Synchronous rectification control circuit, chip and electronic equipment

Abstract

The present application provides a synchronous rectification control circuit, chip and electronic device, the circuit includes: a threshold voltage adjustment circuit and a driving current control circuit; the threshold voltage adjustment circuit obtains the drain-source voltage of the synchronous rectifier in the current cycle, and compares it with the secondary turn-on threshold voltage of the current cycle to obtain a time interval, compares the time interval with a preset duration, and adjusts the secondary turn-on threshold voltage of the next cycle according to the comparison result, the time interval is the duration of the drain-source voltage of the current cycle being less than the secondary turn-on threshold voltage of the current cycle; the driving current control circuit obtains the difference between the drain-source voltage of the synchronous rectifier in the current cycle and the secondary turn-on threshold voltage of the current cycle, obtains a deviation voltage, and adjusts the driving current according to the deviation voltage. The secondary turn-on threshold voltage is adaptive to the change of the freewheeling current, and the driving current is adaptive to the size of the parasitic capacitance, so as to improve the efficiency of the synchronous rectification controller.

Description

Technical Field

[0001] The present application relates to the technical field of power management chips, and in particular to a synchronous rectification control circuit, chip and electronic equipment. Background Art

[0002] With the development of electronic technology, high efficiency and small size have become a trend. Under this trend, synchronous rectification technology is widely used in various switching power supply topologies. Synchronous rectification technology is a technology used to improve power conversion efficiency and is widely used in AC-DC (alternating current-direct current) converters and DC-DC (direct current-direct current) converters.

[0003] Traditional rectifiers usually use diodes for rectification. Since the forward voltage drop of the diode is usually around 0.7V, the power loss is significant in high-current application scenarios. In order to reduce losses, metal-oxide-semiconductor field-effect transistors (MOSFETs) are used to replace diodes in synchronous rectification technology. Since MOSFETs have low on-resistance, they can significantly reduce conduction losses, especially in low-voltage, high-current application scenarios, where the advantages are more obvious.

[0004] However, there are still some technical problems in the synchronous rectification technology. One of the problems is that when the freewheeling current in the secondary coil changes and the parasitic capacitance of the MOSFET is different, it is necessary to timely and reasonably adjust the drain-source voltage of the MOSFET to reduce the efficiency loss of the synchronous rectification controller. During the freewheeling process of the secondary coil, the smaller the drain-source voltage of the MOSFET, the smaller the power loss on the MOSFET, but the drain-source voltage of the MOSFET cannot be too small. When the drain-source voltage of the MOSFET is close to the maximum second turn-on threshold of the MOSFET, there is a possibility that the synchronous rectification MOSFET will be turned off incorrectly or cannot be turned off in time. Summary of the invention

[0005] The present application provides a synchronous rectification control circuit, chip and electronic device to improve the efficiency of the synchronous rectification controller. The specific technical solution is as follows:

[0006] In a first aspect, the present application provides a synchronous rectification control circuit, the synchronous rectification control circuit comprising: a threshold voltage adjustment circuit and a drive current control circuit;

[0007] The threshold voltage adjustment circuit is used to obtain the drain-source voltage of the synchronous rectifier in the current cycle, and compare the drain-source voltage with the secondary turn-on threshold voltage of the synchronous rectifier in the current cycle to obtain a time interval, compare the time interval with a preset duration, and adjust the secondary turn-on threshold voltage of the synchronous rectifier in the next cycle according to the comparison result, wherein the time interval is the duration of the drain-source voltage of the synchronous rectifier in the current cycle being less than the secondary turn-on threshold voltage of the current cycle;

[0008] The driving current control circuit is used to obtain the difference between the drain-source voltage of the synchronous rectifier in the current cycle and the secondary turn-on threshold voltage in the current cycle, obtain a deviation voltage, and adjust the driving current of the synchronous rectifier according to the deviation voltage, wherein the driving current is the driving current input to the control end of the synchronous rectifier when the synchronous rectifier is turned on for the second time.

[0009] In a possible design, the preset duration includes a first preset duration and a second preset duration;

[0010] The comparing the time interval with the preset duration, and adjusting the secondary turn-on threshold voltage of the synchronous rectifier in the next cycle according to the comparison result, comprises:

[0011] When the time interval is greater than the first preset time length, adjusting the secondary turn-on threshold voltage of the synchronous rectifier tube in the next cycle to the first threshold voltage;

[0012] When the time interval is less than the second preset time length, adjusting the secondary turn-on threshold voltage of the synchronous rectifier tube in the next cycle to the second threshold voltage;

[0013] When the time interval is less than the first preset time length and greater than the second preset time length, adjusting the secondary turn-on threshold voltage of the synchronous rectifier in the next cycle to a third threshold voltage;

[0014] The absolute value of the first threshold voltage is smaller than the absolute value of the third threshold voltage, the absolute value of the third threshold voltage is smaller than the absolute value of the second threshold voltage, and the absolute value of the third threshold voltage is proportional to the time interval.

