On Sun, 06 Sep 2009 11:50:43 -0700, Jim Thompson wrote:

On Sun, 06 Sep 2009 13:33:45 -0500, Tim Wescott
wrote:

On Sat, 05 Sep 2009 14:08:54 -0700, Jim Thompson wrote:

On Sat, 05 Sep 2009 12:43:20 -0700, Jim Thompson
wrote:

On Sat, 05 Sep 2009 14:01:59 -0500, Tim Wescott
wrote:

On Sat, 05 Sep 2009 11:03:51 -0700, life imitates life wrote:

On Sat, 05 Sep 2009 12:48:41 -0500, John Fields
wrote:

On Sat, 05 Sep 2009 09:41:06 -0700, Jim Thompson
wrote:

I haven't done a relay driver circuit for, literally, eons.

Where do I look for reed relays that work on 3.3V supplies with
specications for the coil inductance?

Thanks!

---
That's a toughie.

I can't recall ever seeing inductance data on a spec sheet; I think
you'll probably have to go to the manufacturer for that one.

JF

Would not the real question be why would someone concern himself
with the solenoid inductance of a miniature relay? I could see it
if it were huge.

Jim designs custom IC's, so (I assume) he's concerning himself with
it so he can make the output stage of his circuit both economical and
robust. He may even care about making the relay turn off quickly.

It seems like a perfectly valid concern to me, even if the circuit in
question _isn't_ custom -- what if you're powering the relay from
logic, and want to insure fast & safe turn-off?

Dead-on, Tim!

...Jim Thompson

Like this...

http://www.analog-innovations.com/SE...elayDriver.pdf

In the discrete world, with more voltage tolerance available, you can
scale this to larger controlled flyback potentials, for fast turn-off.

...Jim Thompson

Clever.

I first came up with this scheme for a light-weight flyback switcher
built on a bipolar process, circa 1975.

I assume that the gate threshold of MP1 guarantees that the drain of MN1
never exceeds your max voltage?

That and the ratio of the 10K to 33K resistor.


I could see a potential for this to oscillate on turn-off, with the
inductor working against the delays in the two FETS,

FET's are sub-nanosecond

but if it did it may
well not matter, and your relay coil is probably sluggish enough to keep
it from happening anyway.

Do you get to tune the gate thresholds of the individual parts, or is
that usually locked in by the process?

Usually locked by the process though, occasionally, I run onto processes
that have a bunch of different device _types_, some even offering
depletion mode MOS devices... nice for kick-starting micro-power stuff
;-)

...Jim Thompson

When I was in school in the early '80's all the IC design stuff was
digital, and we were all told that no one was going to get a job
designing an analog IC ever again, 'cause they were all going to go away.

Silly me, I listened and stayed away from IC design entirely. But I have
fun with what I do...

--
www.wescottdesign.com