An ACF circuit and control method

Abstract

The application discloses an ACF circuit and a control method, the circuit comprises a master control circuit, a load sampling control circuit, a driving circuit and an ACF power stage circuit, the load sampling control circuit is used for distinguishing the load mode of the ACF circuit, and whether the driving circuit is connected with a clamping MOS tube driving signal is synchronously controlled, under different loads, the influence of the working of the ACF clamping MOS tube on the working of the synchronous rectification circuit is avoided, the working advantages of the flyback synchronous rectification under DCM and the working advantages of the trailing edge non-complementary ACF synchronous rectification under CCM are retained, the function of the synchronous rectification circuit for reducing the conduction loss and improving the efficiency is also retained, the problem of the abnormal working of the synchronous rectification caused by the working of the primary side clamping tube is effectively solved, and the reliability of the product is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of converter control, in particular to an ACF circuit and a control method. BACKGROUND

[0002] In order to realize lossless absorption of the primary side leakage energy of the flyback converter and zero voltage turn-on of the main power switch tube, an active clamp circuit is usually introduced. The existing flyback converter with an active clamp circuit (hereinafter referred to as ACF) is shown in FIG. 1, wherein the main power switch tube TR301, the main power transformer T301, the output synchronous rectification MOS tube TR303, the input filter capacitor C301 and the output filter capacitor C302 constitute the flyback converter, and the clamp MOS tube TR302 and the clamp capacitor C303 are the added active clamp circuit and are connected in parallel between the positive power output and the negative power output of the flyback converter. Figure 4

[0003] For the above-mentioned circuit, patent number CN 103795260 B discloses a non-complementary flyback active clamp converter, which details the timing and working process of the non-complementary flyback active clamp converter. Generally, in the control scheme, the clamp MOS tube TR302 has a fixed duty ratio and is turned on at the trailing edge of the off interval of the main power switch tube TR301. By controlling the trailing edge non-complementary drive of the clamp MOS tube TR302, the energy of the primary side leakage inductance is recycled and utilized, and the valley conduction is realized through the resonance of the main power switch tube TR301 to reduce the switching loss of the main power switch tube TR301. At the same time, in order to reduce the conduction loss of the secondary side rectification circuit, the drive circuit of the synchronous rectification MOS tube as shown in FIG. 2 is usually used, and the Vds negative voltage of the secondary side synchronous rectification MOS tube TR303 is usually sampled as shown in FIG. 3 for synchronous rectification drive control: when the main power transformer T301 secondary side current does not drop to 0 under the discontinuous mode DCM of the flyback transformer, the VD pin of the drive chip U201 samples the Vds_out voltage as a negative voltage, the drive enables the MOS tube TR303 to be turned on, when the main power transformer T301 secondary side current drops to 0, the Vds_out voltage is higher than 0, the drive turns off the synchronous rectification MOS tube TR303, and waits for the SYN control of the primary side synchronous signal PLUSE signal to judge again in the next period. Figure 5 Figure 4

[0004] ​​​When the ACF circuit applies the rear edge non-complementary clamping scheme and the negative voltage conduction synchronous rectification scheme simultaneously, in the DCM mode, the drive signal G_H of the clamping MOS tube cannot guarantee the duty cycle to be completely consistent every cycle, and due to the influence of the parasitic parameters in the circuit, the positive forward current pulse width and amplitude released to the transformer secondary side when the clamping MOS tube TR302 is turned on are different, which causes the Vds_out signal collected by the drive chip U201 to be different, and the synchronous rectification drive duty cycle of adjacent cycles is inconsistent (for details Figure 7 The drive duty cycle of the adjacent two cycles of the corresponding synchronous rectification drive Vgs_s occurs, which causes the output voltage ripple to oscillate; after an output filter is added, the oscillation frequency is close to the LC resonance point of the output filter, thereby amplifying the output voltage ripple oscillation amplitude, and causing the load device to work abnormally. SUMMARY

[0005] In view of the problems in the prior art, the present application provides an ACF circuit and a control method, when the load sampling control circuit detects that the ACF circuit works in the DCM mode, the clamping MOS drive signal Hin is closed, which avoids the problem that the working process of the clamping MOS tube interferes with the negative voltage sampling of the secondary side synchronous rectification drive; when the load sampling control circuit detects that the ACF circuit works in the CCM mode, the clamping MOS drive signal Hin is released, which ensures the normal clamping resonance function, ensures the stability of the output voltage ripple without oscillation under all working conditions, and improves the reliability of the load device.

[0006] To achieve the above object, the present application provides the following technical scheme:

[0007] In a first aspect, an ACF circuit is provided, comprising: a master control circuit, a drive circuit and an ACF power stage circuit, a first output terminal of the master control circuit is connected with a first input terminal of the drive circuit, a second output terminal is connected with a second input terminal of the drive circuit; a first output terminal of the drive circuit is connected with a first input terminal of the ACF power stage circuit, a second output terminal is connected with a second input terminal of the ACF power stage circuit; further comprising: a load sampling control circuit, the load control circuit comprises: an operational amplifier U102A, an operational amplifier U103A, a resistor R103, a resistor R104, a resistor R105, a resistor R106, a resistor R107, a resistor R108, a resistor R109; one end of the resistor R103 is connected with one end of the resistor R108, and then connected with an output terminal of the operational amplifier U102A; the other end of the resistor R103 is connected with the first input terminal of the drive circuit; one end of the resistor R104 is connected with one end of the resistor R105, and then connected with a reverse input terminal of the operational amplifier U102A, the other end of the resistor R104 is connected with a reference voltage VCC; one end of the resistor R106 and one end of the resistor R107 are connected with the other end of the resistor R108, and then connected with a forward input terminal of the operational amplifier U102A; a reverse input terminal of the operational amplifier U103A is connected with an output terminal, and the other end of the resistor R106 is connected, to form a voltage follower; one end of the resistor R109 is connected with a forward input terminal of the operational amplifier U103A, and the other end of the resistor R109 is used for connecting an output voltage and a load sampling signal FB; the other end of the resistor R107 and the other end of the resistor R105 are commonly grounded.

