CN218547338U

CN218547338U - Programmable soft start control circuit for push-pull topology

Info

Publication number: CN218547338U
Application number: CN202223306970.3U
Authority: CN
Inventors: 杨亚峰
Original assignee: Shanghai Fengtian Electronics Co ltd
Current assignee: Shanghai Fengtian Electronics Co ltd
Priority date: 2022-12-08
Filing date: 2022-12-08
Publication date: 2023-02-28
Anticipated expiration: 2032-12-08

Abstract

The utility model relates to the field of soft start control circuits of switch power supplies, in particular to a programmable soft start control circuit for push-pull topology, which comprises a singlechip, a drive chip, a voltage stabilizer, an amplifier and a comparator; the single chip microcomputer is supplied with power under the condition of voltage stabilization through the voltage stabilizer, is provided with two PWM output ports and can output two PWM driving signals through software design programming; the driving chip can amplify the power of the two PWM driving signals output by the singlechip and then drive the two power MOS tubes to work; the amplifier is used for amplifying the current sampling signals of the push-pull power MOS tube cycle by cycle; the comparator can compare the amplified cycle-by-cycle current signals with a set current limiting value, and output high-level pulses to be fed back to an AD sampling port of the single chip microcomputer when the amplified cycle-by-cycle current signals exceed the current limiting value, so that output control of two paths of PWM signals is performed.

Description

Programmable soft start control circuit for push-pull topology

Technical Field

The utility model relates to a switching power supply's soft start control circuit field specifically is a soft start control circuit able to programme for push-pull topology.

Background

The power conversion circuit design of the switching power supply product generally uses a PWM control chip, and the PWM control chip mainly has the functions of generating a PWM control signal through a self-contained oscillator, driving a power MOS (metal oxide semiconductor) tube of the switching power supply topological circuit to work, monitoring output voltage or current feedback in real time, and outputting and adjusting the duty ratio of the PWM signal, thereby realizing the related design function of the switching power supply topological circuit.

The PWM control chip usually has a soft start control circuit, and the function of the soft start control circuit is realized by an external capacitor connected to an SS pin of the PWM control chip. The PWM control chip is added with a soft start control circuit to have the following functions: after the soft start control circuit is added, the PWM control chip can control the duty ratio of the PWM driving signal to slowly increase from 0% at the moment of starting the switching power supply topology circuit until a feedback loop is established and the duty ratio is stable, so that the problems of instantaneous and overhigh surge current and voltage spike generated by a power MOS tube due to full duty ratio output of the PWM signal at the moment of starting the machine are effectively solved. When the problem is serious, the voltage and current endurance capability of the power MOS tube can be exceeded, the service life of the power MOS tube is shortened, and even the power MOS tube is damaged. The soft start control circuit can effectively reduce the voltage and current stress of the power MOS tube of the switching power supply at the moment of starting the power supply, improve the design allowance of voltage resistance and current reduction resistance of the power MOS tube, and prolong the design service life of the power MOS tube.

Referring to fig. 2, a typical push-pull topology circuit applied to an inverter product of a vehicle-mounted power supply is shown: a simplified push-pull topological circuit is used, and a secondary side circuit has no energy storage inductor; the PWM control chip is of a current type, and an attached CS pin can detect currents flowing through two push-pull power MOS tubes Q1 and Q2 cycle by cycle and carry out current limiting protection; a soft start control circuit of the soft start control circuit is realized by an external capacitor of a self-contained soft start function pin SS pin, a constant current source is usually arranged in a chip of the SS pin, and the soft start control circuit can control the external capacitor to be charged with constant current when starting the machine, so that the soft start function is realized. By increasing the capacitance of the soft start capacitor, the charging duration can be increased, thereby setting the total duration of the soft start process.

