Relay Arc Supression Circuit

Why diode in series with the zener?

Anyway. Remove the diode and zener, place across the LED.

Or actually, an ordinary diode across the LED. Turns off, and relay coil switches ends, and the 330 ohm resistor is used as a snubber to absorb the energy. Depends on the ratio between the 330 ohm and the relay coil impedence, and the Vce of the transistor.

schreef in bericht news: snipped-for-privacy@u72g2000cwu.googlegroups.com...

I would try this: +5Vdc | +---------------+------------------------+ | | | | | | 330 Ohm Diode | | | | | +---------+ 5Vdc Relay Coil | | | | LED | 5.1V Zener | | | | | | | | | | | | | +-----+ +------------------------+ | | +---+---+ To Micro----1kohm--+B C |Transistor | E | +---+---+ | | | GND

Do you feel the Zener voltage is important? I only ever used simple diodes across the relay coil. The voltage is quite a bit smaller to collapse the magnetic field, but how long do you believe that collapse will take driven into 0.7V? If the zener is removed, the LED is protected. If you change to a 3.3V zener, your reverse voltage will hit about 5V - on the edge, but better. If you feel strongly that the zener is needed, I like Ian Stirling's idea of the doide across the LED which also gives you a snubber resistor.

The LED is supposed to be on when the transistor provides a ground showing that the relay is active. Wouldn't this connection reverse bias the zener (acutally it would foward bias it but zeners are normally used in reverse bias). So I don't think the LED would function properly.

Thanks!

If you have time visit:

This is where I based the zener diode in series decision. Could you point me to a better reference? The article above will discuss the diode sereis resistor method you mention as well but concludes a zener is a better way to go for minimizing hold up time. I'm certain this type of circuit is done routinely so any other resources would be great.

Thanks for your time!

Hmmm, I'm no expert at all. That said, enlighten me! I thought the rule of thumb was to target a zener voltage near the realy coil voltage (5Vdc). I think the gist is that this will effectively start the magnetic collapse sooner and provide a path for a 5.1 + 0.7 amount on energy absoprtion back to the rail. If you go to high, it never activates as the zener knee voltage is not met. If you go too low you don't get the benefit of the zener and it acts more like a solo diode. When both are in play, this aids in releasing the armature more quickly. The load on the contact side of the realy is another realy coil which drives an inductive laod.

Thanks for your time!

"For those applications that cannot tolerate lengthened hold-up time, a resistor may be placed in series with the diode. The resistor does, however, lessen the effectiveness of the diode and, usually, a compromise must be reached by trial and error."

That is so sad.

Best regards, Spehro Pefhany

Is holdup time an issue for you? We never had a need for 2 ms vs 9 ms. see:

Would you mind providing a link to the relay you're using? (to help determine holdup time)

Are you running a high voltage through the relay contacts such that contact arcing is your big concern?

By using a 3.3V Zener instead of 5.1V, you have a Zener + Diode reverse voltage maximum of about 5V instead of your measured 7.5V. The Zener plus diode at highest current gives you the max reverse voltage for your LED.

If you want to use the Zener because you feel the reduced holdup is important, consider a higher voltage zener and either 1) a diode reversed across the LED or 2) a cap across the LED that just needs to keep the reverse voltage from getting to 5V during the coil discharge.

You didn't show the cathodes of the diode or zener, so I made some assumptions.

I assumed that the cathode of the diode is at top, and cathode of zener is at bottom.

So the LEd would be on when the transistor is on, through the forward biased zener.

At turn off, the top diode is forward biased (while the inductance discharges through the two diodes), so the LED sees no more reverse voltage than than the top diode's forward drop.

Hmmmm, so the zener sinks the stored energy at relay releae to GND in this design. How would you recommend the sizing of the zener? I surmise it would be < Vce max of the transistor? Doesn't this present a similar problem as I have with the reverse bias on the LED? What I mean is, the zener will clamp to some V but suppose the stored energy is >> V then the transistor could be zapped anyway, right? And of course the diode doesn't relate to the stored energy in this design except for blocking any current during stored energy release.

Thanks for your time.

--- To what article and to whom are you responding?

Read this, From:

"Summarize what you're following up.

