CN219372268U - Synchronous rectification control circuit, DRV (digital video recorder) adjusting circuit and switching power supply - Google Patents

Abstract

The utility model discloses a synchronous rectification control circuit, a DRV (digital video) regulating circuit and a switching power supply, and relates to the technical field of electronic circuits. Comprises a conduction control circuit, a turn-off control circuit, a driving circuit and a DRV adjusting circuit. The conduction control circuit is used for sending a conduction signal; the turn-off control circuit is used for sending out a turn-off signal; the driving circuit is used for switching on the MOSFET according to the on signal or switching off the MOSFET according to the off signal; the DRV adjusting circuit is used for reducing the grid driving voltage before the MOSFET is turned off; the DRV adjusting circuit comprises a first control circuit, a second control circuit, a pull-down current source circuit and N amplifying circuitsA circuit, N is not less than 2; any discharge circuit is conducted to discharge so as to reduce the DRV voltage value. The utility model reduces the drop of DRV from high level to V _REG The DRV is prevented from being excessively reduced, the turn-off speed of the MOSFET is accelerated, and the stability is improved.

Description

Synchronous rectification control circuit, DRV (digital video recorder) adjusting circuit and switching power supply

Technical Field

The utility model relates to the technical field of electronic circuits, in particular to a synchronous rectification control circuit, a DRV (digital video) regulating circuit and a switching power supply.

Background

Switching power supplies typically use synchronous rectification control circuits to drive metal-oxide semiconductor field effect transistors (MOSFETs) to perform the rectification function. During the MOSFET on period, the synchronous rectification control circuit samples the Voltage (VDS) at the source-drain ends of the MOSFET, and when the VDS is higher than the MOSFET off threshold value, the MOSFET is turned off after the turn-off delay (td 2).

The synchronous rectification control circuit needs to adjust the gate drive voltage (DRV) to a desired target value (V) in a short time before the MOSFET starts to turn on until the VDS reaches the MOSFET OFF threshold (VTH_OFF) _REG ). The gate voltage of the MOSFET can be gradually reduced from a high level voltage by reducing the DRV so that the MOSFET is ready to go from a lower voltage to an off state. When the voltage across the MOSFET is relatively low, the VDS is adjusted to a certain range, which speeds up the turn-off speed of the MOSFET.

In some cases, the synchronous rectification control circuit is externally connected to the power supply VCC. The magnitude by which the MOSFET begins to turn on the DRV is generally dependent on the magnitude of VCC. In a typical application, when the power supply VCC is 5V and the DRV voltage (gate driving voltage) adjusting circuit is operated, the DRV voltage (gate driving voltage) needs to be adjusted from the power supply VCC (5V in the typical application scenario) to the desired target value V in a relatively short time _REG So that the subsequent MOSFET will go from a lower voltage to an off state at any time.

In some other applications the supply voltage VCC is raised to a higher voltage level, i.e. the supply voltage VCC is higher than 5 volts. Thus, the DRV voltage (gate driving voltage) is adjusted by the DRV voltage (gate driving voltage) adjusting circuitVoltage) is adjusted, it is necessary to pull down from a higher voltage to a desired target value V _REG Thereby the adjustment time becomes long; meanwhile, in the traditional synchronous rectification control circuit, only one normally-on discharge circuit is designed to discharge, and in order to improve the pull-down speed, a large pull-down current is needed to be considered, however, if the large pull-down current is used, the DRV is easy to excessively pull down.

Disclosure of Invention

An object of an embodiment of the present utility model is to provide a synchronous rectification control circuit, a DRV adjusting circuit and a switching power supply for reducing the drop of DRV from high level to V _REG And prevents excessive drop of DRV, thereby improving both the turn-off speed of the MOSFET and the stability.

In order to achieve the above object, the embodiment of the present utility model provides the following solutions:

a synchronous rectification control circuit, comprising:

the conduction control circuit is used for sending a conduction signal;

the turn-off control circuit is used for sending out a turn-off signal;

the driving circuit is respectively connected with the on control circuit, the off control circuit and the MOSFET and is used for conducting the MOSFET according to the on signal or switching off the MOSFET according to the off signal;

the grid driving voltage DRV adjusting circuit is connected with the MOSFET and used for reducing the grid driving voltage before the MOSFET is turned off; the DRV adjusting circuit comprises a first control circuit, a second control circuit and N discharging circuits, wherein N is not less than 2;

when the DRV is higher than the reference voltage, the first control circuit is in a conducting state so as to reduce the voltage value of the DRV; when DRV is smaller than or equal to the reference voltage or the drain voltage of the MOSFET is larger than or equal to a second threshold voltage, the first control circuit is in an off state;

the N discharging circuits are connected with the MOSFET; any discharge circuit can discharge when being conducted so as to reduce the voltage value of the DRV; any discharge circuit is a normally-on discharge circuit or a controlled circuit controlled by the second control circuit;

the second control circuit is used for controlling the DRV not to drop to the required target value V _REG And when the DRV is smaller than or equal to the third threshold value, the controlled circuit is controlled to be turned on, and when the DRV is smaller than or equal to the third threshold value, the controlled circuit is controlled to be turned off.

