An optocoupler equivalent is only equivalent when five specs match: output type, current transfer ratio (CTR) rank, common-mode rejection (CMR) and the voltage it was tested at, isolation rating, and temperature range. Package and pinout come first, but they are where most cross-reference charts stop. A PC817 and an EL817 share the same 4-pin DIP pinout. A 6N137 and an HCPL-0601 share the same 10 MBd logic output. In both pairs one part can still fail in the other's socket. The sections below check each spec against real datasheet numbers, using the Sharp PC817 and the Broadcom 6N137 family as reference points. Figures are as of November 2026.
Optocoupler equivalent chart by family
Optocouplers only cross-reference inside their own output family. A transistor-output part never replaces a logic-gate, triac-driver or gate-driver part, even when the pin count matches. Start by finding the family your part belongs to, then use the five checks that follow.
| Family | Typical part numbers | Package | Usually swappable within the family | What still differs |
|---|---|---|---|---|
| Transistor output, DC input, 4-pin | PC817, LTV-817, EL817, PS2501-1, TLP521-1 | 4-pin DIP, SMD gull-wing options | Yes, pin 1 anode, 2 cathode, 3 emitter, 4 collector | CTR rank letter, VCEO, temperature range, isolation approvals |
| Transistor output with base pin, 6-pin | 4N25, 4N35, CNY17 | 6-pin DIP | Within the 6-pin group only | CTR grade suffix, base-pin use in the design |
| AC input, transistor output | TLP290-4, PC814 | SO-16 (quad), 4-pin DIP | Only with other AC-input parts | A DC-input part in this socket conducts on one half-cycle only |
| 10 MBd logic output | 6N137, HCPL-2601, HCPL-2611, HCPL-0600, HCPL-0601, HCPL-0611 | 8-pin DIP (26xx, 6N137), SO-8 (06xx) | Yes, same pinout and enable pin | CMR spans 1,000 to 15,000 V/µs across the family |
| Triac driver | MOC3021, MOC3041 | 6-pin DIP | Within the triac-driver group only | Zero-cross or random-phase, trigger current (MOC3021: 15 mA max) |
| IGBT and MOSFET gate driver | HCPL-3120 | 8-pin DIP | Only gate driver for gate driver | Peak output current, UVLO thresholds, CMR |
Where a chart lists a part in two rows, check the datasheet. A common chart error is a 4-pin PC817 listed against a 6-pin 4N35 socket, and the search "pc817 vs 4n35" shows buyers try the swap. The pin counts differ, so the parts are not interchangeable without a layout change.
Check 1: CTR rank letter, not just the base part number
The letter after PC817 sets a guaranteed CTR window, and it can differ by a factor of four. Sharp's PC817XxNSZ1B datasheet specifies collector current at IF = 5 mA, VCE = 5 V and 25 °C for each rank:
- Rank A: 4.0 to 8.0 mA (CTR 80 to 160%)
- Rank B: 6.5 to 13 mA (130 to 260%)
- Rank C: 10 to 20 mA (200 to 400%)
- Rank D: 15 to 30 mA (300 to 600%)
- No rank mark: 2.5 to 30 mA
Take a board that drives a 1 kΩ pull-up to 5 V from 5 mA of LED current. Pulling the output low needs about 5 mA of collector current. A PC817C guarantees at least 10 mA, double what the circuit needs. A PC817A guarantees only 4 mA, and an unranked PC817 only 2.5 mA, so either can leave the output stuck between logic levels. All three are sold as "PC817", so a buyer approving on base part number alone would pass them. When a second-source datasheet uses different letters, compare the mA windows directly and ignore the letters. Also note that every number above is a 25 °C value. LED output falls with heat and with years of operation, which is why the rank you buy should leave headroom above your design minimum.
Check 2: CMR value and the test voltage behind it
CMR equivalence depends on the common-mode voltage in the test condition, not only the V/µs number. Broadcom's 6N137 family datasheet (AV02-0940EN) lists these minimums:
- 6N137: 1,000 V/µs at |VCM| = 10 V
- HCPL-0600 and HCPL-2630: 5,000 V/µs at |VCM| = 1 kV
- HCPL-0601 and HCPL-2601: 10,000 V/µs at |VCM| = 1 kV
- HCPL-0611 and HCPL-2611: 15,000 V/µs at |VCM| = 1 kV
All of these share a 10 MBd typical speed, the same pinout and the same enable input, which is why charts call them equivalent. They are equivalent going up the list and not going down. A 6N137 is tested at a 10 V common-mode step. Fitted into an HCPL-0601 socket on a 400 V inverter board, it can glitch on every switching edge. Moving from a 6N137 to an HCPL-2601 is an upgrade. The reverse is a field failure that will not show up on the bench.
