Driving a 180ma relay from PIC port

[Michael]

Does anyone know of a transistor I can use that has enough gain to sink the ground connection on a relay that's drawing about 180ma? (Open collector configuration). Using a 16C65B...can't remember how much current a PIC can source.

Tried a 4401 and some others but they won't latch on.

THANKS

[tico]

2n3904 200 mA

or you can go wild with a 2n2222 1.0 A

[Michael]

Yeah but the PIC won't supply enough current to keep them latched on. I tried a 4401...same animal as a 2222.

[Acetronics2]

Will you provide a part of scheme ... ???

Alain

[Pic_User]

Tried a 4401 and some others but they won't latch on.

Hi Michael,

The PICs supply 25 mA per pin. That should be more than enough to hold those small signal transistor on. You may be looking at a different type of problem.
-Adam-

[skimask]

Hi Michael,

The PICs supply 25 mA per pin. That should be more than enough to hold those small signal transistor on. You may be looking at a different type of problem.
-Adam-

Do you have a ~1K-ish resistor on the base?

[tico]

use this circuit found towards the bottom of the page

http://rentron.com/PICX6.htm

[Michael]

I'm driving a 2N4401 with a 1K....even did a 560 ohm. An open collector config to turn on/off the ground circuit to the relay.

I'm actually using the input to the LM317 on my power supply (around 8 volts) for positive relay voltage. (5v relay)

Using pin D4 on the PIC, which works fine (goes high for 15 seconds) but using the transistor to the relay will just give a momentary pulse and won't engage.

However, if I tie the ground circuit directly and bypass the 4401, the relay works perfectly....so I know the power supply is fine.

Maybe the transistor on resistance is too high but like I say, surely there's a part someone has used to sink 180ma without a problem.

[Acetronics2]

Hi, Michael

Could ever your Pic have a RESET when power applied to your relay ... mmmmh ???

That could be a very good explanation ...

do try a LED instead of the coil ... just to see what's happening ...

sooo ...

1) do you have a BIG tank capacitor on your pic supply ( say 1000µF + )???
2) do you have the .1µF capacitor between vdd and vss ( the closest to the Pic )
3) did you think to the reverse diode ( 1n400x) // on the relay coil ???

Alain

PS ... once more: a scheme IS necessary to the troubleshooting !!!