Key Features and Benefits
The MOC3021 offers several key features and benefits:
- High isolation voltage (7500 VRMS)
- Low input current (5 mA)
- High current transfer ratio (CTR) (> 100% @ IF = 5 mA)
- Wide operating temperature range (-40°C to +85°C)
- UL recognized and CSA approved
These features make the MOC3021 suitable for a wide range of applications requiring reliable isolation between low voltage control circuits and high voltage loads.
Pin Configuration and Functions
The MOC3021 has a 6-pin DIP package with the following pin configuration:
| Pin | Symbol | Function |
|---|---|---|
| 1 | NC | No Connection |
| 2 | ANODE | Anode of IRED |
| 3 | CATHODE | Cathode of IRED |
| 4 | MAIN TERMINAL 1 | Main terminal 1 of bilateral switch |
| 5 | MAIN TERMINAL 2 | Main terminal 2 of bilateral switch |
| 6 | NC | No Connection |
The IRED is connected between pins 2 and 3, while the bilateral switch is connected between pins 4 and 5. Pins 1 and 6 have no internal connection.
Absolute Maximum Ratings
The MOC3021 has the following absolute maximum ratings:
| Parameter | Symbol | Value | Unit |
|---|---|---|---|
| Input Forward Current | IF | 50 | mA |
| Peak Forward Current (1 μs pulse width, 300 pps) | IFP | 1 | A |
| Reverse Input Voltage | VR | 6 | V |
| Power Dissipation | PD | 100 | mW |
| Operating Temperature Range | Topr | -40 to +85 | °C |
| Storage Temperature Range | Tstg | -40 to +100 | °C |
| Isolation Voltage (RMS, 1 minute) | VISO | 7500 | V |
Exceeding these ratings may cause permanent damage to the device.
Electrical Characteristics
The MOC3021 has the following electrical characteristics at TA = 25°C, unless otherwise specified:
| Parameter | Symbol | Min | Typ | Max | Unit | Test Condition |
|---|---|---|---|---|---|---|
| Input Forward Voltage | VF | – | 1.2 | 1.5 | V | IF = 10 mA |
| Input Reverse Current | IR | – | – | 10 | μA | VR = 6 V |
| Input Capacitance | Cin | – | 30 | – | pF | f = 1 MHz, VF = 0 |
| Peak Off-State Voltage | VDRM | – | 400 | – | V | – |
| Peak On-State Current | ITRM | – | 100 | – | mA | – |
| On-State Voltage | VTM | – | – | 3 | V | ITM = 100 mA |
| Off-State Current | IDRM | – | – | 100 | nA | VDM = 400 V |
| Current Transfer Ratio | CTR | 100 | 300 | – | % | IF = 5 mA, VCE = 10 V |
| Isolation Resistance | RISO | 10^11 | – | – | Ω | VIO = 500 VDC |
| Capacitance | Cio | – | 0.6 | – | pF | f = 1 MHz, VIO = 0 |
| Turn-On Time | ton | – | 5 | 15 | μs | IF = 5 mA, RL = 100 Ω |
| Turn-Off Time | toff | – | 15 | 50 | μs | IF = 5 mA, RL = 100 Ω |
These characteristics help designers understand the device’s behavior under various operating conditions and design circuits that meet the application requirements.
Applications
The MOC3021 is widely used in various applications requiring isolation between low voltage control circuits and high voltage loads, such as:
- Solid-state relays (SSRs)
- Motor drivers
- Switching power supplies
- Lighting control systems
- Industrial automation and control systems
Solid-State Relays (SSRs)
Solid-state relays are electronic switches that use semiconductor devices to switch high voltage loads, offering several advantages over electromechanical relays, such as:
- No moving parts, resulting in longer life and higher reliability
- Faster switching speeds
- No contact bounce or arcing
- Silent operation
- Smaller size and weight
The MOC3021 is commonly used as the input stage of an SSR, providing isolation between the low voltage control circuit and the high voltage load circuit. A typical SSR circuit using the MOC3021 is shown below:
MOC3021
+---------+
+-----|ANODE |
| | NC |
| |CATHODE |
| | MT1 |-----+
+-----+-----| MT2 | |
| +---------+ |
| |
| |
| |
| |
| ~~~
~~~ | |
| | | |
| | | |
| | | |
| |
~~~ |
| |
| |
| +---+
| | |
+-------------------------+ +-----+
|
~~~
LOAD
In this circuit, the MOC3021 is driven by a low voltage control signal connected to the IRED (pins 2 and 3). When the IRED is forward biased, it emits infrared light, which activates the bilateral switch (pins 4 and 5), allowing current to flow through the load connected to the switch. The load can be an AC or DC device, such as a heater, lamp, or motor.
