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A low-power switching power supply suitable for embedded system requirements

Posted by: Yoyokuo 2022-01-08 Comments Off on A low-power switching power supply suitable for embedded system requirements

With the development of computer technology, semiconductor technology and Electronic application technology, embedded systems are widely used in industrial control, process control, instrumentation, aerospace and aviation due to their small size, high reliability, low power consumption, and high software and hardware integration. , Automobiles and ships, network communications, military equipment, consumer products, and many other fields. In these systems, the structure and performance of the power supply play a key role, especially for systems that require multiple power supplies powered by 220V AC power, the rationality and reliability of the power supply design is particularly important.In the past, the commonly used linear power supply of transformer step-down, rectification and filtering, in the embedded system

With the development of computer technology, semiconductor technology and electronic application technology, embedded systems are widely used in industrial control, process control, instrumentation, aerospace and aviation due to their small size, high reliability, low power consumption, and high software and hardware integration. , Automobiles and ships, network communications, military equipment, consumer products, and many other fields. In these systems, the structure and performance of the power supply play a key role, especially for systems that require multiple power supplies powered by 220V AC power, the rationality and reliability of the power supply design is particularly important. In the past, the commonly used linear power supply after transformer step-down, rectification and filtering is insufficient when the embedded system requires small size and high utilization rate. It has become an urgent need to seek a switching power supply with small size, high efficiency, low cost, and good reliability. Based on the experience in practical applications, this article takes the low-power monolithic switching power supply integrated circuit FSD200 as the core to design and implement a low-power switching power supply suitable for the needs of embedded systems.

1 System principle

In many embedded systems in the industrial control field, the input is usually 220V AC mains, and the system requires multiple DC power supplies to drive power devices and microprocessor systems. The principle structure block diagram of a typical switching power supply is shown in Figure 1. The 220V alternating current of the power grid first passes through the rectifier circuit and is fed to the FSD200.

A low-power switching power supply suitable for embedded system requirements

Fig. 1 The principle block diagram of the embedded medium and small power multi-channel switching power supply. After the output of this device is isolated and coupled by a transformer, the regulated output is 12V DC. Its size can be realized by changing the voltage stabilizing circuit part. The voltage output terminal is composed of a TL431 precision regulator and a linear optocoupler to form a feedback loop to control the pulse width modulation ratio in the FSD200 to achieve a stable output of the switching power supply. After the 12V DC voltage is obtained, the DC/DC converter can be used to obtain the 5V, 3.3V, and 2.7V required by the system.

2 FSD200 structure principle

FSD200 is a low-power monolithic switching power supply integrated circuit launched by Fairchild in recent years. The output power is 7W. It integrates PWM control and power MOS tube, and has overheat protection, overload protection, undervoltage lockout, soft start, current limit, etc. Function, its unique frequency jitter circuit can better reduce electromagnetic interference.

 

A low-power switching power supply suitable for embedded system requirements

  

Figure 2 FSD200 internal functional block diagram

When the FSD200 single-chip switching power supply is started, the DC high-voltage power supply enters the high-voltage regulator inside the chip through the 8th pin Vstr, and then stabilizes it to 7V as the working voltage U cc of the chip. The voltage lock module is charged. The external capacitor of the 5th pin V cc is generally selected in the range of 10 ~ 47 μ F. This method eliminates the need for the normal switching power supply to use the feedback coil to provide the operating voltage.

FSD200 is a voltage control mode device. Like a typical switching power supply circuit, it uses a linear optocoupler PC817 and an adjustable precision regulator TL431 to form a voltage feedback network on the secondary side of a high-frequency transformer. When the load change causes the output voltage to change, the feedback network will feed back the signal to the fourth pin Vfb, compare it with the sawtooth wave sent by the oscillator, and produce the corresponding PWM wave pulse width change, and finally make the output of the secondary side of the high-frequency transformer The voltage is stable and the feedback control is completed.

3 TL431 structure principle

TL431 is a three-terminal adjustable precision voltage reference integrated circuit with good thermal stability, developed by Texas Company. It has three pins, among which K is the control terminal, A is the ground terminal, and R is the sampling terminal. It is composed of multi-stage amplifier circuit, bias circuit, compensation and protection circuit. In principle, it is a multi-stage DC amplifier with single-ended input and single-ended output. The equivalent functional block diagram is shown in Figure 3, which consists of a 2.5V precision reference voltage source, a voltage comparator and an output switch tube.

The Links:   B141XG09-V1 CM200DU-12H