CN203911793U - Zero-cross detection circuit applied to switch power supply synchronous rectification converter - Google Patents

Abstract

The utility model provides a zero-cross detection circuit applied to a switch power supply synchronous rectification converter. The circuit comprises a working state control circuit, a detection signal conversion circuit and a detection signal comparison circuit. The working state control circuit receives a main switch MOS tube drive signal Vd and outputs a control signal Vcol to the detection signal conversion circuit. The detection signal conversion circuit receives a zero-cross detection point signal Vz and outputs a comparison signal Icop to the detection signal comparison circuit. Zero-cross of the detection point signal is judged by the detection signal comparison circuit, and a signal Vout is outputted to control connection and disconnection of a synchronous MOS tube. When the converter works in a discontinuous inductive current mode, the zero-cross state of inductive current is automatically detected by the zero-cross detection circuit, and the synchronous MOS tube is timely disconnected so that generation of a current backward flow phenomenon is prevented. With design of the structure of the zero-cross detection circuit, change of environment temperature and a manufacturing technology angle has extremely low influence on the output signal of the zero-cross detection circuit.

Description

A zero-crossing detection circuit applied to synchronous rectification converter of switching power supply

technical field

The utility model relates to the design of a synchronous rectification converter of a switching power supply, in particular to a current zero-crossing detection circuit of a synchronous rectification converter.

Background technique

In the design process of the converter, if it is an asynchronous structure, it is necessary to use a diode to realize freewheeling. The use of freewheeling diodes in non-synchronous converters is beneficial to higher voltage output and lower production costs. However, the freewheeling diode will generate more power consumption when the current is large, which is not conducive to the improvement of the efficiency of the converter. The synchronous rectification converter uses a power MOS tube instead of a freewheeling diode, and requires the gate voltage of the power MOS tube to be synchronized with the phase of the rectified voltage. The power MOS tube is called a synchronous MOS tube. Since the on-state resistance of the synchronous MOS tube is very low, the efficiency of the synchronous rectification converter is very high. However, when the synchronous rectification converter works in the inductor current discontinuous mode, if the synchronous MOS tube cannot be turned off in time when the inductor current is zero, the current backflow phenomenon will occur. Backflow of current will increase the power consumption of the converter and damage the components. Therefore, it is important to design a stable and accurate current zero-crossing detection circuit in the synchronous rectification converter.

Utility model content

The technical problem to be solved by the utility model is to provide a zero-crossing detection circuit applied to a synchronous rectification converter of a switching power supply.

The technical scheme of the utility model is as follows: it is applied to the zero-crossing detection circuit of the synchronous rectification converter of the switching power supply, which includes a working state control circuit, a detection signal conversion circuit and a detection signal comparison circuit. The working state control circuit receives the driving signal of the main switch MOS tube, and outputs the working state control signal to the detection signal conversion circuit. The detection signal conversion circuit receives the zero-crossing detection point signal, and outputs a comparison signal to the detection signal comparison circuit. The detection signal outputs the comparison result as a control signal to the gate of the synchronous MOS transistor.

Applied in the zero-crossing detection circuit of the synchronous rectification converter of the switching power supply, the working state control circuit includes the main switch MOS tube drive signal input terminal, the inverter, the 1st MOS tube and the 2nd MOS tube. Wherein, the main switch MOS tube driving signal input terminal is connected to the input terminal of the inverter, and is connected to the gate of the No. 2 MOS tube. The output end of the inverter is connected to the gate of the No. 1 MOS transistor, and the drain of the No. 1 MOS transistor is connected to the drain of the No. 2 MOS transistor. The source of the No. 2 MOS tube is grounded.