[0015] In a possible design, the driving current control circuit includes: a current generating circuit, a current mirror circuit and a driving current generating circuit; the current mirror circuit is electrically connected to the current generating circuit and the driving current generating circuit respectively;

[0016] The current generating circuit is used to obtain a first current according to the deviation voltage, and transmit the first current to the current mirror circuit;

[0017] The current mirror circuit is used to obtain a second current according to the first current, and transmit the second current to the drive current generating circuit;

[0018] The driving current generating circuit is used to generate the driving current according to the second current.

[0019] In a possible design, the current generating circuit includes: an operational amplifier, a first switch tube and a first resistor;

[0020] The non-inverting input terminal of the operational amplifier is used to access the deviation voltage, the inverting input terminal of the operational amplifier is electrically connected to the second terminal of the first switch tube and the first terminal of the first resistor respectively, and the output terminal of the operational amplifier is electrically connected to the control terminal of the first switch tube;

[0021] The first end of the first switch tube is electrically connected to the current mirror circuit;

[0022] A second end of the first resistor is grounded.

[0023] In one possible design, the current mirror circuit includes a current mirror;

[0024] The first end of the current mirror is electrically connected to the first end of the first switch tube, and the second end of the current mirror is electrically connected to the input end of the drive current generating circuit.

[0025] In one possible design, the driving current generating circuit includes: a constant current source;

[0026] The output end of the constant current source is electrically connected to the input end of the drive current generating circuit. The output end of the drive current generating circuit serves as the output end of the drive current control circuit and is electrically connected to the control end of the synchronous rectifier.

[0027] In a possible design, the synchronous rectifier is an N-type MOSFET.

[0028] In one possible design, when the drain-source voltage is less than the secondary turn-on threshold voltage of the synchronous rectifier in the current cycle, the drive current is output; when the drain-source voltage is greater than the secondary turn-on threshold voltage of the synchronous rectifier in the current cycle, the drive current is zero.

[0029] In a second aspect, the present application provides a chip, comprising: the synchronous rectification control circuit of the above-mentioned first aspect.

[0030] In a third aspect, the present application provides an electronic device, comprising: the chip of the second aspect above.

[0031] Beneficial effects of the embodiments of the present application:

[0032] In the embodiment of the present application, the threshold voltage adjustment circuit adjusts the secondary turn-on threshold voltage of the synchronous rectifier in the next cycle according to the duration of the drain-source voltage of the synchronous rectifier in the current cycle being less than the secondary turn-on threshold voltage of the current cycle, so that the secondary turn-on threshold voltage is adaptive to the change of the freewheeling current in the secondary coil, thereby improving the efficiency of the synchronous rectifier controller. At the same time, the drive current control circuit adjusts the drive current according to the deviation voltage, so that the drive current is adaptive to the size of the parasitic capacitance on different synchronous rectifiers, thereby improving the efficiency of the synchronous rectifier controller, and ultimately achieving the purpose of improving the efficiency of the synchronous rectifier controller. In addition, by adjusting the secondary turn-on threshold voltage and the drive current, the drain-source voltage is maintained at a reasonable level, which can improve the efficiency of the synchronous rectifier controller while improving the situation where the synchronous rectifier is over-turned due to the presence of noise.

[0033] The beneficial effects provided in the above-mentioned second aspect and various possible designs of the above-mentioned second aspect can refer to the beneficial effects brought about by the above-mentioned first aspect and various possible implementation methods of the first aspect, and will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0035] Figure 1 A schematic diagram of a synchronous rectification circuit structure of an LLC converter provided in the related art;

[0036] Figure 2 A signal timing diagram of a synchronous rectification circuit of an LLC converter provided in the related art;

[0037] Figure 3 A synchronous rectification control circuit provided in an embodiment of the present application;

[0038] Figure 4 A logic control diagram of a threshold voltage adjustment circuit provided in an embodiment of the present application;

[0039] Figure 5 A relationship diagram between a secondary turn-on threshold voltage Vth2 and a duration △t provided in an embodiment of the present application;

[0040] Figure 6 A driving current control circuit provided in an embodiment of the present application;

[0041] Figure 7 A signal timing diagram provided in an embodiment of the present application when the parasitic capacitance Ciss is small;

[0042] Figure 8 A signal timing diagram provided in an embodiment of the present application when the parasitic capacitance Ciss is large. DETAILED DESCRIPTION

[0043] In this application, "at least one" means one or more, and "plurality" means two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone, where A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, at least one of a, b, or c alone can represent: a, b, c, a and b, a and c, or a, b, and c, where a, b, and c can be single or multiple. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0044] The directions or positional relationships indicated by terms such as "center", "longitudinal", "lateral", "up", "down", "left", "right", "front", and "back" are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present application and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present application.

