A new hybrid synchronous rectification drive circuit

Abstract

The present application relates to a novel hybrid synchronous rectification drive circuit, which includes a freewheeling element arranged in a rectification circuit, two synchronous rectifiers, a first drive unit and a second drive unit. The rectification circuit includes a primary circuit and a secondary circuit. The two synchronous rectifiers are connected in parallel and are located in the secondary circuit. The freewheeling element is located at the common end of two controlled switches. The first drive unit and the second drive unit are both used to control the working state of a synchronous rectifier, so that the two synchronous rectifiers cooperate with the freewheeling element to alternately conduct. The first drive unit and the second drive unit respectively include a detection member to detect a current signal or a voltage signal in the rectification circuit. The detection member can detect the current signal or the voltage signal in the rectification circuit. By driving the current signal or the voltage signal in different directions, the first drive unit and the second drive unit can control the two synchronous rectifiers to alternately conduct, reduce the loss of the rectifier, and obtain a more ideal waveform.

Description

Technical Field

[0001] The present application relates to the field of field effect transistor drive circuits, and in particular to a novel hybrid synchronous rectification drive circuit. Background Art

[0002] Synchronous rectification technology is used in switching power supplies to reduce the loss of rectifier tubes and improve efficiency. Specifically, it uses low on-resistance MOSFETs to replace diodes to achieve the rectification function of the secondary side of the transformer. Since MOSFETs are unipolar devices, they require a dedicated control drive signal.

[0003] The synchronous rectification driving circuit in the related art is not suitable for circuits with too low or too high output voltage. In addition, in the commutation zone after the primary main switch of the circuit is turned on and off, the body diode of the synchronous rectification tube is turned on, resulting in large losses. Summary of the invention

[0004] In order to reduce the loss of synchronous rectifier tubes, the present application provides a novel hybrid synchronous rectification drive circuit.

[0005] A novel hybrid synchronous rectification drive circuit provided in the present application adopts the following technical solution:

[0006] A novel hybrid synchronous rectification drive circuit comprises a freewheeling element arranged in a rectification circuit, two synchronous rectifier tubes, a first drive unit and a second drive unit, wherein the rectification circuit comprises a primary circuit and a secondary circuit, the two synchronous rectifier tubes are connected in parallel and are located in the secondary circuit, and the freewheeling element is located at a common end of the two controlled switches;

[0007] The first driving unit and the second driving unit are both used to control the working state of one of the synchronous rectifier tubes so that the two synchronous rectifier tubes cooperate with the freewheeling element to be alternately turned on. The first driving unit and the second driving unit respectively include a detection component for detecting the current signal or voltage signal in the rectifier circuit.

[0008] By adopting the above technical solution, the detection device can detect the current signal or voltage signal in the rectifier circuit. By driving the current signal or voltage signal in different directions, the first drive unit and the second drive unit can control the two synchronous rectifier tubes to alternately conduct, thereby reducing the loss of the rectifier tube and obtaining a more ideal waveform.

[0009] Optionally, the detection element is a current transformer arranged on the primary circuit or an auxiliary winding arranged on the same side as the secondary circuit.

[0010] By adopting the above technical solution, the current transformer can detect the current signal in the circuit, and the auxiliary winding can detect the voltage signal in the secondary circuit.

[0011] Optionally, the first driving unit and the second driving unit both include a clamp, a switch unit and an energy storage component with charging and discharging functions, the cathode of the clamp is connected to the energy storage component, and the switch unit is used to drive the synchronous rectifier.

[0012] By adopting the above technical solution, the energy storage component can be charged and discharged to provide sufficient electric energy for the switch unit, the clamping component can limit the current flow direction in the first drive unit and the second drive unit, and the switch unit can enhance the current driving capability of the signal detected by the detection component.

[0013] Optionally, the clamping element is a diode.

[0014] Optionally, the energy storage element is a capacitor.

[0015] Optionally, the switch unit includes two switch elements connected in series, and the two switch elements are turned on alternately.

[0016] By adopting the above technical solution, the two switch elements that are alternately turned on can respectively control the charging process and the discharging process of the energy storage component.

