Triac output optocoupler for AC load switching
The IL4208 from Vishay is a single-channel optocoupler with a triac output, designed to switch AC loads from a low-voltage logic or microcontroller signal. Its 5300 Vrms isolation rating provides a reinforced safety barrier between the control side and the mains-powered load, making it a standard choice for industrial motor drives, solid-state relays, and appliance controls where galvanic isolation is mandatory. The output triac is rated for 800 V off-state voltage, covering 240 VAC line switching with healthy margin, and can handle 300 mA RMS on-state current — enough to drive small AC loads like contactor coils, solenoids, or indicator lamps directly without an external triac. A minimum static dV/dt of 10 kV/µs ensures the triac does not falsely trigger from fast voltage transients common on inductive or noisy AC lines, a critical parameter in motor-drive and power-supply environments.
Sizing the load and drive current
The 300 mA RMS on-state current sets the maximum continuous load. If your load draws more, the IL4208 can drive the gate of a larger external triac or SCR. Forward voltage is 1.16 V typical, so a 3.3 V supply with a 1 kΩ resistor delivers about 2.1 mA — above the trigger threshold but well under the 60 mA absolute maximum. Hold current is 500 µA. If the load current drops below that near the AC zero-cross, the triac may turn off prematurely. For lightly inductive or resistive loads, confirm the minimum load current exceeds Ih over the full operating range.
The IL4208 comes in a 6-pin DIP package with 0.300-inch (7.62 mm) body width, a standard through-hole footprint that suits point-to-point wiring or breadboard prototyping. The 6-DIP supplier device package is the same as the industry-standard footprint used by many second-source optocouplers, easing board layout. The part is ROHS3 compliant.
It holds approvals from CQC, CSA, cUR, and UR, covering North American and Chinese safety standards — a useful qualification for equipment destined for those markets.