A solid-state relay is designed for the purpose of switching a DC or AC load, some of them are capable of switching both AC and DC loads. Their output (AC, DC, or AC/DC) depends on the type of switching device used in their circuits, such as a transistor (either MOS or bipolar), a TRIAC, or an SCR.
In this project, we are making a 12V DC solid state relay using an optocoupler and MOSFET. Solid State Relays are used in the place of mechanical relays. Mechanical relays have lots of moving parts. As the name suggests this relay is in solid-state and does not have any moving parts, it provides all the functionality the same as a mechanical relay and is able to switch ON and OFF much faster than them.
Hardware Components
The following components are required to make a 12V Solid State Relay Circuit
| S.no | Component | Value | Qty |
|---|---|---|---|
| 1. | DC supply | 5-12V | 1 |
| 2. | Optocoupler | PC817 | 1 |
| 3. | MOSFET | BUZ71A | 1 |
| 4. | Resistors | 470Ω, 10K | 1, 1 |
BUZ71A Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of BUZ71A
PC817 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of PC817
12V Solid State Relay Circuit
Working Explanation
The working of this circuit is quite simple and easy to understand. The 5-12V input signal is given to the circuit which is fed into the PC817 optocoupler. The internal phototransistor of the optocoupler activates and sends the output which becomes the input of the BUZ71A MOSFET. The MOSFET starts conducting and the DC load connected across the transistor gets activated.
This circuit can easily drive the DC load of 10 amperes. To drive a higher DC load you can use a high ampere MOSFET transistor. For example, the IRFZ44N MOSFET can drive a load of 40 amperes. You must use a heatsink with any MOSFET transistor you use.
Applications and Uses
- If you are driving motors etc., this circuit can be used as an isolator for your microcontrollers or Arduino projects.
- It can be used as a Latching circuit
- If you require a high load switching you can use this circuit.
