CN220492876U - Flyback synchronous rectification drive circuit based on digital isolation - Google Patents

Abstract

The utility model discloses a flyback synchronous rectification drive circuit based on digital isolation, which comprises a single-ended flyback main circuit and a synchronous rectification MOS isolation drive circuit; the single-ended flyback main circuit comprises an input end, a main switching tube Q1, a main transformer T1, a rectifying tube Q2, an output end, a PWM control chip, an MOS tube driving circuit and an output feedback circuit; the synchronous rectification MOS isolation driving circuit comprises a digital isolation chip and a synchronous rectification MOS tube driving circuit; the MOS tube driving circuit is connected with the PWM control chip, and the PWM control chip is also connected with the output feedback circuit and the digital isolation chip respectively; the digital isolation chip is also connected with the synchronous rectification MOS tube driving circuit; the effect is that: through the cooperation of the digital isolation chip and the synchronous rectification MOS tube driving circuit, the phenomenon of sharing of the primary side MOS tube and the secondary side MOS tube is avoided, and the circuit efficiency and the reliability are improved.

Description

Flyback synchronous rectification drive circuit based on digital isolation

Technical Field

The utility model relates to the technical field of power supplies, in particular to a flyback synchronous rectification drive circuit based on digital isolation.

Background

At present, a power supply product outputting low-voltage and high-current in a single-ended flyback mode has replaced a traditional diode rectification mode by a synchronous rectification technology, so that the efficiency of the product is greatly improved, and synchronous rectification in an intermittent mode (DCM), a critical conduction mode (CRM) and a Current Continuous Mode (CCM) flyback mode is the most widely used at present; the DCM and CRM flyback modes have no common hidden trouble because of the control signals of the primary side and the secondary side, and the driving circuit is simple and reliable; in the single-ended flyback mode with lower input voltage and larger input current, the primary side peak current of the CCM flyback circuit is small, the EMC characteristic is good, and compared with other two current modes, the CCM flyback circuit has obvious advantages, but the secondary side synchronous rectification scheme is complex, and various problems are easy to generate due to unreasonable circuit scheme. The method comprises the following steps:

firstly, in a CCM flyback mode, a common drive synchronous rectification scheme takes a synchronous signal from a secondary side, so that the problem that a primary side MOS tube and a secondary side synchronous rectification tube are common cannot be solved, the flyback synchronous rectification efficiency in the CCM mode is low, and compared with a diode rectification circuit, the synchronous rectification circuit has no advantage;

secondly, in a CCM flyback mode, a driving scheme of primary side synchronization and secondary side synchronization is realized by using a magnetic device, the requirement on the magnetic device is high, waveform distortion is easy to generate, and meanwhile, the isolation withstand voltage of the magnetic device used for driving is low, so that the integral isolation withstand voltage value of a flyback power supply is limited;

third, the secondary side self-driven synchronous rectification generates reverse circulation under the no-load mode due to the bidirectional conduction characteristic of MOS, and the no-load loss is large and the power device generates serious heat.

Disclosure of Invention

The utility model aims to provide a flyback synchronous rectification drive circuit based on digital isolation, which is used for solving the defect of low synchronous rectification efficiency caused by sharing a primary side MOS tube and a secondary side rectifying tube in the prior art.

The technical scheme adopted by the utility model is as follows: a flyback synchronous rectification drive circuit based on digital isolation comprises a single-ended flyback main circuit and a synchronous rectification MOS isolation drive circuit; the single-ended flyback main circuit comprises an input end, a main switching tube Q1, a main transformer T1, a rectifying tube Q2, an output end, a PWM control chip, an MOS tube driving circuit and an output feedback circuit; the synchronous rectification MOS isolation driving circuit comprises a digital isolation chip and a synchronous rectification MOS tube driving circuit; the main switching tube Q1 and the rectifying tube Q2 are MOS tubes;

