Solar inverter power supply design based on SG3525A

Introduction
　　: This article involves the specific technical issues of a topic in the Guangming Project. The basic principle of this project is that the inverter is powered by a DC battery, uses solar energy to charge the battery, and then the inverter power supply outputs 220V, 50Hz AC power for users to use. During the development process, high-power tubes sometimes randomly burn out. This article provides a solution to this phenomenon.

Figure 1 SG3525A driver MOS power tube circuit diagram

Figure 2 Waveform diagram during operation of the inverter

(a)

(b)

Figure 3 (A) Inverter slow start (B) Inverter hard start

SG3525A and inverter power supply

　　The core device used in the inverter developed in this project is SG3525A. Its basic performance and working process are briefly described below.

SG3525A basic performance
　　SG3525A PWM switching power supply integrated controller includes all control circuits required for switching voltage stabilization. It is equipped with an undervoltage lockout circuit and a slow start circuit to provide a reference voltage with a precision of 5V±1%. Its switching frequency is as high as 200KHz or more, which is suitable for driving N-channel MOS power tubes. This project uses SG3525A to generate a 50Hz quasi-sinusoidal square wave to provide an output power signal for the inverter to drive the N-channel MOS power transistor 90N08, as shown in Figure 1.

Inverter working process:
　　When SG3525A is powered on (12V), it will output two columns of 50Hz reverse square waves with an amplitude of 9V. These two square waves enter the four branches shown in G1, G2, G3, and G4 respectively (Figure 1), and are output after being adjusted by each circuit respectively. The output pulse sequence is shown in Figure 2(B). The final modulation is synthesized into AC square waves output at both ends A and B. Its waveform is shown in Figure 2(A). The 50Hz sequence square wave enters the power transformer DT from both ends A and B. After being boosted by the transformer, the inverter power supply outputs a 220V, 50Hz AC square wave. According to the different needs of the market, we produce various series of inverter power supplies of 200W, 600W and 800W.

The occurrence and solution of the problem
　　
　　: The inverter can operate for a long time under rated load conditions, but when the load is switched or when there is serious disturbance in the external circuit, the high-power tube MOSFET90N08 will occasionally burn out. Now let’s analyze it with an 800W inverter.

　　Slow start: In the state shown in Figure 3(A), full load is applied to the inverter output, and then the inverter is started to run, and everything works normally.

　　Hard start: The state shown in Figure 3(B) is to force a hard start by closing switch K1 after filling the load. At this time, the phenomenon of short-circuit burning of high-power field effect tubes occasionally occurs. After analysis, it is found that when the high-power tube TV3 driven by G3 has not been completely turned off, G4 turns on the corresponding high-power tube TV4. If TV3 and TV4 are turned on at the same time, Will cause short circuit phenomenon. At this time, the high-power tube will be burned. When point D and point C, point E and point F are exchanged with each other, the time difference between the two tubes turning on is about 100ms. This ensures that the push signals of G3 and G4 will not turn on VT3 and VT4 at the same time, thus avoiding short circuit. Phenomenon. Until now, high-power tubes have not been burned due to hard start and external circuit interference.

References
1 Wang Jianying, Chang Minhui, eds. New switching power supply technology. Beijing: Electronic Industry Press. 2001.7
2 Zhang Zhansong, Cai Xuansan, eds. Principle and design of switching power supply. Beijing: Electronic Industry Press. 2000.3