It is applied to a zero-crossing detection circuit of a synchronous rectification converter of a switching power supply, and the detection signal conversion circuit includes a zero-crossing detection point signal input terminal and MOS tubes 1 to 7. The zero-crossing detection point signal input terminal is connected to the source of the No. 1 MOS tube through the working state control circuit. The gate of the MOS transistor No. 1 is connected to the gate of the MOS transistor No. 2, and the drain of the MOS transistor No. 1 is connected to the drain of the MOS transistor No. 3. The source of the MOS transistor No. 2 is connected to the drain of the MOS transistor No. 6, and the drain of the MOS transistor No. 2 is connected to the drain of the MOS transistor No. 4. The source of the No. 3 MOS transistor is connected to the power supply, and the gate of the No. 3 MOS transistor is connected to the drain of the No. 5 MOS transistor. The gate of the MOS transistor No. 4 is connected to the gate of the MOS transistor No. 5, and the source of the MOS transistor No. 4 is connected to the power supply. The gate of the MOS transistor No. 5 is connected to the gate of the MOS transistor No. 3, and the source of the MOS transistor No. 5 is connected to the power supply. The gate of the No. 6 MOS transistor is connected to the power supply, and the source of the No. 6 MOS transistor is grounded. The gate of the MOS transistor No. 7 is connected to the drain of the MOS transistor No. 1, and the source of the MOS transistor No. 7 is connected to the source of the MOS transistor No. 2.

Applied in the zero-crossing detection circuit of the synchronous rectification converter of the switching power supply, the detection signal comparison circuit includes a synchronous MOS transistor control signal output terminal and MOS transistors No. 1 to No. 5. The gate of the MOS transistor No. 1 is connected to the gate of the MOS transistor No. 2, and the source of the MOS transistor No. 1 is connected to the power supply. The drain of the No. 1 MOS transistor is connected to the drain of the No. 7 MOS transistor in the detection signal conversion circuit. The source of the No. 2 MOS transistor is connected to the power supply, and the drain of the No. 2 MOS transistor is connected to the drain of the No. 3 MOS transistor. The gate of the MOS transistor No. 3 is connected to the drain of the MOS transistor No. 4, and the drain of the MOS transistor No. 3 is connected to the control signal output terminal of the synchronous MOS transistor. The gate of the MOS transistor No. 4 is connected to the gate of the MOS transistor No. 5, and the drain of the MOS transistor No. 4 is connected to the power supply. The drain of the No. 5 MOS transistor is connected to the gate of the No. 4 MOS transistor in the detection signal conversion circuit. The gate of the MOS transistor No. 5 is connected to the gate of the MOS transistor No. 3, and the source of the MOS transistor No. 5 is grounded.

The utility model is mainly used in the zero-crossing detection of the inductor current of the synchronous rectification converter of the switching power supply. When the converter works in the intermittent mode of the inductor current, the zero-crossing detection circuit will automatically detect the zero-crossing state of the inductor current and turn off the synchronous MOS tube to prevent the occurrence of current backflow phenomenon. Through the design of the zero-crossing detection circuit structure, the output signal is only determined by the parameters and bias current of the MOS tube in the circuit. Therefore, the change of the ambient temperature and the change of the manufacturing process angle have very little influence on the output signal of the utility model.

Description of drawings

Fig. 1 is a system structure block diagram of the present utility model;

Fig. 2 is the connection circuit diagram of the utility model in the switching power converter;

Fig. 3 is a structural circuit diagram of the utility model;

Fig. 4 is the relationship diagram of the output voltage and the detection point current of the utility model under different ambient temperatures;

Detailed ways

In order to facilitate the understanding of the utility model, the utility model will be described in more detail below in conjunction with the accompanying drawings and specific embodiments. The preferred embodiments of the utility model are given in the description and accompanying drawings, but the utility model can be realized in many different forms, and are not limited to the embodiments described in the specification. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present utility model more thorough and comprehensive.

It should be noted that when a certain element is fixed to another element, it includes directly fixing the element to the other element, or fixing the element to the other element through at least one other element in the middle. When an element is connected to another element, it includes directly connecting the element to the other element, or connecting the element to the other element through at least one intervening other element.

