tip120 switching 12v 1A solenoid= insufficient current?

Im trying to switch 12V 1A solenoid with tip120 transistor. External power supply to solenoid with gnds linked. Insufficient current at solenoid. Seems arduino not providing sufficient current to saturate transistor?
Don't have access to a fet to use instead. Need urgent work around! Could I get away with using 2 digital pins to supply extra base current?

Maybe the solenoid doesn’t like the TIP’s Darlington VCE “loss”.
Darlingtons have lots of gain.
Maybe it’s your circuit.
Given the urgency, why didn’t you include your schematic, etc.?

Sorry, trying to juggle lots of things. Working a lot out as I go (learning). Here's the schematic.
I'm getting 4.8V at the base from D51, 12.2V on the collector but only 6.4V on the emmiter.
Power supply is 12v taken directly from ATX PSU.
Everything else works fine.
Anyone got any suggestions?

I can't make heads or tails of that "circuitlab" thing
Why couldn't you post a JPG or something that anyone could check out?

From your description you're doing something wrong, I think.

The emitter should be at Gnd and the solenoid should be between +12 and the collector.
(Don't forget about that flyback diode across the coil.)

Would a capacitor across emitter to ground perhaps be helpful to deliver the inductive load needed to get the solenoid moving?

Apologies if my forum etiquette is not up to scratch. Not a big forum user. But some help, even if it's just to tell me what I'm doing is all wrong , would be greatly appreciated.


Did you read my last Reply?

Just did, sorry!

Like I say, not a big forum user, how do I post a jpg inbetween the /img bits?

THe solenoid is between emitter and ground. Is that not ok? I figured I could put it whichever side of the transistor!

No, it is NOT “OK”
I told that it wasn’t.

Here is how it ought to be (dwg attached)


Using an emitter-follower as a switch is a classic mistake, usually just leads to extremely
hot or blow transistors and frustration.

Switching = common-emitter (or common-source if a FET).

There are some very rare exceptions to this rule, of course, but not here.

[If "emitter-follower" and "common-emitter" confuse you, wikipedia explains.]

Thank you both very much for your help.

I'll be switching it round in a minute with my fingers crossed!

Phew!! Thank you so much!

It now works perfectly.

Good job too as this thing goes live tomorrow with loads of kids climbing all over it.

Thank you both very much for your help.

"Both?" What both?
Sometimes I don't know why I even bother.

Runaway pancake -you for telling me what I was doing wrong.

And MarkT for actually providing some kind of explanation and showing a basic level of friendliness!

Interesting - I mean irksome. I provided the actual help, but "Hooray!" for the drive-by.
Despite many views over 2 hours, nobody paid you so much as never-mind.
I should have left you as you were: foundering and grasping at straws.

Look I really appreciate you taking the time to help me. And I made a point of thanking you. Twice in fact. Should I not have thanked anyone else that offered me their knowledge as well?
I don't really understand what the problem is. I thought the purpose of these forums was to share, teach, inspire, get help and advice, etc etc and build a community. Why do you have a problem with me extending my thanks to others that helped me too?

As I said you helped me by suggesting what I was doing wrong. My presence here obviously annoyed you from the start though, you made that clear in your tone.

I thanked MarkT for offering a source of information on a principle I had no knowledge of. Without that extra bit of info my problem would have been solved buti would have had no idea why.

share, teach, inspire, get help and advice,…
As I said you helped me by suggesting what I was doing wrong. My presence here obviously annoyed you from the start though, you made that clear in your tone.

I didn’t suggest what you were doing wrong, I told you and provided corrective action.

It’s nothing to do with your “presence”, but your lack of preparation and having to dig the information out of you.
You brought nothing to the table but your angst.
That and there’s Mr. Drive-by.

To be frank, given such an error as yours and that time was a-wastin’, I thought an explanation unnecessary, inexpedient, and not worth my time.
I thought it’d be enough to solve your problem for you.

Ok. Well let's put it down to a difference of attitude. Anyway, thanks for your help, genuinely and with sincerity. Let's leave it at that shall we.