[0045] The terms "connected" and "connected" should be understood in a broad sense. For example, the "connected" or "connected" of a circuit structure can refer to not only physical connection, but also electrical connection or signal connection. For example, it can be directly connected, that is, physically connected, or indirectly connected through at least one intermediate element, as long as the circuit is connected, or it can be the internal connection of two elements; signal connection can refer to signal connection through a circuit or through a media medium, such as radio waves. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0046] For LLC converters, see Figure 1 , Figure 1 As shown in the schematic diagram of the synchronous rectification circuit structure of an LLC converter provided in the related art, Figure 1 as shown in the figure, the figure includes two channels. For the convenience of explanation, the freewheeling current in Channel 1 is denoted as Isec1, and the freewheeling current in Channel 2 is denoted as Isec2. Without distinguishing the channels, the freewheeling current in the secondary coil can be collectively referred to as Isec. Taking Channel 1 as an example, within one cycle, when the freewheeling current Isec1 in the secondary coil starts to freewheel, the synchronous rectification MOSFET (i.e., Q1) has not yet conducted. At this time, Isec1 starts to freewheel through the body diode of the MOSFET (i.e., Q1). Usually, within one cycle, the conduction of the synchronous rectification MOSFET includes two turn-on processes. Refer to Figure 2 , Figure 2 As shown in the signal timing diagram of the synchronous rectification circuit of an LLC converter provided in the related art, Figure 2 as shown in the figure, at time T1, when the drain-source voltage V_ds is less than the first turn-on threshold Vth_1 (Vth_1 < 0), refer to Figure 1 and Figure 2 , the synchronous rectification controller outputs a current Isource_1 through the pin DRV1 to charge the parasitic capacitance of the control terminal (i.e., the Gate terminal) of the MOSFET (i.e., Q1). The voltage VG_1 at the Gate terminal starts to gradually increase, causing the MOSFET (i.e., Q1) to conduct. After that, the turn-on threshold of the MOSFET (i.e., Q1) switches to the second turn-on threshold Vth_2 (Vth_1 < Vth_2 < 0). At time T2, when the drain-source voltage V_ds is greater than the second turn-on threshold Vth_2, the synchronous rectification controller outputs a current Isource_1 of 0 through the pin DRV1, and the voltage VG_1 at the Gate terminal no longer increases; at time T3, when the drain-source voltage V_ds is less than the second turn-on threshold Vth_2 again, the current Isource_1 output by the pin DRV1 is not 0, and the voltage VG_1 at the Gate terminal continues to increase, reducing the conduction impedance of the MOSFET. Usually, the first turn-on threshold Vth_1 is less than the second turn-on threshold Vth_2.

[0047] Refer to Figure 2In the prior art, for the LLC converter, the synchronous rectification controller usually sets the second turn-on threshold Vth_2 of the MOSFET to a fixed value within one cycle. When the second turn-on threshold Vth_2 is a fixed value, when the freewheeling current Isec in the secondary coil is large and lasts for a long time, the on-resistance of the MOSFET may be large, so that the absolute value |V_ds| of the drain-source voltage V_ds is large. When the duration is long, it will affect the working efficiency of the synchronous rectification controller, resulting in a decrease in the efficiency of the synchronous rectification controller. In addition, at time T3-T4, when the drain-source voltage V_ds is less than the second turn-on threshold Vth_2 again, the output current Isource_1 of the pin DRV1 is not 0. In the prior art, the current Isource_1 for charging the Gate terminal of the MOSFET for the second time is usually set to a fixed value Iconst_1. When the parasitic capacitance of the MOSFET (i.e. Figure 1 When the Cgd+Cgs in the gate is small, under normal circumstances, the drain-source voltage V_ds is greater than the second turn-on threshold Vth_2. If there is noise during the secondary coil freewheeling process, the drain-source voltage V_ds will be less than the second turn-on threshold Vth_2, resulting in false triggering. At this time, when the MOSFET is turned on for the second time, the pin DRV output current Isource_1 will charge the Gate end of the MOSFET, so that the voltage VG_1 at the Gate end is charged very high, and the absolute value of the drain-source voltage V_ds |V_ds| drops rapidly. When the noise disappears, since the voltage VG_1 at the Gate end is charged very high, it will be very slow to reduce the voltage VG_1 at the Gate end, which will affect the working efficiency of the synchronous rectifier controller and reduce the efficiency of the synchronous rectifier controller. When the parasitic capacitance of the MOSFET (i.e. Figure 1 When Cgd+Cgs) in the synchronous rectifier is large, since the current Isource_1 is a fixed value Iconst_1, when the drain-source voltage V_ds is less than the second turn-on threshold Vth_2, it is difficult to quickly increase the voltage VG_1 at the Gate end, which will affect the working efficiency of the synchronous rectifier controller and reduce the efficiency of the synchronous rectifier controller.