As shown in Figure 1, the zero-crossing detection circuit applied to the synchronous rectification converter of the switching power supply includes a working state control circuit, a detection signal conversion circuit and a detection signal comparison circuit. The working state control circuit receives the driving signal Vd of the main switch MOS tube, and outputs the control signal Vcol to the detection signal conversion circuit. The working state control circuit judges the working state of the converter, and determines whether the zero-crossing detection circuit is in a high-impedance state or a zero-crossing detection state. The detection signal conversion circuit receives the zero-crossing detection point signal Vz, and outputs a comparison signal Icop to the detection signal comparison circuit. The detection signal comparison circuit judges whether the detection point signal crosses zero, and outputs the signal Vout to control the opening and closing of the synchronous MOS tube.

As shown in FIG. 2 , the drain of the main switch MOS transistor M1 is connected to the power supply, and the source of the main switch MOS transistor is connected to port 1 of the inductor L1 . The drain of the synchronous MOS transistor M2 is connected to the No. 1 port of the inductor L1, and the source of the synchronous MOS transistor M2 is grounded. The positive output end of the MOS transistor drive circuit is connected to the gate of the main switch MOS transistor M1, and the inverting output end of the MOS transistor drive circuit is connected to the gate of the synchronous MOS transistor M2 through the input end of the AND gate AND. The zero-crossing detection point signal Vz receiving end of the zero-crossing detection circuit is connected to the No. 1 port of the inductor L1, and the main switch MOS tube driving signal Vd receiving port of the zero-crossing detection circuit is connected to the signal output end of the driving circuit. The signal Vout output port of the zero-crossing detection circuit is connected to the gate of the synchronous MOS transistor M2 through the lower input terminal of the AND gate AND. When the signal collected by the zero-crossing detection point signal Vz receiving end of the zero-crossing detection circuit is lower than the set threshold, the output signal Vout of the zero-crossing detection circuit is at low level, and the synchronous MOS transistor M2 is turned off. When the zero-crossing detection point signal is greater than the threshold, the output signal Vout of the zero-crossing detection circuit is at a high level, and the switching state of the synchronous MOS transistor M2 is controlled by the drive circuit.

As shown in FIG. 3 , the port Vd, the port Vz, the MOS transistor NT1 and the MOS transistor NT2 together constitute a working state control circuit. Among them, the port Vd receives the driving signal of the main switch MOS tube, and the port Vz receives the zero-crossing detection point signal. The port Vd is connected to the gate of the MOS transistor NT1 through an inverter, and the port Vd is connected to the gate of the MOS transistor NT2. The port Vz is connected to the source of the MOS transistor NT1. The drain of the MOS transistor NT1 is connected to the drain of the MOS transistor NT2, and the source of the MOS transistor NT2 is grounded. When the main switch MOS transistor is turned on, the port Vd receives a high-level signal, the MOS transistor NT1 is turned off, and the MOS transistor NT2 is turned on. Due to the disconnection of the MOS transistor NT1 and the conduction of the MOS transistor NT2, the detection point signal is isolated, and the zero-crossing detection circuit outputs a low level, which does not affect the normal operation of the converter.

The MOS transistors MS1 to MOS transistors MS7 together form a detection signal conversion circuit, wherein the port Vz is connected to the source of the MOS transistor MS5 through the working state control circuit. The gate of the MOS transistor MS5 is connected to the gate of the MOS transistor MS4, and the drain of the MOS transistor MS5 is connected to the drain of the MOS transistor MS3. The source of the MOS transistor MS4 is connected to the drain of the MOS transistor MS7, and the drain of the MOS transistor MS4 is connected to the drain of the MOS transistor MS2. The source of the MOS transistor MS3 is connected to the power supply, and the gate of the MOS transistor MS3 is connected to the drain of the MOS transistor MS1. The gate of the MOS transistor MS2 is connected to the gate of the MOS transistor MS1, and the source of the MOS transistor MS2 is connected to the power supply. The gate of the MOS transistor MS1 is connected to the gate of the MOS transistor MS3, and the source of the MOS transistor MS1 is connected to the power supply. The gate of the MOS transistor MS7 is connected to the power supply, and the source of the MOS transistor MS7 is grounded. The gate of the MOS transistor MS6 is connected to the drain of the MOS transistor MS5, and the source of the MOS transistor MS6 is connected to the source of the MOS transistor MS4. The detection signal conversion circuit converts the received detection point voltage signal into a corresponding proportional current signal, and outputs the comparison signal Icop to the detection signal comparison circuit for comparison with the set threshold, and then judges the working state of the converter.

