EL357N

The EL357N-G series is Everlight Electronics' four-pin SOP phototransistor photocoupler: an infrared emitting gallium arsenide diode optically coupled to a silicon phototransistor in a compact surface-mount outline with a 2.0 mm profile. Pin configuration is 1 anode, 2 cathode, 3 emitter, 4 collector — the same arrangement as the PC817S, LTV-817S and Toshiba TLP281, which is why the EL357N is treated across the industry as a PC817-class second source. The series is halogen-free, RoHS and EU REACH compliant, and carries UL and cUL approval under file E214129, VDE approval 132249, SEMKO, NEMKO, DEMKO and FIMKO certificates, plus CQC.

The datasheet (DPC-0000014 Rev 9) specifies 3750 Vrms isolation for one minute with the input pins shorted and the output pins shorted, 50 mA maximum input forward current, 1 A peak forward current on a 1 µs pulse, 6 V reverse voltage, 70 mW input dissipation derating at 2.9 mW/°C, 150 mW collector dissipation derating at 3.7 mW/°C above 70 °C, 200 mW total package dissipation, 50 mA maximum collector current, 80 V minimum collector-emitter breakdown at IC = 0.1 mA, and a -55 °C to +110 °C operating range. The LED forward voltage is 1.2 V typical and 1.4 V maximum at IF = 20 mA, reverse leakage is 10 µA maximum at VR = 4 V, collector-emitter dark current is 100 nA maximum at VCE = 20 V, saturation voltage is 0.1 V typical and 0.2 V maximum at IF = 20 mA with IC = 1 mA, isolation resistance is 5 x 10^10 Ω minimum at 500 Vdc, floating capacitance is 0.6 pF typical, and rise and fall times are 18 µs maximum at VCE = 2 V, IC = 2 mA and RL = 100 Ω.

Current transfer ratio is graded at IF = 5 mA and VCE = 5 V — the same test condition Sharp uses for the PC817 — with EL357N (blank) covering 50 % to 600 %, grade A 80 % to 160 %, B 130 % to 260 %, C 200 % to 400 %, D 300 % to 600 %, E 100 % to 200 % and F 150 % to 300 %. Grade C is the industry default for TL431-based flyback feedback, where enough loop gain at end of life matters more than drive efficiency; grades D and above suit low-power supplies that must minimize LED current. Always design to the minimum CTR at high temperature and after LED degradation, which typically halves the initial ratio after years at elevated current and temperature. With 18 µs maximum rise and fall times, this is a feedback and slow-digital isolator, not a bus isolator.

Two sourcing points deserve emphasis. First, pin compatibility with the PC817S does not mean specification compatibility: Sharp rates the PC817 at 5000 Vrms while the EL357N is rated 3750 Vrms and the Toshiba TLP281 at 2500 Vrms, so if reinforced insulation across mains is part of your safety case, verify the working insulation voltage and the approval certificate for the brand actually mounted. Second, the EL357N is a common target for off-bin and remarked product; the failure mode is a reel labeled grade C that measures like grade A, which shows up as a marginal feedback loop months later. Screen by measuring CTR at IF = 5 mA and VCE = 5 V on samples, checking saturation voltage and dark current, inspecting laser marking and reel labels against the full ordering code (for example EL357N(C)-TA-G), and buying through the authorized Everlight channel. MOQ is tape-and-reel quantity dependent on the packing code; Shenzhen stock ships in 1 to 2 days.