Worked example from our own stock: GlobX holds 42,000 pcs of HCPL-0601-500E (Avago/Broadcom, date code 22+, part status Active, stored in Germany). The "-500E" suffix means tape and reel, lead-free. A buyer upgrading an SO-8 HCPL-0600 position on a drive controller can move to this part. It has the same footprint and a CMR rating twice as high at the same 1 kV test condition. That is a one-line BOM change rather than a requalification. The reverse, replacing an HCPL-0601 with a cheaper HCPL-0600, halves the CMR margin, and we would flag it on the quote.
Check 3: isolation rating and the option suffix
Two parts with the same base number can carry different isolation ratings, set by an option code in the suffix. In the same Broadcom datasheet, standard HCPL-xxxx parts are UL 1577 recognized at 3,750 Vrms for one minute. The 5,000 Vrms rating applies only to the widebody HCNW parts and to Option 020 of the DIP types. Working-voltage approval to IEC/EN/DIN EN 60747-5-5 needs Option 060, rated VIORM = 567 Vpeak for the SO-8 06xx parts and 630 Vpeak for the DIP 6N137 and 26xx parts.
For EU machinery and drive builders, 60747-5-5 is often the line in the safety file that matters, and an equivalent without the 060 option fails the audit even if it works electrically. Digital isolators have the same trap. TI's ISO7762DBQR in SSOP-16 is rated 3,000 Vrms, while the ISO7762 in the wide SOIC-16 (DW) package reaches 5,000 Vrms. The suffix decides which rating you get. Our part number suffix decoder covers how to read these codes before ordering.
Check 4: speed and output stage
A transistor-output optocoupler cannot replace a logic-output one above a few kilohertz. The PC817 datasheet gives a typical rise time of 4 µs, a maximum of 18 µs and a cut-off frequency of 80 kHz typical. The 6N137 family runs at 10 MBd. So "pc817 vs 6n137" is not a substitution question. A PC817 in a 6N137 socket cannot carry a 1 Mbps RS-485 or encoder signal, and the pin count differs anyway.
Speed also bites in the other direction. A faster part in a slow socket can pass noise spikes the original part filtered out. If the original was a 4-pin transistor type on a 24 V PLC input, keep the replacement in the same family, even if a faster part fits the footprint.
Check 5: temperature range
The PC817 is rated for -30 to +100 °C operating in Sharp's datasheet, so it does not cover the -40 °C minimum that most industrial and outdoor equipment in Europe specifies. Buyers miss this check most often, because the 4-pin transistor family looks fully interchangeable. For comparison:
- Broadcom 6N137 and HCPL-26xx/06xx family: AC and DC parameters guaranteed from -40 to +85 °C
- Toshiba TLP290-4(TP,E), an AC-input quad coupler: -55 to +110 °C. GlobX stocks 5,000 pcs, date code 21+, Active.
- TI ISO7762 digital isolator: -55 to +125 °C
If the original part was a -40 °C grade, every candidate on your chart needs that minimum in writing. Broadcom also states that the 6N137 family is not AEC-Q100 qualified and not recommended for automotive use. Rule it out for vehicle electronics regardless of how well it matches electrically.
When no optocoupler equivalent exists: emulators and digital isolators
When the original part is end-of-life with no in-family match, the usual exit is an opto emulator or a digital isolator. These parts use capacitive or magnetic coupling instead of an LED, so there is no CTR to age. TI's ISOM8710 opto emulator accepts a diode-style input (2 to 20 mA forward current) and runs up to 25 Mbps with a minimum CMTI of 125 kV/µs and 3,750 Vrms isolation. It ships in a 5-pin SOIC, so it does not drop into an 8-pin 6N137 or HCPL-0601 footprint.
Digital isolators such as the ISO7762 go further, with 6 channels at up to 100 Mbps, but they need a supply on both sides of the barrier. A PCB respin is usually needed, so budget for it. That is the same decision the onsemi PD27509X notice forced on FOD2741 users. For a broader method of qualifying a non-identical replacement, see our guide to second-sourcing electronic components.
Five-line approval checklist for an optocoupler substitute
- Same family and pin count as the original (table above).
- CTR window in mA at the original's test current, covering your design minimum with margin.
- CMR at an equal or higher common-mode test voltage, not just an equal V/µs figure.
- Isolation rating and option suffix (UL 1577 Vrms, IEC 60747-5-5 VIORM) that match your safety file.
- Operating temperature range that includes the original's minimum and maximum.
Then check the parts themselves. The rank letter is a printed mark on the body, so a remarked lot can pass a cheap unranked part off as a rank C. Ask for date codes and lot traceability, and apply the checks in our counterfeit avoidance guide before you approve a lot.
Send GlobX the original part number, the rank or option you need and your annual volume. We will come back within 24 hours with in-family equivalents we can ship from European stock, and we will say so when a substitute would need a requalification.