the positive end of the input end is connected with one end of a primary coil of the main transformer T1, and the main switch tube Q1 is respectively connected with the other end of the primary coil of the main transformer T1, the negative end of the input end and the MOS tube driving circuit; the MOS tube driving circuit is also connected with the PWM control chip, and the PWM control chip is also respectively connected with the output feedback circuit and the digital isolation chip;

the digital isolation chip is further connected with the synchronous rectification MOS tube driving circuit, the synchronous rectification MOS tube driving circuit is further connected with the rectifying tube Q2, the negative end of the output end and one end of the secondary side coil of the main transformer T1 respectively, the negative end of the output end is further connected with the rectifying tube Q2, and the other end of the secondary side coil of the main transformer T1 is connected with the output feedback circuit and the positive end of the output end respectively.

Preferably, a sampling resistor is further disposed between the main switch Q1 and the negative terminal of the input terminal.

Preferably, a sampling end of the sampling resistor is connected with the PWM control chip.

Preferably, a current comparison circuit is further connected between the PWM control chip and the digital isolation chip, an input end of the current comparison circuit is connected with a sampling end of the sampling resistor, and an output end of the current comparison circuit is connected with the digital isolation chip.

Preferably, the rectifying tube Q2 is a MOS tube, and the MOS tube has a body diode.

Preferably, the synchronous rectification MOS tube driving circuit comprises a synchronous rectification chip, wherein the model of the synchronous rectification chip is NCP4306;

the TRIG/DIS pin and the EN pin of the synchronous rectification chip are respectively connected with the digital isolation chip, the OUT pin of the synchronous rectification chip is connected with the grid electrode of the rectifying tube Q2, and the CS pin of the synchronous rectification chip is connected with the drain electrode of the rectifying tube Q2.

Preferably, the model of the digital isolation chip is ISO7720.

By adopting the technical scheme, the method has the following advantages:

1, through the cooperation of a digital isolation chip and a synchronous rectification MOS tube driving circuit, the synchronous rectification MOS on the secondary side is rapidly turned off in a CCM flyback mode, the phenomenon of sharing the MOS tubes on the primary side and the secondary side is avoided, and the circuit efficiency and reliability are improved;

2, the digital isolation chip is matched with current detection of the primary side, so that the synchronous rectification chip is turned off in a light load state, the efficiency in the light load state is improved, and the heat productivity of products is reduced;

and 3, the digital isolation chip is used for replacing a magnetic isolation device, so that the distortion of a secondary side driving signal is avoided, and the reliability of the circuit is improved.

Drawings

Fig. 1 is a schematic structural diagram of a flyback synchronous rectification driving circuit based on digital isolation according to an embodiment of the present utility model.

Detailed Description

In order to make the technical problems, technical solutions and advantages to be solved by the present utility model more apparent, the following detailed description will be given with reference to the accompanying drawings and specific embodiments, which are used to illustrate the present utility model, but are not intended to limit the scope of the present utility model.

Referring to fig. 1, the present embodiment provides a flyback synchronous rectification driving circuit based on digital isolation, which includes a single-ended flyback main circuit and a synchronous rectification MOS isolation driving circuit; the single-ended flyback main circuit comprises an input end, a main switching tube Q1, a main transformer T1, a rectifying tube Q2, an output end, a PWM control chip, an MOS tube driving circuit and an output feedback circuit; the synchronous rectification MOS isolation driving circuit comprises a digital isolation chip and a synchronous rectification MOS tube driving circuit; the main switching tube Q1 adopts an MOS tube;

the positive end of the input end is connected with one end of a primary coil of the main transformer T1, and the main switch tube Q1 is respectively connected with the other end of the primary coil of the main transformer T1, the negative end of the input end and the MOS tube driving circuit; the MOS tube driving circuit is also connected with the PWM control chip, and the PWM control chip is also respectively connected with the output feedback circuit and the digital isolation chip;

the digital isolation chip is further connected with the synchronous rectification MOS tube driving circuit, the synchronous rectification MOS tube driving circuit is further connected with the rectifying tube Q2, the negative end of the output end and one end of the secondary side coil of the main transformer T1 respectively, the negative end of the output end is further connected with the rectifying tube Q2, and the other end of the secondary side coil of the main transformer T1 is connected with the output feedback circuit and the positive end of the output end respectively.

