What types of photocouplers are available?
- 1. Transistor Coupler
- When photocouplers were initially marketed, only this type was available. It is still used in a wide range of fields because of its low price and high versatility. There are products featuring high conversion efficiency, high withstand voltage, low input drive capability, etc.
- 2. High-Speed IC Output Coupler
- It has integrated light receiving elements in order to provide a high-speed capability. Compared with the signal transmission capability of the transistor output type of up to tens of kHz at most, this type provides high-speed signal transmission of 1 to 10 MHz. There are mainly two product groups; 1) general-purpose products intended to transmit logic signals, and 2) those having specific capabilities such as driving the gates/bases of the power elements (IGBT).
- 3. Triac Coupler
- This type of couplers are mainly used for controlling AC loads such as motors, and solenoids, which are directly connected to the 100 or 200 Vrms commercial power sources used in the households, offices and factories. Making use of a triac with high element withstand voltage, they can turn on/off with a microcurrent of 10-odd mA, providing electrical insulation. A single element can only control an AC current of about 100 mA, but a combination with a power triac makes it possible to control an AC current of up to several amperes. Some products incorporate the power triac in a phototriac.
- 4. Photorelay
- Equipped with a MOSFET in an output stage, this element has the capabilities equivalent to a mechanical relay and read relay. It is also capable of switching analog signals because the MOSFET has linear output characteristics.
