1. Form a switching circuit:
When the input signal ui is low level, the transistor V1 is in a cut-off state, the current of the light-emitting diode in the photocoupler B1 is approximately zero, and the output terminal The resistance between Q11 and Q12 is very large, which is equivalent to the switch "off"; when ui is high level, v1 is turned on, the light-emitting diode in B1 emits light, and the resistance between Q11 and Q12 becomes smaller, which is equivalent to the switch "on" .
2. Form a logic circuit:
Circuit "AND gate" logic circuit. Its logical expression is P=A. B. Two photosensitive tubes are connected in series. Only when the input logic levels A=1 and B=1, the output P=1. In the same way, logic circuits such as "OR gate", "NAND gate" and "NOR gate" can also be formed.
3. Isolated coupling circuit:
This is a typical AC coupling amplifier circuit. Appropriately selecting the current limiting resistor Rl of the light-emitting circuit so that the current transfer ratio of B4 is a constant can ensure the linear amplification effect of the circuit.
4. High-voltage voltage stabilizing circuit:
The driver tube needs to use a transistor with a higher withstand voltage. When the output voltage increases, the bias voltage of V55 increases, and the forward current of the light-emitting diode in B5 increases, causing the inter-electrode voltage of the photosensitive tube to decrease. The bias voltage of the adjustment tube be decreases and the internal resistance increases, causing the output voltage to decrease. , while maintaining the stability of the output voltage.
Prospects
Optocouplers are widely used in a variety of electronic devices. With the rapid development of digital communication technology and the expanding application of automatic control components such as optical isolators and solid-state relays in the machinery industry, especially the application promotion of microprocessors in various fields and the gradual improvement of product performance, optocouplers The application market will continue to expand.