[0008] In a second aspect, an ACF circuit is provided, comprising: a master control circuit, a drive circuit and an ACF power stage circuit; a first output terminal of the master control circuit is connected with a first input terminal of the drive circuit, a second output terminal is connected with a second input terminal of the drive circuit; a first output terminal of the drive circuit is connected with a first input terminal of the ACF power stage circuit, a second output terminal is connected with a second input terminal of the ACF power stage circuit;

[0009] Further comprising: a load sampling control circuit, an input terminal of the load sampling control circuit is used for connecting an output voltage and a load sampling signal FB, an output terminal is connected with a first input terminal of the drive circuit, the load sampling signal FB is used for reflecting a working mode of the ACF circuit, the load sampling control circuit is used for judging the working mode of the ACF circuit according to the load sampling signal FB;

[0010] When the load sampling control circuit determines that the ACF circuit works in the DCM mode, the load sampling control circuit and the master control circuit jointly turn off a clamping MOS tube drive signal Hin connected with the first input terminal of the drive circuit, so that the drive circuit outputs a turn-off signal to control a MOS tube TR302 of the ACF power stage circuit to be closed;

[0011] When the load sampling control circuit determines that the ACF circuit works in CCM mode, the load sampling control circuit and the master control circuit jointly release the clamping MOS tube driving signal Hin connected to the first input end of the drive circuit, so that the drive circuit outputs a conduction signal to control the MOS tube TR302 of the ACF power stage circuit to be turned on.

[0012] Preferably, when the load sampling control circuit determines that the ACF circuit works in DCM mode, the load sampling control circuit and the master control circuit jointly turn off the clamping MOS tube driving signal Hin connected to the first input end of the drive circuit, so that the drive circuit outputs an off signal to control the MOS tube TR302 of the ACF power stage circuit to be turned off, in particular:

[0013] When the load sampling control circuit determines that the ACF circuit works in DCM mode, the load sampling control circuit outputs a low-level signal to control the clamping MOS tube driving signal Hin to be turned off, so that the drive circuit outputs an off signal to control the MOS tube TR302 of the ACF power stage circuit to be turned off, so that the duty cycle of the clamping MOS tube driving signal Hin is the same in each cycle in the DCM mode.

[0014] Preferably, when the load sampling control circuit determines that the ACF circuit works in CCM mode, the load sampling control circuit and the master control circuit jointly release the clamping MOS tube driving signal Hin connected to the first input end of the drive circuit, so that the drive circuit outputs a conduction signal to control the MOS tube TR302 of the ACF power stage circuit to be turned on, in particular:

[0015] When the load sampling control circuit determines that the ACF circuit works in CCM mode, the load sampling control circuit outputs a high-level signal or is suspended to control the clamping MOS tube driving signal Hin connected to the first input end of the drive circuit and output by the first output end of the master control circuit, so that the drive circuit outputs a conduction signal to control the MOS tube TR302 of the ACF power stage circuit to be turned on, so that the ACF circuit maintains a normal working state in the CCM mode.

[0016] Preferably, the load sampling control circuit comprises: an operational amplifier U102A, an operational amplifier U103A, a resistor R103, a resistor R104, a resistor R105, a resistor R106, a resistor R107, a resistor R108, a resistor R109; one end of the resistor R103 is connected to one end of the resistor R108, and the output end of the operational amplifier U102A is connected; the other end of the resistor R103 is connected to the first input end of the driving circuit as the output end of the load sampling control circuit; one end of the resistor R104 and one end of the resistor R105 are connected to the reverse input end of the operational amplifier U102A, and the other end of the resistor R104 is connected to the reference voltage VCC; one end of the resistor R106 and one end of the resistor R107 are connected to the other end of the resistor R108, and the positive input end of the operational amplifier U102A is connected; the reverse input end and the output end of the operational amplifier U103A are connected, and the other end of the resistor R106 is connected, to form a voltage follower; one end of the resistor R109 is connected to the positive input end of the operational amplifier U103A, and the other end of the resistor R109 is connected to the input end of the load sampling control circuit for connecting the output voltage and the load sampling signal FB; the other end of the resistor R107 and the other end of the resistor R105 are commonly grounded.

[0017] Preferably, the load sampling control circuit further comprises a resistor R110, one end of the resistor R110 is connected to the input voltage Vin, and the other end is connected to the positive input end of the operational amplifier U102A.

[0018] Preferably, the main control circuit comprises: a main control chip U101, a resistor R101, and a resistor R102; one end of the resistor R101 is connected to the GATE_H pin of the main control chip U101, and the other end of the resistor R101 is connected to the first output end of the main control circuit for outputting the clamping MOS tube driving signal Hin; one end of the resistor R102 is connected to the GATE_L pin of the main control chip U101, and the other end of the resistor R102 is connected to the second output end of the main control circuit for outputting the signal Lin.

