paralleling relay coils

Translation, anyone?

Given one driver, five parallel coils, one diode, and an optional resistor, I can't see how you'd get any difference in EMI. What is "phase adding"?

A clamped relay coil, actuated now and then, won't make significant EMI.

"John Larkin" wrote in message news: snipped-for-privacy@4ax.com...

Operating Vin is only 15V, Device Max is 20v. Vdrop is 1.4v at 800ma

I wouldn't use it at 18v.

Cheers

Abs max is 20, and 18 is less than 20. But the part I posted is obviously the ADJ version. With 18 in and 12 out, the regulator only sees 6 volts.

It will lose just about a volt at 300 mA. One should check the relay data sheet to make sure that's OK.

ivers.pdf

the

sheet

Circuit #2 produces neg voltage across coil on turn-off, bad choice. Circui t #5 also potential transient over-voltage at turn-on due to diode capacita nce. Circuit #3 is really strange, hard to say but likely PNP is saturated so coil -Vdiode at turn off is applied to output of 1117. Y

I drew what it does. When the mosfet is on, there's +1.25 volts across the relay coil.

That's insane.

Ditto insane. It's a simple voltage regulator followed by a switch. When the switch disconnects the coil from the regulator, they are disconnected.

Threads like this are fun. It's amazing how many people, even people who work in electronics, don't understand simple circuits.

Pretty close. And very good design advice. In reality it will be about

?-)

That's not how that works and you know it.

Yeah, my impression is that they set the original design specs based on unregulated power from the mains plus temperature. Those hairy-eared relay designers didn't really add vast unnecessary margin.

Best regards, Spehro Pefhany

If you disagree, post an serious explanation or a Spice file.

I'd like to see it, too!

John S

I know, and it's real easy to blow a coil open with over-voltage, +15% usually does it, sometimes less.

loads. Is it necessary to have fly-back diode for each relay coil or just one 1N400x diode in parallel is sufficient? Each coil is 300 ohms.

Just a general comment on the topic of relay coil transient suppression: W hile connecting a diode across the coil is a common practice, the technique has its drawbacks. Robert Baer alluded to this in his earlier post. The diode increases the release time of the relay. Even if you are not concern ed with switching time per se, a slow release can cause excessive contact a rcing and even welding. My favorite technique is to connect a diode in ser ies with a Zener and place the combination across the coil. This allows th e voltage across the coil to rise, thus minimizing the increase in release time, while keeping the voltage across the driver transistor within safe li mits. This topic is discussed at length in the ?Engineers; Relay Handboo k? published by the National Association of Relay Manufacturers. In my co py (Fifth Edition) it?s covered in paragraph 15.3.9 under the topic ?Su ppressing Relay-Coil Transients.?

In that case, here's another idea:-

\ +12~18V _ _ o o | )| 1N4003 - )| ^_)| | | | 100K ||-+ ___ ||| | | .-. | | | | | | 2.5R | '-' | | +----- + | === GND

It's even possible this is short-circuit resistant if you treat the MOSFET well thermally.

Best regards, Spehro Pefhany

Looks to be easy way. I think it should be NPN.

Right, thanks. The P/N is correct, symbol is wrong.

--sp