Optionally, the first control circuit includes:

a pull-down current source circuit;

the first controller is used for controlling the pull-down current source circuit to be conducted when the DRV is higher than the reference voltage so as to reduce the voltage value of the DRV to the reference voltage; and controlling the pull-down current source circuit to be disconnected when the voltage value of the DRV is equal to the reference voltage.

Optionally, the first controller is specifically configured to:

comparing the magnitudes of the DRV and the reference voltage, the magnitudes of the drain voltage and the first threshold voltage, and the magnitudes of the drain voltage and the second threshold voltage; the first threshold voltage is less than the second threshold voltage;

if DRV is larger than the reference voltage, drain voltage is larger than the first threshold voltage and smaller than the second threshold voltage, controlling the pull-down current source circuit to be closed;

and if the DRV is smaller than or equal to the reference voltage and the drain voltage is larger than the second threshold voltage, controlling the pull-down current source circuit to be disconnected.

Optionally, the first controller includes:

the reverse input end of the first comparator is used for inputting the DRV, and the forward input end of the first comparator is used for inputting the reference voltage;

the positive input end of the second comparator is used for inputting the first threshold voltage, and the negative input end of the second comparator is used for inputting the drain voltage;

the first input end of the NOR gate is connected with the output end of the first comparator, and the second input end of the NOR gate is connected with the output end of the second comparator;

the positive input end of the third comparator is used for inputting the drain voltage, and the negative input end of the third comparator is used for inputting the second threshold voltage;

the input end of the inverter is connected with the output end of the third comparator;

a first switch;

the first input end of the NAND gate is connected with the output end of the NAND gate, and the second input end of the NAND gate is connected with the output end of the inverter; the output end of the NAND gate is used for outputting a control signal for controlling the first switch.

Optionally, the second control circuit is specifically configured to:

if DRV is greater than or equal to the third threshold voltage and the drain voltage is greater than or equal to the second threshold voltage, controlling the controlled circuit to be conducted;

and if the DRV is smaller than the third threshold voltage and the drain voltage is larger than or equal to the second threshold voltage, controlling the controlled circuit to be disconnected.

Optionally, the second control circuit includes:

a fourth comparator, wherein a forward input end of the fourth comparator is used for inputting the DRV, and a reverse input end of the fourth comparator is used for inputting the third threshold voltage;

the control end of the second switch is connected with the output end of the fourth comparator, and the second switch is used for opening or closing the controlled circuit;

and the positive input end of the amplifier is used for inputting the drain voltage, the negative input end of the amplifier is used for inputting the second threshold voltage, and the output end of the amplifier is connected with the discharge circuit.

The utility model also provides a DRV regulating circuit which is applied to the synchronous rectification control circuit, and is connected with the MOSFET and used for reducing the grid driving voltage before the MOSFET is turned off;

the DRV adjustment circuit includes: the first control circuit, the second control circuit and N discharge circuits, wherein N is not less than 2; wherein:

when the DRV is higher than the reference voltage, the first control circuit is in a conducting state so as to reduce the voltage value of the DRV; when DRV is smaller than or equal to the reference voltage or the drain voltage of the MOSFET is larger than or equal to a second threshold voltage, the first control circuit is in an off state;

the N discharging circuits are connected with the MOSFET; any discharge circuit can discharge when being conducted so as to reduce the voltage value of the DRV; any discharge circuit is a normally-on discharge circuit or a controlled circuit controlled by the second control circuit;

the second control circuit is used for: and when the DRV is not reduced to the required target value VREG and is larger than a third threshold value, controlling the controlled circuit to be conducted, and when the DRV is smaller than or equal to the third threshold value, controlling the controlled circuit to be disconnected.

Optionally, the controlled circuit includes a first NMOS transistor; the normally-on discharge circuit comprises a second NMOS tube;

the output end of the amplifier is respectively connected with the grid electrode of the first NMOS tube and the grid electrode of the second NMOS tube; the drain electrode of the first NMOS tube is connected with the grid electrode of the MOSFET through the second switch;

the drain electrode of the second NMOS tube is connected with the grid electrode of the MOSFET;

the sources and the substrates of the first NMOS tube and the second NMOS tube are grounded.

Optionally, the first NMOS transistor and the second NMOS transistor have different parameters.

The utility model also provides a switching power supply applying the synchronous rectification control circuit, which comprises: the synchronous rectification control circuit, the capacitor, the transformer, the positive electrode interface and the negative electrode interface;

the capacitor is connected with the positive electrode interface and the negative electrode interface respectively, and is used for storing electric energy;

the negative electrode interface is grounded;

the positive electrode interface is connected with one end of the transformer; the other end of the transformer is connected with the drain end of the MOSFET; the source end of the MOSFET and the substrate are grounded;

the synchronous rectification control circuit is connected with the MOSFET.

According to the specific embodiment provided by the utility model, the following technical effects are disclosed:

the embodiment of the utility model provides a synchronous rectification control circuit, a DRV regulating circuit and a switching power supply, wherein the synchronous rectification control circuit comprises a conduction control circuit, a turn-off control circuit, a driving circuit and a DRV regulating circuit. The circuits cooperate as follows: the conduction control circuit is used for sending a conduction signal; the turn-off control circuit is used for sending out a turn-off signal; the driving circuit is used for switching on the MOSFET according to the on signal or switching off the MOSFET according to the off signal; the DRV adjusting circuit is used for reducing the grid driving voltage before the MOSFET is turned off.