[0019] Preferably, the ACF power stage circuit comprises: a capacitor C301, a capacitor C302, a capacitor C303, a transformer T301, a resistor R301, a resistor R302, a resistor R303, a resistor R304, a resistor R305, a resistor R306, a MOS tube TR301, a MOS tube TR302 and a MOS tube TR303; one end of the resistor R301 is connected with the second output end of the driving circuit as the second input end of the ACF power stage circuit; the other end of the resistor R301 is connected with one end of the resistor R302 and the gate of the MOS tube TR301; the other end of the resistor R302 and the source of the MOS tube TR301 are grounded; the drain of the MOS tube TR301 is connected with one end of the resistor R303, the source of the MOS tube TR302 and the heteronym end of the primary winding of the transformer T301; the other end of the resistor R303 is connected with the gate of the MOS tube TR302 and one end of the resistor R304; the other end of the resistor R304 is connected with the first output end of the driving circuit as the first input end of the ACF power stage circuit; the drain of the MOS tube TR302 is connected with one end of the capacitor C303; the other end of the capacitor C303 is connected with one end of the capacitor C301 and the homonym end of the primary winding of the transformer T301, and is used for connecting an input voltage Vin; the heteronym end of the secondary winding of the transformer T301 is connected with one end of the capacitor C302, and is used as the output end Vout of the ACF circuit; the other end of the capacitor C302, the source of the MOS tube TR303 and one end of the resistor R305 are grounded; the drain of the MOS tube TR303 is connected with the homonym end of the secondary winding of the transformer T301; the gate of the MOS tube TR303 is connected with the other end of the resistor R305 and one end of the resistor R306; the other end of the resistor R306 is used for connecting the output end Vgs_s of the driving circuit of the secondary side synchronous rectification MOS tube.

[0020] Preferably, the driving circuit comprises: a driving chip U301, a bootstrap diode D301 and a bootstrap capacitor C307; the HIN pin of the driving chip U301 is used as the first input end of the master control circuit and is used for inputting a clamping MOS tube driving signal Hin; the LIN pin of the driving chip U301 is used as the second input end of the master control circuit and is used for inputting a clamping MOS tube driving signal Lin; the anode of the bootstrap diode D301 is connected with the power supply VCC pin of the driving chip U301 and is used for connecting a power supply signal VDD_P; the cathode of the bootstrap diode D301 is connected with the VB pin of the driving chip U301 and one end of the bootstrap capacitor C307, and is used as the first output end of the driving circuit and is connected with the first input end of the ACF power stage circuit and is used for outputting a signal G_H; the other end of the bootstrap capacitor C307 and the HB pin of the driving chip U301 are commonly connected with the drain of the MOS tube TR301; the LO pin of the driving chip U301 is used as the second output end of the driving circuit and is connected with the second input end of the ACF power stage circuit and is used for outputting a signal G_L.

[0021] In a third aspect, a control method of the ACF circuit is provided. When the load sampling control circuit determines that the ACF circuit works in the DCM mode according to the load sampling signal FB, the load sampling control circuit and the main control circuit jointly turn off the drive signal Hin of the clamping MOS connected to the first input end of the drive circuit, so that the output signal of the drive circuit controls the MOS TR302 of the ACF power stage circuit to be turned off.

[0022] When the load sampling control circuit determines that the ACF circuit works in the CCM mode according to the load sampling signal FB, the load sampling control circuit and the main control circuit jointly release the drive signal Hin of the clamping MOS connected to the first input end of the drive circuit, so that the output signal of the drive circuit controls the MOS TR302 of the ACF power stage circuit to be turned on.

[0023] Compared with the prior art, the present application has the following beneficial effects:

[0024] 1. The present application realizes single control of the clamping MOS drive signal of the ACF circuit under different load modes, retains the function of reducing the switching loss of the main switch tube in the CCM mode, and thus can ensure that the determination of the secondary side synchronous rectification negative voltage sampling signal is not disturbed in the DCM mode, and improves the product reliability.

[0025] 2. The present application sets the load sampling control circuit outside the drive circuit, can control the upper tube drive adjustment through the sampling of the input voltage Vin, improves the flexibility of debugging and the reliability of the power supply.

[0026] 3. The present application retains the working advantages of the flyback synchronous rectification in the DCM mode and the trailing edge non-complementary ACF synchronous rectification in the CCM mode, retains the role of reducing the conduction loss and improving the efficiency of the synchronous rectification circuit, and maintains the characteristics of low cost and high performance of the synchronous rectification ACF application scheme. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 The principle block diagram of the ACF circuit of the first embodiment is shown;

[0028] Figure 2 The principle diagram of the load sampling control circuit of the first embodiment is shown;

[0029] Figure 3 The typical principle diagram of the main control circuit of the present application is shown;

[0030] Figure 4 The typical principle diagram of the drive circuit and the ACF power stage circuit is shown;

[0031] Figure 5 The schematic diagram of the driving circuit of the secondary side synchronous rectification MOS tube of the ACF power stage;

[0032] Figure 6 The schematic diagram of the ACF circuit of the second embodiment;

[0033] Figure 7 The waveform diagram of the inconsistent synchronous rectification driving in the DCM mode after adding the negative voltage sampling synchronous rectification control scheme to the trailing edge non-complementary ACF of the prior art in the background art;

[0034] Figure 8 The synchronous rectification driving waveform measured under the same load after applying the circuit of the embodiment to the trailing edge non-complementary ACF. DETAILED DESCRIPTION

[0035] The technical solutions of the present application will be described in detail below with reference to the accompanying drawings of the embodiments of the present application. It should be understood that the specific embodiments described herein are only used to explain the present application and do not limit the present application.

