MOC3021S-TA1 - 400V Triac Driver Optocoupler, 6-SMD | Lite-On
MPN: MOC3021S-TA1 ✓ Active| Qty | Unit Price | Extended |
|---|---|---|
| 1 | $0.16 | $0.16 |
| 10 | $0.14 | $1.40 |
| 100 | $0.11 | $11.00 |
| 500 | $0.09 | $45.00 |
| 1,000 | $0.0722 | $72.20 |
| 3,000 | $0.0605 | $181.50 |
MOC3021S-TA1 Overview
An optotriac or triac-driver optoisolator is a category of optocoupler whose output stage is a photosensitive silicon switch that emulates a triac. The category sits within the broader optocoupler family (LED-photodetector isolation devices) and the wider signal-and-power isolation hierarchy. Triac-driver optoisolators are used wherever a low-power control circuit must command a high-voltage AC load while maintaining galvanic isolation for safety and noise immunity.
Key features of the MOC3021S-TA1 include: 5000 Vrms isolation voltage (Viso), 400 V minimum repetitive peak off-state voltage (VDRM), 100 V/us minimum critical rate of rise of off-state voltage (dV/dt), a forward input LED current typically driven at 10-15 mA (IF on = 8 mA max per datasheet), and a peak on-state output current of 1 A. The device is a non-zero-cross (random-phase) triac driver; it triggers the load triac on the next available mains half-cycle regardless of the AC line voltage crossing point, which makes it suitable for resistive heating loads but less ideal for low-power or highly inductive loads where EMI must be minimized.
The device operates as an optically-coupled trigger: the input LED emits infrared light proportional to forward current; the light strikes the photosensitive silicon bilateral switch, which latches into conduction once its threshold is exceeded. This optical coupling provides the 5000 Vrms safety barrier while the silicon switch handles the AC line voltage on the load side.
Typical applications include solid-state relays (SSRs), AC motor speed controllers, lamp dimmers, solenoid and valve drivers, industrial controls, and interface circuits between microcontrollers and triac-SCR power stages controlling AC mains loads up to 400 V peak (approximately 240 VAC RMS mains).
When designing with this device, note that the MOC3021S-TA1 is a non-zero-cross driver; if zero-cross switching is required (to reduce EMI and inrush current on inductive loads), select the MOC3041S or MOC3042S/3043S family members instead. A snubber RC network (typically 100 ohm + 0.01 uF) across the triac is recommended for inductive loads.
This page synthesizes distributor pricing, drop-in replacement alternatives, and practical design notes not found in the Lite-On datasheet alone, helping engineers select and source the MOC3021S-TA1 with full parametric and supply-chain context.
Drop-in alternatives for MOC3021S-TA1 — same package, pin-to-pin compatible. Different-package parts requiring PCB rework are excluded.
Quick Comparison Tool — Select alternative parts for side-by-side comparison:
MOC3020S-TA1
✅ Drop-In📋 Reference alternative (not in catalog)
MOC3022S-TA1
✅ Drop-In📋 Reference alternative (not in catalog)
MOC3023S-TA1
✅ Drop-In📋 Reference alternative (not in catalog)
MOC3021SR2M
✅ Drop-In📋 Reference alternative (not in catalog)
FODM3011R2
✅ Drop-In📋 Reference alternative (not in catalog)
MOC3021S-TA1 Specifications
| Manufacturer | Lite-On Technology Corporation |
| Part Number | MOC3021S-TA1 |
| Part Series | MOC3020 - MOC3023 |
| Output Type | Triac / SCR (non-zero-cross, random-phase) |
| Number of Channels | 1 |
| Isolation Voltage (Viso) | 5000 Vrms (minimum) |
| Repetitive Peak Off-State Voltage (VDRM) | 400 V (minimum) |
| Critical Rate of Rise of Off-State Voltage (dV/dt) | 100 V/us (minimum) |
| Peak On-State Output Current (ITM) | 1 A |
| Forward LED Current - On (IF(on)) | 8 mA (maximum) |
| Reverse LED Voltage (VR) | 6 V (maximum) |
| Package / Case | 6-SMD, Gull Wing |
| Mounting Type | Surface Mount |
| Operating Temperature | -40C to +100C |
| Zero-Cross Circuit | No (random-phase) |
| Approvals | UL, VDE (per Lite-On datasheet) |
| RoHS Status | Compliant |
MOC3021S-TA1 Pin Configuration
| Pin 1 | Anode (LED+) — Input LED anode; connect to current-limiting resistor from logic supply or driver |
| Pin 2 | Cathode (LED-) — Input LED cathode; typically tied to logic ground |
| Pin 3 | NC — Not connected (no internal connection) |
| Pin 4 | Main Terminal 1 (MT1) — Triac output terminal 1; typically tied to the load side of AC line |
| Pin 5 | Main Terminal 2 (MT2) — Triac output terminal 2; typically tied to AC neutral or load return |
| Pin 6 | Gate (substrate) — Substrate/gate; typically tied to MT1 for the MOC3021 family |
Typical Applications
MOC3021S-TA1 is suitable for 6 applications: Solid-State Relay (SSR) Output Stage, AC Lamp Dimmer / Phase-Angle Control, Microcontroller-to-AC-Load Interface, Industrial Control and PLC Output Modules, Home Appliance AC Switching (Washing Machines, Cookers, HVAC), Telecom and IT Equipment Power Control.
