The PC817 is a single-channel optocoupler containing an infrared LED optically coupled to a phototransistor, with a four-pin DIP package. A common practical use is transferring a low-speed on/off signal between electrically isolated circuits, using an LED current-limiting resistor on the input and a collector pull-up on the output.

Scope and verification: This library project is named PC817 but does not establish an exact manufacturer ordering code. Its description states 35 V and CTR 50–300%; those figures could not be verified against the project's attached datasheet, whose extraction remained pending after retries. The verified specifications below instead describe Sharp PC817XxNSZ1B, document OP18002EN, dated January 15, 2018; do not automatically assign its 80 V rating to an unidentified PC817. Obtain the actual purchased manufacturer's full MPN, CTR rank and current datasheet before releasing a BOM. No schematic, footprint or component metadata was changed.

Absolute maximum ratings are stress limits, not recommended operating targets. The Sharp ratings below are specified at ambient temperature 25 °C unless a different condition is stated.

The cited Sharp pinout is 1 Anode, 2 Cathode, 3 Emitter, 4 Collector. Orient the package from its manufacturer's top-view diagram and pin-1 mark, not from an assumed underside view.

Isolation rule: GND_IN and GND_OUT must remain electrically separate if galvanic isolation is required. The device has no VCC supply pin, exposed base pin, enable pin or intrinsic logic-level output driver.

Use the following active-high input, active-low output topology:

The engineering equation is R_IN = (V_DRIVE − VF − V_DRIVER_DROP) / IF. For a preliminary nominal calculation only, assume V_DRIVER_DROP = 0, VF = 1.2 V, and target IF = 5 mA. The 1.2 V value is a datasheet typical at 20 mA, not a guaranteed value at 5 mA; the following results are design estimates based on that explicit assumption.

A 0.125 W resistor has substantial margin over these nominal losses, but final selection must use maximum drive voltage, minimum VF, resistor tolerance, driver source/sink limits, ambient temperature and derating. For a GPIO, use its guaranteed VOH at the desired current—not just the nominal rail voltage. The 430 Ω example falls slightly below the datasheet's 5 mA CTR test point; it therefore does not automatically inherit that minimum CTR guarantee.

CTR = 100 × IC / IF. At the cited 50% minimum CTR test point, IF = 5 mA gives IC = 2.5 mA at VCE = 5 V and 25 °C. This is not a guaranteed saturation sink current at 0.2 V or a guaranteed hot/cold or aged-device value.

For a 10 kΩ pull-up and an illustrative target VOL = 0.2 V, required pull-up current is (3.3 − 0.2)/10,000 = 0.31 mA or (5 − 0.2)/10,000 = 0.48 mA, plus receiver leakage. These calculations quantify the load; they do not prove the device meets that VOL. Sharp's saturation-voltage test uses IF = 20 mA and IC = 1 mA, different from this example.

Check receiver VIL/VIH, worst-case CTR versus current and temperature, LED aging, output leakage and switching speed. Measure VOL and pulse timing on hardware at temperature corners. Use a Schmitt-trigger receiver when slow transitions could violate the receiver's edge-rate requirements. Deep phototransistor saturation and a high-value pull-up can make turn-off substantially slower than the datasheet test circuit.

The following are engineering layout recommendations, not manufacturer-specific numerical PCB rules:

Verification limit: one other-manufacturer candidate was verified for pinout and electrical values; a second manufacturer's candidate was identified but its detailed datasheet evidence remained unavailable. Neither is approved here as an unconditional drop-in replacement, and no footprint geometry was edited or validated.

No unsupported third alternative is presented merely to fill the table. Qualification must include operating voltage, worst-case CTR, output leakage, saturation behavior, pulse timing, temperature, safety approvals and exact PCB footprint—not just the four-pin symbol.

Research date: October 6, 2026. Distributor stock, pricing and lead time are dynamic; no purchase or live-stock guarantee is made.

Outstanding release checks: identify the actual manufacturer and full PC817 ordering code; resolve its voltage/CTR description mismatch; verify its numerical package geometry; obtain citation-backed Lite-On compatibility evidence before qualifying a second manufacturer's replacement.