[0036] First embodiment

[0037] As Figure 1 The schematic diagram of the ACF circuit of the present embodiment is shown, and in the present embodiment, an ACF circuit is provided, which is in a trailing edge non-complementary working mode and includes a main control circuit, a driving circuit and an ACF power stage circuit; a first output end of the main control circuit is connected with a first input end of the driving circuit, and a second output end is connected with a second input end of the driving circuit; a first output end of the driving circuit is connected with a first input end of the ACF power stage circuit, and a second output end is connected with a second input end of the ACF power stage circuit;

[0038] Further including a load sampling control circuit, an input end of the load sampling control circuit is used to access an output voltage and a load sampling signal FB, and an output end is connected with a first input end of the driving circuit; the load sampling signal FB is used to reflect the working mode of the ACF circuit, and the load sampling control circuit is used to determine the working mode of the ACF circuit according to the load sampling signal FB;

[0039] When the load sampling control circuit determines that the ACF circuit works in the DCM mode, the load sampling control circuit and the main control circuit jointly turn off the clamping MOS tube driving signal Hin accessed by the first input end of the driving circuit, so that the driving circuit outputs an off signal to control the MOS tube TR302 of the ACF power stage circuit to be closed;

[0040] When the load sampling control circuit determines that the ACF circuit works in the CCM mode, the load sampling control circuit and the main control circuit jointly release the clamping MOS tube driving signal Hin connected to the first input end of the driving circuit, so that the driving circuit outputs the on signal to control the MOS tube TR302 of the ACF power stage circuit to be turned on.

[0041] Specifically, the load sampling control determines the working mode of the ACF circuit according to the load sampling signal FB, that is, the load sampling signal FB is compared with a preset determination value, when the load sampling signal FB is lower than the preset determination value, it is determined that the ACF circuit works in the DCM mode, and when the load sampling signal FB is higher than the preset determination value, it is determined that the ACF circuit works in the CCM mode; in the specific implementation process, the range of the value of the load sampling signal FB when the ACF circuit works in the DCM mode is preset, and the range of the value of the load sampling signal FB when the ACF circuit works in the CCM mode is preset.

[0042] Specifically, the load sampling signal FB connected by the load sampling control circuit can reflect the load carrying condition of the power supply system using the ACF circuit, the load carrying condition of the power supply system includes that the ACF circuit works in the DCM mode or the CCM mode, and the load sampling signal FB is provided by the chip of the product, which will not be described in detail here; when the load sampling control circuit detects that the ACF circuit works in the DCM mode, the clamping MOS driving signal Hin is turned off, which avoids the problem that the working process of the clamping MOS tube interferes with the auxiliary side synchronous rectification driving negative pressure sampling; when the load sampling control circuit detects that the ACF circuit works in the CCM mode, the clamping MOS driving signal Hin is released, which ensures the normal clamping resonance function and ensures that the output voltage ripple is stable and does not oscillate under all working conditions, thereby improving the reliability of the load equipment.

[0043] In the specific implementation process, the load sampling control circuit can directly turn off the clamping MOS tube driving signal Hin, or can adjust the clamping MOS tube driving signal Hin in real time according to the load condition, control the rising edge or falling edge of the clamping MOS tube driving signal Hin, thereby adjust the duty cycle of the clamping MOS tube driving signal Hin, and through the adjustment of the duty cycle of the clamping MOS tube driving signal Hin, the duty cycle of the synchronous rectification driving signal of the driving synchronous rectification MOS tube TR303 is the same every cycle in the DCM mode, thereby improving the stability of the equipment.

[0044] In one embodiment, when the load sampling control circuit determines that the ACF circuit works in the DCM mode, the load sampling control circuit and the main control circuit jointly turn off the clamping MOS tube driving signal Hin connected to the first input end of the driving circuit, so that the driving circuit outputs the off signal to control the MOS tube TR302 of the ACF power stage circuit to be turned off, specifically:

[0045] When the load sampling control circuit determines that the ACF circuit is working in DCM mode, the load sampling control circuit outputs a low-level signal to control the clamp MOS tube drive signal Hin to be turned off, so that the drive circuit outputs a turn-off signal to control the MOS tube TR302 of the ACF power stage circuit to be turned off.

[0046] In one embodiment, when the load sampling control circuit determines that the ACF circuit is working in CCM mode, the load sampling control circuit and the master control circuit jointly release the clamp MOS tube drive signal Hin connected to the first input terminal of the drive circuit, so that the drive circuit outputs a turn-on signal to control the MOS tube TR302 of the ACF power stage circuit to be turned on, specifically:

[0047] When the load sampling control circuit determines that the ACF circuit is working in CCM mode, the load sampling control circuit outputs a high-level signal or is suspended to control the clamp MOS tube drive signal Hin output by the first output terminal of the master control circuit and connected to the first input terminal of the drive circuit, so that the drive circuit outputs a turn-on signal to control the MOS tube TR302 of the ACF power stage circuit to be turned on, so that the ACF circuit remains in the normal working state in CCM mode.

[0048] Specifically, the clamp MOS tube drive signal Hin is output by the first output terminal of the master control circuit and connected to the first input terminal of the drive circuit. When the load sampling control circuit determines that the ACF circuit is working in DCM mode, the load sampling control circuit outputs a low-level signal to make the first input terminal of the drive circuit continuously low, thereby turning off the MOS tube drive signal Hin output by the first output terminal of the master control circuit. Since the clamp MOS tube drive signal Hin connected to the first input terminal of the drive circuit is pulled low to a low level, the amplitude of the clamp MOS tube drive signal Hin is lower than the threshold voltage of the input pin of the drive circuit for judging a high level, so the drive circuit outputs a low-level turn-off signal to control the MOS tube TR302 of the ACF power stage circuit to be turned off. Similarly, when the load sampling control circuit determines that the ACF circuit is working in CCM mode, the load sampling control circuit outputs a high-level signal or is suspended to make the first input terminal of the drive circuit continuously high, thereby the master control circuit can normally output the MOS tube drive signal Hin to the drive circuit, so that the drive circuit outputs a high-level turn-on signal to control the MOS tube TR302 of the ACF power stage circuit to be turned on, so that the ACF circuit remains in the normal working state in CCM mode.