[0048] In the prior art, when the second turn-on threshold Vth_2 and the current Isource_1 for charging the Gate terminal of the MOSFET for the second time are fixed values, when the freewheeling current in the secondary coil changes or the parasitic capacitance of the MOSFET changes, the efficiency of the synchronous rectification controller will be reduced.

[0049] In order to improve the efficiency of a synchronous rectification controller, an embodiment of the present application provides a synchronous rectification control circuit, a chip and an electronic device.

[0050] The synchronous rectification control circuit may be a chip or a circuit module.

[0051] Among them, the chip may include a synchronous rectification control circuit.

[0052] In this application, electronic devices may include, but are not limited to: adapters, chargers, tablet computers, smart home devices, vehicles, and wearable devices.

[0053] See also Figure 3 , Figure 3 A synchronous rectification control circuit 1000 provided in an embodiment of the present application is as follows: Figure 3 As shown, the synchronous rectification control circuit 1000 may include: a threshold voltage adjustment circuit 100 and a drive current control circuit 200 .

[0054] The threshold voltage adjustment circuit 100 is used to obtain the drain-source voltage of the synchronous rectifier in the current cycle, and compare the drain-source voltage with the secondary turn-on threshold voltage of the synchronous rectifier in the current cycle to obtain a time interval, compare the time interval with a preset duration, and adjust the secondary turn-on threshold voltage of the synchronous rectifier in the next cycle according to the comparison result, wherein the time interval is the duration that the drain-source voltage of the synchronous rectifier in the current cycle is less than the secondary turn-on threshold voltage of the current cycle.

[0055] The driving current control circuit 200 is used to obtain the difference between the drain-source voltage of the synchronous rectifier in the current cycle and the secondary turn-on threshold voltage of the current cycle, obtain the deviation voltage, and adjust the driving current of the synchronous rectifier according to the deviation voltage, wherein the driving current is the driving current input to its control end when the synchronous rectifier is turned on for the second time.

[0056] The synchronous rectification controller may include a sampling pin VD and a control pin DRV, wherein the sampling pin VD is used to collect the voltage of the drain and source of the MOSFET to obtain the drain-source voltage Vds; the control pin DRV is electrically connected to the control end (i.e., the gate Gate) of the synchronous rectifier MOSFET, and is used to charge the gate Gate, thereby controlling the switching state of the synchronous rectifier MOSFET. The function of the synchronous rectification controller is to control the synchronous rectifier MOSFET according to the drain-source voltage Vds. The synchronous rectification control circuit in the present application is applied to the synchronous rectification controller, and is used to control the synchronous rectifier according to the drain-source voltage.

[0057] In the present application, the synchronous rectifier can be a metal-oxide semiconductor field effect transistor (MOSFET), a gallium nitride transistor (GAN), or a silicon carbide transistor (SiC), and the embodiments of the present application do not specifically limit this.

[0058] In the present application, the secondary turn-on threshold voltage of the synchronous rectifier tube when it is turned on for the second time in a cycle is adjusted. According to the drain-source voltage of the synchronous rectifier tube in the current cycle and the secondary turn-on threshold voltage of the current cycle, the secondary turn-on threshold voltage of the next cycle is modulated so that the secondary turn-on threshold voltage is a variable voltage value. In one example, for the first cycle, the drain-source voltage of the first cycle and the secondary turn-on threshold voltage of the first cycle are obtained. The secondary turn-on threshold voltage of the first cycle is usually set according to design requirements, for example, the secondary turn-on threshold voltage Vth2 of the first cycle is -50mV; according to the drain-source voltage of the first cycle and the secondary turn-on threshold voltage of the first cycle, the secondary turn-on threshold voltage Vth2 of the second cycle is obtained, for example, the secondary turn-on threshold voltage Vth2 of the second cycle is -30mV; according to the drain-source voltage of the second cycle and the secondary turn-on threshold voltage of the second cycle, at this time, the secondary turn-on threshold voltage Vth2 of the second cycle is -30mV, and the secondary turn-on threshold voltage Vth2 of the third cycle is obtained, for example, the secondary turn-on threshold voltage Vth2 of the third cycle is -70mV; and so on. In the present application, in addition to the secondary turn-on threshold voltage of the first cycle being usually set according to design requirements, the secondary turn-on threshold voltage of the next cycle is calculated based on the secondary turn-on threshold voltage of the previous cycle.

