Solid State Relay Circuit Using Mosfet

Mosfet solid state relay developed by rodney tan phd version 1 00 dec 2019 this circuit demonstrates how solid state relay can be constructed using a mosfet and four diodes.

Solid state relay circuit using mosfet. Ssr or solid state relays are high power electrical switches that work without involving mechanical contacts instead they use solid state semiconductors like mosfets for switching an electrical load. The two output pins are connected to the mosfet drains. Ssrs can be used for operating high power loads through a small input trigger voltage with negligible current. It is a solid state device that replaces a coil activated mechanical switch with an optically isolated input stage driving a mosfet.

Using highly reliable custom designed mosfet technology cotomos provides high performance for applications requiring low input power and virtually unlimited life. When using a mosfet or any type of field effect transistor for that matter as a solid state switching device it is always advisable to select ones that have a very low r ds on value or at least mount them onto a suitable heatsink to help reduce any thermal runaway and damage. A mosfet relay offers several advantages over a more traditional ssr solid state relay using a triac or back to back scrs. For more on mosfets see.

This mosfet solid state relay is applicable for both ac and dc circuits. Dc output circuit ac output circuit and ac dc output circuit. In an absence of an external trigger the lower mosfet stays switched off allowing the upper mosfet to conduct through the 10k resistor connected across the positive and the gate of the mosfet. A mosfet relay offers superior performance to an electromechanical relay in many applications.

A simple high current spdt solid state dc relay or a dc ssr can be constructed using a couple of mosfets and an optocoupler as shown in the digaram above. The dc output circuit typically uses bipolar component such as igbt or mosfet as the output component and the ac output circuit usually uses two thyristors or one triac as the output component. What differs here is the use of two mosfets in addition to the photovoltaic opto coupler circuit. Power mosfets used as a switch generally have surge current.

5 illustrates the tip3123 solid state relay a commercial device. Cotomos mosfet relays are a reliable economical and readily available solid state switching solution by coto technology.