns the rectifier switch tube M4 into an off state to prevent the residual voltage at the secondary output end from discharging to the ground through the rectifier switch tube M3 or the rectifier switch tube M4.

[0071] In one embodiment, the rectifier switch tube M3 and the rectifier switch tube M4 are both MOS tubes.

[0072] The preset value may be 90% to 100% of the input voltage.

[0073] When the output voltage is lower than the preset value, when the duty is small, the energy transmitted from the transformer to the secondary circuit is small, resulting in a small and discontinuous output inductor current. At this time, the residual voltage at the secondary output end will be discharged to the ground through the rectifier switch tube M3 or the rectifier switch tube M4. In order to avoid this problem, the rectifier switch tube M3 and the rectifier switch tube M4 are both in the disconnected state, which can avoid damage to the rectifier switch tube M3 or the rectifier switch tube M4.

[0074] In this case, the rectification is performed by relying on the body diode of the rectifying switch tube M3 or the rectifying switch tube M4. Due to the unidirectional conduction characteristic of the diode, the output residual voltage will not be discharged to the ground.

[0075] Step 103: When the output voltage is greater than or equal to a preset value, the first self-driving circuit causes the rectifier switch tube M3 to be selectively turned on according to the voltage condition at one end of the secondary winding L2; the second self-driving circuit causes the rectifier switch tube M4 to be selectively turned on according to the voltage condition at the other end of the secondary winding L2, wherein the rectifier switch tube M3 and the rectifier switch tube M4 are alternately turned on to rectify the voltage.

[0076] In this case, the branch between the rectifier switch tube M3 and the secondary winding L2 is in a conducting state, and the branch between the rectifier switch tube M4 and the secondary winding L2 is also in a conducting state. Whether the rectifier switch tube M3 and the rectifier switch tube M4 are turned on depends on the voltage of the secondary winding L2. Because the voltage of the secondary winding L2 is a square wave, the rectifier switch tube M3 and the rectifier switch tube M4 are turned on alternately to perform rectification.

[0077] When the output voltage reaches 90%-100% of the input voltage, the primary side duty value is large, the output inductor current is large and continuous, the output voltage will not discharge to the ground through the rectifier MOS switch tube, and will not damage the rectifier switch tube, thereby ensuring the stability of the output voltage and facilitating the normal operation of the load.

[0078] In this embodiment, a first self-driving circuit and a second self-driving circuit are respectively arranged at the control ends of the rectifier switch tube M3 and the rectifier switch tube M4. In the initial startup stage, the first self-driving circuit makes the rectifier switch tube M3 non-conductive, and the second self-driving circuit makes the rectifier switch tube M4 non-conductive, so that the output residual voltage will not be discharged to the ground through the rectifier switch tube M3 or the rectifier switch tube M4, thereby effectively avoiding the rectifier switch tube from being damaged due to excessive discharge current, thereby improving the reliability and stability of the entire circuit.

[0079] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An active clamp forward converter with pre-bias start function, characterized in that: include: A transformer T, the transformer T comprises a primary winding L1 and a secondary winding L2, a main switch tube M1 and a clamp switch tube M2 are provided on the primary winding L1 side; wherein the main switch tube M1 and the clamp switch tube M2 are alternately turned on to convert an input voltage into an output voltage; One end of the secondary winding L2 is connected to one end of the energy storage inductor L3, and the other end of the energy storage inductor L3 is used to connect to the load; one end of the secondary winding L2 is also connected to one end of the rectifier switch tube M4, and the other end of the rectifier switch tube M4 is grounded; the other end of the secondary winding L2 is connected to one end of the rectifier switch tube M3, and the other end of the rectifier switch tube M3 is grounded; a first self-driving circuit is also provided between one end of the secondary winding L2 and the control end of the rectifier switch tube M3; a second self-driving circuit is also provided between the other end of the secondary winding L2 and the control end of the rectifier switch tube M4; When the output voltage is lower than a preset value, the first self-driving circuit is used to turn the rectifier switch tube M3 off, and the second self-driving circuit is used to turn the rectifier switch tube M4 off; when the output voltage is greater than or equal to the preset value, the first self-driving circuit is used to selectively turn on the rectifier switch tube M3 according to the voltage condition at one end of the secondary winding L2; the second self-driving circuit is used to selectively turn on the rectifier switch tube M4 according to the voltage condition at the other end of the secondary winding L2.