Solid-State Relay (SSR) Output Stage
The MOC3021S-TA1 fits solid-state relay (SSR) AC output stages because its 5000 Vrms isolation creates the safety barrier required between the low-voltage DC control input and the mains-voltage AC load, while its 400 V minimum VDRM rating covers both 110 VAC and 240 VAC RMS mains. Place the device inside the SSR module between the input photodiode driver circuit (typically a 5 mA to 15 mA current source or logic-level GPIO with current-limiting resistor) and the gate of the external power triac (such as a BTA16 or BTA25). Unlike an electromechanical relay, this SSR stage provides zero-cross-free switching at any AC phase angle, enabling phase-controlled dimming and proportional AC motor control with no moving parts and unlimited switching cycles. The 1 A peak on-state current rating supports direct triggering of most standard triacs in the BTA/BTB family, eliminating the need for additional gate-driver circuitry.
Recommended
AC Lamp Dimmer / Phase-Angle Control
The MOC3021S-TA1 is well suited for AC lamp dimming circuits because its random-phase (non-zero-cross) triggering allows the designer to fire the load triac at any point along the AC sine wave, enabling classic phase-angle dimming of incandescent and dimmable LED loads. The 400 V minimum VDRM rating covers the peak of both 120 VAC and 240 VAC mains with adequate headroom. Drive the input LED from a microcontroller GPIO through a current-limiting resistor (typically 330 ohm for 5 V logic yielding ~10 mA forward current), and connect the output side directly to the gate of a TRIAC such as the BTA16. Unlike zero-cross optoisolators that would prevent proportional dimming, the MOC3021S-TA1 fires whenever the LED is on, enabling smooth brightness control from near-zero to full output.
Recommended
Microcontroller-to-AC-Load Interface
The MOC3021S-TA1 fits microcontroller-to-AC-load interface circuits that require a safety-isolated control path for switching solenoids, valves, heaters, and small AC motors from a 3.3 V or 5 V GPIO pin. The 5000 Vrms isolation protects the low-voltage MCU from mains transients and fault conditions, while the 1 A peak output current drives the gate of an external power triac capable of handling the AC load current. Place a 100 ohm + 0.01 uF RC snubber across the load triac to limit dV/dt and prevent false triggering on inductive loads. The non-zero-cross characteristic is acceptable for resistive heaters and inductive solenoids where some EMI is tolerable, making the MOC3021S-TA1 a cost-effective isolation choice in industrial control and home-automation products.
Recommended
Industrial Control and PLC Output Modules
The MOC3021S-TA1 is widely deployed in industrial PLC output modules and process-control equipment because its UL and VDE safety approvals combined with 5000 Vrms reinforced isolation satisfy regulatory requirements for industrial control panels. The 6-SMD gull-wing surface-mount package supports automated PCB assembly, and the 400 V VDRM rating accommodates direct 240 VAC industrial supply operation. The device couples a 24 V PLC logic output to a 240 VAC industrial load through a power triac, providing the safety barrier required between the control cabinet electronics and the field-side AC power wiring. Its 100 V/us dV/dt rating handles typical industrial load transients adequately when paired with a snubber RC network.
Recommended
Home Appliance AC Switching (Washing Machines, Cookers, HVAC)
The MOC3021S-TA1 fits home-appliance AC switching subsystems such as washing-machine motor controls, cooker hot-plate relays, and HVAC damper actuator drivers. Its 5000 Vrms isolation meets IEC 60335 household appliance safety standards, while its small 6-SMD outline saves PCB area compared to electromechanical relays. The device reliably switches inductive motor and solenoid loads from a low-voltage MCU control signal through an external triac. Designers appreciate the long operational life (no mechanical wear) and silent switching compared to electromechanical relays in noise-sensitive appliance environments. With operational temperatures up to +100 C, it operates reliably inside the warm enclosures of cooking and laundry appliances.
