Optoisolator - Optical galvanic isolation systems
The optocoupler contains a light source . This is almost always an IR LED , which converts the electrical input signal into light, a dielectric optical channel, and a light detector that detects the emitter light. It generates electricity directly or modulates electric current flowing from an external power source. This sensor may be a photoresistor, photodiode, phototransistor or phototriac. Because LEDs can detect light in addition to emitting it, it is possible to construct symmetrical bidirectional optical isolators using them. Typically, optocouplers transmit digital signals (on-off), although some techniques allow their use with analog signals.
Advantages of using galvanic isolation in electronic systems
Electronic equipment and signal and power transmission lines may be subject to voltage spikes induced by lightning, electrostatic discharge, etc. A lightning strike can cause a voltage increase of up to 10,000 V. Such high voltage spikes can damage input circuits as well as entire electronic devices. The main function of an optocoupler is to block such high voltages. This element eliminates the risk of transient states occurring in the signal path. Commercially available optocouplers withstand input voltages up to 10 kV and pulses with a rise time of up to 25 kV/μs.
The most important parameters of optocouplers
When selecting a galvanic isolator , regardless of the type, you need to pay attention to two parameters. One of them is the maximum allowable transmission rate , which will limit the communication speed through the optical isolation barrier. The second parameter is the maximum allowable potential difference between the primary and secondary sides of the system. Most optoisolators on the market use inexpensive, bipolar silicon phototransistor sensors. They achieve average data transfer speeds, sufficient for applications such as signal isolation in automation or protection of digital interfaces. The fastest optoisolators use PIN photodiodes in the photoconduction mode.
Easy implementation in the system
Modern integrated optocouplers require only a minimum number of external components to operate. Elements of this type are adapted to their role - the role of galvanic isolators of digital lines, therefore the input and output of the system operate in the TTL logic standard - 5 V, 3.3 V and others, as needed. Only two resistors are needed to implement a typical optocoupler with an LED and a phototransistor. Multiple optocouplers available in our store, containing several insulators in one housing, facilitate installation and reduce the area on the PCB occupied by galvanic isolation of signals.