[0049] In the specific implementation of this embodiment, when the load sampling control circuit determines that the ACF circuit is working in DCM mode, the load sampling control circuit outputs a low-level signal to directly turn off the clamping MOS transistor drive signal Hin, thereby turning off the MOS transistor TR302. This control is relatively simple.

[0050] like Figure 2 The diagram shows the schematic of a load sampling control circuit. As a specific implementation of the load sampling control circuit, the circuit includes: operational amplifier U102A, operational amplifier U103A, resistors R103, R104, R105, R106, R107, R108, and R109. One end of resistor R103 is connected to one end of resistor R108, and then connected to the output terminal of operational amplifier U102A. The other end of resistor R103 serves as the output terminal of the load sampling control circuit and is connected to the first input terminal of the drive circuit. One end of resistor R104 is connected to one end of resistor R105, and then connected to operational amplifier U102A. The inverting input terminal of operational amplifier U102A is connected, and the other end of resistor R104 is connected to the reference voltage VCC. One end of resistor R106, one end of resistor R107, and the other end of resistor R108 are connected to the non-inverting input terminal of operational amplifier U102A. The inverting input terminal and output terminal of operational amplifier U103A are connected to the other end of resistor R106 to form a voltage follower. One end of resistor R109 is connected to the non-inverting input terminal of operational amplifier U103A, and the other end of resistor R109 serves as the input terminal of the load sampling control circuit, used to input the output voltage and the load sampling signal FB. The other ends of resistor R107 and resistor R105 are grounded together.

[0051] like Figure 3 The diagram shown is a schematic of the main control circuit. As a specific implementation of the main control circuit, the main control circuit includes: a main control chip U101, resistor R101, and resistor R102; one end of resistor R101 is connected to the GATE_H pin of the main control chip U101, and the other end of resistor R101 serves as the first output terminal of the main control circuit, used to output the clamping MOS transistor drive signal Hin; one end of resistor R102 is connected to the GATE_L pin of the main control chip U101, and the other end of resistor R102 serves as the second output terminal of the main control circuit, used to output the signal Lin.

[0052] like Figure 4As shown in the principle diagram of the driving circuit and the ACF power stage circuit, as a specific embodiment of the ACF power stage circuit, the ACF power stage circuit comprises: a capacitor C301, a capacitor C302, a capacitor C303, a transformer T301, a resistor R301, a resistor R302, a resistor R303, a resistor R304, a resistor R305, a resistor R306, a MOS tube TR301, a MOS tube TR302 and a MOS tube TR303; one end of the resistor R301 is connected with the second output end of the driving circuit as the second input end of the ACF power stage circuit, and the other end is connected with one end of the resistor R302 and the gate of the MOS tube TR301; the other end of the resistor R302 and the source of the MOS tube TR301 are grounded; the drain of the MOS tube TR301 is connected with one end of the resistor R303, the source of the MOS tube TR302 and the heteronym end of the primary winding of the transformer T301; the other end of the resistor R303 is connected with the gate of the MOS tube TR302 and one end of the resistor R304; the other end of the resistor R304 is connected with the first output end of the driving circuit as the first input end of the ACF power stage circuit; the drain of the MOS tube TR302 is connected with one end of the capacitor C303; the other end of the capacitor C303 is connected with one end of the capacitor C301 and the homonym end of the primary winding of the transformer T301, and is used for connecting the input voltage Vin; the heteronym end of the secondary winding of the transformer T301 is connected with one end of the capacitor C302, and is used as the output end Vout of the ACF circuit; the other end of the capacitor C302, the source of the MOS tube TR303 and one end of the resistor R305 are grounded; the drain of the MOS tube TR303 is connected with the homonym end of the secondary winding of the transformer T301, and the gate of the MOS tube TR303 is connected with the other end of the resistor R305 and one end of the resistor R306; the other end of the resistor R306 is used for connecting the output end Vgs_s of the driving circuit of the secondary synchronous rectification MOS tube.

[0053] As a specific embodiment of the driving circuit, the driving circuit comprises: a driving chip U301, a bootstrap diode D301, a bootstrap capacitor C307; the HIN pin of the driving chip U301 is the first input end of the master control circuit, used for connecting the clamping MOS tube driving signal Hin; the LIN pin is the second input end of the master control circuit, used for connecting the clamping MOS tube driving signal Lin; the anode of the bootstrap diode D301 is connected with the power supply VCC pin of the driving chip U301, and then used for connecting the power supply signal VDD_P; the cathode of the bootstrap diode D301 is connected with the VB pin of the driving chip U301 and one end of the bootstrap capacitor C307, and then connected with the first input end of the ACF power stage circuit as the first output end of the driving circuit, used for outputting the signal G_H; the other end of the bootstrap capacitor C307 and the HB pin of the driving chip U301 are commonly connected with the drain of the MOS tube TR301, and the LO pin of the driving chip U301 is the second output end of the driving circuit, connected with the second input end of the ACF power stage circuit, used for outputting the signal G_L.

[0054] Specifically, in the embodiment, the operational amplifier U102A and the operational amplifier U103A are both rail-to-rail operational amplifiers.

