CN-115575700-A - Zero-crossing detection circuit

CN115575700ACN 115575700 ACN115575700 ACN 115575700ACN-115575700-A

Abstract

The invention provides a zero-crossing detection circuit which comprises a detection module, a narrow pulse width generation module and an output signal processing module. The detection module is used for outputting a zero-crossing trigger falling edge when the voltage of the detection point rises to reach a preset voltage; the narrow pulse width generation module is used for outputting a high-level pulse signal with a preset pulse width when receiving the zero-crossing trigger falling edge; the output signal processing module is used for executing operation based on a working state signal of an upper tube, an output signal of the detection module and an output signal of the narrow pulse width generation module; and outputting a control signal for turning off the lower tube when the upper tube is judged to be in a disconnected state based on the working state signal and the high-level pulse signal is received. Through the configuration, zero-crossing detection is realized, more accurate control information is provided for a subsequent control module or a control algorithm, and the problems of low efficiency or difficult starting of the system in the prior art are solved.

Inventors

LI RUIPING
XU JINLONG

Assignees

SHANGHAI XINLONG SEMICONDUCTOR TECH CO LTD

Dates

Publication Date: 20230106
Application Date: 20221109
Priority Date: 20221109

Claims (10)

1. A zero-crossing detection circuit is characterized by being used for a BUCK synchronous rectification circuit, wherein the BUCK synchronous rectification circuit comprises an upper tube, a lower tube, an energy storage inductor and a detection point, the connection point of the upper tube, the lower tube and the energy storage inductor is configured as the detection point, and the zero-crossing detection circuit comprises a detection module, a narrow pulse width generation module and an output signal processing module; the detection module is used for outputting a zero-crossing trigger falling edge when the voltage of the detection point rises to reach a preset voltage, and the absolute value of the difference value between the preset voltage and 0V is not more than 100mV; the narrow pulse width generation module is used for outputting a high-level pulse signal with a preset pulse width when the zero-crossing trigger falling edge is received; the output signal processing module is used for executing operation based on the working state signal of the upper tube, the output signal of the detection module and the output signal of the narrow pulse width generation module; and outputting a control signal for turning off the lower tube when the upper tube is judged to be in a disconnected state based on the working state signal and the high-level pulse signal is received.
2. A zero-crossing detection circuit as claimed in claim 1, wherein the detection module comprises a voltage detection unit for changing a voltage waveform of an output terminal of the voltage detection unit when a voltage rise at the detection point reaches a preset voltage; the voltage detection unit comprises a current mirror, a first triode, a second triode, a resistor and a first NMOS (N-channel metal oxide semiconductor) tube; the current mirror comprises a current mirror input end and two current mirror output ends, the current mirror input end is used for obtaining bias current, and current output proportion parameters of the two current mirror output ends are the same; the first triode and the second triode are both NPN triodes, one of the output ends of the two current mirrors is connected with the collector of the first triode, the other of the output ends of the two current mirrors is connected with the collector of the second triode, the base of the first triode is connected with the base of the second triode, the collector of the first triode is connected with the base of the first triode, and the emitter of the second triode is used for grounding; an emitting electrode of the first triode is connected with one end of the resistor, the other end of the resistor is connected with a source electrode of the first NMOS tube, a drain electrode of the first NMOS tube is used for connecting the detection point, and a grid electrode of the first NMOS tube is used for connecting a power supply; the collector of the second triode is configured as the output end of the voltage detection unit.
3. A zero-crossing detection circuit according to claim 2, wherein the electrical parameter of the voltage detection unit satisfies- (I1 m R1+ V) T * ln (n)) = Vm, where Vm is the preset voltage, I1 is the current value of the bias current, m is the current output ratio parameter of the two current mirror output ends, n is the ratio of the emitter area of the second triode to the emitter area of the first triode, R1 is the resistance of the resistor, and V is T Is a thermal voltage.
4. A zero-crossing detection circuit as claimed in claim 2, wherein the detection module further comprises a falling edge acceleration unit for increasing a slope of a falling edge of the output signal of the voltage detection unit; the falling edge acceleration unit comprises a first inverter and a second inverter, wherein the input end of the first inverter is connected with the output end of the voltage detection unit, the output end of the first inverter is connected with the input end of the second inverter, and the output end of the second inverter is configured as the output end of the zero-crossing triggered falling edge.
5. A zero-crossing detection circuit as claimed in claim 1, wherein the preset pulse width is less than 200ns.
6. A zero-crossing detection circuit as claimed in claim 1, wherein the narrow pulse width generation module comprises a first PMOS transistor, a second PMOS transistor, a third PMOS transistor, a second NMOS transistor, a third NMOS transistor, a fourth NMOS transistor and a first nor gate element; the source electrode of the first PMOS tube is used for being connected with a power supply, the drain electrode of the first PMOS tube is connected with the drain electrode of the second NMOS tube, the source electrode of the second NMOS tube is used for being grounded, the grid electrode of the first PMOS tube is connected with the grid electrode of the second NMOS tube, and the grid electrode of the first PMOS tube is connected with the output end of the zero-crossing trigger falling edge; the source electrode of the second PMOS tube is used for being connected with a power supply, the drain electrode of the second PMOS tube is connected with the drain electrode of the third NMOS tube, the source electrode of the third NMOS tube is used for being grounded, the grid electrode of the second PMOS tube is connected with the grid electrode of the third NMOS tube, and the grid electrode of the second PMOS tube is connected with the drain electrode of the first PMOS tube; the source electrode of the third PMOS tube is used for being connected with a power supply, the drain electrode of the third PMOS tube is connected with the drain electrode of the fourth NMOS tube, the source electrode of the fourth NMOS tube is used for being grounded, the grid electrode of the third PMOS tube is connected with the grid electrode of the fourth NMOS tube, and the grid electrode of the third PMOS tube is connected with the drain electrode of the second PMOS tube; one of the input ends of the first NOR gate element is connected with the drain electrode of the third PMOS tube, and the other input end of the first NOR gate element is connected with the output end of the zero-crossing triggered falling edge.
7. A zero-crossing detection circuit as claimed in claim 6, comprising at least one of the following features: the ratio of the channel length of the first PMOS tube to the channel width of the first PMOS tube is more than 10; the product of the channel length of the third NMOS tube and the channel width of the third NMOS tube is between 50um 2 ~500um 2 To (c) to (d); and the number of the first and second groups, the channel length of the third PMOS tube is selected from the minimum value allowed in the manufacturing process, and the channel length of the fourth NMOS tube is selected from the minimum value allowed in the manufacturing process.
8. A zero-crossing detection circuit as claimed in claim 1, wherein the output signal processing module is further configured to output a control signal for turning off the lower tube when the upper tube is determined to be in the on state based on the operating state signal.
9. A zero-crossing detection circuit as claimed in claim 4, wherein the output signal processing module comprises a second NOR gate element, a third NOR gate element and a fourth NOR gate element; one of the input ends of the second nor gate element is connected with the output end of the narrow pulse width generation module; the other of the inputs of the second nor gate element is connected to the output of the third nor gate element; one of the input ends of the third nor gate element is connected with the output end of the second nor gate element, and the other of the input ends of the third nor gate element is used for acquiring the working state signal, wherein when the working state signal is at a high level, the working state signal corresponds to that the upper tube is in an open state; the output of the third nor gate element is further connected to one of the inputs of the fourth nor gate element, the other of the inputs of the fourth nor gate element being connected to the output of the first inverter; and an output signal of the fourth nor gate element is used as an output signal of the zero-crossing detection circuit, or the output signal of the fourth nor gate element is inverted and then used as an output signal of the zero-crossing detection circuit.
10. A zero-crossing detection circuit as claimed in claim 9, wherein the operating state signal is a drive signal of the upper tube.