[0059] Specifically, the drain-source voltage Vds of the synchronous rectifier in the current cycle is obtained through the threshold voltage adjustment circuit, and the drain-source voltage Vds is compared with the secondary turn-on threshold voltage Vth2 of the current cycle, and the duration of the drain-source voltage Vds of the current cycle being less than the secondary turn-on threshold voltage Vth2 of the current cycle is calculated, that is, the time interval △t is obtained, and the time interval △t is compared with the preset duration, and according to the comparison result, the secondary turn-on threshold voltage Vth2 of the next cycle is adjusted.

[0060] The preset duration can be set according to design needs.

[0061] The threshold voltage adjustment circuit adjusts the secondary turn-on threshold voltage Vth2 of the next cycle according to the duration of the drain-source voltage Vds of the current cycle being less than the secondary turn-on threshold voltage Vth2 of the current cycle, so that the secondary turn-on threshold voltage is a variable voltage value. The loss on the synchronous rectifier MOSFET can be obtained according to the duration of the drain-source voltage Vds of the current cycle being less than the secondary turn-on threshold voltage Vth2 of the current cycle. When the freewheeling current Isec in the secondary coil changes, causing the loss on the synchronous rectifier MOSFET to increase, by adjusting the secondary turn-on threshold voltage Vth2, the secondary turn-on threshold voltage Vth2 is adapted to the change of the freewheeling current Isec in the secondary coil, so that the loss on the synchronous rectifier MOSFET is controlled, thereby achieving the purpose of improving the efficiency of the synchronous rectifier controller.

[0062] The drive current control circuit obtains the difference between the drain-source voltage Vds of the synchronous rectifier in the current cycle and the secondary turn-on threshold voltage Vth2 of the current cycle, and obtains the deviation voltage |Vds-Vth2|. The drive current Isource is adjusted according to the deviation voltage |Vds-Vth2| so that the drive current Isource output from the pin DRV adapts to the size of the parasitic capacitance on the synchronous rectifier MOSFET.

[0063] The driving current Isource is adjusted according to the deviation voltage |Vds-Vth2|, so that the driving current Isource adapts to the size of the parasitic capacitance on different synchronous rectifier MOSFETs, which affects the charging speed of the voltage VG at the Gate end of the synchronous rectifier MOSFET, so that the voltage VG at the Gate end can change quickly, thereby achieving the purpose of improving the efficiency of the synchronous rectification controller.

[0064] In the embodiment of the present application, the threshold voltage adjustment circuit is used to adjust the secondary turn-on threshold voltage Vth2 of the synchronous rectifier in the next cycle according to the duration of the drain-source voltage Vds of the synchronous rectifier in the current cycle being less than the secondary turn-on threshold voltage Vth2 of the current cycle, so that the secondary turn-on threshold voltage Vth2 is adaptive to the change of the freewheeling current Isec in the secondary coil, thereby improving the efficiency of the synchronous rectifier controller. At the same time, the drive current control circuit is used to adjust the drive current Isource according to the deviation voltage |Vds-Vth2|, so that the drive current Isource is adaptive to the size of the parasitic capacitance on the MOSFET of different synchronous rectifiers, thereby improving the efficiency of the synchronous rectifier controller, and finally achieving the purpose of improving the efficiency of the synchronous rectifier controller. In addition, by adjusting the secondary turn-on threshold voltage Vth2 and the drive current Isource, the drain-source voltage Vds is maintained at a reasonable level, and while improving the efficiency of the synchronous rectifier controller, the situation where the synchronous rectifier is over-turned due to the presence of noise can also be improved.

[0065] In a possible embodiment, the preset duration includes a first preset duration tmax and a second preset duration tmin.

[0066] Compare the time interval with a preset duration, and adjust the secondary turn-on threshold voltage for the next cycle according to the comparison result, including: when the time interval △t is greater than the first preset duration tmax, adjust the secondary turn-on threshold voltage Vth2 of the synchronous rectifier tube for the next cycle to the first threshold voltage Vth2max; when the time interval △t is less than the second preset duration tmin, adjust the secondary turn-on threshold voltage Vth2 of the synchronous rectifier tube for the next cycle to the second threshold voltage Vth2min; when the time interval △t is less than the first preset duration tmax and greater than the second preset duration tmin, adjust the secondary turn-on threshold voltage Vth2 of the synchronous rectifier tube for the next cycle to the third threshold voltage Vth2mid; wherein, the absolute value |Vth2max| of the first threshold voltage is less than the absolute value |Vth2mid| of the third threshold voltage, the absolute value |Vth2mid| of the third threshold voltage is less than the absolute value |Vth2min| of the second threshold voltage, and the absolute value |Vth2mid| of the third threshold voltage is proportional to the time interval △t.