The DRV adjusting circuit comprises a first control circuit, a second control circuit, a pull-down current source circuit and N discharging circuits (N is not less than 2). The N discharging circuits are connected with the MOSFET; any one of the discharge circuits is a normally-on discharge circuit or a controlled circuit controlled by a second control circuit. The controlled circuit is controlled by the second control circuit, when the DRV does not drop to the required target value V _REG And is turned on when it is greater than a third threshold, or turned off otherwise.

In different occasions, the adjustment process of the DRV adjustment circuit is as follows:

for the case that VCC is higher than the reference voltage (which may be referred to as a second case), since the initial voltage of DRV is determined by VCC when MOSFET is turned on, the initial voltage of DRV is higher than the reference voltage, and the first control circuit will be in on state to reduce the voltage value of DRV; meanwhile, the second control circuit and the N discharging circuits also play a role in pulling down the DRV.

After the DRV is reduced from the initial voltage to the reference voltage or when the drain voltage of the MOSFET is equal to or greater than the second threshold voltage, the first control circuit enters an off state, after which the second control circuit and the N discharge circuits continue to function.

And when VCC is equal to the reference voltage (which may be referred to as the first occasion), the first control circuit is always in an off state after the MOSFET is turned on. Meanwhile, the second control circuit and the N discharge circuits can act to pull down the DRV.

Compared with the first occasion, the first control circuit can participate in the adjustment of the DRV in the second occasion, thereby shortening the pulling down of the DRV to V _REG The time required for the second occasion is kept consistent with the time required for the first occasion.

In either case, after the MOSFET is turned on, the second control circuit and the N discharge circuits function (operate) as follows: after DRV has not fallen to the desired target value V _REG When the voltage value is larger than the third threshold value, the second control circuit controls the controlled circuit to be in a conducting state, at the moment, the N discharging circuits are discharged together rapidly to reduce the voltage value of the DRV (if the first control circuit participates in pulling down the DRV together in the second occasion), compared with the design that one normally-on discharging circuit is arranged in the traditional synchronous rectification control circuit, the discharging speed is faster, namely the DRV is reduced to the required target value V _REG Faster, and thus increases the turn-off speed of the MOSFET.

And when the DRV is smaller than or equal to a third threshold value, the second control circuit controls the controlled circuit to be disconnected, and the normally-on discharging circuit still works after that. Compared with the discharging of N discharging circuits, the discharging circuit can slow down the descending speed of the DRV and avoid the excessive drop-down of the DRV, so that the DRV adjusting circuit is easier to enter a stable adjusting state, the stability of the synchronous rectification control circuit is improved, and meanwhile, the stability of a switching power supply applying the synchronous rectification control circuit is also improved.

In summary, the technical scheme provided by the embodiment of the utility model can reduce the drop of DRV from high level to V _REG And prevents excessive drop of DRV, thereby improving both the turn-off speed of the MOSFET and the stability.

Drawings

In order to more clearly illustrate the embodiments of the present utility model or the technical solutions of the prior art, the drawings that are needed in the embodiments will be briefly described below, it being obvious that the drawings in the following description are only some embodiments of the present utility model and that other drawings can be obtained according to these drawings without inventive effort to a person skilled in the art.

Fig. 1 is a schematic structural diagram of a synchronous rectification control circuit according to an embodiment of the present utility model;

fig. 2 is a graph of a partial node change of a synchronous rectification control circuit DRV according to an embodiment of the present utility model;

FIG. 3 is a graph showing another partial node variation of a synchronous rectification control circuit DRV according to an embodiment of the present utility model;

fig. 4 is a schematic structural diagram of a switching power supply using a synchronous rectification control circuit according to an embodiment of the present utility model.

Symbol description:

the switching on control circuit-1, the switching off control circuit-2, the driving circuit-3, the grid driving voltage DRV regulating circuit-4, the first comparator-41, the second comparator-42, the NOR gate-43, the third comparator-44, the inverter-45, the first switch-46, the NAND gate-47, the pull-down current source circuit-48, the fourth comparator 49, the second switch-410, the amplifier-411, the normally-on discharging circuit-412, the controlled circuit-413, the capacitor-5, the transformer-6, the positive electrode interface-7 and the negative electrode interface-8.

Detailed Description

The structures and the scenes described in the embodiments of the present application are for more clearly describing the technical solutions of the embodiments of the present application, and do not constitute a limitation on the technical solutions provided by the embodiments of the present application, and as a person of ordinary skill in the art can know that, with the appearance of a new scene, the technical solutions provided by the embodiments of the present application are equally applicable to similar technical problems.

In this application, the terms "exemplary" or "such as" are used to mean an example, instance, or illustration. Any embodiment or design described herein as "exemplary" or "for example" should not be construed as preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary" or "such as" is intended to present related concepts in a concrete fashion.

The embodiment of the utility model aims to provide a synchronous rectification control circuit, a DRV regulating circuit and a switching power supply, which reduce DRV decreases from high to V _REG And prevents excessive drop of DRV, thereby improving both the turn-off speed of the MOSFET and the stability.

The switching power supply uses a synchronous rectification control circuit to drive the MOSFET to complete the rectification function.