[0055] As Figure 5 shown in FIG. 6 is a schematic diagram of a driving circuit of a secondary side synchronous rectification MOS tube of the ACF power stage circuit in the embodiment, which is a synchronous rectification mode, and uses a negative voltage of a Vds of the secondary side synchronous rectification MOS tube TR303 for synchronous rectification driving control: the flyback transformer (ACF circuit) works in the discontinuous mode DCM, when the transformer T301 secondary side current does not drop to 0, the VD pin of the driving chip U201 samples the Vds_out voltage as a negative voltage, and the driving enables the MOS tube TR303 to be turned on, when the T301 secondary side current drops to 0, the Vds_out voltage is higher than 0, the driving turns off the MOS tube TR303, and waits for the synchronous signal PLUSE signal controlled by the primary side SYN to judge the next period again;

[0056] Taking the example of directly turning off the clamping MOS tube signal Hin when the load sampling control circuit judges that the ACF circuit works in the DCM mode, the specific working process of the ACF circuit in the embodiment is as follows:

[0057] The output signal of the follower composed of the operational amplifier U103A is defined as U FB-in , the sampled load sampling signal FB

[0058] is U FB , and U FB-in = U FB (1)

[0059] Define the voltage value of the reference voltage VCC pin of the main control chip U101 as U VCC The voltage at the inverting input terminal of op-amp U102A is U -in , has: U -in =U VCC ×R105(R 105 +R 104 (2)

[0060] Define the supply voltage of op-amp U102A as the same as the supply voltage of U101, U VDD_P The positive input voltage is U +in , when U FB-in When the voltage is lower than the set threshold:

[0061]

[0062] WhenU FB-in When the voltage exceeds the set threshold:

[0063]

[0064] By combining equations (1), (2), and (3), we can obtain that when:

[0065]

[0066] That is, when the ACF circuit operates in DCM mode, the output of op-amp U102A is low, and the main control circuit maintains the output of the GATE_H pin. However, since resistor R101 is connected to the output of the load sampling control circuit as the first output terminal, meaning one end of resistor R101 is pulled low by op-amp U102A, the output signal of the GATE_H pin is superimposed on resistor R101, making the first output terminal continuously a low-level signal. Because the clamping MOS transistor drive signal Hin input to the first input terminal of the drive circuit is pulled low, and the amplitude of the clamping MOS transistor drive signal Hin is lower than the threshold voltage for the drive circuit input pin to judge as high level, therefore... The drive circuit outputs a low-level turn-off signal, and the output signal G_H of the drive circuit is continuously low, controlling the clamping MOS transistor drive signal of the ACF power stage circuit to remain low, and the MOS transistor TR302 remains continuously turned off; when the ACF circuit is operating in DCM mode, if the value of the load sampling signal FB is within the range of formula (5), that is, when the value of the load sampling signal FB is lower than the set judgment value, the active clamping MOS transistor TR302 can be turned off in DCM mode to avoid the operation of the MOS transistor TR302 in DCM mode interfering with the sampling of the secondary side synchronous rectification. After implementation, the drive voltage of the secondary side synchronous rectification of the product can be guaranteed to be stable. For details, please refer to Figure 8 , Figure 8 The synchronous rectification drive waveform measured under the same load after applying the circuit of this embodiment to the trailing edge non-complementary ACF is shown in the figure.Figure 8 The duty cycle of Vgs_s of any two adjacent periods is consistent, avoiding the problem that the working process of the clamping MOS tube interferes with the sampling of the negative voltage of the secondary side synchronous rectification drive.

[0067] By combining (1), (2) and (4), it can be obtained that when:

[0068]

[0069] That is, when the ACF circuit works in the CCM mode, the output of the operational amplifier U102A is high, releasing the drive signal Hin of the output of the clamping MOS tube of the main control circuit, and the output signal G_H of the drive circuit is controlled by the main control chip U101, controlling the drive signal of the clamping MOS tube of the ACF power stage to be a normal trailing edge non-complementary active clamping logic, and the MOS tube TR303 works normally; when the ACF circuit works in the CCM mode, the value of the load sampling signal FB is within the range of formula (6), that is, when the value of the load sampling signal FB is higher than the set determination value, the ACF transformer works in the CCM mode, which can retain the function of reducing the switching loss of the main switch tube in the CCM mode.

[0070] Meanwhile, the above two working states retain the function of reducing the conduction loss and improving the efficiency of the synchronous rectification circuit, maintaining the characteristics of low cost and high performance of the synchronous rectification ACF application scheme.

[0071] In the embodiment, a control method of the ACF circuit is provided, when the load sampling control circuit determines that the ACF circuit works in the DCM mode according to the load sampling signal FB, the load sampling control circuit and the main control circuit jointly turn off the drive signal Hin connected to the first input end of the drive circuit, so that the output off signal of the drive circuit controls the MOS tube TR302 of the ACF power stage circuit to be closed.

[0072] When the load sampling control circuit determines that the ACF circuit works in the CCM mode according to the load sampling signal FB, the load sampling control circuit and the main control circuit jointly release the drive signal Hin connected to the first input end of the drive circuit, so that the output on signal of the drive circuit controls the MOS tube TR302 of the ACF power stage circuit to be turned on.

[0073] The working process of the control method is the same as that of the above-mentioned ACF circuit, and will not be described here.

