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MOC3021 Triac Driver: Pinout, Datasheet, Equivalent [Video]

Author: Mia Date: 1 Apr 2021  275

moc3021 datasheet

The MOC3021 is a Zero-Crossing TRIAC driven Optocoupler or Optoisolator.


As we know, the term Optocoupler/Optoisolator means the same thing that we use light to indirectly couple circuit sets. The speciality of MOC3021 is that it has a Zero-Crossing ability and is driven by a Triac.

This video tells how to make an Arduino based 110/220vac Bulb dimming Control system using MOC3021


MOC3021 Description

MOC3021 Pinout

MOC3021 Features

MOC3021 Equivalent

Where to use MOC3021 Phototransistor Optocoupler

How to Use MOC3021 Phototransistor Optocoupler

MOC3021 Applications

MOC3021 Package

Component Datasheet


MOC3021 Description

MOC3021 belongs to the MOC301XM and MOC302XM series from ON Semiconductor, they are optically isolated triac driver devices. These devices contain a GaAs infrared emitting diode and a light activated silicon bilateral switch, which functions like a triac. They are designed for interfacing between electronic controls and power triacs to control resistive and inductive loads for 115 VAC operations.


The MOC3021 comes in an internal light-emitting diode and a TRIAC based light activating based transistor. This optocoupler provides protection from HIGH resistive and inductive loads. It has the ability to flow the current up to 1A. 


MOC3021 Optocoupler work on the IR based and it keeps any kind of current to flow towards the circuit. The optocoupler comes only in one package but the single package could be used with any circuit. In HIGH load the operating temperature always affects the circuit performance, but MOC3021 has the ability to operate in HIGH temperature and it also increases the optocoupler life.

MOC3021 Pinout

moc3021 moc3021 pinout
MOC3021 MOC3021 Pinout


Pin Name Description
Anode (A) Anode pin of the IR LED. Connected to logic input
Cathode (C) Cathode pin of the IR LED
NC No Connection - Cannot be used
Triac Main Terminal 1 One end of the Triac which is present inside the IC
NC No Connection – Cannot be used
Triac Main Terminal 2 Other end of the Triac which is present inside the IC


MOC3021 Features

  • Opto-isolator with Zero-Crossing Triac Driver

  • Input LED Diode Forward Voltage: 1.15V

  • LED Forward Latch Current: 15mA

  • TRIAC output terminal voltage: 400V (max)

  • TRIAC peak output current: 1A

  • Available as 6-pin PDIP with and without M-suffix

MOC3021 Equivalent


Alternatives Opto-couplers: MCT2E (non-Zero transistor), MOC3041 (Non-Zero Cross TRIAC), FOD3180 (High-Speed MOSFET),

Where to use MOC3021 Phototransistor Optocoupler

Since the output is driven by the TRIAC, we can drive loads up to 400V and the triac can operate in both directions, so controlling the AC loads will not be a problem. Also, since it has a zero-crossing capability, when the AC load is switched on for the first time, the TRIAC will start conduction only after the AC wave reaches 0V, so we can avoid direct peak voltages to the Load and thus prevent it from being damaged. It also has a decent rise and fall time and can therefore be used to control the output voltage.


This feature of the MOC3021 makes it the ideal choice for controlling high voltage AC loads through digital controllers such as MPU/MCU. Since the output is controlled, the intensity of the light or the speed of the AC motor can be controlled. So if you're looking for an opto-isolator to control an AC application through DC, this IC might be the right choice for you.

How to Use MOC3021 Phototransistor Optocoupler

The MOC3021 is normally used to control the AC appliance, such as the brightness of the bulb, the speed of the motor, etc. Either way, due to its limited current rating, an opto-coupler will not be allowed to drive loads directly. In our case, they are normally connected to another power switch like the Triac, this TRIAC will be able to provide enough current to drive the loads and will be controlled using an opto-coupler. A simple circuit diagram in which the AC bulb is controlled by a microcontroller is shown below.

MOC3021 Microcontroller Interfacing DiagramMOC3021 Microcontroller Interfacing Diagram


The MOC3021 can be used to switch loads by simply switching the LED on or off, or we can also use PWM signals to switch the LED and thus the TRIAC. When the TRIAC is switched by using PWM signals, the output voltage across the load can be controlled by controlling the speed/brightness of the load.


It is important to understand the switching speed of the opto-coupler when trying to switch AC loads. This switching speed depends on the voltage amplitude controlled by the TRIAC and the operating ambient temperature. The graph below will give you a good understanding of how long it takes.

MOC3021 Switching Speed Graphic

MOC3021 Switching Speed Graphic


For example, at 30 degrees Celsius of ambient temperature, the rate of voltage change with respect to time will be 9V per unit time, where the unit time is uS. So we can change 9V in one micro second.

MOC3021 Applications

  • AC Light dimmers

  • Strode lights

  • AC motor speed control

  • Noise coupling circuits

  • Controlling AC loads using MCU/MPU

  • Ac/DC Power control

MOC3021 Package

MOC3021 Package

Component Datasheet

MOC3021 Datasheet


  • What is MOC3021?

MOC3021 is a zero crossing based optoisolator consists of gallium arsenide infrared emitting diodes, optically coupled to a silicon-based triac. ... It is having internal TRIAC installed which gives it a capability to control any external switching devices like HIGH POWER TRIAC, MOSFETS, and Solid States Relay.

  • What is an optocoupler used for?

When used correctly, an Optocoupler can effectively: Remove electrical noise from signals. Isolate low-voltage devices from high-voltage circuits. Allow you to use small digital signals to control larger AC voltages.

  • How are optocouplers measured?

Using the diagram in the right identify the pins; first the anode and cathode of the LED ( in this case pins 1 and 2 ), and then using an ohmmeter set on the 'X1 Ohm' domain, measure between pins 1 and 2, and you should get one reading measuring one way and no reading the opposite way (just like you check a diode).


Ordering & Quality

Photo Mfr. Part # Company Description Package PDF Qty Pricing
MOC3021M MOC3021M Company:ON Semiconductor Remark:OPTOISOLATOR 4.17KV TRIAC 6DIP Package:6-DIP (0.300", 7.62mm)
In Stock:2217
1+: $0.62000
10+: $0.48400
100+: $0.31030
500+: $0.26682
1000+: $0.20601
2500+: $0.18615
5000+: $0.17374
10000+: $0.16754
MOC3021SR2M MOC3021SR2M Company:ON Semiconductor Remark:OPTOISOLATOR 4.17KV TRIAC 6SMD Package:6-SMD, Gull Wing
In Stock:3000
1000+: $0.22695
2000+: $0.21182
5000+: $0.20426

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