Is there a pin-compatible replacement for MOC3021S-TA1?

The Vishay IL420 and IL4208 series are likely pin-compatible as they use the same standard 6-SMD package. However, they are not drop-in replacements because their input trigger current is much lower, which necessitates a change to the input drive circuit.

What risks should I check before replacing MOC3021S-TA1?

The main risk is electrical. The suggested alternatives have a much more sensitive input (lower trigger current). Using them without changing the input resistor could damage the device's LED. Always verify the package lead form also matches your PCB layout.

MOC3021S-TA1 Alternatives, Datasheet & Cross Reference | LITEON

MOC3021S-TA1 is a 400V non-zero crossing triac driver optocoupler in a 6-SMD package. Key alternatives include the Vishay IL420 and IL4208 series, which offer higher voltage ratings but require review of the input drive circuit.

AI replacement insight

Electrical riskmedium

Input trigger current is much lower, requiring circuit modification.

Package risklow

All candidates use the same standard 6-SMD package.

Can it be replaced directly?

While no drop-in replacement is confirmed without circuit review, the Vishay IL420 is a form, fit, and function compatible alternative to the MOC3021S-TA1, sharing the same package and non-zero crossing function.

Best replacement path

The Vishay IL420 series is a strong functional alternative with a higher 600V rating. For applications requiring more margin, the IL4208 offers an 800V upgrade.

Main risk

The primary risk is the significant difference in LED trigger current (IFT). Replacements are much more sensitive (1.3-2mA vs 15mA), requiring adjustment of the input series resistor.

Recommended alternatives

A functional alternative with a higher voltage rating, but requires input circuit modification due to higher sensitivity.

View details

Alternative comparison matrix

Feature / factor	MOC3021S-TA1	IL420-X009T	IL420-X017	IL4208-X007	Compatibility / risk
Package	6-SMD	6-SMD	6-SMD	6-SMD	6-SMD — Package matches.; IL420-X017: Package matches.; IL4208-X007: Package matches.
Zero Crossing	No	No	No	No	No — Both are non-zero crossing (random phase) drivers.; IL420-X017: Both are non-zero crossing (random phase) drivers.; IL4208-X007: Both are non-zero crossing (random phase) drivers.
Voltage	400 V	600 V	600 V	800 V	600 V / 800 V — Higher off-state voltage provides more margin.; IL420-X017: Higher off-state voltage provides more margin.; IL4208-X007: Significant upgrade in off-state voltage.
Current	15 mA	2 mA	2 mA (typ)	1.3 mA (typ)	2 mA / 2 mA (typ) / 1.3 mA (typ) — Much more sensitive input; requires input resistor review.; IL420-X017: Much more sensitive input; requires input resistor review.; IL4208-X007: Extremely sensitive input; requires input resistor review.
Temperature	-40°C to +100°C	-55°C to +100°C	-	-	-55°C to +100°C — Wider operating temperature range.

Application & sourcing insights

Questions & answers

The best alternatives for MOC3021S-TA1 are from the Vishay IL420 (600V) and IL4208 (800V) series. They are functionally equivalent non-zero crossing drivers but offer higher voltage ratings. However, they require circuit review due to a more sensitive input.