5300Vrms isolation in a 4-DIP through-hole package
The Vishay SFH628A-4 is a single-channel optoisolator with a transistor output, rated for 5300Vrms isolation. It comes in a 4-DIP through-hole package (0.300", 7.62mm pitch), making it a drop-in fit for boards that need a reinforced safety barrier between primary and secondary sides—think industrial motor drives, PLC digital inputs, or AC-line sensing circuits where galvanic isolation is non-negotiable. The input side accepts both AC and DC signals, so you can couple a line waveform or a DC logic level through the same LED without worrying about polarity.
The current transfer ratio ranges from 160% minimum to 500% maximum, both specified at 1 mA forward current. That means with 1 mA through the LED, the output transistor can sink at least 1.6 mA and up to 5 mA. For a typical 5 V logic input, a 10 kΩ pull-up resistor needs only 0.5 mA from the output—well within the CTR floor, even with LED aging and temperature derating. The wide CTR spread (bin '4') lets you design for the minimum and still have headroom, without over-driving the LED. Output saturation is capped at 400 mV (Vce(sat)), which keeps the logic-low voltage clean for TTL or CMOS inputs.
The wide range also means the CTR and switching times (3.5 µs rise, 5 µs fall typical) stay predictable across temperature extremes—important when the opto is part of a feedback loop or a safety-rated digital input.