The output port Vout and the MOS transistors ME1 to ME5 together form a detection signal comparison circuit, wherein the gate of the MOS transistor ME1 is connected to the gate of the MOS transistor ME2, and the source of the MOS transistor ME1 is connected to the power supply. The drain of the MOS transistor ME1 is connected to the drain of the MOS transistor MS6 in the detection signal conversion circuit. The source of the MOS transistor ME2 is connected to the power supply, and the drain of the MOS transistor ME2 is connected to the drain of the MOS transistor ME3. The gate of the MOS transistor ME3 is connected to the drain of the MOS transistor ME4, and the drain of the MOS transistor ME3 is connected to the signal output terminal Vout. The gate of the MOS transistor ME4 is connected to the gate of the MOS transistor ME5, and the drain of the MOS transistor ME4 is connected to the power supply. The drain of the MOS transistor ME5 is connected to the gate of the MOS transistor MS2 in the detection signal conversion circuit. The gate of the MOS transistor ME5 is connected to the gate of the MOS transistor ME3, and the source of the MOS transistor ME5 is grounded.

The threshold value of the detection signal comparison circuit is I(R _NT2 - 2R _NT1 )/R _M2 . Where R _NT1 is the on-state resistance of the MOS transistor NT1, R _NT2 is the on-state resistance of the MOS transistor NT2, R _M2 is the on-state resistance of the synchronous MOS transistor, and I is the current flowing through the drain and source of the MOS transistor. When the detection point signal is less than the threshold, the port Vout outputs a low level, and the synchronous MOS tube is turned off. When the detection point signal is greater than the threshold, the port Vout outputs a high level, and the synchronous MOS tube is controlled by the drive circuit.

As shown in Figure 4, the relationship between the output voltage Vout and the checkpoint current signal Icop of the zero-crossing detection circuit applied to the synchronous rectification converter of the switching power supply under different ambient temperatures. Wherein, the power supply voltage Vcc is 5V, and the driving signal Vd of the main switch MOS transistor is low level. Four temperature points were detected respectively, among which the detection temperature point of curve A was 150 degrees Celsius, the detection temperature point of curve B was 90 degrees Celsius, the detection temperature point of curve C was 35 degrees Celsius, and the detection temperature point of curve D was -50 . It can be seen from FIG. 4 that the average value of the current signal Icop at the detection point where the output voltage Vout reverses is 35.3mA. For different detection temperature points, the maximum relative error of the current signal Icop at the detection point where the output voltage Vout reverses is 0.5 mA. It can be seen that the structural design of the zero-crossing detection circuit applied to the synchronous rectification converter of the switching power supply makes the influence of the ambient temperature on the output voltage Vout very small.

Furthermore, the embodiments of the present utility model also include a zero-crossing detection circuit applied to a synchronous rectification converter of a switching power supply formed by combining the technical features of the above-mentioned embodiments.

It should be noted that the above-mentioned technical features continue to be combined with each other to form various embodiments not listed above, which are all regarded as the scope of the description of the utility model; Improvement or transformation, and all these improvements and transformations should belong to the protection scope of the appended claims of the present utility model.

