Driving a 180ma relay from PIC port

[RunningMan]

MMBD4148SE would be a good general purpose diode, you could also put a 5.5v varistor between the IO on the pic and the gate on the FET if you wanted maximum protection, although I think it's generally not needed. In my opinion if you were to put an over-voltage device on the circuit the Varistor would work better because it acts faster than a zener. Any reasonable package (assuming surface mount)...like 0805 would work.

Incidentally, I was looking at your requirement to not draw more current thru the regulator and in my mind this low-side drive would ensure you are not sourcing thru your power supply for the pic. I am assuming this is an external relay or something you don't want mixing in with your signals on the board.

This particular circuit i have suggested has been tested to well beyond 1Million cycles on a bench. we finally decided we'd beat it to death and took it off the supply during testing. This circuit would also appear to reduce or at least simplify your drive circuit design. BJTs are cool, but the FET is a bit less mysterious for driving a circuit like this.

[Michael]

Thanks.

I need to stock up on a good general purpose FET so I'll grab some NDS7002.

I would like to keep my relay from drawing through the regulator, so I'll breadboard something.

As they say in Indiana....Cheers.

[jamie_s]

I have always used bd681 with a 1k on the base, supports upto 3 or 4 amps with a heatsink.
Emitter to ground and load between + and collector. if driving a relay, then put a 1n4004 across the transistor

[Ioannis]

I just poped-in the thread and I bet the problem in the first place was the reseting of the PIC. So as very good stated by Alain the circuit should have good decoupling on the 317 and the PIC. The coil of 180mA sure spikes hard!

Every regulator need large capacitors on the in and out pins! Do not forget it!

The transistors like the ones refered are enough to drive the relay. Also add to the list the BC337 (0.5A/45V)

Ioannis

[jamie_s]

My supply circuits are generally as shown in the dodgey mspaint attachment.

This only powers the pic, any other devices ie relays etc are powered from the source or seperate regulators. I use this circuit in automotive projects without issue.

[mister_e]

100 uF at the output might be high and loose some fast spikes, i would add 10uF tantalum on input and output as well. At the input you can use higher than 100uF.

Without having the whole thing here, it's hard to find the best suggestion. Many nice tips have already been said.

[Pic_User]

Hi Michael,
How did the new transistors work out?
-Adam-