When you click "Reply" under "show options" to follow up an existing article, Google Groups includes the full article in quotes, with the cursor at the top of the article. Tempting though it is to just start typing your message, please STOP and do two things first. Look at the quoted text and remove parts that are irrelevant. Then, go to the BOTTOM of the article and start typing there. Doing this makes it much easier for your readers to get through your post. They'll have a reminder of the relevant text before your comment, but won't have to re-read the entire article. And if your reply appears on a site before the original article does, they'll get the gist of what you're talking about."

-- John Fields Professional Circuit Designer

schreef in bericht news: snipped-for-privacy@i39g2000cwa.googlegroups.com...

Use what John Popelish told you. You obviously don't have a clue about diodes and zeners, so take the advice and stop questioning.

The 3.3 is my punt plan for the current artwork or to populate a 0 ohm resistor where the zener is.

Here's what I'm not understanding...with the 5.1 zener and per my o'scope, it appears the worst case reverse bias on the LED is 7.5 as I aforementioned and I see about 3V across the series resistor, Rs. So this sums to ~10.5 Vdc. So does the 5V rail + 5.1 (zener) + 0.7 (diode) create a voltage of about 10.8 reverse bias? This seems wrong to me as the 5V rail is fixed but empirically the 10.5 is close to the

Thanks again for your time.

RTFMed, thanks for that. I'd been using the reply at the bottom of the post and by default no text is included whatsoever. Sorry for the confustion I rarely use the web interface and usually use Knode to post...my bad.

On 14 Mar 2006 10:55:01 -0800, snipped-for-privacy@revco.spx.com wrote:

--- Huh???

Go to:

download the simulator, and run this:

Version 4 SHEET 1 880 680 WIRE -384 176 -384 64 WIRE -384 320 -384 176 WIRE -384 416 -384 400 WIRE -352 176 -384 176 WIRE -208 176 -272 176 WIRE -112 320 -112 288 WIRE -112 416 -384 416 WIRE -112 416 -112 400 WIRE -48 288 -112 288 WIRE 16 176 -144 176 WIRE 80 288 32 288 WIRE 144 176 80 176 WIRE 144 176 144 144 WIRE 144 192 144 176 WIRE 144 240 144 192 WIRE 144 416 -112 416 WIRE 144 416 144 336 WIRE 208 64 -384 64 WIRE 208 144 144 144 WIRE 272 192 144 192 WIRE 272 272 272 192 WIRE 272 416 144 416 WIRE 272 416 272 336 WIRE 272 448 272 416 FLAG 272 448 0 SYMBOL npn 80 240 R0 SYMATTR InstName Q1 SYMATTR Value 2N4401 SYMBOL ind 192 48 R0 SYMATTR InstName L1 SYMATTR Value .1 SYMATTR SpiceLine Rser=100 SYMBOL zener 288 336 R180 WINDOW 0 -42 32 Left 0 WINDOW 3 -120 0 Left 0 SYMATTR InstName D1 SYMATTR Value BZX84C15L SYMBOL diode 16 192 R270 WINDOW 0 32 32 VTop 0 WINDOW 3 0 32 VBottom 0 SYMATTR InstName D2 SYMATTR Value 1N4148 SYMBOL res -256 160 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R1 SYMATTR Value 300 SYMBOL voltage -112 304 R0 WINDOW 3 -152 153 Left 0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR Value PULSE(0 5 .1 1e-6 1e-6 .1 .2 3) SYMATTR InstName V1 SYMBOL voltage -384 304 R0 WINDOW 3 -6 144 Left 0 WINDOW 123 0 0 Left 0 WINDOW 39 0 0 Left 0 SYMATTR Value 5 SYMATTR InstName V3 SYMBOL LED -208 192 R270 WINDOW 0 72 32 VTop 0 WINDOW 3 0 32 VBottom 0 SYMATTR InstName D3 SYMATTR Value QTLP690C SYMBOL res 48 272 R90 WINDOW 0 0 56 VBottom 0 WINDOW 3 32 56 VTop 0 SYMATTR InstName R2 SYMATTR Value 1000 TEXT -418 506 Left 0 !.tran 1

-- John Fields Professional Circuit Designer

RTFMed, thanks for that. I'd been using the reply at the bottom of the post and by default no text is included whatsoever. Sorry for the confustion I rarely use the web interface and usually use Knode to post...my bad.