The main function of optocoupler in the power supply circuit is to realize isolation while photoelectric conversion and avoid mutual interference. The function of disconnector is particularly prominent in the circuit.
The signal travels in one direction. Input and output are completely electrically isolated. The output signal has no effect on the input. Strong anti-interference ability, stable operation, no contact, long service life and high transmission efficiency. Optocoupler is a new device developed in the 1970s. At present, it is widely used in electrical insulation, level conversion, interstage coupling, driving circuit, switching circuit, chopper, multivibrator, signal isolation, interstage isolation, pulse amplification circuit, digital instrument, long-distance signal transmission, pulse amplifier, solid-state device, state relay (SSR), instrument, communication equipment and microcomputer interface. In the monolithic switching power supply, the linear optocoupler is used to form the optocoupler feedback circuit, and the duty cycle is changed by adjusting the control terminal current to achieve the purpose of accurate voltage regulation.
The main function of optocoupler in switching power supply is to isolate, provide feedback signal and switch. The power supply of the optocoupler in the switching power supply circuit is provided by the secondary voltage of the high-frequency transformer. When the output voltage is lower than the zener voltage, turn on the signal optocoupler and increase the duty cycle to increase the output voltage. On the contrary, turning off the optocoupler will reduce the duty cycle and reduce the output voltage. When the secondary load of the high-frequency transformer is overloaded or the switch circuit fails, there is no optocoupler power supply, and the optocoupler controls the switch circuit not to vibrate, so as to protect the switch tube from being burned. Optocoupler is usually used with TL431. The two resistors are sampled in series to the 431r terminal for comparison with the internal comparator. Then, according to the comparison signal, the ground resistance of 431k end (the end where the anode is connected with the optocoupler) is controlled, and then the brightness of the light-emitting diode in the optocoupler is controlled. (there are light-emitting diodes on one side of the optocoupler and phototransistors on the other side) the intensity of the light passing through. Control the resistance at the CE end of the transistor at the other end, change the LED power drive chip, and automatically adjust the duty cycle of the output signal to achieve the purpose of voltage stabilization.
When the ambient temperature changes sharply, the temperature drift of the amplification factor is large, which should not be realized by optocoupler. Optocoupler circuit is a very important part of switching power supply circuit.
Post time: May-03-2022