Control 12V 1w solenoid with 5v MCU Gate, Nchannel JFET or MOSFET

I need to control a 12V 1watt solenoid using a 5V ttl signal from a microprocessor.
I think this calls for a JFET or MOSFET.
The max Vds=14.0V.
The Vload = 12V
The Vgs =3V (voltage range to “turn on” the MOSFET)
The Vcc = 5V (voltage of the I/O pin, must be higher than Vgs)

Also I need to know any current limiting resistors from the MCU to gate, and any resistors from the gate line to the drain line. I need SMD components.

Hello Idaho,

Yes, a MOSFET could be used for this application. As a starting point, consider the 2N7002P MOSFET.

A representative schematic is included as Figure 1. Here, the relay is replaced with an equivalent resistor. The simulation uses the popular through-hole 2N7000. For your application, the results will be similar. Finally, the microcontroller is replaced with a STDT switch. The resistor value is not critical but should be included to accommodate the gate capacitance. Please click on the schematic to enter the interactive simulation.

Tech Tip: Remember to include a diode in parallel with the relay coil. Failure to include a diode will result in the destruction of the MOSFET. On a related note, if speed of relay contact opening is important, there are better performing alternatives. However, the diode is a reliable performer suitable for the majority of applications.

Figure 1: Schematic of a microcontroller driving a relay via a MOSFET.
Figure 1: Schematic of a microcontroller driving a relay via a MOSFET.

One of the important device characteristics related to your design is shown in the datasheet. In Figure 2 we see that the MOSFET will have a low V_{DS} at you chosen I_D. For you application 3.3 and 5.0 VDC provide nearly identical results. Notice that a higher I_D would change the situation. Higher gate voltage is required to fully turn on the MOSFET.

Figure 2: Chart showing the voltage across the MOSFET for a given gate voltage and drain current.

Please let us know if you have any further question or comments.

Best Wishes,


P.S. Kindly include a picture of your design. I am curious how the components are being used.

1 Like