Optocoupler principle and function
Time:2018-07-12 Hits:927
An optical coupler (OC) is also known as an opto-isolator. The optical coupler transmits electrical signals in light as a medium. It has good isolation for input and output electrical signals, so it is widely used in various circuits. It has become one of the most versatile and versatile optoelectronic devices. An optical coupler generally consists of three parts: light emission, light reception, and signal amplification. The input electrical signal drives a light-emitting diode (LED) to emit a certain wavelength of light, which is received by the photodetector to generate a photocurrent, which is further amplified and output.
The signal is unidirectionally transmitted, and the input end and the output end are completely electrically isolated. The output signal has no influence on the input end, strong anti-interference ability, stable operation, no contact, long service life and high transmission efficiency. Optocouplers were developed in the 1970s and are widely used in electrical insulation, level shifting, interstage coupling, drive circuits, switching circuits, choppers, multivibrators, signal isolation, interstage isolation, Pulse amplifier circuit, digital instrumentation, long-distance signal transmission, pulse amplification, solid state relay (SSR), instrumentation, communication equipment and computer interface. In the monolithic switching power supply, the optocoupler feedback circuit can be constructed by using a linear optical coupler, and the duty ratio is changed by adjusting the current of the control terminal to achieve the purpose of precision voltage regulation.
The main parameters:
The technical parameters of the optocoupler mainly include LED forward voltage drop VF, forward current IF, current transfer ratio CTR, insulation resistance between input stage and output stage, and collector-emitter reverse breakdown voltage V (BR). ) CEO, collector-emitter saturation voltage drop VCE(sat). In addition, parameters such as rise time, fall time, delay time, and storage time need to be considered when transmitting digital signals.
The most important parameter is the current amplification factor transmission ratio CTR (Curremt-Transfer Ratio). It is usually expressed by the DC current transfer ratio. When the output voltage remains constant, it is equal to the percentage of the DC output current IC to the DC input current IF. When the current amplification factor hFE of the receiving tube is constant, it is equal to the ratio of the output current IC, which is usually expressed as a percentage. There are formulas:
CTR=IC/ IF×100%