2. The active clamp forward converter with pre-bias start-up function according to claim 1, characterized in that: One end of the primary winding L1 is connected to the positive electrode of the input power supply, and the other end of the primary winding L1 is connected to one end of the main switch tube M1, and the other end of the main switch tube M1 is grounded; the other end of the primary winding L1 is also connected to one end of the clamping capacitor C1, and the other end of the clamping capacitor C1 is connected to one end of the clamping switch tube M2, and the other end of the clamping switch tube M2 is connected to the negative electrode of the input power supply.

3. The active clamp forward converter with pre-bias start-up function according to claim 1, characterized in that: The first self-driving circuit includes a first switch unit and a second switch unit, the control end of the first switch unit is connected to the other end of the energy storage inductor L3, one end of the first switch unit is connected to the control end of the second switch unit, and the other end of the first switch unit is grounded; One end of the second switch unit is connected to one end of the secondary winding L2 , and the other end of the second switch unit is connected to the control end of the rectifier switch tube M3 .

4. The active clamp forward converter with pre-bias start-up function according to claim 3, characterized in that: The first switch unit includes a transistor Q1 and a transistor Q2, the base of the transistor Q1 serves as a control terminal of the first switch unit, the collector of the transistor Q1 is connected to the base of the transistor Q2, and the emitter of the transistor Q1 is grounded; The base of the transistor Q2 serves as the control end of the second switch unit, the emitter of the transistor Q2 is connected to one end of the secondary winding L2, and the collector of the transistor Q2 is connected to the control end of the rectifier switch tube M3.

5. The active clamp forward converter with pre-bias start-up function according to claim 4, characterized in that: The transistor Q1 is an NPN transistor, and the transistor Q2 is a PNP transistor.

6. The active clamp forward converter with pre-bias start-up function according to claim 1, characterized in that: The second self-driving circuit comprises a third switch unit and a fourth switch unit, the control end of the third switch unit is connected to the other end of the energy storage inductor L3, one end of the third switch unit is connected to the control end of the fourth switch unit, and the other end of the third switch unit is grounded; One end of the fourth switch unit is connected to the other end of the secondary winding L2 , and the other end of the fourth switch unit is connected to the control end of the rectifier switch tube M4 .

7. The active clamp forward converter with pre-bias start-up function according to claim 6, characterized in that: The third switch unit comprises a transistor Q3 and a transistor Q4, the base of the transistor Q3 serves as a control terminal of the third switch unit, the collector of the transistor Q3 is connected to the base of the transistor Q4, and the emitter of the transistor Q3 is grounded; The base of the transistor Q4 serves as the control end of the fourth switch unit, the emitter of the transistor Q4 is connected to the other end of the secondary winding L2, and the collector of the transistor Q4 is connected to the control end of the rectifier switch tube M4.

8. The active clamp forward converter with pre-bias start-up function according to claim 7, characterized in that: The transistor Q3 is an NPN transistor, and the transistor Q4 is a PNP transistor.

9. The active clamp forward converter with pre-bias start-up function according to any one of claims 1 to 8, characterized in that: The main switch tube M1 , the clamp switch tube M2 , the rectifier switch tube M3 and the rectifier switch tube M4 are all MOS tubes.

10. A control method for an active clamp forward converter with a pre-bias start function, characterized in that: include: Controlling the main switch tube M1 and the clamp switch tube M2 to be turned on alternately to convert the input voltage into an output voltage; When the output voltage is lower than a preset value, the first self-driving circuit turns the rectifier switch tube M3 off, and the second self-driving circuit turns the rectifier switch tube M4 off, so as to prevent the residual voltage at the secondary output end from discharging to the ground through the rectifier switch tube M3 or the rectifier switch tube M4; When the output voltage is greater than or equal to a preset value, the first self-driving circuit causes the rectifier switch tube M3 to selectively conduct according to the voltage condition of one end of the secondary winding L2; The second self-driving circuit enables the rectifier switch tube M4 to be selectively turned on according to the voltage condition of the other end of the secondary winding L2.

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