Double-transistor forward secondary fly-wheel diode peak suppression circuit

Abstract

The utility model discloses a double-transistor forward secondary fly-wheel diode peak suppression circuit, and aims to solve the problem of reverse recovery of a secondary fly-wheel diode in a double-transistor forward converter and solve the problem that an active clamping circuit is adopted in the prior art, but an auxiliary switch and a corresponding control circuit need to be added, so that the cost is increased, and the reliability is reduced. According to the utility model, after the primary side of the transformer is connected in series with the inductor, the loop current slope is changed, so that the peak voltage of the secondary fly-wheel diode is reduced.

Description

Technical Field

[0001] The utility model belongs to the field of power electronic equipment, and particularly relates to a converter secondary freewheeling diode spike suppression circuit. Background Art

[0002] The dual-tube forward converter has become one of the most widely used topologies in small and medium power converters due to its low voltage stress on the primary switch tube, its ability to resist bridge arm shoot-through, and its high reliability. With the increase of switching frequency, the secondary freewheeling diode is often the weak link of the entire converter, because the fast recovery diode has a reverse recovery problem, and the reverse recovery problem of the secondary freewheeling diode is particularly serious. Reverse recovery will produce a very high voltage spike on the secondary freewheeling diode (even if the new material SIC diode is used, it will have a higher spike voltage), endangering the safe operation of the secondary freewheeling diode. The common method is to use an RCD clamp circuit on the secondary freewheeling diode side. The structure is simple and the cost is low, but because part of the reverse recovery energy is consumed in the resistance of the clamp circuit, the efficiency is reduced, and the voltage spike can generally only be limited to twice the transformer secondary voltage (the effect of improving the spike voltage is not obvious). The use of an active clamp circuit can also reduce voltage spikes and reverse recovery losses, but an auxiliary switch and corresponding control circuit need to be added, which increases the cost and reduces reliability. Utility Model Content

[0003] In order to solve the above technical problems, the utility model proposes a double-tube forward secondary freewheeling diode spike suppression circuit, which reduces the di / dt when the secondary freewheeling diode is turned off by connecting an auxiliary inductor in series with the primary of the power transformer, thereby reducing the voltage spike when the diode is turned off.

[0004] The technical solution adopted by the utility model is: a double-tube forward secondary freewheeling diode spike suppression circuit, comprising: a first MOS tube VT1, a second MOS tube VT2, a primary clamping circuit, a first transformer T1, a second transformer T2, a rectifier circuit, a freewheeling circuit, and an equivalent constant current source circuit; the primary clamping circuit comprises an inductor L3, a third diode VD3, and a sixth diode VD6;

[0005] The gate of the first MOS transistor VT1 is connected to VGS3, the source of the first MOS transistor VT1 is connected to the first end of the inductor L3, the second end of the inductor L3 is connected to the positive electrode of the third diode VD3, the negative electrode of the third diode VD3 is connected to the drain of the first MOS transistor VT1, the positive electrode of the third diode VD3 is also connected to the negative electrode of the sixth diode VD6, and the positive electrode of the sixth diode VD6 is connected to the power ground PGND; the source of the first MOS transistor VT1 is connected to the negative electrode of the fifth diode VD5, and the positive electrode of the fifth diode VD5 is connected to the power ground PGND; the second end of the inductor L3 is connected to the first end of the primary winding of the first transformer T1, and the second end of the primary winding of the first transformer T1 is connected to the first end of the primary winding of the second transformer T2; the second end of the primary winding of the second transformer T2 is connected to the drain of the second MOS transistor VT2, the gate of the second MOS transistor VT2 is connected to VGS2, and the source of the second MOS transistor VT2 is connected to the power ground PGND;

[0006] The first secondary terminal of the first transformer T1 is connected to the input terminal of the rectifier circuit, and the second secondary terminal of the first transformer T1 is connected to the input terminal of the freewheeling circuit. The output terminals of the rectifier circuit and the freewheeling circuit are respectively connected to the first terminal of the equivalent constant current source circuit; the second terminal of the equivalent constant current source circuit is connected to the input terminal of the freewheeling circuit.