In implementation, the rectifying tube Q2 adopts a MOS tube, and the MOS tube is provided with a body diode; the PWM control chip adopts chips such as UC3843 or LM 5021;

the synchronous rectification MOS tube driving circuit comprises a synchronous rectification chip, wherein the model adopted by the synchronous rectification chip is NCP4306;

the TRIG/DIS pin and the EN pin of the synchronous rectification chip are respectively connected with the digital isolation chip, the OUT pin of the synchronous rectification chip is connected with the grid electrode of the rectifying tube Q2, and the CS pin of the synchronous rectification chip is connected with the drain electrode of the rectifying tube Q2;

the digital isolation chip is a double-channel digital isolation chip, the input signal INA of the digital isolation chip is output by the primary side PWM control chip, and the on and off of the primary side MOS tube are controlled after the digital isolation chip passes through the MOS driving circuit;

the digital isolation chip adopts ISO7720 of TI company or CA-IS3720 of Chuanji micro company, and the digital isolation chip IS not limited in this regard;

the chip has lower propagation delay (signal transmission delay is lower than 15 nS), higher isolation withstand voltage (maximum 5000 Vac), selectable positive and negative logic output and small-volume chip packaging. The chip supplies the same phase (i.e. synchronous signal) of the primary side PWM driving signal to the TRIG/DIS synchronous end of the secondary side driving circuit, and after the TRIG/DIS signal is inverted in phase, the rising edge is used for controlling the turn-off of the secondary side MOS tube (i.e. rectifying tube Q2). The turn-on of the secondary side MOS transistor is controlled by detecting the zero crossing point of the drain electrode signal CS of the MOS transistor. The circuit controls the opening dead time of the primary side MOS tube and the secondary side synchronous rectifying tube to be more than 10nS by utilizing the time delay of the primary side MOS driving circuit, the time delay of the digital isolation chip and the time delay of the drain electrode opening signal of the secondary side MOS tube;

the existence of dead time of each MOS tube is utilized, so that the common time cannot exist between the primary side MOS tube and the secondary side MOS tube, and the common problem of the primary side MOS tube and the secondary side MOS tube of the common driving circuit is solved; the reliability of the circuit is improved in various transient states.

The output feedback circuit and the MOS tube driving circuit are applied to the prior art with mature application in the switching power supply; the output feedback circuit is an output voltage feedback circuit, and has the functions of enabling the system to be in a negative feedback closed loop state, improving the output voltage precision, stabilizing the output voltage, and enabling a common switching power supply to be provided with the output voltage feedback circuit, wherein the common switching power supply comprises a comparator, an error amplifier, a reference voltage source and the like, and the common switching power supply is well known to a person skilled in the art; as not an innovative part of the present application, no further description is made here.

Further, in order to avoid the situation that the efficiency is reduced due to the reverse flow of the secondary synchronous rectification MOS tube during light load, a sampling resistor is further arranged between the main switching tube Q1 and the negative electrode end of the input end, and the sampling end of the sampling resistor is connected with the PWM control chip;

and a current comparison circuit is further connected between the PWM control chip and the digital isolation chip, the input end of the current comparison circuit is connected with the sampling end of the sampling resistor, and the output end of the current comparison circuit is connected with the digital isolation chip.

The sampling resistor is R1 in the drawing, and a sampling signal is input to the PWM control chip and the current comparison circuit; the current comparison circuit is composed of a conventional comparator and an operational amplifier, and the circuit realizes the enabling control of the synchronous rectification circuit of the secondary side by detecting a primary side current signal; under the condition of low current signal, detecting current passing through INB channel of the digital isolation chip, and turning off synchronous rectification chip at secondary side so as to make MOS tube work only in state of conducting body diode to reduce loss of light load; when the current signal increases, the secondary synchronous rectification circuit enters a normal working state.