[0074] Second embodiment

[0075] Since the setting of formula (5) and formula (6) in the first embodiment can only ensure that the working mode of the ACF circuit can be accurately controlled under a certain fixed input voltage Vin state, the FB voltage of the ACF circuit working in the DCM and CCM mode is inconsistent when the input voltage Vin range is relatively wide, i.e. under different input voltage Vin conditions. Different from the first embodiment, in the present embodiment, in order to make up for this difference, an input voltage compensation signal can be introduced, as shown in formula (7) and formula (8). Figure 6 As shown in the figure, the load sampling control circuit further comprises a resistor R110, one end of the resistor R110 is connected with the input voltage Vin, and the other end is connected with the positive input end of the operational amplifier U102A.

[0076] Specifically, the supply voltage of the operational amplifier U102A is defined as U VDD_P , the positive input end voltage of the operational amplifier U102A is defined as U +in , the input voltage of the ACF power stage is defined as U Vin , and when the voltage U FB-in is lower than the set determination value, there is:

[0077]

[0078] When the voltage U FB-in is higher than the set determination value, there is:

[0079]

[0080] Compared with the first embodiment, only formula (3) and formula (4) are replaced by the above formula (7) and formula (8) respectively, and formula (1) (2) (7) (8) can be solved to obtain the threshold value of the load sampling signal FB for judging different working modes of the ACF circuit under different input voltages Vin. Here, no further description is given.

[0081] The above is only a preferred embodiment of the present application, and the skilled in the art of the present application can also make changes and modifications to the above specific embodiments. Therefore, the present application is not limited to the specific control method disclosed and described above, and some modifications and changes of the present application should also fall within the protection scope of the claims of the present application. In addition, although some specific terms are used in the present specification, these terms are only for convenience of explanation and do not constitute any limitation on the present application.

Claims

1. An ACF circuit, comprising: The system comprises a main control circuit, a drive circuit, and an ACF power stage circuit. The first output terminal of the main control circuit is connected to the first input terminal of the drive circuit, and the second output terminal is connected to the second input terminal of the drive circuit. The first output terminal of the drive circuit is connected to the first input terminal of the ACF power stage circuit, and the second output terminal is connected to the second input terminal of the ACF power stage circuit. The system is characterized by further comprising a load sampling control circuit, which includes operational amplifier U102A, operational amplifier U103A, resistors R103, R104, R105, R106, R107, R108, and R109. One end of resistor R103 is connected to one end of resistor R108 and then connected to the output terminal of operational amplifier U102A. The other end of resistor R103 is connected to the first input terminal of the drive circuit; one end of resistor R104 is connected to one end of resistor R105 and then connected to the inverting input terminal of operational amplifier U102A, and the other end of resistor R104 is connected to the reference voltage VCC; one end of resistor R106, one end of resistor R107, and the other end of resistor R108 are connected to the non-inverting input terminal of operational amplifier U102A; the inverting input terminal and output terminal of operational amplifier U103A are connected to the other end of resistor R106 to form a voltage follower; one end of resistor R109 is connected to the non-inverting input terminal of operational amplifier U103A, and the other end of resistor R109 is used to connect the output voltage and the load sampling signal FB; the other end of resistor R107 and the other end of resistor R105 are grounded together.

2. An ACF circuit, comprising: Main control circuit, drive circuit and ACF power stage circuit; The first output terminal of the main control circuit is connected to the first input terminal of the drive circuit, and the second output terminal is connected to the second input terminal of the drive circuit; the first output terminal of the drive circuit is connected to the first input terminal of the ACF power stage circuit, and the second output terminal is connected to the second input terminal of the ACF power stage circuit. The feature is that it further includes: a load sampling control circuit, wherein the input terminal of the load sampling control circuit is used to receive the output voltage and the load sampling signal FB, and the output terminal is connected to the first input terminal of the drive circuit, wherein the load sampling signal FB is used to reflect the working mode of the ACF circuit, and the load sampling control circuit is used to determine the working mode of the ACF circuit based on the load sampling signal FB. When the load sampling control circuit determines that the ACF circuit is working in DCM mode, the load sampling control circuit and the main control circuit jointly turn off the clamping MOS transistor drive signal Hin connected to the first input terminal of the drive circuit, so that the drive circuit outputs a turn-off signal to control the MOS transistor TR302 of the ACF power stage circuit to turn off. When the load sampling control circuit determines that the ACF circuit is operating in CCM mode, the load sampling control circuit and the main control circuit jointly release the clamping MOS transistor drive signal Hin connected to the first input terminal of the drive circuit, so that the drive circuit outputs a conduction signal to control the MOS transistor TR302 of the ACF power stage circuit to conduct.

3. The ACF circuit according to claim 2, characterized in that, When the load sampling control circuit determines that the ACF circuit is operating in DCM mode, the load sampling control circuit and the main control circuit jointly turn off the clamping MOS transistor drive signal Hin connected to the first input terminal of the drive circuit, so that the drive circuit outputs a turn-off signal to control the MOS transistor TR302 of the ACF power stage circuit to turn off. Specifically: When the load sampling control circuit determines that the ACF circuit is operating in DCM mode, the load sampling control circuit outputs a low-level signal to control the clamping MOS transistor drive signal Hin to turn off, so that the drive circuit outputs a turn-off signal to control the MOS transistor TR302 of the ACF power stage circuit to turn off.

4. The ACF circuit according to claim 2, characterized in that, When the load sampling control circuit determines that the ACF circuit is operating in CCM mode, the load sampling control circuit and the main control circuit jointly release the clamping MOS transistor drive signal Hin connected to the first input terminal of the drive circuit, so that the drive circuit outputs a turn-on signal to control the MOS transistor TR302 of the ACF power stage circuit to turn on. Specifically: When the load sampling control circuit determines that the ACF circuit is operating in CCM mode, the load sampling control circuit outputs a high-level signal or leaves it floating, and controls the first input terminal of the drive circuit to connect to the clamping MOS transistor drive signal Hin output by the first output terminal of the main control circuit, so that the drive circuit outputs a conduction signal to control the MOS transistor TR302 of the ACF power stage circuit to conduct, so that the ACF circuit maintains the normal working state in CCM mode.