Fig. 1 shows an exemplary structure of the above synchronous rectification control circuit, including an on control circuit 1, an off control circuit 2, a driving circuit 3, and a gate driving voltage DRV adjustment circuit 4. The roles of the following sections are described:

the on control circuit 1, the off control circuit 2, and the drive circuit 3 are described in detail below.

Still referring to fig. 1, the on control circuit 1 includes: the first input terminal, the second input terminal and the first output terminal.

In one example, the first input terminal inputs the drain Voltage (VDET), the second input terminal inputs the Turn-on reference voltage (vth_on), the first output terminal is connected to the driving circuit 3, and the first output terminal outputs the Turn-on signal (turn_on). VDET is used to detect and reflect the magnitude of the source-drain terminal voltage VDS of NMOS transistor (MN 0). When secondary side freewheeling begins, the MOSFET is in an off state, and secondary side current flows through the parasitic diode D0 of the MOSFET to realize freewheeling, and negative VDS voltage is formed at both ends of the parasitic diode, namely VDET is reduced from positive voltage to negative voltage. When the on control circuit 1 detects that the negative voltage of VDET is lower than the reference voltage vth_on, a turn_on signal is output and the MOSFET will be turned on after a delay td 1.

The off control circuit 2 includes: a third input, a fourth input and a second output.

In one example, the third input terminal inputs the drain Voltage (VDET), the fourth input terminal inputs the off reference voltage (vth_off), the second output terminal is connected to the driving circuit 3, and the second output terminal is for outputting the off signal (turnoff). VDET is used to detect and reflect the magnitude of the source-drain terminal voltage VDS of NMOS transistor (MN 0). During the on period of the MOSFET, the source-drain terminal voltage VDET of the NMOS transistor MN0 gradually increases (gradually changes from negative voltage to positive voltage) as the freewheel current decreases. When VDET rises to the off threshold Vth_off, the MOSFET will turn off after a delay td 2. The reference voltage vth_off is greater than the reference voltage vth_on.

The driving circuit 3 is respectively connected with the on control circuit 1, the off control circuit 2 and the MOSFET, and the driving circuit 3 is used for switching on the MOSFET according to the on signal or switching off the MOSFET according to the off signal.

The input end of the driving circuit 3 is respectively connected with a signal Turn-on signal Turn_on and a signal Turn-off signal Turn_off, the output end outputs DRV, the high level of the DRV is VCC, and the low level is the grounding voltage. The output DRV drives the MOSFET to achieve the purpose of opening and closing the MOSFET.

The grid driving voltage DRV adjusting circuit 4 is connected with the MOSFET and is used for reducing the grid driving voltage before the MOSFET is turned off; the DRV adjusting circuit comprises a first control circuit, a second control circuit and N discharging circuits, wherein N is not less than 2. Those skilled in the art can flexibly design the number of discharge circuits, such as 2, 3, 5, etc., and will not be described herein.

Referring to fig. 1, the MOSFET may include an NMOS transistor (denoted by MN0 in fig. 1) and a diode (denoted by D0 in fig. 1), for example. The gate input (or access) DRV of the MOSFET, the source and substrate terminals are grounded. The diode is a parasitic diode of the NMOS transistor.

The first control circuit is described in detail below.

When the DRV is higher than the reference voltage, the first control circuit is in a conducting state so as to reduce the voltage value of the DRV.

When the DRV is smaller than or equal to the reference voltage or the drain voltage of the MOSFET is larger than or equal to the second threshold voltage, the first control circuit is in an off state.

For example, the reference voltage may be an internal power VCCI, or a fixed reference voltage may be fixed by a person skilled in the art, and the person skilled in the art may flexibly design the VCCI or the fixed reference voltage, for example, 4 v, 5v, 6 v, etc., which are not described herein. When the supply voltage VCC is greater than the minimum allowable operating voltage of the DRV adjustment circuit 4 and not greater than 5 volts, the internal supply VCCI is equal to the supply voltage VCC.

The first control circuit may be implemented using a variety of circuit configurations. In one example, the first control circuit may include a pull-down current source circuit 48 and a first controller.

The first controller is specifically configured to:

comparing the magnitudes of the DRV and the reference voltage, the magnitudes of the drain voltage and the first threshold voltage Vth1, and the magnitudes of the drain voltage and the second threshold voltage Vth 2; the first threshold voltage Vth1 is smaller than the second threshold voltage Vth2.

When the DRV is higher than the reference voltage or the drain voltage of the MOSFET is greater than the first threshold voltage and less than the second threshold voltage, the first controller controls the pull-down current source circuit 48 to be turned on, and the first control circuit is in a turned-on state to reduce the voltage value of the DRV to the reference voltage. When the voltage value of the DRV is equal to or less than the reference voltage and the drain voltage of the MOSFET is equal to or greater than the second threshold voltage, the first controller controls the pull-down current source circuit 48 to be turned off, and the first control circuit is in an off state, and the voltage value of the DRV stops decreasing.

It should be noted that, when the MOSFET starts to turn on, the size of DRV is generally determined by the size of VCC. The comparison of the DRV and the reference voltage is equivalent to comparing the magnitude of VCCI and VCC when the MOSFET starts to turn on, since DRV is equal to VCCI.