According to the scheme, the digital isolation chip is matched with the synchronous rectification MOS tube driving circuit, so that the synchronous rectification MOS on the secondary side is rapidly turned off in a CCM flyback mode, the phenomenon of sharing the MOS tubes on the primary side and the secondary side is avoided, and the circuit efficiency and reliability are improved; the digital isolation chip is matched with current detection of the primary side, so that the synchronous rectification chip is turned off in a light load state, the efficiency in the light load state is improved, and the heat productivity of products is reduced; the digital isolation chip is used for replacing a magnetic isolation device, so that the distortion of a secondary side driving signal is avoided, the reliability of a circuit is improved, a high-power-density small-volume module power supply is realized, and the isolation withstand voltage is more than or equal to 3000 Vac.

Finally, it should be noted that the above description is only specific embodiments of the present utility model, but the scope of the present utility model is not limited thereto, and any changes or substitutions that may be easily contemplated by those skilled in the art within the technical scope of the present utility model should be included in the scope of the present utility model.

Claims (7)

1. The flyback synchronous rectification drive circuit based on digital isolation is characterized by comprising a single-ended flyback main circuit and a synchronous rectification MOS isolation drive circuit; the single-ended flyback main circuit comprises an input end, a main switching tube Q1, a main transformer T1, a rectifying tube Q2, an output end, a PWM control chip, an MOS tube driving circuit and an output feedback circuit; the synchronous rectification MOS isolation driving circuit comprises a digital isolation chip and a synchronous rectification MOS tube driving circuit; the main switching tube Q1 adopts an MOS tube;

the positive end of the input end is connected with one end of a primary coil of the main transformer T1, and the main switch tube Q1 is respectively connected with the other end of the primary coil of the main transformer T1, the negative end of the input end and the MOS tube driving circuit; the MOS tube driving circuit is also connected with the PWM control chip, and the PWM control chip is also respectively connected with the output feedback circuit and the digital isolation chip;

the digital isolation chip is further connected with the synchronous rectification MOS tube driving circuit, the synchronous rectification MOS tube driving circuit is further connected with the rectifying tube Q2, the negative end of the output end and one end of the secondary side coil of the main transformer T1 respectively, the negative end of the output end is further connected with the rectifying tube Q2, and the other end of the secondary side coil of the main transformer T1 is connected with the output feedback circuit and the positive end of the output end respectively.

2. The flyback synchronous rectification driving circuit based on digital isolation according to claim 1, wherein a sampling resistor is further arranged between the main switching tube Q1 and the negative terminal of the input terminal.

3. The flyback synchronous rectification drive circuit based on digital isolation according to claim 2, wherein a sampling end of the sampling resistor is connected with the PWM control chip.

4. The flyback synchronous rectification drive circuit based on digital isolation according to claim 3, wherein a current comparison circuit is further connected between the PWM control chip and the digital isolation chip, an input end of the current comparison circuit is connected with a sampling end of the sampling resistor, and an output end of the current comparison circuit is connected with the digital isolation chip.

5. The flyback synchronous rectification driving circuit based on digital isolation according to claim 1, wherein the rectification tube Q2 is a MOS tube, and the MOS tube is provided with a body diode.

6. The flyback synchronous rectification drive circuit based on digital isolation according to claim 2, wherein the synchronous rectification MOS tube drive circuit comprises a synchronous rectification chip, and the model of the synchronous rectification chip is NCP4306;

the TRIG/DIS pin and the EN pin of the synchronous rectification chip are respectively connected with the digital isolation chip, the OUT pin of the synchronous rectification chip is connected with the grid electrode of the rectifying tube Q2, and the CS pin of the synchronous rectification chip is connected with the drain electrode of the rectifying tube Q2.

7. The flyback synchronous rectification drive circuit based on digital isolation according to any one of claims 1 to 6, wherein the digital isolation chip is of the type ISO7720.