Motor Drivers
The MOC3021 can also be used in motor driver circuits to provide isolation between the low voltage control logic and the high voltage motor windings. A simple DC motor driver circuit using the MOC3021 and a power MOSFET is shown below:
MOC3021
+---------+ +-------+
+-----|ANODE | | |
| | NC | | |
| |CATHODE | | |
| | MT1 |-----+---|GATE |
+-----+-----| MT2 | | | |
| +---------+ | |DRAIN |
| | | |
| | +---+---+
| | |
| ~~~ |
| | | ~~~
| | | | |
| | | | |
| | | | |
| | |
| ~~~ ~~~
| | |
| | |
| | |
| | +---+
| | | |
+---------------------------+ | +-----+
| |
~~~ ~~~
| | | |
+ +
-
DC
MOTOR
In this circuit, the MOC3021 is used to control the gate of the power MOSFET, which switches the current through the DC motor. When the IRED is forward biased, the bilateral switch turns on, allowing current to flow into the gate of the MOSFET, turning it on and allowing current to flow through the motor. The MOC3021 provides isolation between the low voltage control logic and the high voltage motor circuit, protecting the control circuit from voltage spikes and noise generated by the motor.
Switching Power Supplies
The MOC3021 can be used in switching power supplies to provide feedback isolation between the output and the control circuit. A typical Flyback Converter using the MOC3021 for feedback isolation is shown below:
+-------+
| |
| |
+-----|ANODE |
| | NC |
| |CATHODE|
| | MT1 |-----+
+-------------------+-----| MT2 | |
| +-------+ |
| |
| |
| |
| ~~~
~~~ | |
| | | |
| | | |
| | | |
| |
~~~ |
| |
| |
| +---+
| | |
+-------------------------------------+ +-----+
|
~~~
FEEDBACK
NETWORK
In this circuit, the MOC3021 is used to provide isolation between the secondary side feedback network and the primary side control circuit. The feedback network senses the output voltage and current, and generates a feedback signal that is optically coupled to the control circuit through the MOC3021. The control circuit uses this feedback signal to regulate the output voltage and current by adjusting the switching duty cycle of the power MOSFET on the primary side.
Frequently Asked Questions (FAQ)
-
Q: What is the purpose of the MOC3021 optocoupler?
A: The MOC3021 optocoupler is used to provide electrical isolation between low voltage control circuits and high voltage load circuits, while allowing the control circuit to switch the load on and off. -
Q: What is the maximum isolation voltage of the MOC3021?
A: The MOC3021 has a maximum isolation voltage of 7500 VRMS (RMS voltage, 1 minute duration). -
Q: What is the typical current transfer ratio (CTR) of the MOC3021?
A: The typical current transfer ratio of the MOC3021 is 300% at an input forward current of 5 mA and a collector-emitter voltage of 10 V. -
Q: What is the maximum peak off-state voltage of the MOC3021?
A: The maximum peak off-state voltage of the MOC3021 is 400 V. -
Q: What are some common applications of the MOC3021?
A: The MOC3021 is commonly used in applications such as solid-state relays (SSRs), motor drivers, switching power supplies, lighting control systems, and industrial automation and control systems.
Conclusion
The MOC3021 optocoupler is a versatile device that provides reliable isolation between low voltage control circuits and high voltage load circuits, making it suitable for a wide range of applications. By understanding the MOC3021 datasheet, its configuration, and its applications, designers can effectively use this device to create robust and efficient circuits that meet their application requirements.
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