Meanwhile, there is also a relationship between VCCI and vcc—vcci may be generated by VCC and VCCI is less than or equal to VCC. In design, at least the power supply voltage of the output driving part device is VCC, and the power supply of the other devices is internal power supply VCCI. For example, the power supplies of the on control circuit 1, the off control circuit 2 and the driving circuit 3 may be VCC, and the power supplies of the other circuits may be internal power VCCI. The synchronous rectification control circuit may include a plurality of internal power VCCIs.

The voltage variation range of the power supply VCC is large, and in a typical application, VCCI is equal to 5V; when the power supply VCC is larger than 5V, the internal power supply VCCI is equal to 5V; and when the power supply is greater than the minimum allowable operating voltage and not higher than 5V, the internal power supply VCCI is equal to the power supply VCC.

In one example, the first threshold voltage may specifically be minus 80 millivolts or minus 70 millivolts. The second threshold voltage may in particular be minus 40 millivolts or minus 30 millivolts.

Of course, the function of the first controller may be implemented using a circuit structure. Still referring to fig. 1, the first controller illustratively includes at least: a first comparator 41, a second comparator 42, a nor gate 43, a third comparator 44, an inverter 45, a first switch 46 and a nand gate 47. Wherein:

the inverting input of the first comparator 41 is used for inputting DRV and the inverting input of the first comparator 41 is used for inputting a reference voltage (e.g. VCCI).

The forward input terminal of the second comparator 42 is used for inputting the first threshold voltage Vth1, and the reverse input terminal of the second comparator 42 is used for inputting the drain voltage.

A first input of the nor gate 43 is connected to the output of the first comparator 41, and a second input of the nor gate 43 is connected to the output of the second comparator 42.

The third comparator 44 has a positive input terminal for inputting the drain voltage and a negative input terminal for inputting the second threshold voltage Vth2.

An input of the inverter 45 is connected to an output of the third comparator 44.

A first input terminal of the nand gate 47 is connected to an output terminal of the nor gate 43, and a second input terminal of the nand gate 47 is connected to an output terminal of the inverter 45; the output of the nand gate 47 is used for outputting a control signal for controlling the first switch 46.

The first switch 46 is used to open or close the pull-down current source circuit 48 in accordance with a control signal. The pull-down current source circuit 48 is used to drop the DRV from VCC to VCCI.

In one example, pull-down current source circuit 48 may be embodied as a conventional current source.

The functions of the devices are as follows:

the first comparator 41 is used for detecting the magnitudes of the DRV and the internal power VCCI, and when the DRV is greater than the internal power VCCI, the first comparator 41 outputs a low level. The first comparator 41 outputs a low level as one of the conditions under which the first switch 46 is closed.

The first comparator 41 is configured to detect the magnitudes of the drain Voltage (VDET) and the first threshold voltage (Vth 1), and when the drain voltage is greater than the first threshold voltage Vth1, the second comparator 42 outputs a low level. The second comparator 42 outputs a low level as the second condition for the first switch 46 to be closed.

The nor gate 43 inputs a low level at both the first input terminal and the second input terminal, and the nor gate 43 outputs a high level.

The drain voltage is less than the second threshold voltage Vth2, and the third comparator 44 outputs a high level.

The third comparator 44 outputs a high level, the output terminal of the third comparator 44 is connected to the input terminal of the inverter 45, and the inverter 45 outputs a low level.

The nor gate 43 outputs a high level, the inverter 45 outputs a low level, and the nand gate 47 outputs a high level, at which time the first switch is closed, otherwise the first switch 46 is opened. Specifically, when DRV is greater than the internal power supply VCCI and the drain voltage is greater than the first threshold voltage, that is, when both conditions that the first switch 46 is closed are satisfied, the first switch 46 is closed, the pull-down current source circuit 48 is turned on, DRV discharges, and the voltage decreases. One end of the pull-down current source circuit 48 is connected to the first switch 46, and the other end is grounded. The first switch 46 is opened when the DRV is not higher than the internal power VCCI, and the first switch 46 is forcibly opened when the drain voltage is greater than the second threshold voltage, i.e., one of two conditions that the first switch 46 is closed is not satisfied, the first switch 46 is opened.

In one example, the first switch 46 may be embodied as an NMOS switch tube or a transmission gate.

The second control circuit is described in detail below.

After DRV has not fallen to the desired target value V _REG And greater than the third threshold Vth3, the second control circuit controls the controlled circuit 413 to be turned on.

When DRV is equal to or less than the third threshold Vth3, the second control circuit controls the controlled circuit 413 to be turned off.

Still referring to fig. 1, the second control circuit includes at least N discharge circuits and a fourth comparator 49, a second switch 410, and an amplifier 411, as an example. The N discharge circuits include a normally-on discharge circuit 412 and a controlled circuit 413.

The second control circuit may be implemented using a variety of circuit configurations. In one example, the second control circuit includes at least N discharge circuits and a second controller.

The second controller is specifically configured to:

the magnitudes of DRV and the third threshold voltage Vth3, and the magnitudes of the drain voltage and the second threshold voltage Vth2 are compared.

When the DRV is equal to or greater than the third threshold voltage and the drain voltage is equal to or greater than the second threshold voltage (Vth 2), the second controller controls the controlled circuit 413 to be turned on. When the DRV is less than the third threshold voltage and the drain voltage is greater than or equal to the second threshold voltage, the second controller controls the controlled circuit 413 to be turned off. N discharging circuits are connected with the MOSFET; both the normally-on discharge circuit 412 and the controlled circuit 413 are capable of discharging when turned on to reduce the voltage value of the DRV.

