Why Are Photocouplers Necessary?

In the photocoupler, the primary side (LED side) and the secondary side (light-receiving-device side) are electrically insulated. Therefore, even if the potentials on the primary side and the secondary side (even GND potential) are different, the primary side electrical signal can be transmitted to the secondary side.

In the inverter application shown in the figure on the right, a controlling unit such as a microcontroller operates usually at low DC voltage. On the other hand, IPMs and IGBTs drive loads that need high voltage such as 200 V AC. High-voltage system parts can be controlled directly from the microcomputer via a coupler.

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