relay coil inductance

Here's a pretty good pdf with explanation of different spike suppresion methods. It lists drop out times for the different methods, for one particular relay and values.

PS. A diode is the slowest dropout time listed. Mike

Note also that the diode is also the best at suppressing the spike.

Note also that UNsupressed is the only way to get it fast. ALL the other methods slow it.

ALL of the other methods violate his 'issues' list.

In many cases, that is the most important constraint (the spike). Note also that all the figures are for 12V relays, which are not in much use on modern low voltage circuit designs these days.

I am quite certain that any 3.3V relay you choose to examine will prove to be faster than any of the numbers that more than 10 year old document measured. Even the diode.

Who cares? Just use the standard RC snubber across the coil; 100 ohms should be fine.

I thought that maybe Phil had assumed a pseudonym, but this guy is less knowledgeable both in electronics and vile language.

--
www.wescottdesign.com

All the pussy that you are is doing is looking to get a rise out of me.

That only amounted to me chuckling at the depth of your stupidity.

1. it is.

You should learn to read... it's a custom chip issue. I posted a link to a proper solution.

BTW, 100 Ohms and a coil current of 33mA would produce 6.6V (net, 3.3V supply) on the drain, exceeding the 5.5V maximum operating rating.

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

Or buy a peak Atlas LCR meter and measure it.

ISTR an appnote floating about on the net that recommends using a combination of diode and zener to clamp the back emf, apparently if you just clamp it with a single diode, the back emf drives a current round the diode/solenoid circuit which causes hesitant unlatching.

Probably this one?

Note, life imitates life finds no wisdom in a ten year old document. Mike

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I remember it too, but I don\'t remember where I found it.

The gist of it, as I recall, was that the higher the back EMF is allowed
to rise before it\'s clamped, the faster the relay will open.

 
JF

e

Beware of the inductance you measure. The inductance changes hugely when the relay is activated. As the plunger pulls in, the current decreases sharply and the inductance increases. As the plunger pulls away you get a second bump of counter EMF.

Unlikely but: The designer may want to dump the power back into a higher supply as the relay opens. This makes the rate of decrease in the current on the supply slower.

=A0 =A0...Jim Thompson

A capacitor across the coil makes the contacts open faster. Try it, it works.

Ian, Did you miss seeing this...

A little better than a flyback diode, and no destructive currents running in my substrate ;-)

I had to conjure that up from memory... first done so long ago (BC: before CAD), it only exists somewhere in my paper archives ;-)

...Jim Thompson

--
|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
|       http://www.analog-innovations.com           |    1962     |
             
I love to cook with wine.      Sometimes I even put it in the food.

,

Even if it doesn't turn wipe out the transistor, suddenly some flip- flop or two inside the chip that drives the transistor can change states. The collector swing way positive and then tries to go way negative on the collector biases the C-B junction on, pulls the base below ground and thus pulls the pin of the chip below ground

Diode+resistor or diode+zener are both a lot faster than just a diode.

Or even just a series or shunt resistor, if you can spare the power.

No clamp at all is even faster; just let it fly up and ring, with suitable precautions.

The untimate would be to apply a large reverse voltage to the coil until the current goes to zero. That's what happens automagically in a linear amp driving an inductive load with current feedback.

Reeds are usually pretty lossy, lots of coil resistance, so may be OK with just a diode. But they are terrible gadgets in general. In my experience, they are nowhere near as reliable as claimed, and they bounce/twang forever.

John

Show me where that was ever stated, you fact morphing retard!

--
Mercury wetted don\'t.

JF

That's not the one I was thinking of, it was probably a Tyco appnote.