Description

Zero-crossing detection circuit Technical Field The invention relates to the field of integrated circuits, in particular to a zero-crossing detection circuit of a switching power supply. Background The zero-crossing detection means that for the BUCK synchronous rectification circuit, under normal conditions, the current direction of a lower tube (i.e. a power tube connected between a switch pin and the ground and used for freewheeling an inductive current) flows from the ground to the switch pin (generally referred to as an SW pin); however, if the system works in a light load mode, after the low tube freewheeling is completed, the capacitor at the output end forms a loop through the inductor and the low tube to charge the inductor, in the process, the current direction of the low tube is changed from the original position from the ground to the switch pin to the ground, in the process, the current of the low tube is reduced from one value to zero and then is increased from zero to another value (the direction is opposite), and in the process, the current has a point of becoming zero. When the BUCK synchronous rectification circuit runs, the time coordinate of the zero-crossing point needs to be detected, and the time coordinate is used for providing a basis for switching off the lower tube for the later stage. When an upper tube (a power tube connected to an input end of a system and a switch pin) is turned off, a lower tube is in a follow current state, the current direction of the lower tube is from the ground to the switch pin, the voltage at the SW pin is lower than 0V at the moment, the voltage at the SW point rises along with the reduction of the current of the lower tube and gradually approaches to 0V, but because the transmission of a line has delay, the point of SW reaching 0V cannot be directly detected normally (namely the current of the lower tube is zero), and a value (such as-30 mV) of the SW point voltage which is slightly lower than 0V is selected as a zero-crossing detection point. For the BUCK-type BUCK synchronous rectification circuit, if the zero-crossing detection and zero-crossing turn-off circuit is not provided, when the load is light, the current of the inductor flows in the reverse direction under certain conditions, the process is equivalent to that the output capacitor charges the inductor, and because the current always flows, extra energy loss is caused, so that when the load is light, the efficiency of the system is low. In addition, under some conditions (e.g., large duty cycle, heavy load), a circuit without over-zero detection may cause system start-up difficulties. That is, there is a problem in the prior art that the efficiency of the system is low or the start-up is difficult. Disclosure of Invention The invention aims to provide a zero-crossing detection circuit to solve the problems of low system efficiency or difficult starting in the prior art. In order to solve the technical problem, the invention provides a zero-crossing detection circuit, which is used for a BUCK synchronous rectification circuit, wherein the BUCK synchronous rectification circuit comprises an upper tube, a lower tube, an energy storage inductor and a detection point, the connection point of the upper tube, the lower tube and the energy storage inductor is configured as the detection point, and the zero-crossing detection circuit comprises a detection module, a narrow pulse width generation module and an output signal processing module. The detection module is used for outputting a zero-crossing trigger falling edge when the voltage of the detection point rises to reach a preset voltage, and the absolute value of the difference value between the preset voltage and 0V is not more than 100mV; the narrow pulse width generation module is used for outputting a high-level pulse signal with a preset pulse width when the zero-crossing trigger falling edge is received; the output signal processing module is used for executing operation based on the working state signal of the upper tube, the output signal of the detection module and the output signal of the narrow pulse width generation module; and outputting a control signal for turning off the lower tube when the upper tube is judged to be in a disconnected state based on the working state signal and the high-level pulse signal is received. Optionally, the detection module includes a voltage detection unit, and the voltage detection unit is configured to change a voltage waveform of an output terminal of the detection unit when the voltage at the detection point rises to reach the preset voltage. The voltage detection unit comprises a current mirror, a first triode, a second triode, a resistor and a first NMOS (N-channel metal oxide semiconductor) tube; the current mirror comprises a current mirror input end and two current mirror output ends, the current mirror input end is used for obtaining bias current, and current output proportion parameters of t