CN100405724C - Synchronous rectification self-driving circuit for forward converter with resonant reset - Google Patents

Abstract

The invention discloses a synchronous rectification self-driving circuit of a resonant reset forward converter, which includes a rectifier tube, a freewheeling tube, a first switch tube and a second switch tube, and the rectifier tube forms a rectifier circuit with a secondary side of a transformer, an output inductance, and an output capacitor. The freewheeling tube, the output inductance and the output capacitor form a freewheeling loop, and the output voltage signal higher than the driving level of the freewheeling tube or the output voltage signal higher than the driving level of the freewheeling tube after boosting is coupled through the second switch tube To the control pole of the freewheeling tube, the output terminal of the first switching tube is coupled to the control pole of the freewheeling tube, and the switching states of the second switching tube and the first switching tube are synchronized with the freewheeling tube and the rectifying tube respectively. Since the output voltage signal greater than the driving level of the freewheeling tube or its boost signal is coupled to the freewheeling tube control pole, the rising edge level of the freewheeling tube is controlled to improve the efficiency of the module. As the output voltage decreases, the second switching tube is turned off, so that the freewheeling tube is turned off, and there will be no shutdown negative pressure.

Description

Synchronous rectification self-driving circuit for forward converter with resonant reset

【Technical field】：

The invention relates to a synchronous rectification self-driving circuit of a resonant reset forward converter.

【Background technique】:

With the development of modern communication technology, low-voltage and high-current isolated DC/DC converters have been widely used, and resonant reset forward converters have been widely used because of their simple and reliable topology and small output voltage ripple. In low-voltage and high-current applications, in order to improve the efficiency of the converter, synchronous rectification has become a necessary solution. The driving of synchronous rectification is one of the key factors affecting the efficiency of the converter. Therefore, many driving schemes have been proposed [1], [2], [3], [4], which are respectively from the following literature: Literature [1] From: [1] Alou, P.Cobos, J.A.Garcia, C.Prieto, R.Uceda, J. "Design guidelines for a resonant reset forward converter with self-driven synchronous rectification", Industrial Electronics, Control and Instrumentation, 1997.IECON 97.23rd International Conferenceon, Volume: 2, 1997, Page(s): 593-598vol.2. Document [2] from: Yee, H.P.Sawahata, S. "A balanced review of synchronous rectifiers in DC/DC converters", AppliedPower Electronics Conference and Exposition, 1999.APEC'99.Fourteenth Annual, Volume: 1, 1999, Page( s): 582-588 vol.1. Literature [3] from: Xie Xuefei; Liu, J.C.P.Poon, F.N.K.Pong, B.M.H, "Two methods to drive synchronous rectifiers during dead time in forward topologies", Applied Power Electronics Conference and Exposition, 2000.APEC2000.VoIEme 2, 2000, Page(s): 993-999 vol.2. Literature [4] from: Xiaogao Xie J.M Zhang Guangyi Luo Dezhi JiaoZhaoming Qian. "An Improved Self-driven Synchronous Rectification for a ResonantReset Forward Converter", 2003.APEC'03.Eighteenth Annual, Volume: 1, 2003, Pages( : 348-351vol1.1. The self-driving solution has been widely used because of its simplicity, reliability and low cost. The self-driving scheme and key waveforms used in literature [1] and [2] are shown in Figure 1. After the magnetic reset ends, the driving level of the freewheeling tube on the secondary side is zero before the start of the next cycle. During this period (called Dead Time), the output current flows through the body diode connected in parallel with the freewheeling tube, which increases the conduction loss and thus reduces the efficiency of the converter. Reference [3] proposes a self-driving circuit called gate-level charge retention and its key waveforms are shown in Figure 2. The driving level of the freewheeling tube during the dead time of the resonant reset forward circuit using this technology is High level, so as to ensure that the output current flows through the freewheeling tube itself, thereby reducing conduction loss and improving efficiency. But we should notice that after the main switch tube S1 is turned off, the rising edge of the drive level of the freewheeling tube is very slow, which also affects the efficiency of the converter. In addition, when the power is turned off, negative pressure will inevitably appear in the above two solutions, and corresponding measures must be taken in practical applications, which increases the complexity of the circuit. The self-driving scheme and key waveforms proposed in literature [4] are shown in Figure 3. It solves the problem of slow rise in the drive level of the freewheeling tube in literature [2] and further improves the module efficiency, but its circuit is slightly complicated. And increase the design difficulty of the transformer.

【Invention content】：

The purpose of the present invention is to solve the above problems and provide a synchronous rectification self-driving circuit for a resonant reset forward converter, which is simpler and more reliable, and will not cause shutdown negative voltage.