Claims (7)

1. A zero-crossing detection circuit applied to a synchronous rectification converter of a switching power supply, is characterized in that it comprises an operating state control circuit, a detection signal conversion circuit and a detection signal comparison circuit; The working state control circuit receives the driving signal of the main switch MOS tube, and outputs the working state control signal to the detection signal conversion circuit; The detection signal conversion circuit receives the zero-crossing detection point signal, and outputs a comparison signal to the detection signal comparison circuit; The detection signal outputs the comparison result as a control signal to the gate of the synchronous MOS transistor. 2. The zero-crossing detection circuit applied to a synchronous rectification converter of a switching power supply according to claim 1, wherein the working state control circuit comprises a main switch MOS transistor drive signal input terminal, an inverter, a No. 1 MOS transistor and a No. 2 MOS transistor. No. MOS tube. 3. The zero-crossing detection circuit applied to the synchronous rectification converter of switching power supply according to claim 2, characterized in that, the main switch MOS tube drive signal input terminal is connected to the input terminal of the inverter, and is connected to the gate of No. 2 MOS tube pole; The output end of the inverter is connected to the gate of the MOS transistor No. 1, the drain of the MOS transistor No. 1 is connected to the drain of the MOS transistor No. 2; the source of the MOS transistor No. 2 is grounded. 4. The zero-crossing detection circuit applied to a synchronous rectification converter of a switching power supply according to claim 1, wherein the detection signal conversion circuit includes a zero-crossing detection point signal input terminal and MOS tubes 1 to 7. 5. The zero-crossing detection circuit applied to the synchronous rectification converter of the switching power supply according to claim 4, wherein the zero-crossing detection point signal input terminal is connected to the source of No. 1 MOS tube through the working state control circuit; The gate of the MOS transistor No. 1 is connected to the gate of the MOS transistor No. 2, and the drain of the MOS transistor No. 1 is connected to the drain of the MOS transistor No. 3; The source of the No. 2 MOS tube is connected to the drain of the No. 6 MOS tube, and the drain of the No. 2 MOS tube is connected to the drain of the No. 4 MOS tube; The source of No. 3 MOS tube is connected to the power supply, the gate of No. 3 MOS tube is connected to the drain of No. 5 MOS tube; the gate of No. 4 MOS tube is connected to the gate of No. 5 MOS tube, and the source of No. 4 MOS tube Connect the power supply; The gate of the No. 5 MOS tube is connected to the gate of the No. 3 MOS tube, the source of the No. 5 MOS tube is connected to the power supply; the gate of the No. 6 MOS tube is connected to the power supply, and the source of the No. 6 MOS tube is grounded; The gate of the MOS transistor No. 7 is connected to the drain of the MOS transistor No. 1, and the source of the MOS transistor No. 7 is connected to the source of the MOS transistor No. 2. 6. The zero-crossing detection circuit applied to a synchronous rectification converter of a switching power supply according to claim 1, wherein the detection signal comparison circuit comprises a synchronous MOS transistor control signal output terminal and MOS transistors No. 1 to No. 5. 7. the zero-crossing detection circuit that is applied to the synchronous rectification converter of switching power supply according to claim 6 is characterized in that, the grid of No. 1 MOS tube is connected with the grid of No. 2 MOS tube, and the source of No. 1 MOS tube is connected power supply; The drain of No. 1 MOS tube is connected to the drain of No. 7 MOS tube in the detection signal conversion circuit; The source of the No. 2 MOS tube is connected to the power supply, and the drain of the No. 2 MOS tube is connected to the drain of the No. 3 MOS tube; The gate of the MOS transistor No. 3 is connected to the drain of the MOS transistor No. 4, and the drain of the MOS transistor No. 3 is connected to the synchronous MOS transistor control signal output terminal; The gate of the No. 4 MOS transistor is connected to the gate of the No. 5 MOS transistor, and the drain of the No. 4 MOS transistor is connected to the power supply; The drain of the MOS transistor No. 5 is connected to the gate of the MOS transistor No. 4 in the detection signal conversion circuit; The gate of the MOS transistor No. 5 is connected to the gate of the MOS transistor No. 3, and the source of the MOS transistor No. 5 is grounded.