[0067] The first preset duration and the second preset duration can be set according to design requirements, and the first threshold voltage, the second threshold voltage, and the third threshold voltage can be set according to design requirements.

[0068] See Figure 4 , Figure 4 is the logic control diagram of a threshold voltage adjustment circuit provided by an embodiment of the present application. As Figure 4 shown, detect the duration △t when the drain-source voltage Vds in the current cycle is less than the secondary turn-on threshold voltage Vth2 in the current cycle. If △t > tmax, then Vth2 for the next cycle = Vth2max; if △t < tmin, then Vth2 for the next cycle = Vth2min; if tmax > △t > tmin, then Vth2 for the next cycle ∝ △t (that is, |Vth2mid| is proportional to the time interval △t).

[0069] See Figure 5 , Figure 5 is the relationship diagram between the secondary turn-on threshold voltage Vth2 and the duration △t provided by an embodiment of the present application. As Figure 5 shown, the time interval △t = t4 - t3. The third threshold voltage Vth2mid is a function proportional to △t. Figure 5In the process, according to the duration △t that the drain-source voltage Vds of the current cycle is less than the secondary turn-on threshold voltage Vth2 of the current cycle, the secondary turn-on threshold voltage of the next cycle is adjusted. When the duration △t is too long, |Vth2| is reduced. When the duration △t is too short, |Vth2| is increased, so that the distance between the drain-source voltage Vds of the next cycle and the secondary turn-on threshold voltage Vth2 changes, so that the secondary turn-on threshold voltage Vth2 adapts to the change of the freewheeling current Isec in the secondary coil, thereby improving the efficiency of the synchronous rectification controller.

[0070] In one possible embodiment, see Figure 6 , Figure 6 A driving current control circuit provided in an embodiment of the present application is as follows: Figure 6 As shown, the driving current control circuit 200 includes: a current generating circuit 201, a current mirror circuit 202 and a driving current generating circuit 203; the current mirror circuit 202 is electrically connected to the current generating circuit 201 and the driving current generating circuit 203 respectively.

[0071] The current generating circuit 201 is used for obtaining a first current Id1 according to the deviation voltage |Vds−Vth2|, and transmitting the first current Id1 to the current mirror circuit 202 .

[0072] The current mirror circuit 202 is used for obtaining the second current Id2 according to the first current Id1 , and transmitting the second current Id2 to the driving current generating circuit 203 .

[0073] The driving current generating circuit 203 is used to generate the driving current Isource according to the second current Id2.

[0074] In one possible embodiment, see Figure 6 The current generating circuit 201 includes: an operational amplifier EA, a first switch tube M1 and a first resistor R1.

[0075] The non-inverting input terminal of the operational amplifier EA is used to access the deviation voltage |Vds-Vth2|, the inverting input terminal of the operational amplifier EA is electrically connected to the second end of the first switch tube M1 and the first end of the first resistor R1 respectively, and the output terminal of the operational amplifier EA is electrically connected to the control terminal of the first switch tube M1.

[0076] A first terminal of the first switch tube M1 is electrically connected to the current mirror circuit 202 .

[0077] A second end of the first resistor R1 is grounded.

[0078] In a possible embodiment, the type of the first switch tube M1 can be any one of a gallium nitride transistor, a bipolar junction transistor, an insulated gate bipolar transistor, a metal-oxide-semiconductor field effect transistor, a field-controlled thyristor, a gate turn-off thyristor, and a transmission gate. This application does not make any specific limitation on this.

[0079] In one example, when the first switch tube M1 is a bipolar transistor, the control end of the first switch tube M1 refers to the base of the bipolar transistor, the first end of the first switch tube M1 can be the collector or emitter of the bipolar transistor, and correspondingly, the second end of the first switch tube M1 can be the emitter or collector of the bipolar transistor; when the first switch tube M1 is a metal-oxide-semiconductor field-effect transistor, the control end of the first switch tube M1 refers to the gate of the metal-oxide-semiconductor field-effect transistor, the first end of the first switch tube M1 can be the drain or source of the metal-oxide-semiconductor field-effect transistor, and correspondingly, the second end of the first switch tube M1 can be the source or drain of the metal-oxide-semiconductor field-effect transistor.

[0080] For example, when the first switch tube M1 is an N-type MOSFET, the control end of the first switch tube M1 refers to the gate of the N-type MOSFET, the first end of the first switch tube M1 refers to the drain of the N-type MOSFET, and the second end of the first switch tube M1 refers to the source of the N-type MOSFET.