Recommended
Telecom and IT Equipment Power Control
The MOC3021S-TA1 is used in telecom and IT equipment power-control subcircuits where low-voltage digital logic must safely interface with AC mains for functions such as power-factor-correction stage switching, fan-speed control, or system power-on sequencing. The 5000 Vrms isolation protects sensitive digital circuitry from mains-borne transients and surge events, while the 6-SMD package supports the high-density PCB layouts common in modern telecom and server equipment. Its compatibility with both 110 VAC and 240 VAC worldwide mains voltages (within the 400 V VDRM limit) makes it attractive for globally-deployed equipment where a single design must support multiple regional mains standards.
Recommended
Recommended Products Summary
Engineering reference data for MOC3021S-TA1 — comparison, design guidance, and compliance information.
Selection Guide
Comparison with Alternatives
| Parameter | This Product | MOC3020S-TA1 | MOC3022S-TA1 | MOC3023S-TA1 | MOC3021SR2M | FODM3011R2 |
|---|---|---|---|---|---|---|
| Brand | Lite-On | Lite-On (same brand) | Lite-On (same brand) | Lite-On (same brand) | Vishay (cross-brand) | onsemi (cross-brand) |
| Package | 6-SMD Gull Wing | 6-SMD Gull Wing - same | 6-SMD Gull Wing - same | 6-SMD Gull Wing - same | 6-SMD Gull Wing - same | 6-SMD Gull Wing - same |
| Repetitive Peak Off-State Voltage (VDRM) | 400 V (min) | 400 V (min) | 400 V (min) | 400 V (min) | 400 V (min) | 400 V (min) |
| Isolation Voltage (Viso) | 5000 Vrms | 5000 Vrms | 5000 Vrms | 5000 Vrms | 5300 Vrms | 3750 Vrms |
| Zero-Cross Circuit | No (random-phase) | No (random-phase) | No (random-phase) | No (random-phase) | No (random-phase) | No (random-phase) |
| LED Trigger Current (IF(on)) | 8 mA (max) | 8 mA (max) | 8 mA (max) | 8 mA (max) | 10 mA (typ) | 15 mA (max) |
Key Differentiators
- Same-family coverage within the MOC3020-MOC3023 series (vs MOC3020S-TA1, MOC3022S-TA1, MOC3023S-TA1)
- Higher isolation voltage rating than cross-brand alternates (vs FODM3011R2 (onsemi))
- Lower LED trigger current than cross-brand alternate (vs FODM3011R2 (onsemi))
- Industry-standard 6-SMD footprint shared with all alternatives (vs all 5 alternatives)
Design Notes
Select a series current-limiting resistor for the input LED such that the forward current IF stays within the 8 mA maximum trigger current plus design margin. For a 5 V logic high driving a 1.2 V typical VF LED, a 470 ohm resistor yields approximately 8 mA forward current. For 3.3 V logic, use a 270 ohm resistor. Always include the resistor; direct drive without current limiting will damage the LED junction. Provide a reverse-protection diode across the LED if reverse-polarity transients are possible.
Pair the MOC3021S-TA1 with an RC snubber (typically 100 ohm in series with 0.01 uF to 0.1 uF, rated for the line voltage) across the external power triac when driving inductive loads such as solenoids, motors, transformers, or relays. The snubber limits the dV/dt seen across the triac during turn-off, preventing false retriggering through the MOC3021S-TA1. Without a snubber, inductive kickback can latch the triac on indefinitely and damage the load.
Estimated: at full 1 A peak on-state current with a typical 1.5 V drop, the MOC3021S-TA1 dissipates up to 1.5 W internally during the brief conduction phase. Since conduction is intermittent (only when the external triac fires), the average dissipation is much lower. Ensure the PCB copper pad beneath the device provides adequate heat-sinking, and verify that the operating ambient temperature stays within the -40 C to +100 C datasheet range, especially in sealed appliance or industrial enclosures with limited airflow.
Maintain at least 8 mm clearance (creepage and clearance distance) between the input side (pins 1-3) and the output side (pins 4-6) of the MOC3021S-TA1 on the PCB to preserve the 5000 Vrms isolation rating in production. Do not route any traces, copper pours, or via under the device body between input and output sides. Place the external RC snubber as close to the AC load triac as possible, and keep the gate-drive trace from MOC3021S-TA1 pin 4/6 to the triac gate short to minimize noise pickup.
Compliance Information
RoHS and REACH compliant per Lite-On datasheet. UL and VDE approved for reinforced insulation. AEC-Q100 not applicable (industrial/commercial grade optocoupler, not automotive qualified).
