Feedback control circuit diagram of small DC switching power supply

Probe domestic switch needle KG-300K needle head diameter is 3.0mm normally open switch needle

Overview:
This paper first introduces the related concepts and principles of the feedback control circuit, and then analyzes the specific design process of the feedback control circuit in the DC switching power supply designed in this paper. In order to realize the design idea of ​​low power and high efficiency, the PWM type current regulation method combining optocoupler 817 and three-terminal shunt regulator TL431 is adopted. Theoretical analysis and experimental results show that the system designed by this design has good stability and reliability, which further verifies the rationality and effectiveness of the design.

0 INTRODUCTION Currently, various electronic devices in the modern communication devices, in order to meet certain requirements in various operating conditions, or to achieve a predetermined number of technical indicators, the feedback control circuit has been widely used. As an automatic adjustment circuit in electronic equipment and systems, the main function of the feedback control circuit is that when the electronic system is subjected to some disturbance, the system can correct some parameters of the system through the adjustment function of its feedback control circuit, thereby The system indicators still reach the predetermined accuracy. The feedback control circuit is generally composed of a comparator, a control signal generator, and a four-part device controllable feedback network composed of a negative feedback loop is closed, as shown in FIG.

1 a schematic view of a feedback control circuit in the compact, low-power design and high efficiency, the feedback control circuit corresponding to the design herein DC switching power main technical requirements are as follows:
Input AC voltage: VACMIN=85V; VACMAX=265V; input voltage frequency: fL=50Hz; output voltage: VO=36V; output power: PO=72W; power efficiency: η=80%; loss factor Z: Z=0.6 ( Z represents the ratio of secondary loss to total loss).
DC switching power supply corresponding to the composition shown in FIG.

FIG feedback control circuit 2 corresponding to DC switching power supply schematic composition.

1. Feedback Control Circuit Design Process The feedback control circuit in the switching power supply is used to ensure the stability of the output voltage and current under load changes. The DC switching power supply corresponding to the feedback control circuit designed in this paper uses PWM pulse width modulation to keep the output voltage stable. Among them, PWM modulation is divided into current control mode and voltage control mode. Compared with the latter, the former has better voltage regulation rate and load regulation rate, which can reduce the number of components, reduce the cost, and improve the power of the switching power supply. Further ensuring the stability of the system and significantly improving the dynamic characteristics of the system, especially for the miniaturization, modularization and high efficiency of the system.
In addition, the feedback commonly used for DC switching power supplies is negative feedback. In feedback, the feedback that is usually used has the lowest cost of using primary feedback (only for low-power applications); the optocoupler/voltage regulator has low feedback cost and good output accuracy; and the output is also used with optocoupler/TL431 feedback The best precision. Taking into account the principle of low power and high efficiency embodied in the design of this paper, it is decided to use the PWM-type current regulation control method of the three-terminal shunt regulator TL431 and the optocoupler PC817 for reference, sampling, isolation and amplification, respectively. Negative feedback loop.
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