[0007] Beneficial effects of the utility model: The utility model reduces the di / dt when the secondary freewheeling diode is turned off by connecting the auxiliary inductor in series with the primary of the power transformer, thereby reducing the voltage spike when the diode is turned off; the dual-tube forward converter of the utility model is generally used in occasions where the input voltage is below 1000V, and can also be used in high input voltage occasions when combined with other topologies. The circuit of the utility model has the following advantages:

[0008] ① It can reduce the voltage spike of the freewheeling diode of the rectifier circuit and improve reliability;

[0009] ② The converter switch is turned on by ZCS and turned off by ZVS;

[0010] ③The converter switch is turned on inductively. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 The waveform diagram provided by the utility model;

[0012] Figure 2 A circuit schematic diagram provided for the utility model;

[0013] Figure 3 The waveforms at both ends of the secondary freewheeling diode provided by the utility model;

[0014] Among them, (a) is the waveform at both ends of the secondary freewheeling diode without the primary side series inductor, and (b) is the waveform at both ends of the secondary freewheeling diode after the primary side series inductor is connected. DETAILED DESCRIPTION

[0015] In order to facilitate those skilled in the art to understand the technical content of the present invention, the present invention is further explained below with reference to the accompanying drawings.

[0016] The primary clamping circuit of the utility model is as follows Figure 2 As shown, the structure is simple and can be connected in series with the primary of the power transformer through an auxiliary inductor, thereby reducing the di / dt when the secondary freewheeling diode VD8 is turned off, thereby reducing the voltage spike when the diode is turned off.

[0017] like Figure 2 The schematic diagram of the circuit is shown. The primary clamping circuit consists of an auxiliary inductor L3 and two clamping diodes VD3 and VD6. In order to simplify the circuit state analysis, the transition process is ignored here and only the steady-state process is analyzed. Assuming that all devices are ideal, the equivalent junction capacitance Cs1=Cs2=Cs in parallel with the MOS tube. The capacity of the MOS tube equivalent junction capacitance can be referred to the corresponding MOS tube specification; and assuming that the filter inductor L4 is large enough, the filter inductor L4, the filter capacitor E1 and the load resistor RL can be regarded as a constant current source with a current of I0. When the circuit is working stably, the following are the common features: Figure 1 The 10 switching modes shown in the figure have corresponding equivalent circuits as follows: Figure 2 As shown; the main waveforms are as follows Figure 1 As shown in the figure, the load resistance RL includes RF and other power-consuming devices.

[0018] when Figure 2 When VT1 and VT2 are turned on, due to the effect of inductor L3, the inductor current cannot change suddenly, and the current in the primary circuit rises at a certain slope. When the primary MOS tube is turned on, the secondary rectifier diode VD4 is turned on and the freewheeling diode VD8 is turned off. Figure 3 As shown in (a), if there is no inductor L3 connected in series on the primary side, when the primary MOS tubes VT1 and VT2 are turned on, the power supply voltage is applied to both ends of the primary side of the transformer, and is coupled to the secondary side through the transformer. The rectifier diode VD4 is turned on and the freewheeling diode VD8 is turned off. Since the diode has a reverse recovery time, the transformer secondary voltage is applied to both ends of the freewheeling diode at the moment when the primary MOS tube is turned on, forcibly closing the diode. At this time, a larger DI / DT will be generated, so a higher peak voltage will be generated. The RC absorption circuit connected at both ends of the diodes VD4 and VD8 will not play much role. Figure 3 (b) After the primary side is connected in series with the inductor, the slope of the loop current is changed, thereby reducing the peak voltage of the secondary freewheeling diode. When the primary MOS tube is turned off, the energy on the inductor is fed back to the busbar through the embedded diodes VD3 and VD6.

[0019] Figure 2The diodes VD5 and VD7 are the transformer reset circuit, the diode D6, the resistors R13 and R14 are the drive branch of VT1, the diode D12, the resistors R32 and R38 are the drive branch of VT2, the diode D10 is the primary current detection rectifier, and the function of R23, R24 and R25 is to convert the current signal into a voltage signal for use in other circuits. Figure 2 Among them, R15 and C15 are connected in parallel with diode VD4 to form the absorption circuit of VD4, and C19, R20 and VD8 are connected in parallel to form the absorption circuit of VD8.

[0020] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the scope of protection of the present invention is not limited to such specific statements and embodiments. For those skilled in the art, the present invention may have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention shall be included in the scope of the claims of the present invention.

