5300 Vrms isolation, 800 V off-state — the AC load isolator
The Vishay VO4258H is a single-channel optoisolator with a Triac output, designed to switch AC loads from a low-voltage control side while providing 5300 Vrms galvanic isolation. It handles an off-state voltage of 800 V and can conduct up to 300 mA RMS on-state current, making it a fit for driving solenoids, small motors, relays, and resistive AC loads in industrial and appliance controls.
5 kV/µs dV/dt — why it matters for inductive loads
The minimum static dV/dt of 5 kV/µs is the key spec for this part class. When switching inductive loads like a contactor coil or a small transformer, the rapid voltage rise across the Triac after turn-off can falsely trigger it back on if the dV/dt immunity is too low. The VO4258H's 5 kV/µs rating gives solid margin for 50/60 Hz line applications without an external snubber in many cases. There is no zero-crossing circuit, so the Triac fires immediately on the LED trigger — useful for phase-control or random-turn-on schemes, but the load current must be considered for EMI.
Temperature range and approvals
It carries approvals from BSI, cUR, FIMKO, and UR, easing compliance for equipment sold into North American and European markets. The LED forward voltage is 1.2 V typical, with a maximum DC forward current of 60 mA and a maximum LED trigger current of 2 mA — the low trigger current means a standard GPIO or open-collector output can drive it directly.