5000Vrms isolation — the safety barrier for mains-tied designs
The HCPL4503TSR2VM is a single-channel optocoupler from onsemi, built around a phototransistor output with a base terminal brought out. The 5000Vrms isolation rating qualifies it for reinforced insulation between the primary and secondary sides of a power supply, motor drive, or PLC digital input — the same isolation class used in medical and industrial equipment where a single-fault condition must not create a shock hazard.
CTR range and LED drive budget
Current transfer ratio spans 19% to 50% at a forward current of 16 mA. The 19% minimum is the number that governs the worst-case design: at 16 mA input, the output transistor can sink at least 3 mA (19% of 16 mA). If your load requires 5 mA, you need to increase the LED current or choose a part with a higher CTR floor. The 50% maximum matters for the pull-up resistor — too large a resistor with a high-CTR unit saturates the output transistor slowly, stretching the turn-off time beyond the 260ns typical. Forward voltage is 1.45V typical at the LED, with an absolute maximum forward current of 25 mA. The 8 mA output current per channel is the continuous collector current rating — the transistor itself, not the CTR, limits the load side. For driving a logic input with a 10 kΩ pull-up to 5V, the 0.5 mA load is well within the 8 mA ceiling.
Package and temperature grade
This covers most factory-floor, outdoor telecom cabinet, and HVAC controller environments. The 5000Vrms isolation is tested per the component-level standard; system-level creepage and clearance still depend on the PCB layout and any conformal coating.