DC SSR

Simple DC SSR circuit which is cheaper than a genuine one and can handle greater loads than the cheap fakes available that all seem to fail at around 30A. Left part of the ciruit is just to represent an optocoupler which isolates your signal/controller from the rest of the circuit. In real life it shouldn't be grounded but required in this case just to run the simulation. Middle part is a mosfet driver triggered by the optocoupler. It uses an isolated supply, as when I have a high power supply I usually have an auxillary 12v supply available (for controllers, fans, etc...). The 1Mohm resistor is to reference the negative of the driver to the source of the mosfet and limit any current in case the mosfet fails. Right side of the circuit is the high power supply and load (bulb) with suitably high power mosfet. It's shown as low side driving, but if your using an isolated supply for the driver then an N channel mosfet can be used for low or high side driving aslong as the 1Mohm resistor is connected to it's source. Mosfets need the appropriate voltage and current ratings, but a low drain to source impedance is also important. The lower the impedance the less they will heat up and longer they will last. Mosfets (of the same type) can be put in parallel to increase current capacity as if more current flows though one it will heat up and increase it's impedance, shifting current to the other. But make sure the total current they can handle is quite a bit higher than the required current as they may not be loaded equally.

published 5 years ago