Introduction to MOC3021

The MOC3021 is a 6-pin DIP (Dual Inline Package) optocoupler that consists of a gallium arsenide infrared emitting diode (IRED) and a light-activated silicon bilateral switch. The input LED is optically coupled to the output phototransistor, allowing for electrical isolation between the input and output circuits.

Key Features of MOC3021

• High isolation voltage (7500 V peak)
• Low input current (5 mA typical)
• High current transfer ratio (CTR) (100% typical)
• Wide operating temperature range (-40°C to +85°C)
• UL recognized and CSA certified

MOC3021 Pin Configuration

The MOC3021 has a 6-pin configuration, with pins arranged as follows:

Pin Number	Function
1	Anode
2	Cathode
3	NC
4	Emitter
5	Collector
6	NC

NC stands for “No Connection.”

Schematic Diagram

The following schematic diagram illustrates the internal structure of the MOC3021:

         +-----+
1 Anode -|     |- 6 NC
2 Cathode-|     |- 5 Collector
    NC   -|     |- 4 Emitter
         +-----+

Electrical Characteristics

Absolute Maximum Ratings

Parameter	Symbol	Value	Unit
Forward Input Current	IF	60	mA
Peak Forward Input Current	IFP	3	A
Reverse Input Voltage	VR	6	V
Power Dissipation	PD	100	mW
Junction Temperature	Tj	100	°C
Storage Temperature Range	Tstg	-55 to +150	°C
Lead Soldering Temperature	–	260	°C

Electrical Characteristics (Ta = 25°C)

Parameter	Symbol	Min.	Typ.	Max.	Unit
Forward Voltage	VF	–	1.2	1.5	V
Reverse Current	IR	–	–	10	µA
Collector-Emitter Breakdown Voltage	VCEO	400	–	–	V
Collector Dark Current	ICEO	–	–	50	nA
Current Transfer Ratio	CTR	50	100	600	%

Applications of MOC3021

The MOC3021 finds applications in various fields, such as:

Power Supply

In power supply circuits, the MOC3021 is used for:
– Isolated feedback in switched-mode power supplies (SMPS)
– Over-voltage and over-current protection
– Soft-start circuits

Motor Control

The MOC3021 is employed in motor control applications for:
– Isolating control signals from high-voltage motor drives
– Protecting microcontrollers and other low-voltage circuitry
– Providing phase control in AC motor drives

Industrial Automation

In industrial automation systems, the MOC3021 is utilized for:
– Isolating input and output signals in programmable logic controllers (PLCs)
– Interfacing with sensors and actuators
– Ensuring safe operation in harsh industrial environments

MOC3021 Application Circuits

Basic Isolated Driver Circuit

The following circuit demonstrates a basic isolated driver using the MOC3021:

          +5V
           |
          +-+
          | |
          | | R1
          | | 330Ω
          +-+
           |
           |     MOC3021
           |   +-----+
           +---|     |---+
               |     |   |
               |     |   | R2
               |     |   | 1kΩ
               +-----+   |
                   |     |
                   |     |
                  +-+   +-+
                  | |   | |
                  | |   | | Load
                  | |   | |
                  +-+   +-+
                   |     |
                  GND   GND

In this circuit, when a logic high signal is applied to the input (anode), the IRED inside the MOC3021 turns on, activating the phototransistor. This allows current to flow through the load connected to the output (collector and emitter). R1 limits the input current, while R2 ensures proper turn-off of the phototransistor.

AC Power Control Circuit

The MOC3021 can also be used for AC power control, as shown in the following circuit:

                  MOC3021
         +-----+       +-----+
Hot -----|     |-------|     |-----+
         |     |       |     |     |
         |     |       |     |     |
         |     |       |     |     | TRIAC
         +-----+       +-----+     |
            |             |        |
            |             |        |
            |             |        |
            +-------------+        |
                                   |
                                   |
                                   |
Neutral ------------------------------+

In this circuit, the MOC3021 is used to isolate the control circuit from the high-voltage AC power. The TRIAC is triggered by the MOC3021’s output, allowing for phase control of the AC load. This configuration is commonly used in dimmer circuits, temperature controllers, and motor speed control applications.

FAQs

1. What is the main purpose of the MOC3021?
   The main purpose of the MOC3021 is to provide electrical isolation between input and output circuits while allowing for signal transmission.

2. What is the typical forward current required to turn on the IRED in the MOC3021?
   The typical forward current required to turn on the IRED in the MOC3021 is 5 mA.

3. Can the MOC3021 be used for AC power control?
   Yes, the MOC3021 can be used for AC power control in conjunction with a TRIAC, as shown in the AC power control circuit example.

4. What is the maximum isolation voltage provided by the MOC3021?
   The MOC3021 provides a maximum isolation voltage of 7500 V peak.

5. What is the typical current transfer ratio (CTR) of the MOC3021?
   The typical current transfer ratio (CTR) of the MOC3021 is 100%.

Conclusion

The MOC3021 is a versatile optocoupler that offers reliable electrical isolation and signal transmission capabilities. Its key features, such as high isolation voltage, low input current, and wide operating temperature range, make it suitable for a broad range of applications in power supply, motor control, and industrial automation systems.

By understanding the MOC3021 datasheet, pin configuration, electrical characteristics, and application circuits, designers can effectively integrate this device into their projects, ensuring safe and efficient operation. With its robust performance and industry certifications, the MOC3021 continues to be a popular choice for engineers and hobbyists alike.