By using the typical soft start control circuit shown in fig. 2, at the start-up moment of the push-pull topology circuit, since the initial voltage of the secondary side high-voltage aluminum electrolytic capacitor C2 is 0V, the secondary side is basically in a short-circuit state, and thus the primary side power MOS transistors Q1 and Q2 have a large current impact at the start-up moment. Although the soft start circuit of the PWM control chip can effectively reduce the current impact, the duty ratio of the PWM signal is increased from 0% at a constant speed, the time for increasing the duty ratio from 0% to 3% is still short, so that the current impact at the moment of starting is still large, the CS pin of the current type PWM controller is still easily pushed to a current-limiting protection voltage value frequently, the PWM signal is restarted and a soft start function is triggered for many times, the problem can not be effectively eliminated only by increasing the current-limiting protection threshold and increasing the capacitance value of a soft start capacitor to relieve the problem. With the continuous increase of the design power of the vehicle-mounted power inverter product, when a push-pull topology circuit is continuously used, the capacitance value of the high-voltage aluminum electrolytic capacitor C2 at the secondary side of the push-pull topology circuit must be correspondingly adjusted and increased, which further causes that the soft start circuit of the existing PWM control chip cannot meet the requirements more and more. Firstly, the selection of the power MOS tube determines that the threshold of the current-limiting protection cannot be infinitely increased, so that the power MOS tube is prevented from exceeding the design margin of the current-tolerant de-rating of the power MOS tube; secondly, the capacitance value of the capacitor of the soft start circuit of the PWM control chip cannot be infinitely increased, so that the start time of the product is infinitely prolonged and even exceeds 500ms, and finally the product cannot be accepted by people.

SUMMERY OF THE UTILITY MODEL

An object of the utility model is to provide a soft start control circuit able to programme for push-pull topology to solve the problem that proposes in the above-mentioned background art.

In order to achieve the above purpose, the utility model provides a following technical scheme: a programmable soft start control circuit for push-pull topology comprises a single chip microcomputer, a driving chip, a voltage stabilizer, an amplifier and a comparator. The single chip microcomputer is supplied with power under the condition of voltage stabilization through the voltage stabilizer, is provided with two PWM output ports, and can output two PWM driving signals through software design programming; the driving chip can amplify the power of the two PWM driving signals output by the singlechip and then drive the two power MOS tubes to work; the amplifier is used for amplifying the current sampling signals of the push-pull power MOS tube cycle by cycle; the comparator can compare the amplified cycle-by-cycle current signals with a set current limiting value, and output high-level pulses to be fed back to an AD sampling port of the single chip microcomputer when the amplified cycle-by-cycle current signals exceed the current limiting value, so that output control of two paths of PWM signals is performed.

Preferably, the input of the voltage stabilizer is connected with B +, and the output stabilized voltage provides stabilized voltage power supply for the single chip microcomputer;

preferably, two PWM signal outputs of the single chip microcomputer are connected with a driving chip, two power MOS tubes of the push-pull topology circuit are driven to work through the driving chip, and a current sampling port AD1 of the single chip microcomputer is connected with the comparator.

Preferably, the amplifier and the comparator can amplify and compare periodic currents of two paths of power MOS tubes of the push-pull topology circuit, and finally output an overcurrent signal to an AD sampling port of the single chip microcomputer.

Preferably, the single chip can read the cycle-by-cycle overcurrent signals sent by the comparator through the AD port and output and control the two paths of PWM signals so as to respond to overcurrent protection in real time.

Preferably, the type of the single chip microcomputer is S9KEAZN32AMLCR.

Compared with the prior art, the beneficial effects of the utility model are that: the utility model discloses push-pull topology circuit to current vehicle mounted power inverter product use improves, especially carries out programmable design with soft start control circuit part through software, promotes its power application upper limit and from 300W to 3000W or even higher, provides a feasible and reliable design scheme for more high-power vehicle mounted power inverter product; meanwhile, the singlechip originally in the circuit is used for PWM output control, so that a PWM control chip is omitted, the integration level of the product is higher, the circuit design is more simplified, the material cost is reduced, and the design quality of the product is improved.

Drawings

Fig. 1 is a schematic circuit diagram of the present invention;

FIG. 2 is a circuit diagram of a soft start control circuit of a simplified push-pull topology circuit;

the reference numbers in the figures: 1. a voltage regulator; 2. a single chip microcomputer; 3. a driving chip; 4. a comparator; 5. an amplifier.

Detailed Description

The technical solutions in the embodiments of the present invention will be described clearly and completely with reference to the accompanying drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments in the present invention, all other embodiments obtained by a person skilled in the art without creative work belong to the protection scope of the present invention.

Referring to fig. 1-2, the present invention provides a technical solution: a programmable soft start control circuit for push-pull topology comprises a voltage stabilizer 1, a single chip microcomputer 2, a driving chip 3, a comparator 4 and an amplifier 5; the single chip microcomputer 2 is used for voltage stabilization power supply through a voltage stabilizer 1, the single chip microcomputer 2 is provided with two PWM output ports, outputs two PWM signals and drives two push-pull power MOS tubes Q1 and two power MOS tubes Q2 after passing through a driving chip 3; the amplifier 5 amplifies cycle-by-cycle currents of the power MOS tube Q1 and the power MOS tube Q2 sampled by the resistor R1 and then inputs the amplified currents into the comparator 4; the comparator 4 compares the received cycle-by-cycle current amplification signal with a set overcurrent protection value, and outputs an overcurrent pulse signal to the singlechip 2.