In order to achieve the above object, the present invention proposes a synchronous rectification self-driving circuit of a resonant reset forward converter, including a rectifier tube, a freewheeling tube, a first switch tube and a second switch tube, and the rectifier tube is connected to the secondary side of the transformer, The output inductance and the output capacitor form a rectification circuit, and the freewheeling tube, the output inductance and the output capacitor form a freewheeling circuit, and the output voltage signal higher than the driving level of the freewheeling tube or the signal higher than the driving level of the freewheeling tube after boosting The output voltage signal is coupled to the base of the freewheeling tube through the second switching tube, the switching state of the second switching tube is synchronized with the freewheeling tube, the output terminal of the first switching tube is coupled to the control pole of the freewheeling tube, and the first switching tube The switching state is synchronized with the rectifier tube.

Due to the adoption of the above scheme, the output voltage signal greater than the driving level of the freewheeling tube or its boost signal is coupled to the control pole of the freewheeling tube through the second switch tube, thereby controlling the rising edge level of the freewheeling tube and improving the module efficiency , in addition, the conduction of the freewheeling tube is directly controlled by the output voltage signal or its boost signal through the second switch tube, the circuit structure is simple, and when the power is turned off, the second switch tube is disconnected , so that the freewheeling tube is turned off, so that there will be no shutdown negative pressure.

[Description of drawings]:

Fig. 1 is the circuit diagram of the first embodiment of the synchronous rectification self-drive of the prior art resonant reset forward converter;

Fig. 1a is a key waveform diagram of the first embodiment of the synchronous rectification and self-driving of the prior art resonant reset forward converter;

Fig. 2 is the circuit circuit diagram of the second embodiment of the synchronous rectification self-drive of the prior art resonant reset forward converter;

Fig. 2a is a key waveform diagram of the second embodiment of the synchronous rectification self-driven forward converter with resonant reset in the prior art;

Fig. 3 is the circuit diagram of the third embodiment of the synchronous rectification self-driving circuit of the prior art resonant reset forward converter;

Fig. 3a is a key waveform diagram of the third embodiment of the synchronous rectification self-driving circuit of the resonant reset forward converter in the prior art;

Fig. 4 is the circuit diagram of the first embodiment of the synchronous rectification self-driving circuit of the resonant reset forward converter of the present invention;

Fig. 4a is a key waveform diagram of the first embodiment of the synchronous rectification self-driving circuit of the resonant reset forward converter of the present invention;

Fig. 5 is the circuit diagram of the second embodiment of the synchronous rectification self-driving circuit of the resonant reset forward converter of the present invention;

【Detailed ways】:

The present invention will be described in further detail below through specific embodiments and in conjunction with the accompanying drawings.

Embodiment 1: As shown in Figure 4, a resonant reset forward converter, the main switching tube S1, the transformer T, the switching capacitor Cr, the rectifier tube SR1, the freewheeling tube SR2, the first switching tube Q1, and the second switching tube Q2, boost circuit and output inductor L and output capacitor. The boost circuit includes a drive winding. The secondary side of the transformer, the output inductor L, the output capacitor C and the rectifier tube SR1 form a rectification circuit, the output inductor L, the output capacitor C and the freewheel tube SR2 form a freewheel circuit, and the first switch tube Q1 is an NPN transistor or NPN A switching device such as a channel field effect tube, the second switching tube Q2 is a switching device such as a PNP transistor or a P channel field effect tube, and the freewheeling tube SR1 and the rectifier tube SR2 are field effect tubes, and the output voltage of the driving winding is The signal terminal is connected to the emitter of the second switching tube Q2 (PNP transistor), and the output terminal of the drive winding senses the voltage on the output inductor L and is boosted to connect to the emitter of the second switching tube Q2 to generate The signal to drive the freewheeling tube SR2. The collector of the second switching tube Q2 is connected to the grid of the freewheeling tube SR2, and the switch state of the second switching tube Q2 is synchronized with the freewheeling tube SR2, and its base is connected in parallel with the second diode D2 and the second resistor R2 is connected to the drain of the freewheeling tube SR2. The switching state of the first switching tube Q1 is synchronized with that of the rectifying tube SR1. The control electrode of the first switching tube Q1, that is, the grid, is connected to the drain of the freewheeling tube SR2 through the first diode D1 and the first resistor R1 connected in parallel, and the output terminal of the first switching tube, that is, the collector is connected to To the gate of freewheeling tube SR2. The emitter of the first switching transistor Q1 is connected to the source of the freewheeling transistor SR2.

The resistor and diode in the above implementation scheme are optional devices, which can adjust the dead time between the rectifier tube and the freewheeling tube drive, which is beneficial to optimize the efficiency. In FIG. 4 , in this solution, the small-signal MOSFET in FIG. 2 is replaced by a triode as the first switch tube Q1 . However, MOSFETs must be used in Figure 2 of the prior art. This is because the leakage current between the drain and the source of the MOSFETs is small. During Dead Time, the drive level of the freewheeling tube can be maintained, and the triode The leakage current between the collector and the emitter of the MOSFET is much larger than that of the MOSFET. From the analysis of the following principles, it can be seen that in this scheme, since the drive level of the freewheeling tube is only related to the output voltage and the turn ratio of the drive winding and the output inductance, the transistor can be used instead of the MOSFET tube, thereby reducing the cost.