In one example, the normally-on discharge circuit 412 and the controlled circuit 413 discharge simultaneously faster than just the normally-on discharge circuit 412.

The controlled circuit 413 includes a first NMOS transistor; the normally-on discharge circuit 412 includes a second NMOS transistor.

In one example, the normally-on discharge circuit 412 may include a second NMOS transistor. The controlled circuit 413 may include one or more first NMOS transistors, and those skilled in the art may flexibly design the number of the first NMOS transistors, for example, 1, 2, 3, etc., which are not described herein.

The first NMOS transistor and the second NMOS transistor have different parameters, which may be different sizes.

In one example, when the second switch 410 is closed, the first NMOS transistor and the second NMOS transistor together adjust the DRV, resulting in a faster discharge rate; when the second switch 410 is turned off, the first NMOS transistor does not adjust the DRV any more, and no discharge current is generated, and only the second NMOS transistor adjusts the DRV, so that the discharge speed is reduced. The first NMOS tube is used as a rapid adjustment tube of the DRV; the second NMOS tube is used as an adjusting tube of the DRV.

The second controller may be a chip.

Of course, the function of the second controller may also be implemented by a circuit structure. Illustratively, still referring to FIG. 1, the second controller includes at least: a fourth comparator 49, a second switch 410 and an amplifier 411. Wherein:

the positive terminal of the fourth comparator 49 is used for inputting DRV, and the negative input terminal of the fourth comparator 49 is used for inputting the third threshold voltage Vth3.

The second switch 410 is connected to the output of the fourth comparator 49, and the second switch 410 is used to open or close the controlled circuit 413.

The positive input terminal of the amplifier 411 is used for inputting the drain voltage, and the negative input terminal of the amplifier 411 is used for inputting the second threshold voltage Vth2. The output end of the amplifier 411 is connected to the gate of the first NMOS transistor (MN 1) and the gate of the second NMOS transistor (MN 2), respectively. The drain electrode of the first NMOS tube is connected with the MOSFET through a second switch 410; the drain electrode of the second NMOS tube is connected with the DRV; the sources of the first NMOS tube and the second NMOS tube and the substrate are grounded.

In one example, the drain voltage is greater than the second threshold voltage Vth2, and the amplifier 411 outputs a high level. The output end of the amplifier 411 is connected with the drain electrode of the first NMOS tube and the drain electrode of the second NMOS tube respectively, the drain electrode of the first NMOS tube is connected with the MOSFET through the second switch 410, and when the amplifier 411 outputs a high level and the second switch 410 is closed, the first NMOS tube and the second NMOS tube start discharging.

If the DRV is greater than the third threshold voltage Vth3, the second switch 410 is turned on, and after the second switch 410 is turned on, the first NMOS transistor MN1 and the second NMOS transistor MN2 are discharged together, so as to enter a fast discharge stage. The other end of the second switch 410 is connected to the DRV. If the DRV voltage is equal to the third threshold voltage Vth3, the second switch 410 is turned on, the first NMOS MN1 stops discharging, and only the second NMOS MN2 discharges the DRV slowly, so that overdischarge of the DRV can be avoided, and the DRV adjusting circuit is easier to enter a stable adjusting state.

The functions of the devices are as follows:

the fourth comparator 49 is configured to compare the DRV with the third threshold voltage Vth3, and when the DRV is greater than the third threshold voltage Vth3, the fourth comparator 49 outputs a high level. The fourth comparator 49 outputs a high level as a condition that the second switch 410 is closed.

In one example, the third threshold voltage Vth3 may specifically be minus 10 millivolts or minus 5 millivolts.

The amplifier 411 is configured to compare the drain voltage with the second threshold voltage Vth2, and when the drain voltage is greater than the second threshold voltage Vth2, the amplifier 411 outputs a high level.

Typical applications for synchronous rectification control circuits may include two types:

application field integration, fig. 2 is a graph of partial node voltage of the synchronous rectification control circuit in an application field according to an embodiment of the present utility model. As shown in fig. 2, when the secondary side freewheeling starts, the MOSFET is in an off state, and the secondary side current flows through the parasitic diode D0 of the MOSFET to realize freewheeling, and a negative source-drain Voltage (VDS) is formed across the parasitic diode D0, that is, VDET is changed from a positive voltage to a negative voltage. When VDET falls to the turn-on threshold (Vth_on), the MOSFET will turn on after a delay (td 1), and DRV goes from low to high. In this application condition, the power supply VCC is 5V, the internal power supply VCCI is set to 5V, and the first switch 46 is not closed. As the freewheel current decreases, VDET gradually increases (changes from negative to positive) and when VDET rises to the second threshold voltage Vth2, the second switch 410 closes, rapidly discharging DRV during tc1, causing the DRV adjustment circuit to enter a steady adjustment state faster. When the DRV drops to the third threshold voltage Vth3, the second switch 410 is turned on, and the DRV discharging speed is slowed down, so that the overdischarge of the DRV can be avoided, and the DRV adjusting circuit is easier to enter the stable adjusting state.

