The chip VIPER12A is a single-chip low-power switching power supply produced by ST Semiconductor Co., Ltd. in 2002. With a fixed 60kHz switching frequency, the chip has a wide range of power supply voltage (9V-38V) : a current control PWM modulator; Undervoltage, overvoltage, overcurrent and overheat protection with hysteresis characteristics. The peripheral circuit of the chip is simple and energy-saving. VIPer12A has the characteristics of simple circuit, stable operation and excellent performance, and is often widely used in low-power switching power supplies, and induction stoves are mostly used in the management chip of auxiliary power supplies.
VIPer12A pin functions:
①② The foot is the switching tube source inside the chip, which is grounded or indirectly grounded in the parallel switching power supply; In the series switching power supply, the external switching transformer is the output end of the power supply.
The foot is the sampling input end of the voltage regulator detection, which is usually connected to the 18v voltage regulator tube detection, and some are connected to the external optocoupler to introduce the feedback voltage.
The foot is the input end of the internal working voltage of the chip, and its working voltage range is between 9v and 38v. When it is less than 9v, the chip stops vibration, and when it is higher than 38v, the internal overvoltage protection or damage is generally 14v to 18v. In induction stoves, voltage is generally introduced to this pin through a diode from the 18v group output.
⑤⑥⑦⑧ foot is the internal switch tube drain of the chip.
The steps to overhaul the switching power supply circuit with VIPer12A as the center are as follows: (The circuit in the above figure is an example)
The most common fault is the circuit abnormality caused by the deterioration and aging of the filter electrolytic capacitor. During maintenance, c111, EC91, EC92, EC93, EC95 are the focus of detection, especially C111 (4.7uf450v) leakage capacity reduction failure, 300v voltage drop, or the ripple coefficient is too large, so that the chip can not work normally and the voltage output is abnormal. When detecting, first measure whether the voltage at both ends of C111 is about 300V, if it is low, including checking whether the D114 diode is bad, and whether an R120 current limiting resistance is larger. EC95 is a filter capacitor of 4 pin operating voltage, which often causes the chip to not work due to failure. The failure of EC91 and EC92 will cause the output voltage to be abnormal, the chip feedback voltage will change, and the entire output will also change, which can cause the power supply to produce weak vibration.
After several electrolytic capacitors are eliminated, several diode anomalies are detected. The Z90 voltage regulator diode in the figure is the sampling tube and the focus of the inspection. If the sampling feedback voltage is not normal, the chip will not work normally.
After checking the above points, if the output voltage is not normal, it is generally the chip itself, and try to replace a new film.
For all the operating voltages in the chip are also based on the chip source pin voltage as a reference point of the circuit, is a parallel voltage regulator circuit, and the circuit you draw above is series.