Definition: An optocoupler (or optoisolator) is an electronic component that transfers electrical signals between two isolated circuits using light. It prevents high voltages from affecting the system receiving the signal.

Key Components

• LED (Light Emitting Diode): Converts electrical input signal to light.
• Photodetector: Detects light and converts it back to an electrical signal (e.g., phototransistor, photodiode, or triac).

Common Types

Applications

• ✔ Isolate microcontrollers from high-voltage circuits
• ✔ Noise suppression in industrial environments
• ✔ Switch-mode power supply feedback loops
• ✔ Digital communication (UART, SPI) isolation
• ✔ Solid-state relays (SSRs)

Key Parameters

CMT (Current Transfer Ratio)

Ratio of output current to input LED current (e.g., 100% = 1mA in → 1mA out)

Isolation Voltage

Up to 5kV typical; ensures safety between input/output

Response Time

From microseconds (general) to nanoseconds (high-speed types)

Operating Temperature

Usually -55°C to +110°C

IN ──┤LED├───┐
              │
             [R]
              │
GND ──────────┘
              │
OUT ──┬─ Collector (C)
      └─ Emitter (E) ── GND
        (via load)
        Base (B) often left floating or pulled down