[0017] Optionally, the two switching elements are an NPN transistor and a PNP transistor.

[0018] By adopting the above technical solution, when the node connecting the two base electrodes is at a high level or a low level, one of the two switch elements is always in a conducting state.

[0019] Optionally, the first driving unit and the second driving unit further include a load resistor respectively.

[0020] By adopting the above technical solution, the load resistor has a current limiting function.

[0021] In summary, the present application includes at least one of the following beneficial technical effects:

[0022] The detection device can detect the current signal or voltage signal in the rectifier circuit. By driving the current signal or voltage signal in different directions, the first drive unit and the second drive unit can control the two synchronous rectifiers to conduct alternately, reduce the loss of the rectifier tubes, and obtain a more ideal waveform. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 4 is a circuit diagram of a novel hybrid synchronous rectification driving circuit according to an embodiment of the present application.

[0024] Explanation of the accompanying drawings: 1. Rectification circuit; 11. Primary circuit; 12. Secondary circuit; 2. Freewheeling element; 3. First drive unit; 4. Second drive unit; 5. Switching unit. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solutions and advantages of this application more clear, the following Figure 1 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.

[0026] The embodiment of the present application discloses a novel hybrid synchronous rectification drive circuit, which is mainly used in an isolated switching power supply and can effectively reduce the loss of a rectifier tube and improve efficiency to obtain a more ideal output waveform.

[0027] Reference Figure 1 The novel hybrid synchronous rectification driving circuit includes a freewheeling element 2 arranged in a rectification circuit 1, two synchronous rectifiers, a first driving unit 3 and a second driving unit 4, wherein the rectification circuit 1 is composed of three parts: a transformer XFMR, a primary circuit 11 and a secondary circuit 12, so as to chop and rectify the input voltage and output a smooth direct current. The freewheeling element 2 is located in the secondary circuit 12, and it can filter the output waveform so that the secondary circuit 12 outputs a relatively smooth direct current. In this process, due to the special structure of the freewheeling element 2 itself, the output waveform of the secondary circuit 12 will lag behind the input waveform of the primary circuit 11. The two synchronous rectifiers are controlled by the first driving unit 3 and the second driving unit 4, so that the two synchronous rectifiers can be turned on alternately to reduce the loss of the rectifiers.

[0028] Specifically, the primary circuit 11 includes a primary winding Np and a main switch Qmain, the primary winding Np and the main switch Qmain are connected in series, and the free ends of the primary winding Np and the main switch Qmain are connected to the two poles of the input voltage. At the same time, a capacitor Cin is connected in parallel to the two poles of the input voltage to filter the input voltage. In the primary circuit 11, the input voltage can be cut into a rectangular wave by controlling the on and off of the main switch Qmain, so as to cut the high-energy input voltage into countless low-energy voltage signals and transmit them to the output end, thereby adjusting the cutting frequency and duty cycle of the input voltage to stabilize the output voltage.

[0029] In the secondary circuit 12, two synchronous rectifiers are respectively connected to the two ends of the secondary winding to form a loop, and one end of the circuit where the freewheeling element 2 is located is connected to the secondary winding, dividing the secondary winding into two parts, and the other end serves as one pole of the output voltage, and forms an output voltage end with the circuit connecting the two synchronous rectifiers. Among them, the circuit where the freewheeling element 2 is located serves as the common end of the loop where the two synchronous rectifiers are located to output direct current. In the embodiment of the present application, the freewheeling element 2 is preferably an inductor Lo. Of course, a capacitor Cout is also connected in parallel between the two poles of the output voltage to filter the output voltage.

[0030] It can be understood that the first drive unit 3 and the second drive unit 4 each include a clamp, a switch unit 5, an energy storage component and a detection component. According to the magnitude and direction of the current signal or voltage signal detected by the detection component, the switch unit 5 can control the charging and discharging process of the energy storage component, so that the synchronous rectifier tubes corresponding to the first drive unit 3 and the second drive unit 4 can be turned on and off, thereby realizing the alternating conduction of the synchronous rectifier tubes.

