CMOS interface circuit

Optocoupler (optical coupler, English abbreviation OC) is also called optical coupler, or optocoupler for short. Optocouplers use light as a medium to transmit electrical signals. It has good isolation effect on input and output electrical signals, so it is widely used in various circuits. At present, it has become one of the most diverse and widely used optoelectronic devices. Optocouplers generally consist of three parts: light emission, light reception and signal amplification. The input electrical signal drives the light-emitting diode (LED) to emit light of a certain wavelength, which is received by the photodetector to generate a photocurrent, which is further amplified and output. This completes the conversion of electricity-optical-electricity, thereby playing the role of input, output, and isolation. Since the input and output of the optocoupler are isolated from each other and the electrical signal transmission is unidirectional, it has good electrical insulation and anti-interference capabilities. And because the input end of the optocoupler is a low-resistance component that works in the current mode, it has strong common-mode suppression capabilities. Therefore, it can greatly improve the signal-to-noise ratio as a terminal isolation component in long-term transmission of information. As an interface device for signal isolation in computer digital communications and real-time control, it can greatly increase the reliability of computer work. The main advantages of the optocoupler are: one-way signal transmission, complete electrical isolation between the input and output ends, the output signal has no impact on the input end, strong anti-interference ability, stable operation, no contacts, long service life, and transmission efficient. Optocouplers are new devices developed in the 1970s and are now widely used in electrical insulation, level conversion, inter-stage coupling, drive circuits, switching circuits, choppers, multivibrators, signal isolation, inter-stage isolation, Pulse amplifier circuits, digital instruments, long-distance signal transmission, pulse amplification, solid state relays (SSR), instrumentation, communication equipment and microcomputer interfaces. In a single-chip switching power supply, a linear optocoupler can be used to form an optocoupler feedback circuit, and the duty cycle can be changed by adjusting the control terminal current to achieve precise voltage stabilization.