CN-122001202-A - Soft start circuit for DC-DC switching power supply chip and control method thereof

CN122001202ACN 122001202 ACN122001202 ACN 122001202ACN-122001202-A

Abstract

The invention discloses a soft start circuit for a DC-DC switching power supply chip and a control method thereof, wherein the soft start circuit comprises a soft start control circuit, a driving circuit, a power full-bridge, an isolation transformer and a rectifying circuit which are sequentially and electrically connected, the soft start control circuit generates N groups of output signals, the N groups of output signals sequentially jump to be effective signals according to preset time intervals, the power full-bridge comprises N groups of full-bridge units connected in parallel, the rectifying circuit is connected with a secondary side inductor of the isolation transformer, receives energy of the isolation transformer and converts the energy into DC power supply output, the feedback circuit is used for detecting whether output voltage of the rectifying circuit reaches a rated value or not and feeds back the feedback signal to the soft start control circuit, the output signal of the soft start control circuit and the feedback signal are subjected to logic operation to generate an enabling control signal, the driving circuit is controlled to drive the corresponding full-bridge units through the enabling control signal, and the quantity of the driven full-bridge units is controlled to enable the magnitude of starting current.

Inventors

XU DONGSHENG
ZHU ZHIYONG

Assignees

广州博之源科技有限公司

Dates

Publication Date: 20260508
Application Date: 20251231

Claims (8)

1. A soft start circuit for a DC-DC switching power supply chip is characterized by comprising a soft start control circuit, a driving circuit, a power full bridge, an isolation transformer and a rectifying circuit which are electrically connected in sequence, The soft start control circuit generates N groups of output signals, N is a positive integer, N is more than or equal to 2, and the N groups of output signals sequentially jump to be effective signals according to a preset time interval; The power full bridge comprises N groups of full bridge units connected in parallel, wherein the input end of each group of full bridge units is connected with a direct current input power supply, and the output end of each group of full bridge units is connected with the primary side inductor of the isolation transformer; The rectifying circuit is connected with a secondary side inductor of the isolation transformer, receives energy transmitted by the isolation transformer and converts the energy into direct-current power supply output; The soft start control circuit is used for detecting the output voltage of the rectifying circuit and generating a feedback signal of whether the output voltage reaches a rated value or not, and further feeding back the feedback signal to the soft start control circuit; The soft start control circuit generates an enabling control signal after performing logic operation on an output signal of the soft start control circuit and a feedback signal of the feedback circuit, the soft start control circuit controls the driving circuit to drive the corresponding full-bridge units through the enabling control signal, and the magnitude of the starting current is controlled through the number of the driven full-bridge units.
2. The soft start circuit for a DC-DC switching power supply chip of claim 1, wherein the driving circuit comprises N driving units, N groups of enable control signals generated by the soft start control circuit are in one-to-one correspondence with the N driving units of the driving circuit, and the N driving units are in one-to-one correspondence with the N groups of full-bridge units of the power full bridge.
3. The soft start circuit for a DC-DC switching power supply chip of claim 1, wherein the conductivities of the switching tubes in the 1 st group of full-bridge cells to the N th group of full-bridge cells of the power full-bridge are increased in multiple.
4. The soft start circuit for a DC-DC switching power supply chip of claim 1, wherein the feedback circuit comprises a pulse generating circuit, a modulating circuit, an isolation capacitor and a demodulation circuit which are sequentially connected, the pulse generating circuit is connected with the output end of the rectifying circuit, the output voltage of the rectifying circuit is detected, a pulse signal is generated as the feedback signal when the output voltage reaches a rated value, and the pulse signal is fed back to the soft start control circuit after passing through the modulating circuit, the isolation capacitor and the demodulation circuit.
5. The soft start circuit for a DC-DC switching power supply chip of claim 4, wherein the soft start control circuit comprises a soft start control signal generating circuit having N signal output ports and a logic operation circuit which is an AND gate circuit having inputs of an output signal of the soft start control signal generating circuit and an inverse signal of the pulse signal and outputs the output signal as the enable control signal.
6. A control method for a soft start circuit of a DC-DC switching power supply chip as claimed in any one of claims 1 to 5, comprising the steps of: After the primary side of an isolation transformer of the DC-DC switching power supply chip is electrified, the soft start control circuit generates N groups of output signals, the N groups of output signals are sequentially hopped to be effective signals according to preset time intervals, and the output signals and feedback signals of the feedback circuit generate enabling control signals after logic operation; after receiving the corresponding enabling control signals, the driving circuit drives corresponding full-bridge units on the rear-stage power full-bridge to sequentially enter a working state, energy is transmitted to the secondary side of the isolation transformer, and the rectifying circuit converts the energy of the secondary side of the isolation transformer into direct-current power supply to be output; The feedback circuit detects the output voltage of the rectifying circuit and outputs a feedback signal to the soft start control circuit, and the soft start control circuit ends the soft start process after receiving the feedback signal that the output voltage reaches the rated value.
7. The control method of claim 6, wherein the soft start control circuit receives a feedback signal that the output voltage of the rectifying circuit reaches a rated value, and the N groups of output signals generated by the soft start control circuit are all hopped to be effective signals, and all N groups of full-bridge units of the full-bridge power are driven to enter a working state by the driving circuit.
8. The control method according to claim 6, wherein the preset time interval for the transition of the N sets of output signals generated by the soft start control circuit to the active signal is 1ms.

