0
\$\begingroup\$

I want to drive a door strike at 24V with a Raspberry Pi. The door strike needs 150mA. I think the current that a Raspberry Pi can drive on one pin is significantly weaker than for example an Arduino, so I really don't want to pick the wrong transistor.

Transistor data sheets still often sound like black magic to me. I was previously planning on using a ULN2803A darlington array, but since I really only need the one output that would be overkill.

I'll add a flyback diode as well since I don't know exactly what the mechanism inside the door strike is, it could be a coil/solenoid of some sorts.

\$\endgroup\$
1
  • \$\begingroup\$ Door strikes use a wound coil solenoid, so a flyback diode is a good precaution. I sometimes put a small DC buzzer in or near the door jamb so people hear that the strike is operating. \$\endgroup\$ – John Canon Nov 23 '19 at 6:43
1
\$\begingroup\$

Your darlington array would work fine. No problem with 'overkill' if you have it on hand and are just trying to make something work. If your load is really only 150mA, you have many options. I would personally recommend a 'logic-level' n-mosfet as a low side switch, such as the NDS351N.

\$\endgroup\$
3
  • \$\begingroup\$ Interesting. The choice for a MOSFET is because of the low current needed to drive it, correct? I see in the datasheet of the NDS351N the following: Drain to Source Voltage (Vdss): 30V, Current - Continuous Drain (Id) @ 25°C: 1.1A Those are the two main values I should be worried about, right? 1.1A is the max load current, and 30V the maximum voltage it can switch? \$\endgroup\$ – blobkat Nov 22 '19 at 17:43
  • \$\begingroup\$ Generally speaking, mosfets are commonly used in this kind of application because of their low RDSON (drain to source on resistance), thus minimizing the voltage drop in the mosfet when driving a load. I recommended a 'logic level' mosfet because, as you mentioned in your post, you can't always drive the gate of such a device with the GPIO pin of a typical microcontroller. This is why dedicated 'gate driver' chips exist for higher power fets. \$\endgroup\$ – Ocanath Nov 22 '19 at 20:29
  • \$\begingroup\$ Thanks. I'll try a VN3205N3-G. Should work! \$\endgroup\$ – blobkat Nov 23 '19 at 17:29

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.