[0031] The detection device is mainly used to detect the current signal or voltage signal in the rectifier circuit 1, and can be a current transformer CST or an auxiliary winding Na. When the detection device is a current transformer CST, the current transformer CST is arranged in the primary circuit 11 and connected in series with the primary winding Np, which has the advantages of small sampling current, small loss and high efficiency.

[0032] When the detection element is the auxiliary winding Na, the auxiliary winding Na and the secondary winding are located on the same side of the transformer, and the same-name ends of the auxiliary winding Na and the secondary winding are in the same direction to ensure the phase relationship between the output voltages of the auxiliary winding Na and the secondary winding.

[0033] In both the first drive unit 3 and the second drive unit 4 , a connection mode is adopted in which the clamping element is connected in series with the switch unit 5 and the energy storage element is connected in parallel to both ends of the switch unit 5 .

[0034] It can be understood that the relationship between the current flowing through the primary winding Np and the current flowing through the secondary winding in the current transformer CST is affected by the ratio of the number of turns of the primary winding Np to the number of turns of the secondary winding. Since the input voltage in the primary circuit 11 is alternating current, the input current in the primary circuit 11 of the rectifier circuit 1 also has two directions, that is, the current in the loop where the secondary winding of the current transformer CST is located also has two directions. For this reason, the clamp can limit the current flowing through a certain section of the circuit to one direction and charge the energy storage component. In an embodiment of the present application, the clamp is preferably a diode, and its cathode is connected to the energy storage component.

[0035] The energy storage device has the functions of charging and discharging, and both the charging process and the discharging process require a period of time, which enables the voltage output by the first drive unit 3 and the second drive unit 4 to match the phase lag generated by the structure of the inductor Lo itself, thereby enabling the two synchronous rectifiers to be alternately turned on to reduce losses. In this application, the energy storage device is a capacitor.

[0036] In order to enhance the current driving capability of the detected signal, the switch unit 5 includes two switch elements that are alternately turned on. One switch element is used to provide a pull-up current for the gate of the synchronous rectifier, and the other switch element is used to provide a pull-down current for the gate of the synchronous rectifier. In this embodiment, the two switch elements are an NPN transistor and a PNP transistor. The NPN transistor and the PNP transistor can be connected by two collectors or two emitters. In both cases, by controlling the potential of the common node of the two bases, one of the NPN transistor and the PNP transistor can be in a conducting state and the other can be in a shut-off state.

[0037] However, in the process of connecting the circuit, one detection element is adapted to one driving unit, that is, one detection element corresponds to a connection mode of an NPN transistor and a PNP transistor. It can be understood that the first driving unit 3 and the second driving unit 4 can adopt one of the two settings.

[0038] Taking the embodiment of the present application as an example, specifically, when the detection component is a current transformer CST, the emitters of the NPN-type transistor and the PNP-type transistor are connected to form a first drive unit 3. Among them, the transistor Q1 is of NPN type, and the transistor Q3 is of PNP type. In the first drive unit 3, three diodes are provided, and three transistors are provided. The secondary winding of the current transformer CST is connected in series with the diode D2, the diode D3, the transistor Q1, and the transistor Q3 to form a closed loop. Specifically, the collector of the transistor Q1 is connected to the cathode of the diode D3, the collector of the transistor Q3 is connected to the opposite end of the secondary winding of the current transformer CST through the diode D1, and the collector of the transistor Q3 is connected to the anode of the diode D1. The emitter of transistor Q2 is connected between diode D2 and diode D3, the base of transistor Q2 is connected to the anode of diode D2, and the collector of transistor Q2 is also connected to the opposite end of the secondary winding of current transformer CST. The bases of transistors Q1 and Q3 are connected to the emitter of transistor Q2, so that transistor Q2 can be used as a pre-transistor to form a logic delay.

[0039] In addition, a capacitor C1 is connected in parallel to the diode D1 to provide an AC path for the signal detected by the current transformer CST and to reset the current transformer CST. A load resistor R1 is also connected in parallel between the base and collector of the transistor Q2 to convert the current value flowing through the current transformer into a voltage value.