The working principle of the above scheme is as follows: during the conduction period of the main switch tube S1, the voltage on the secondary side of the transformer makes the rectifier tube SR1 and the first switch tube Q1 conduct, and at the same time, the voltage V1 across the inductor and the voltage V2 across the drive winding are greater than zero , the base voltage of the second switching tube Q2 is greater than the emitter voltage, the second switching tube Q2 is turned off, and the output current flows through the rectifier tube SR1. After the main switching tube S1 is turned off, the freewheeling tube SR1 and the first switching tube Q1 are also turned off subsequently. Due to the continuity of the output inductor current, the body diode of the freewheeling tube is first turned on, and the voltage V1 at both ends of the inductor and the drive winding The voltage V2 at both ends is less than zero, so the second switch tube Q2 is turned on, and the input capacitance of the freewheeling tube (referring to the parasitic capacitance Cgs between the gate and the source of the freewheeling tube and the parasitic capacitance between the gate and the drain) The sum of capacitors Cgd) is charged, when the voltage between the gate and drain of the freewheeling tube is greater than its threshold voltage, the freewheeling tube SR2 starts to conduct, and the output current completely flows through the freewheeling tube. After the magnetic reset ends, the second switching transistor Q2 and the freewheeling transistor SR2 are still turned on. The driving waveforms of the rectifier SR1 and the freewheeling tube SR2 are shown in Figure 4. They are basically complementary, which is conducive to improving the efficiency of the module, and the driving level of the freewheeling tube SR2 has nothing to do with the input voltage and output current of the module. Only related to the output voltage and the turn ratio of the drive winding and the inductance, the drive level of the freewheel tube SR2 can be flexibly designed. In the process of shutting down, when the output voltage drops to a certain value, the driving level of the freewheeling tube SR2 is lower than the threshold voltage. In short, before the output voltage drops to zero, the freewheeling tube SR2 will be turned off, ensuring Generate shutdown negative pressure.

In the multi-output module using coupled inductors, if the output voltage of one channel is greater than the threshold level of the synchronous freewheeling tube (MOSFET tube) of the other channel or channels, no additional driving winding may be added. If only one of the channels is closed-loop controlled, the remaining channels can obtain corresponding output voltages through reasonable design of transformers. Now take the two-way output module as an example to illustrate, and the details are as follows. As shown in Figure 5, assuming that the output voltage Vo1 is higher than the threshold level of the freewheeling tube SR2, it can be used as the driving voltage of the freewheeling tube SR2. As mentioned above, the driving voltage of the freewheeling tube SR2 is the output voltage Vo1 .

Embodiment 2: As shown in Figure 5, the difference from Embodiment 1 is that the resonant reset forward converter is a two-way output converter, and the first output converter is a closed-loop control circuit. When off, the output voltage signal of this channel is higher than the driving level of the second freewheeling tube to drive the freewheeling tube, and the output terminal of this channel is connected to the emitter of the second switching tube Q2. The base of the second switching tube Q2 is connected to the drain of the freewheeling tube SR2 of the first-way converter through the second resistor R2 and the second diode D2 connected in parallel. The collector of the second switching tube is connected to the gate of the freewheeling tube SR2.

In a word, the present invention has the following advantages: ① The driving levels of the freewheeling tube and the rectifier tube are basically complementary, and are especially suitable for low-voltage and high-current modules; ② The driving level of the freewheeling tube has nothing to do with the input voltage and output current. The turn ratio of the driving winding and the output inductance can obtain a suitable driving level of the freewheeling tube, which is very flexible. ③ It can effectively prevent negative pressure from shutdown. ④The circuit is simple, reliable and flexible, the drive is very ideal, the cost is low, the application prospect is very good, and the practical value is very good. . The main disadvantage of the present invention is that it slightly increases the design difficulty of the output inductance.

Claims (9)

1. the synchronous rectification self-driving circuit of a resonant reset forward converter, comprise rectifying tube (SR1), continued flow tube (SR2), described rectifying tube (SR1) and transformer secondary, outputting inductance (L), output capacitance (C) constitutes commutating circuit, described continued flow tube (SR2) constitutes continuous current circuit with outputting inductance (L) and output capacitance (C), it is characterized in that: also comprise first switching tube (Q1) and second switch pipe (Q2), described rectifying tube (SR1) and continued flow tube (SR2) are field-effect transistor, described first switching tube (Q1) and second switch pipe (Q2) are triode or field-effect transistor, the end that described outputting inductance (L) links to each other with output capacitance (C) is a voltage output end, voltage output end is coupled to the emitter or the source electrode of second switch pipe (Q2), the collector electrode of second switch pipe (Q2) or drain coupled are to the grid of continued flow tube (SR2), be used to drive continued flow tube (SR2), second switch pipe (Q2) on off state and continued flow tube (SR2) are synchronous, first switching tube (Q1) collector electrode or drain coupled are to the grid of continued flow tube (SR2), and the on off state of first switching tube (Q1) and rectifying tube (SR1) are synchronous.