5. The ACF circuit according to claim 2, characterized in that, The load sampling control circuit includes: operational amplifier U102A, operational amplifier U103A, resistors R103, R104, R105, R106, R107, R108, and R109; one end of resistor R103 is connected to one end of resistor R108 and then connected to the output terminal of operational amplifier U102A; the other end of resistor R103 serves as the output terminal of the load sampling control circuit and is connected to the first input terminal of the drive circuit; one end of resistor R104 is connected to one end of resistor R105 and then connected to the inverting input terminal of operational amplifier U102A; resistor R104... The other end is connected to the reference voltage VCC; one end of resistor R106, one end of resistor R107, and the other end of resistor R108 are connected to the positive input terminal of operational amplifier U102A; the inverting input terminal and output terminal of operational amplifier U103A are connected to the other end of resistor R106 to form a voltage follower; one end of resistor R109 is connected to the positive input terminal of operational amplifier U103A, and the other end of resistor R109 serves as the input terminal of the load sampling control circuit, used to input the output voltage and the load sampling signal FB; the other end of resistor R107 and the other end of resistor R105 are grounded together.

6. The ACF circuit according to claim 5, characterized in that, The load sampling control circuit also includes a resistor R110, one end of which is connected to the input voltage Vin, and the other end is connected to the positive input terminal of the operational amplifier U102A.

7. The ACF circuit according to claim 2, characterized in that, The main control circuit includes: a main control chip U101, resistor R101, and resistor R102; one end of resistor R101 is connected to the GATE_H pin of the main control chip U101, and the other end of resistor R101 serves as the first output terminal of the main control circuit, used to output the clamping MOS transistor drive signal Hin; one end of resistor R102 is connected to the GATE_L pin of the main control chip U101, and the other end of resistor R102 serves as the second output terminal of the main control circuit, used to output the signal Lin.

8. The ACF circuit according to claim 2, characterized in that, The ACF power stage circuit includes: capacitors C301, C302, and C303; transformer T301; resistors R301, R302, R303, R304, R305, and R306; MOSFETs TR301, TR302, and TR303; one end of resistor R301 serves as the second input terminal of the ACF power stage circuit and is connected to the second output terminal of the drive circuit; the other end is connected to one end of resistor R302 and the gate of MOSFET TR301; the other end of resistor R302 and the source of MOSFET TR301 are grounded; the drain of MOSFET TR301 is connected to one end of resistor R303, the source of MOSFET TR302, and the opposite-named terminal of the primary winding of transformer T301; the other end of resistor R303 is connected to the gate of MOSFET TR302 and one end of resistor R304; resistor R301... The other end of 04 serves as the first input terminal of the ACF power stage circuit and is connected to the first output terminal of the drive circuit; the drain of MOSFET TR302 is connected to one end of capacitor C303; the other end of capacitor C303 is connected to one end of capacitor C301 and the same-name terminal of the primary winding of transformer T301, and is used to connect the input voltage Vin; the opposite-name terminal of the secondary winding of transformer T301 is connected to one end of capacitor C302, and serves as the output terminal Vout of the ACF circuit; the other end of capacitor C302, the source of MOSFET TR303, and one end of resistor R305 are grounded; the drain of MOSFET TR303 is connected to the same-name terminal of the secondary winding of transformer T301, and the gate of MOSFET TR303 is connected to the other end of resistor R305 and one end of resistor R306; the other end of resistor R306 is used to connect to the output terminal Vgs_s of the drive circuit of the secondary synchronous rectifier MOSFET.

9. The ACF circuit according to claim 8, characterized in that, The driving circuit includes: a driving chip U301, a bootstrap diode D301, and a bootstrap capacitor C307. The HIN pin of the driving chip U301 serves as the first input terminal of the main control circuit, used to connect the clamping MOSFET driving signal Hin. The LIN pin serves as the second input terminal of the main control circuit, used to connect the clamping MOSFET driving signal Lin. The anode of the bootstrap diode D301 is connected to the power supply VCC pin of the driving chip U301, used to connect the power supply signal VDD_P. The cathode of the bootstrap diode D301 is connected to the VB pin of the driving chip U301 and one end of the bootstrap capacitor C307, serving as the first output terminal of the driving circuit and connected to the first input terminal of the ACF power stage circuit, used to output the signal G_H. The other end of the bootstrap capacitor C307 and the HB pin of the driving chip U301 are connected to the drain of the MOSFET TR301. The LO pin of the driving chip U301 serves as the second output terminal of the driving circuit and is connected to the second input terminal of the ACF power stage circuit, used to output the signal G_L.

10. A control method for the ACF circuit according to any one of claims 1-9, characterized in that, When the load sampling control circuit determines that the ACF circuit is working in DCM mode based on the load sampling signal FB, the load sampling control circuit and the main control circuit jointly turn off the clamping MOS transistor drive signal Hin connected to the first input terminal of the drive circuit, so that the drive circuit outputs a turn-off signal to control the MOS transistor TR302 of the ACF power stage circuit to turn off. When the load sampling control circuit determines that the ACF circuit is operating in CCM mode based on the load sampling signal FB, the load sampling control circuit and the main control circuit jointly release the clamping MOS transistor drive signal Hin connected to the first input terminal of the drive circuit, so that the drive circuit outputs a conduction signal to control the MOS transistor TR302 of the ACF power stage circuit to conduct.

Images