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.
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.
Please let us know if you have any further question or comments.
Best Wishes,
APDahlen
P.S. Kindly include a picture of your design. I am curious how the components are being used.
