Driving a 180ma relay from PIC port

[RunningMan]

The other thing you could so is use a N-Channel FET to low-side drive the Relay. In otherwords, keep your driving + to the relay and let the FET close ground on the Relay... My circuits generally use this method where we are driving a relay.

NDS7002 is one N Channel MOS you could use, and put a pull down between it and the micro for insurance. this particular FET is rated at 280mA on the Source to Drain. The gate drive is well below the 25mA.

As for a flyback diode, any general purpose Diode will also work...

[mister_e]

and the Rds is interesting too... interesting current limiting/protection device in some case.

[Pic_User]

2N4401
40 Volts collector voltage
600 mA collector current
DC current gain with 180 mA collector current is about 100 minimum

With a minimum gain of 100 it should be able to switch 180 mA collector current with 1.8 mA from the PIC.

Less than 2 mA.

You may be looking at a different type of problem.
-Adam-

[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