Description

Soft start circuit for DC-DC switching power supply chip and control method thereof Technical Field The invention belongs to the technical field of power supplies, and particularly relates to a soft start circuit for a DC-DC switching power supply chip and a control method thereof. Background In the current industry and communication field, various switching power supplies are increasingly widely applied, and the development direction of the current switching power supply chip is small in size, high in efficiency and high in reliability. The reliability problem of the switching power supply chip usually occurs during the start-up process, so that establishing a stable and safe start-up process plays a crucial role in improving the reliability of the switching power supply chip. A conventional DC-DC switching power supply chip is usually connected in parallel with an energy storage capacitor at an output port to provide a source for load current. In the initial stage of starting the power supply chip, the voltage at two ends of the energy storage capacitor is 0, a larger difference is formed between the voltage and the rated value of the output voltage of the power supply chip, a power circuit in the chip can provide a large amount of current for the energy storage capacitor, the output voltage of the power supply chip can be rapidly increased, and high surge overshoot voltage is generated at two ends of the energy storage capacitor. When the over-voltage is too high, the service life of the internal devices of the power chip is reduced, and even more, the devices connected with the output port are directly damaged, and the performance of the energy storage capacitor is also damaged or reduced. Disclosure of Invention The first object of the present invention is to provide a soft start circuit for a DC-DC switching power supply chip, which solves the problem of output overshoot of the DC-DC switching power supply chip and improves the reliability of the product. A second object is to provide a control method for a soft start circuit of a DC-DC switching power supply chip. The technical scheme adopted by the first object of the invention is as follows: a soft start circuit for DC-DC switch power supply chip comprises a soft start control circuit, a drive circuit, a power full bridge, an isolation transformer and a rectifying circuit which are electrically connected in sequence, The soft start control circuit generates N groups of output signals, N is a positive integer, N is more than or equal to 2, and the N groups of output signals sequentially jump to be effective signals according to a preset time interval; The power full bridge comprises N groups of full bridge units connected in parallel, wherein the input end of each group of full bridge units is connected with a direct current input power supply, and the output end of each group of full bridge units is connected with the primary side inductor of the isolation transformer; The rectifying circuit is connected with a secondary side inductor of the isolation transformer, receives energy transmitted by the isolation transformer and converts the energy into direct-current power supply output; The soft start control circuit is used for detecting the output voltage of the rectifying circuit and generating a feedback signal of whether the output voltage reaches a rated value or not, and further feeding back the feedback signal to the soft start control circuit; The soft start control circuit generates an enabling control signal after performing logic operation on an output signal of the soft start control circuit and a feedback signal of the feedback circuit, the soft start control circuit controls the driving circuit to drive the corresponding full-bridge units through the enabling control signal, and the magnitude of the starting current is controlled through the number of the driven full-bridge units. The soft start circuit of the DC-DC switching power supply chip provided by the invention sequentially enables the driving circuit after the primary side of the chip is electrified, drives the power full bridge which is correspondingly and electrically connected with the driving circuit, transmits energy to the secondary side of the switching power supply chip through the isolation transformer, and feeds back a signal to the soft start control circuit of the primary side through the feedback circuit after the output voltage of the secondary side reaches a rated value, so as to interrupt the soft start process. In the initial stage of starting, the starting current is limited by limiting the number of power full-bridge units connected into the circuit. In the subsequent stage, the number of full-bridge units connected into the circuit is gradually increased, starting current is increased, the output voltage is slowly and steadily increased, and the problem of output overshoot of the DC-DC switching power supply chip is solved. The invention also has the followi