After tc2 time, DRV drops to V _REG And enters a steady adjustment state. DRV from V then _REG Continuing to gradually decrease, by this mechanism, the VDS is adjusted around the second threshold voltage Vth2 when the current through the MOSFET is quite low. As the freewheel current continues to decrease, the MOSFET turns off after a delay td2 when VDET rises to the off threshold voltage (vth_off), at which point DRV is already very low, which can speed up the MOSFET turn-off speed.

In application occasion II, FIG. 3 is a graph of partial node voltage of the synchronous rectification control circuit in application occasion II according to the embodiment of the present utility model. As shown in fig. 3, when the secondary side freewheels begin, the MOSFET is in an off state and the secondary side current flows through the parasitic diode D0 of the MOSFET to effect freewheels, while a negative VDS voltage is developed across the parasitic diode, i.e., VDET drops from positive to negative voltage. When VDET falls to the turn-on threshold Vth_on, the MOSFET will turn on after a delay td1, and DRV changes from low to high. Under this application condition, the power supply VCC is higher than 5V, and the internal power supply VCCI is set to 5V. As the freewheel current decreases, the VDET voltage gradually increases (changes from negative to positive) and when VDET increases to the first threshold voltage Vth1, the first switch 46 is closed, and after discharging DRV to VCCI voltage, the first switch 46 is closed. The subsequent DRV adjustment procedure is the same as the application one in fig. 2 and will not be described here.

As can be seen by comparison, in the second application, there is more than a pull-down current source circuit 48 discharging the DRV from VCC to VCCI, reducing the DRV from VCCI to V _REG The procedure of (2) is independent of VCC, and the adjustment time required in the second occasion is consistent with the adjustment time required in the first occasion.

In summary, the synchronous rectification control circuit reduces the drop of DRV from high level to V _REG And prevents excessive drop of DRV, thereby improving both the turn-off speed of the MOSFET and the stability.

Referring to fig. 4, a switching power supply employing a synchronous rectification control circuit is disclosed. Illustratively, a switching power supply employing a synchronous rectification control circuit includes at least: the synchronous rectification control circuit, the capacitor 5, the transformer 6, the positive electrode interface 7 and the negative electrode interface 8.

In one example, the capacitor 5 is connected to the positive and negative electrode interfaces 7 and 8, respectively, and the capacitor 5 is used to store electrical energy.

The negative electrode interface 8 is grounded.

The positive electrode interface 7 is connected with one end of the transformer 6, and the other end of the transformer 6 is connected with the drain end of the MOSFET; the source terminal of the MOSFET and the substrate are grounded. The transformer 6 includes a primary side inductance and a secondary side inductance. Illustratively, the left side is the primary side inductance and the right side is the secondary side inductance. The secondary side freewheeling means that the secondary side has current flowing through it from the "Ground (GND) -MOSFET-secondary side inductor-positive interface 7 (vout+).

The synchronous rectification control circuit is connected with the MOSFET.

Fig. 4 is a switching power supply employing a synchronous rectification control circuit. As shown in fig. 4, the VDET terminal of the synchronous rectification control circuit detects the VDS voltage of the power transistor MOSFET (MN 0), and outputs DRV to control the on and off of the power transistor MN 0. The grid electrode of MN0 is connected with DRV, the source end and the substrate are grounded, and the drain end is connected with one end of the transformer 6. During the period when the secondary side starts freewheels and the MOSFET is not on, freewheels through parasitic diode D0. The other end of the transformer 6 is an anode interface 7 (VOUT+), a cathode interface 8 (VOUT-) is a grounding end, and the capacitor 5 is connected between the anode interface 7 and the cathode interface 8.

Embodiments of the present utility model also claim DRV adjustment circuits in all of the above embodiments.

In the present specification, each embodiment is described in a progressive manner, and each embodiment is mainly described in a different point from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other.

The principles and implementations of the embodiments of the present utility model have been described herein with reference to specific examples, but the description of the embodiments is only intended to assist in understanding the core ideas of the embodiments of the present utility model; also, it is within the spirit of the embodiments of the present utility model for those skilled in the art to vary from one implementation to another and from application to another. In view of the foregoing, this description should not be construed as limiting the embodiments of the utility model.

Claims (10)

1. A synchronous rectification control circuit, comprising:

the conduction control circuit is used for sending a conduction signal;

the turn-off control circuit is used for sending out a turn-off signal;

the driving circuit is respectively connected with the on control circuit, the off control circuit and the MOSFET and is used for conducting the MOSFET according to the on signal or switching off the MOSFET according to the off signal;

the grid driving voltage DRV adjusting circuit is connected with the MOSFET and used for reducing the grid driving voltage before the MOSFET is turned off; the DRV adjusting circuit comprises a first control circuit, a second control circuit and N discharging circuits, wherein N is not less than 2;

when the DRV is higher than the reference voltage, the first control circuit is in a conducting state so as to reduce the voltage value of the DRV; when DRV is smaller than or equal to the reference voltage or the drain voltage of the MOSFET is larger than or equal to a second threshold voltage, the first control circuit is in an off state;

the N discharging circuits are connected with the MOSFET; any discharge circuit can discharge when being conducted so as to reduce the voltage value of the DRV; any discharge circuit is a normally-on discharge circuit or a controlled circuit controlled by the second control circuit;

the second control circuit is used for controlling the DRV not to drop to the required target value V _REG And when the DRV is smaller than or equal to the third threshold value, the controlled circuit is controlled to be turned on, and when the DRV is smaller than or equal to the third threshold value, the controlled circuit is controlled to be turned off.