[0081] In one possible embodiment, see Figure 6 , the current mirror circuit 202 includes a current mirror CurrentMirror;

[0082] A first end of the current mirror Current Mirror is electrically connected to a first end of the first switch tube M1 , and a second end of the current mirror Current Mirror is electrically connected to an input end of the driving current generating circuit 203 .

[0083] In one possible embodiment, see Figure 6 , the driving current generating circuit 203 comprises: a constant current source;

[0084] The output end of the constant current source is electrically connected to the input end of the driving current generating circuit 203 . The output end of the driving current generating circuit 203 serves as the output end of the driving current control circuit and is electrically connected to the control end Gate of the synchronous rectifier MOSFET.

[0085] See also Figure 6, the specific working principle of the driving current control circuit in the present application is: the deviation between the drain-source voltage Vds and the secondary turn-on threshold voltage Vth2, that is, the deviation voltage |Vds-Vth2|, is processed by the operational amplifier EA, so that the first current Id1=|Vds-Vth2| / R1. The second current Id2 is the current mirror of the first current Id1 through the current mirror circuit, and Id is the fixed current output by the constant current source. The driving current Isource=Id+Id2 at the Gate end after the synchronous rectifier MOSFET is turned on for the second time. The driving current Isource is proportional to |Vds-Vth2| and is no longer a current with a fixed current value. When the parasitic capacitance Ciss (i.e., Cgd+Cgs) is small, the voltage VG at the Gate end is easy to charge high, but because |Vds| is small at this time, |Vds-Vth2| is also small, the driving current Isource will decrease year-on-year, thereby reducing the voltage VG at the Gate end, so that the drain-source voltage Vds remains at a reasonable level. When the parasitic capacitance Ciss (i.e., Cgd+Cgs) is large, the voltage VG at the Gate end rises slowly, but since |Vds| is large at this time, |Vds-Vth2| is also large, the drive current Isource will increase proportionally, thereby increasing the voltage VG at the Gate end, thereby reducing |Vds| and reducing the power loss on the synchronous rectifier MOSFET. That is, the drive current Isource is proportional to the amount by which Vds deviates from Vth2, and adapts to the differences caused by different parasitic capacitances Ciss corresponding to different synchronous rectifier MOSFETs.

[0086] See also Figure 7 , Figure 7 A signal timing diagram when the parasitic capacitance Ciss is small is provided in an embodiment of the present application, such as Figure 7 As shown, the technical solution of the present application adds a driving current control circuit. When the parasitic capacitance Ciss (i.e., Cgd+Cgs) is small, the driving current in the prior art is a fixed value Iconst (i.e., constant current), and the voltage VG at the Gate end is easily charged high. The driving current Isource in the present application adapts to the change of the parasitic capacitance Ciss. When the parasitic capacitance Ciss is small, the driving current Isource will decrease year-on-year, thereby reducing the voltage VG at the Gate end. Therefore, the voltage VG at the Gate end in the present application is lower than the voltage VG at the Gate end in the prior art.

[0087] See also Figure 8 , Figure 8 A signal timing diagram when the parasitic capacitance Ciss is large is provided in an embodiment of the present application, such as Figure 8As shown, the technical solution of the present application adds a driving current control circuit. When the parasitic capacitance Ciss (i.e., Cgd+Cgs) is large, the driving current in the prior art is a fixed value Iconst (i.e., constant current), and the voltage VG at the Gate end rises slowly. The driving current Isource in the present application adapts to the change of the parasitic capacitance Ciss. When the parasitic capacitance Ciss is large, the driving current Isource will increase proportionally, thereby increasing the voltage VG at the Gate end. Therefore, the voltage VG at the Gate end in the present application is higher than the voltage VG at the Gate end in the prior art.

[0088] In a possible embodiment, the synchronous rectifier is an N-type MOSFET.

[0089] Since the on-resistance of N-type MOSFET is small, N-type MOSFET is usually used as the synchronous rectifier.

[0090] In a possible embodiment, when the drain-source voltage is less than the secondary turn-on threshold voltage of the synchronous rectifier in the current cycle, the drive current is output; when the drain-source voltage is greater than the secondary turn-on threshold voltage of the synchronous rectifier in the current cycle, the drive current is zero.

[0091] When the MOSFET is turned on for the second time, when the drain-source voltage Vds is less than the secondary turn-on threshold voltage Vth2 of the current cycle, the control pin DRV outputs a driving current; when the drain-source voltage Vds is greater than the secondary turn-on threshold voltage Vth2 of the current cycle, the driving current output by the control pin DRV is zero.

