Transistor needed to drive a solenoid actuator

SgtWookie

Joined Jul 17, 2007
22,230
Hi, so if I use a MOSFET, the way how I connected up the circuit is not the same as how I connected it using a BJT?
BJT transistors control the collector current by the base current.
MOSFETs control the drain current (Id) by the gate to source voltage (Vgs)

There are 2 resistors for the MOSFET circuits, the 100 Ohm is connected to the pin out of microcontroller, the 10K is connected to the ground. May I know why are there 2 resistors?
The 100 Ohm resistor prevents the gate from "ringing" due to parasitic inductance. It also limits the maximum gate charge/discharge current; in this case to 50mA. A 200 Ohm resistor would be more appropriate.

The 10k resistor is there to keep the MOSFET turned OFF in case the uC is removed, the output pin fails, or the pin is accidentally set to input mode which would leave the gate floating.

Can I use a MOSFET but I connected the circuit as seen on the left (which has only 1K resistor)?
You could, but I wouldn't advise it.

For my case, can I use a BJT transistor instead?
You've tried it, and it didn't work.

You might try decreasing the 1k resistor to 240 to 270 Ohms. This would cause more collector current to flow.
 
Top