Further, the input of the voltage stabilizer 1 is connected with B +, the power is taken from B +, the output of the voltage stabilizer is connected with a VCC power supply pin of the singlechip 2 after voltage stabilization, and voltage stabilization power supply is provided for normal work of the singlechip.

Furthermore, two PWM signal outputs of the single chip microcomputer 2 are connected with the input of the driving chip 3, the sampling port AD1 of the single chip microcomputer is connected with the output of the comparator 4, and two outputs of the driving chip 3 are respectively connected with two push-pull power MOS tubes Q1 and Gate pins of the power MOS tubes Q2.

Further, the input of the comparator 4 is connected to the output of the amplifier 5, and the input of the amplifier 5 is connected to the positive terminal of the current sampling resistor R1.

Further, the type of the single chip microcomputer 2 is S9KEAZN32AMLCR.

The working principle is as follows: when the single-chip microcomputer works normally and stably, two PWM ports of the single-chip microcomputer 2 output two paths of PWM signals with the duty ratio close to 50%, voltage and current are boosted through the driving chip 3, and then two paths of power MOS (metal oxide semiconductor) tubes Q1 and Q2 of the push-pull topology are driven to work alternately, so that the power conversion function is achieved. The programming strategy of the soft start control circuit is divided into three stages to carry out duty ratio independent programming control respectively, so that an ideal soft start effect is achieved, the detailed parameter setting can be finely adjusted and optimized according to the actual design power of a product, and only one example is listed to explain the whole control process; for example: the total soft start time of the first stage is set to be 200ms, the duty ratio of the first 100ms is fixed to be 1%, and the duty ratio of the last 100ms is increased from 1% to 3% at a constant speed; the total soft start time of the second stage is set to be 100ms, and the duty ratio is increased from 3% to 10% at a constant speed; the soft start total time of the third stage is set as 100ms, and the duty ratio is uniformly increased from 10% to close to 50%. The setting can be basically adjusted according to needs and an ideal soft start control function and effect can be realized, and a practical novel design scheme with lower cost and reliable quality is provided for a soft start control circuit of a vehicle-mounted power supply inverter product with higher power.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims

1. A programmable soft start control circuit for a push-pull topology, characterized by: the circuit comprises a voltage stabilizer (1), a singlechip (2), a driving chip (3), a comparator (4) and an amplifier (5); the single chip microcomputer (2) is used for voltage stabilization power supply through the voltage stabilizer (1), the single chip microcomputer (2) is provided with two PWM output ports, outputs two PWM signals and drives two push-pull power MOS tubes Q1 and two power MOS tubes Q2 after passing through the driving chip (3); the amplifier (5) amplifies cycle-by-cycle currents of the power MOS tube Q1 and the power MOS tube Q2 sampled by the resistor R1 and then inputs the amplified currents into the comparator (4); the comparator (4) compares the received cycle-by-cycle current amplification signal with a set overcurrent protection value, and outputs an overcurrent pulse signal to the single chip microcomputer (2).

2. A programmable soft-start control circuit for push-pull topology according to claim 1, characterized by: the input of the voltage stabilizer (1) is connected with the B +, the power is taken from the B +, the output of the voltage stabilizer is connected with the VCC power supply pin of the singlechip (2) after voltage stabilization, and the voltage stabilization power supply is provided for normal work of the singlechip.

3. A programmable soft-start control circuit for a push-pull topology according to claim 1, characterized by: two PWM signal outputs of the single chip microcomputer (2) are connected with the input of the driving chip (3), a sampling port AD1 of the single chip microcomputer is connected with the output of the comparator (4), and two outputs of the driving chip (3) are respectively connected with two push-pull power MOS tubes Q1 and Gate pins of the power MOS tubes Q2.

4. A programmable soft-start control circuit for push-pull topology according to claim 1, characterized by: the input of the comparator (4) is connected with the output of the amplifier (5), and the input of the amplifier (5) is connected with the positive end of the current sampling resistor R1.

5. A programmable soft-start control circuit for push-pull topology according to claim 1, characterized by: the type of the single chip microcomputer (2) is S9KEAZN32AMLCR.