2. the synchronous rectification self-driving circuit of resonant reset forward converter as claimed in claim 1, it is characterized in that: also comprise booster circuit, voltage output end is coupled to the emitter or the source electrode of described second switch pipe (Q2) through described booster circuit; Described booster circuit comprises the driving winding, voltage on the described driving winding induction outputting inductance (L), the end of the same name that drives the voltage output end of winding and outputting inductance (L) is driving winding output, the output that drives winding is coupled to the emitter or the source electrode of second switch pipe (Q2), and the other end that drives winding is coupled to the base stage or the grid of second switch pipe (Q2).

3. the synchronous rectification self-driving circuit of resonant reset forward converter as claimed in claim 1 or 2, it is characterized in that: the base stage of described second switch pipe (Q2) or gate coupled are to the drain electrode of continued flow tube (SR2).

4. the synchronous rectification self-driving circuit of resonant reset forward converter as claimed in claim 1 or 2, it is characterized in that: described first switching tube (Q1) is a NPN type triode, the base stage of first switching tube (Q1) is coupled to the grid of rectifying tube (SR1), and emitter is received the source electrode of rectifying tube (SR1).

5. the synchronous rectification self-driving circuit of resonant reset forward converter as claimed in claim 4, it is characterized in that: also comprise first resistance (R1) and second resistance (R2), the base stage of described first switching tube (Q1) is connected to the drain electrode of continued flow tube (SR2) through first resistance (R1), and described second switch pipe base stage or grid are connected to the drain electrode of continued flow tube (SR2) through second resistance (R2).

6. the synchronous rectification self-driving circuit of resonant reset forward converter as claimed in claim 5, it is characterized in that: also comprise first diode (D1) and second diode (D2), described first diode (D1) is in parallel with first resistance (R1), and anode is connected to the base stage of first switching tube (Q1); Described second diode (D2) is in parallel with second resistance (R2), and anode is connected to the base stage or the grid of second switch pipe (Q2).

7. the synchronous rectification self-driving circuit of resonant reset forward converter as claimed in claim 6, it is characterized in that: described second switch pipe (Q2) is the positive-negative-positive triode.

8. the synchronous rectification self-driving circuit of a multiple resonance reset forward converter, comprise two-way output loop at least, it is characterized in that: the described output loop of two-way at least comprises one road closed control circuit and other output loops of at least one road, described closed control circuit comprises first rectifying tube (D11), first continued flow tube (D21), the first transformer secondary, first outputting inductance (L1) and first output capacitance (C1), first rectifying tube (D11), the first transformer secondary, first outputting inductance (L1) and first output capacitance (C1) constitute first commutating circuit, first continued flow tube (D21), first outputting inductance (L1) and first output capacitance (C1) constitute first continuous current circuit, and the end that described first outputting inductance (L1) links to each other with first output capacitance (C1) is a voltage output end; Described other output loops comprise rectifying tube (SR1), continued flow tube (SR2), rectifying tube (SR1) constitutes commutating circuit with transformer secondary, outputting inductance (L), output capacitance (C), continued flow tube (SR2) constitutes continuous current circuit with outputting inductance (L) and output capacitance (C), and described continued flow tube (SR1) and rectifying tube (SR2) are field-effect transistor; Also comprise first switching tube (Q1) and second switch pipe (Q2), first switching tube (Q1) and second switch pipe (Q2) are triode or field-effect transistor, the emitter of described second switch pipe (Q2) or source-coupled are to the voltage output end of described first outputting inductance (L1), base stage or gate coupled are to the other end of described first outputting inductance (L1), the grid of collector electrode or the drain coupled continued flow tube (SR2) in described other output circuits, described second switch pipe (Q2) on off state and described continued flow tube (SR2) are synchronous, be used to drive described continued flow tube (SR2), the output voltage of described closed control circuit is higher than the drive level of the described continued flow tube (SR2) in other output circuits, the grid of described first switching tube (Q1) collector electrode or the drain coupled continued flow tube (SR2) to described other output circuits, the on off state of first switching tube (Q1) and rectifying tube (SR1) are synchronously.

9. the synchronous rectification self-driving circuit of multiple resonance reset forward converter as claimed in claim 8 is characterized in that: described first rectifying tube (D11) and first continued flow tube (D21) are diode.

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