[0040] In the first driving unit 3, a voltage is outputted from the emitters of the transistors Q1 and Q3 to control a synchronous rectifier SR2 in the secondary circuit 12, that is, the synchronous rectifier SR2 is controlled to be turned on when the voltage exceeds the gate voltage threshold of the synchronous rectifier SR2.

[0041] When the detection element is an auxiliary winding Na, the collectors of the NPN transistor and the PNP transistor are connected to form a second drive unit 4. Among them, the transistor Q4 is a PNP type, and the transistor Q5 is an NPN type. In the second drive unit 4, two diodes and two transistors are provided. The auxiliary winding Na is connected in series with the diode D4, the transistor Q4 and the transistor Q5 to form a closed loop. Specifically, the emitter of the transistor Q4 is connected to the cathode of the diode D4, and the emitter of the transistor Q5 is connected to the auxiliary winding Na. The base of the transistor Q4 is connected to the anode of the diode D4 through the diode D5, and the base of the transistor Q4 is connected to the cathode of the diode D5. The base of the transistor Q5 is also connected to the anode of the diode D4.

[0042] In addition, a load resistor R2 and a load resistor R3 are also provided in the second driving unit 4 to limit the current and protect the circuit. The load resistor R2 is located in the path between the transistor Q5 and the anode of the diode D4, one end of the load resistor R3 is connected between the base of the transistor Q4 and the diode D5, and the other end is connected to the opposite end of the auxiliary winding Na.

[0043] It can be understood that a voltage outputted from the collectors of transistors Q4 and Q5 is used to control another synchronous rectifier SR1 in the secondary circuit 12, that is, when the voltage exceeds the gate voltage threshold of synchronous rectifier SR1, synchronous rectifier SR1 is controlled to be turned on.

[0044] Based on the above circuit connection mode, the working state of the rectifier circuit 1 in this application is as follows:

[0045] For the first drive circuit, when a forward current flows through the primary winding of the current transformer CST, the current generated in the secondary winding of the current transformer CST flows through the diode D2, the diode D3, the transistor Q1 and the transistor Q3 in sequence. At this time, the capacitor C2 in the first drive circuit is in a charging state. When the capacitor C2 is fully charged, the capacitor C2 can be regarded as a power supply with a voltage of 12V. When the base of the transistor Q2 is at a high level, the transistor Q2 is turned off, so that the base of the transistor Q1 is at a high level, that is, the transistor Q1 is turned on, and the capacitor C2 is discharged through the transistor Q1, so that the emitter of the transistor Q1 outputs a voltage greater than the gate voltage threshold of the synchronous rectifier SR2, thereby turning on the synchronous rectifier SR2.

[0046] Of course, in this process, the excess energy of the first driving unit 3 can be stored in the capacitor C2 to prevent the gate driving voltage from being too high, and at the same time, the excess energy can be utilized to reduce the driving loss.

[0047] It can be understood that the input voltage connected to the primary circuit 11 of the rectifier circuit 1 is an unregulated direct current. When the main switch Qmain performs chopping, an alternating current will flow through the primary winding of the current transformer CST. When a negative current flows through the primary winding of the current transformer CST, since the current flowing through the secondary winding of the current transformer CST cannot change suddenly, a reverse voltage is formed on the secondary winding of the current transformer, that is, the base of the transistor Q2 is at a low level, so that the transistor Q2 is turned on. It can be understood that the emitter and collector of the transistor Q2 and the collector of the transistor Q3 are connected to the cathode of the capacitor C2. At this time, the bases of transistors Q1 and Q3 are both at a low level, that is, transistor Q1 is turned off and transistor Q3 is turned on. Correspondingly, the voltage output by the emitter of transistor Q3 decreases, thereby causing the gate drive voltage of synchronous rectifier SR2 to decrease until it is lower than the gate voltage threshold of synchronous rectifier SR2, and finally synchronous rectifier SR2 is turned off.