2. The synchronous rectification control circuit according to claim 1, wherein said first control circuit comprises:

a pull-down current source circuit;

the first controller is used for controlling the pull-down current source circuit to be conducted when the DRV is higher than the reference voltage so as to reduce the voltage value of the DRV to the reference voltage; and controlling the pull-down current source circuit to be disconnected when the voltage value of the DRV is equal to the reference voltage.

3. The synchronous rectification control circuit of claim 2, wherein,

the first controller is specifically configured to:

comparing the magnitudes of the DRV and the reference voltage, the magnitudes of the drain voltage and the first threshold voltage, and the magnitudes of the drain voltage and the second threshold voltage; the first threshold voltage is less than the second threshold voltage;

if DRV is larger than the reference voltage, drain voltage is larger than the first threshold voltage and smaller than the second threshold voltage, controlling the pull-down current source circuit to be closed;

and if the DRV is smaller than or equal to the reference voltage and the drain voltage is larger than the second threshold voltage, controlling the pull-down current source circuit to be disconnected.

4. The synchronous rectification control circuit of claim 3, wherein said first controller comprises:

the reverse input end of the first comparator is used for inputting the DRV, and the forward input end of the first comparator is used for inputting the reference voltage;

the positive input end of the second comparator is used for inputting the first threshold voltage, and the negative input end of the second comparator is used for inputting the drain voltage;

the first input end of the NOR gate is connected with the output end of the first comparator, and the second input end of the NOR gate is connected with the output end of the second comparator;

the positive input end of the third comparator is used for inputting the drain voltage, and the negative input end of the third comparator is used for inputting the second threshold voltage;

the input end of the inverter is connected with the output end of the third comparator;

a first switch;

the first input end of the NAND gate is connected with the output end of the NAND gate, and the second input end of the NAND gate is connected with the output end of the inverter; the output end of the NAND gate is used for outputting a control signal for controlling the first switch.

5. The synchronous rectification control circuit of claim 1, wherein,

the second control circuit is specifically configured to:

if DRV is greater than or equal to a third threshold voltage and the drain voltage is greater than or equal to a second threshold voltage, controlling the controlled circuit to be conducted;

and if the DRV is smaller than a third threshold voltage and the drain voltage is larger than or equal to the second threshold voltage, controlling the controlled circuit to be disconnected.

6. The synchronous rectification control circuit according to claim 5, wherein said second control circuit comprises:

a fourth comparator, wherein a forward input end of the fourth comparator is used for inputting the DRV, and a reverse input end of the fourth comparator is used for inputting the third threshold voltage;

the control end of the second switch is connected with the output end of the fourth comparator, and the second switch is used for opening or closing the controlled circuit;

and the positive input end of the amplifier is used for inputting the drain voltage, the negative input end of the amplifier is used for inputting the second threshold voltage, and the output end of the amplifier is connected with the discharge circuit.

7. A DRV regulation circuit, characterized in that it is applied in the synchronous rectification control circuit as claimed in any one of claims 1-6,

the DRV adjusting circuit is connected with the MOSFET and used for reducing the grid driving voltage before the MOSFET is turned off;

the DRV adjustment circuit includes: the first control circuit, the second control circuit and N discharge circuits, wherein N is not less than 2; wherein:

when the DRV is higher than the reference voltage, the first control circuit is in a conducting state so as to reduce the voltage value of the DRV; when DRV is smaller than or equal to the reference voltage or the drain voltage of the MOSFET is larger than or equal to a second threshold voltage, the first control circuit is in an off state;

the N discharging circuits are connected with the MOSFET; any discharge circuit can discharge when being conducted so as to reduce the voltage value of the DRV; any discharge circuit is a normally-on discharge circuit or a controlled circuit controlled by the second control circuit;

the second control circuit is used for: and when the DRV is not reduced to the required target value VREG and is larger than a third threshold value, controlling the controlled circuit to be conducted, and when the DRV is smaller than or equal to the third threshold value, controlling the controlled circuit to be disconnected.

8. The synchronous rectification control circuit of claim 6, wherein said controlled circuit comprises a first NMOS transistor; the normally-on discharge circuit comprises a second NMOS tube;

the output end of the amplifier is respectively connected with the grid electrode of the first NMOS tube and the grid electrode of the second NMOS tube; the drain electrode of the first NMOS tube is connected with the grid electrode of the MOSFET through the second switch;

the drain electrode of the second NMOS tube is connected with the grid electrode of the MOSFET;

the sources and the substrates of the first NMOS tube and the second NMOS tube are grounded.

9. The synchronous rectification control circuit of claim 8, wherein said first NMOS transistor and said second NMOS transistor are different in parameter.

10. A switching power supply employing a synchronous rectification control circuit, comprising: the synchronous rectification control circuit of any one of claims 1 to 9, and a capacitor, a transformer, a positive interface, and a negative interface;

the capacitor is connected with the positive electrode interface and the negative electrode interface respectively, and is used for storing electric energy;

the negative electrode interface is grounded;

the positive electrode interface is connected with one end of the transformer; the other end of the transformer is connected with the drain end of the MOSFET; the source end of the MOSFET and the substrate are grounded;

the synchronous rectification control circuit is connected with the MOSFET.