Switching power supply optical coupling bad phenomenon!

In a switching power supply, the photocoupler feeds the output voltage back to the front control circuit. If the optocoupler is damaged, the output voltage may be abnormal, and the circuit may enter the overvoltage or overcurrent protection state, with no voltage output. If the optical coupler controls the start and stop of the power supply, if the optical coupler is broken, the power supply cannot start and stop. If an optical coupler is used for voltage stabilizing negative feedback, the optical coupler is disconnected, which may result in abnormal output voltage, protection stop, and power damage.

If the protection circuit is not complete, the general main switch circuit will burn out, secondary filter capacitor may burn out, it is the main component of stable power supply voltage, rarely damage, generally take replacement method, buy a new, one side is a secondary tube, can be measured out, on the other side is impassable, if the amount to have a short circuit, is certainly bad.

The photocoupler in the switching power supply is damaged, resulting in the power supply circuit can not be regulated, and serious conductance power supply does not work.

Basic principle of optocoupler

Electrical signal is added at the input end of the photoelectric coupler to make the source light. The intensity of the light depends on the size of the excitation current. After the light is irradiated to the photoreceptor encapsulated together, the photocurrent is generated due to the photoelectric effect, which is extracted from the output end of the photoreceptor, so as to realize the conversion of electricity to light.

The effect of the optical coupling failure on the circuit

In a switching power supply, the optocoupler is to feedback the output voltage to the preceding control circuit. If the optocoupler is damaged, the output voltage may be abnormal, and the circuit may enter the overvoltage, or overcurrent protection state, with no voltage output. Switching power supply is a power supply that uses modern power electronics technology to control the time ratio of switching tube to turn on and off to maintain stable output voltage. Switching power supply is generally composed of pulse width modulation (PWM) control IC and MOSFET.

The photocoupler in the switching power supply is damaged, resulting in the power supply circuit can not be regulated, and serious conductance power supply does not work.

With the development and innovation of power electronics technology, switching power supply technology is also being innovated. At present, switching power supply is widely used in almost all electronic equipment with the characteristics of small, light weight and high efficiency. It is an indispensable power supply mode for the rapid development of the electronic information industry.

After the light is irradiated to the photoreceptor encapsulated together, the photocurrent is generated due to the photoelectric effect, which is drawn out from the output end of the photoreceptor, so as to realize the conversion of electricity from light to electricity.

The test of optical couplings

Optical coupling is also a component with high damage probability. It is meaningful to test the function of optical coupling online. According to statistics, the drive optocoupler with internal amplifier and the analog input have the most damage.

Drive optical coupler can use pointer multimeter electrical block, generally select X10Ω block can be used, you can use the light emitting diode inside the light coupling point, if the output end of the optical coupler does not need to connect to the power supply, you can directly use the digital multimeter diode block test output response, if the output of the optical coupler needs a power supply, then the test also needs to power the optical coupler. Some circuit board switching power supply, the optocoupler will have electricity, to test the optocoupler directly to the front drive current, multimeter test response voltage can be.

Analog optical couplings such as A7800, A7840, A7860 are common and easily damaged components. A7800, A7840 can be homemade circuit test, the market also has a special test rack sale. The most convenient test method for A7800 and A7840 is to test the voltage between pins 2,3 and 6,7 without removing the power-up. If the input voltage is 0 and the output is -20mV, it is judged that the optical coupler is damaged. A7860 belongs to digital output optical coupler, which is generally paired on the circuit board. To carry out functional test on it, it needs to cooperate with other chip programming, which is troublesome to test. A relatively simple test method is to test the voltage between pin 6 and pin 5 after power-on. If the voltage deviation between two A7860s is too much, one of them will be damaged. In this case, replace both of them.