[0048] Similarly, for the second driving circuit, when the same-name end of the auxiliary winding Na is at a high level, the bases of the transistors Q4 and Q5 are at a high level, that is, the transistor Q5 is turned on, and the transistor Q4 is turned off. This can be understood as: since the diode D4 is in the on state, the capacitor C3 is in a charging state. The conduction of the transistor Q5 reduces the voltage output by the collector of the transistor Q5, thereby making the gate drive voltage of the synchronous rectifier SR1 lower than the gate voltage threshold of the synchronous rectifier SR1, that is, the synchronous rectifier SR1 is in the off state, and the capacitor C3 continues to charge until the charging balance is reached when the voltage at both ends of the auxiliary winding Na is the same.

[0049] On the contrary, when the same-name end of the auxiliary winding Na is at a low level, the diode D4 and the diode D5 are turned off. At the same time, the base of the transistor Q4 is at a low level, that is, the transistor Q4 is turned on, and the capacitor C3 is discharged through the transistor Q4, so that the collector of the transistor Q4 outputs a voltage greater than the gate voltage threshold of the synchronous rectifier SR1, the synchronous rectifier SR1 is turned on, and the voltage of the capacitor C3 reaches a charge and discharge balance with the gate voltage of the synchronous rectifier SR1.

[0050] Obviously, when the same-name end of the auxiliary winding Na is at a high level, the output drive signal is a low voltage, and when the same-name end of the auxiliary winding Na is at a low level, the output drive signal is a high voltage, which makes the waveform of the output voltage closer to the ideal drive waveform.

[0051] The implementation principle of a novel hybrid synchronous rectification driving circuit in an embodiment of the present application is as follows: by setting a first driving unit 3 for controlling the working state of the synchronous rectifier SR2 and a second driving unit 4 for controlling the working state of the synchronous rectifier SR1, the synchronous rectifier SR1 and the synchronous rectifier SR2 are alternately turned on, which can effectively reduce the loss of the rectifier tube and improve the efficiency, so as to obtain a more ideal output waveform.

[0052] The above are all preferred embodiments of the present application, and are not intended to limit the protection scope of the present application. Any feature disclosed in this specification (including the abstract and drawings), unless otherwise stated, can be replaced by other equivalent or alternative features with similar purposes. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

Claims

1. A novel hybrid synchronous rectification drive circuit, characterized in that: The invention comprises a freewheeling element (2) arranged in a rectifier circuit (1), two synchronous rectifier tubes, a first drive unit (3) and a second drive unit (4), wherein the rectifier circuit (1) comprises a primary circuit (11) and a secondary circuit (12), the two synchronous rectifier tubes are connected in parallel and are located in the secondary circuit (12), and the freewheeling element (2) is located at the common end of two controlled switches; The first drive unit (3) and the second drive unit (4) are both used to control the working state of one of the synchronous rectifier tubes, so that the two synchronous rectifier tubes cooperate with the freewheeling element (2) to be alternately turned on, and the first drive unit (3) and the second drive unit (4) respectively include a detection component for detecting a current signal or a voltage signal in the rectifier circuit (1).

2. The novel hybrid synchronous rectification driving circuit according to claim 1 is characterized in that: The detection element is a current transformer arranged on the primary circuit (11) or an auxiliary winding arranged on the same side as the secondary circuit (12).

3. The novel hybrid synchronous rectification driving circuit according to claim 2 is characterized in that: The first drive unit (3) and the second drive unit (4) both comprise a clamping element, a switch unit (5) and an energy storage element with a charge and discharge function, the cathode of the clamping element is connected to the energy storage element, and the switch unit (5) is used to drive the synchronous rectifier tube.

4. The novel hybrid synchronous rectification driving circuit according to claim 3 is characterized in that: The clamping element is a diode.

5. The novel hybrid synchronous rectification driving circuit according to claim 3 is characterized in that: The energy storage component is a capacitor.

6. The novel hybrid synchronous rectification driving circuit according to claim 3 is characterized in that: The switch unit (5) comprises two switch elements connected in series, and the two switch elements are turned on alternately.

7. The novel hybrid synchronous rectification driving circuit according to claim 6 is characterized in that: The two switch elements are an NPN transistor and a PNP transistor.

8. The novel hybrid synchronous rectification driving circuit according to claim 3 is characterized in that: The first drive unit (3) and the second drive unit (4) further include a load resistor respectively.

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