[0092] An embodiment of the present application also provides a chip, which includes: the above-mentioned synchronous rectification control circuit.

[0093] An embodiment of the present application also provides an electronic device, which includes: the above-mentioned chip.

[0094] Finally, it should be noted that the above embodiments are only specific implementation methods of the present application, but the protection scope of the present application is not limited thereto, and any changes or substitutions within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A synchronous rectification control circuit, characterized in that: The synchronous rectification control circuit comprises: a threshold voltage adjustment circuit and a drive current control circuit; The threshold voltage adjustment circuit is used to obtain the drain-source voltage of the synchronous rectifier in the current cycle, and compare the drain-source voltage with the secondary turn-on threshold voltage of the synchronous rectifier in the current cycle to obtain a time interval, compare the time interval with a preset duration, and adjust the secondary turn-on threshold voltage of the synchronous rectifier in the next cycle according to the comparison result, wherein the time interval is the duration of the drain-source voltage of the synchronous rectifier in the current cycle being less than the secondary turn-on threshold voltage of the current cycle; The driving current control circuit is used to obtain the difference between the drain-source voltage of the synchronous rectifier in the current cycle and the secondary turn-on threshold voltage of the current cycle, obtain a deviation voltage, and adjust the driving current of the synchronous rectifier according to the deviation voltage, wherein the driving current is the driving current input to the control end of the synchronous rectifier when the synchronous rectifier is turned on for the second time.

2. The synchronous rectification control circuit according to claim 1, characterized in that: The preset duration includes a first preset duration and a second preset duration; The comparing the time interval with the preset duration, and adjusting the secondary turn-on threshold voltage of the synchronous rectifier in the next cycle according to the comparison result, comprises: When the time interval is greater than the first preset time length, adjusting the secondary turn-on threshold voltage of the synchronous rectifier tube in the next cycle to the first threshold voltage; When the time interval is less than the second preset time length, adjusting the secondary turn-on threshold voltage of the synchronous rectifier tube in the next cycle to the second threshold voltage; When the time interval is less than the first preset time length and greater than the second preset time length, adjusting the secondary turn-on threshold voltage of the synchronous rectifier in the next cycle to a third threshold voltage; The absolute value of the first threshold voltage is smaller than the absolute value of the third threshold voltage, the absolute value of the third threshold voltage is smaller than the absolute value of the second threshold voltage, and the absolute value of the third threshold voltage is proportional to the time interval.

3. The synchronous rectification control circuit according to claim 1, characterized in that: The driving current control circuit comprises: a current generating circuit, a current mirror circuit and a driving current generating circuit; the current mirror circuit is electrically connected to the current generating circuit and the driving current generating circuit respectively; The current generating circuit is used to obtain a first current according to the deviation voltage, and transmit the first current to the current mirror circuit; The current mirror circuit is used to obtain a second current according to the first current, and transmit the second current to the drive current generating circuit; The driving current generating circuit is used to generate the driving current according to the second current.

4. The synchronous rectification control circuit according to claim 3, characterized in that: The current generating circuit comprises: an operational amplifier, a first switch tube and a first resistor; The non-inverting input terminal of the operational amplifier is used to access the deviation voltage, the inverting input terminal of the operational amplifier is electrically connected to the second terminal of the first switch tube and the first terminal of the first resistor respectively, and the output terminal of the operational amplifier is electrically connected to the control terminal of the first switch tube; The first end of the first switch tube is electrically connected to the current mirror circuit; A second end of the first resistor is grounded.

5. The synchronous rectification control circuit according to claim 4, characterized in that: The current mirror circuit comprises a current mirror; The first end of the current mirror is electrically connected to the first end of the first switch tube, and the second end of the current mirror is electrically connected to the input end of the drive current generating circuit.

6. The synchronous rectification control circuit according to claim 3, characterized in that: The driving current generating circuit comprises: a constant current source; The output end of the constant current source is electrically connected to the input end of the drive current generating circuit. The output end of the drive current generating circuit serves as the output end of the drive current control circuit and is electrically connected to the control end of the synchronous rectifier.

7. The synchronous rectification control circuit according to claim 1, characterized in that: The synchronous rectifier is an N-type MOSFET.

8. The synchronous rectification control circuit according to claim 1, characterized in that: When the drain-source voltage is less than the secondary turn-on threshold voltage of the synchronous rectifier in the current cycle, the drive current is output; when the drain-source voltage is greater than the secondary turn-on threshold voltage of the synchronous rectifier in the current cycle, the drive current is zero.

9. A chip, characterized in that: include: A synchronous rectification control circuit as described in any one of claims 1 to 8.

10. An electronic device, characterized in that: include: The chip as claimed in claim 9.

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