Claims

1. A double-tube forward secondary freewheeling diode spike suppression circuit, characterized in that: include: A first MOS tube VT1, a second MOS tube VT2, a primary clamping circuit, a first transformer T1, a second transformer T2, a rectifier circuit, a freewheeling circuit, and an equivalent constant current source circuit; the primary clamping circuit includes an inductor L3, a third diode VD3, and a sixth diode VD6; The gate of the first MOS tube VT1 is connected to the driving voltage VGS3, the source of the first MOS tube VT1 is connected to the first end of the inductor L3, the second end of the inductor L3 is connected to the anode of the third diode VD3, the cathode of the third diode VD3 is connected to the drain of the first MOS tube VT1, the anode of the third diode VD3 is also connected to the cathode of the sixth diode VD6, and the anode of the sixth diode VD6 is connected to the power ground PGND; the drain of the first MOS tube VT1 is also connected to the bus power supply VBUS; the source of the first MOS tube VT1 is connected to the cathode of the fifth diode VD5, and the anode of the fifth diode VD5 is connected to the power ground PGND; the source of the first MOS tube VT1 is also connected to the negative voltage source VSS3; The second end of the inductor L3 is connected to the first end of the primary winding of the first transformer T1, and the second end of the primary winding of the first transformer T1 is connected to the first end of the secondary winding of the second transformer T2; the first end of the primary side of the second transformer T2 is connected to the sampling voltage VCS2; the second end of the primary side of the second transformer T2 is connected to the power ground PGND; The second end of the primary winding of the second transformer T2 is connected to the drain of the second MOS transistor VT2, the gate of the second MOS transistor VT2 is connected to the driving voltage VGS2, and the source of the second MOS transistor VT2 is connected to the power ground PGND; the gate of the second MOS transistor VT2 is connected to the driving voltage VGS4; the source of the second MOS transistor VT2 is also connected to the negative voltage source VSS2; The first secondary terminal of the first transformer T1 is connected to the input terminal of the rectifier circuit, and the second secondary terminal of the first transformer T1 is connected to the input terminal of the freewheeling circuit. The output terminals of the rectifier circuit and the freewheeling circuit are respectively connected to the first terminal of the equivalent constant current source circuit; the second terminal of the equivalent constant current source circuit is connected to the input terminal of the freewheeling circuit.

2. A double-tube forward secondary freewheeling diode spike suppression circuit according to claim 1, characterized in that: The gate of the first MOS tube VT1 is specifically connected to the driving voltage VGS3 through the first driving circuit, and the first driving circuit includes a diode D6, a resistor R13, and a resistor R14; the anode of the diode D6 is connected to the gate of the first MOS tube VT1, the cathode of the diode D6 is connected to the driving voltage VGS3, the first end of the resistor R13 is connected to the gate of the first MOS tube VT1, the second end of the resistor R13 is connected to the driving voltage VGS3, the first end of the resistor R14 is connected to the gate of the first MOS tube VT1, and the second end of the resistor R14 is connected to the source of the first MOS tube VT1.

3. A double-tube forward secondary freewheeling diode spike suppression circuit according to claim 1, characterized in that: The gate of the second MOS tube VT2 is specifically connected to the driving voltage VGS4 through a second driving circuit, and the second driving circuit includes a diode D12, a resistor R32, and a resistor R38; the anode of the diode D12 is connected to the gate of the second MOS tube VT2, the cathode of the diode D12 is connected to the driving voltage VGS3, the first end of the resistor R32 is connected to the gate of the second MOS tube VT2, the second end of the resistor R32 is connected to the driving voltage VGS3, the first end of the resistor R38 is connected to the gate of the second MOS tube VT2, and the second end of the resistor R38 is connected to the source of the second MOS tube VT2.

4. A double-tube forward secondary freewheeling diode spike suppression circuit according to claim 1, characterized in that: Also includes: Diode D10, resistor R23, resistor R24, resistor R25; the positive electrode of diode D10 is connected to the first terminal of the primary side of the second transformer T2, the negative electrode of diode D10 is connected to the driving voltage VGS2, the first terminal of resistor R23 is connected to the driving voltage VGS2, the second terminal of resistor R23 is connected to the power ground PGND, the first terminal of resistor R24 ​​is connected to the driving voltage VGS2, the second terminal of resistor R24 ​​is connected to the power ground PGND, the first terminal of resistor R25 is connected to the first terminal of the primary side of the second transformer T2, and the second terminal of resistor R25 is connected to the second terminal of the primary side of the second transformer T2.

5. A double-tube forward secondary freewheeling diode spike suppression circuit according to claim 1, characterized in that: The rectifier circuit specifically includes two fourth diodes VD4 connected in parallel.

6. A double-tube forward secondary freewheeling diode spike suppression circuit according to claim 5, characterized in that: Also includes: The resistor R15 and the capacitor C15 are connected in series and then connected in parallel with the fourth diode VD4 to serve as an absorption circuit of the fourth diode VD4.

7. A double-tube forward secondary freewheeling diode spike suppression circuit according to claim 1, characterized in that: The freewheeling circuit specifically includes two eighth diodes VD8 connected in parallel.

8. A double-tube forward secondary freewheeling diode spike suppression circuit according to claim 7, characterized in that: Also includes: Capacitor C19 and resistor R20: Capacitor C19 and resistor R20 are connected in series and then connected in parallel with the eighth diode VD8, which serves as an absorption circuit of the eighth diode VD8.

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