[Pars]

Stupid question (probably), but I was adding a relay to an I/V stage I am building. I have +/-15V supplies available in the player. The I/V stage itself will have its own +/- 15V supplies. I figured it would be better to not run the relay from these, but use a +15V from the player instead for this. The relay is the same one(s) I used for the e12 muting boards I have built and is a 12V relay. I was trying to figure out a small, cheap and easy way to drop the 15V down to 12V, and thought of just using a zener, as below. Will this work?

Thanks for any input,

Chris

 

[DanPash]

Why not just use a t092 package 12v reg and a diode to prevent backwards emf?

 

[Bjornboy81]

That should work. Or put a resistor in series with the coil to drop the extra 3 volts.

 

[Bjornboy81]

Quote:

Originally Posted by DanPash /img/forum/go_quote.gif Why not just use a t092 package 12v reg and a diode to prevent backwards emf?

A regulator is overkill for a simple relay, and the diode he has in there already is for the reverse emf.

 

[Pars]

Quote:

Originally Posted by DanPash /img/forum/go_quote.gif Why not just use a t092 package 12v reg and a diode to prevent backwards emf?

Quote:

Originally Posted by Bjornboy81 /img/forum/go_quote.gif That should work. Or put a resistor in series with the coil to drop the extra 3 volts.

I'm running out of board space (had a hard time cramming what is there in :eek), so I didn't want to mess with a regulator, etc. The 1N4004 diode for the relay coil is on the bottom directly under that end of the relay. If I have to, I'll put a resistor in series with the coil as that was my initial thought until I came up with the zener.

 

[luvdunhill]

do you need an LED or two somewhere?

 

[Pars]

I guess I need a series resistor after toasting a couple of zeners tonite breadboarding this (gotta love Ebay... 100 lots

). Seems from an online calculator that around 220 ohms will do what I want (I think).

That said, this is all assuming that the relay would mind seeing 15V (being a 12V relay Omron G6A-234P-ST-US-DC12 IIRC). I assume that 12V is mandatory...

 

[DaKi][er]

You need a resistor for sure in series with the power rail before the zener, otherwise you are dead shorting the zener there and it'll just go poof

Also, 15v into a 12v relay shouldnt be much of an issue, but if you have the zener spare then it wont hurt to have it

 

[heatmizer]

Why not just run the 15 volts into the relay. Max coil voltage is 150% @ 73 degrees F to 200% @ 158 degrees F above stated coil voltage. 15 volts is only is 20% higher.

 

[Bjornboy81]

Quote:

Originally Posted by DaKi][er /img/forum/go_quote.gif You need a resistor for sure in series with the power rail before the zener, otherwise you are dead shorting the zener there and it'll just go poof Also, 15v into a 12v relay shouldnt be much of an issue, but if you have the zener spare then it wont hurt to have it

Why would you be dead shorting it? The way he has it in the schematic should work. Maybe you put it in backwards Pars :???: Sometimes Zeners have the strip on the anode side...I hate inconsistance

Heatmizer has a point, if the data sheet on the relay says it can handle 150% voltage (which most are capable of a rather large voltage window) then go that route.

Good luck

 

[beerguy0]

Quote:

Originally Posted by Bjornboy81 /img/forum/go_quote.gif Why would you be dead shorting it? The way he has it in the schematic should work. Maybe you put it in backwards Pars :???: Sometimes Zeners have the strip on the anode side...I hate inconsistance Heatmizer has a point, if the data sheet on the relay says it can handle 150% voltage (which most are capable of a rather large voltage window) then go that route. Good luck

Um, actually he does need a current limiting resistor for the zener. The schematic shows it directly from +15 to ground. A smoke recipe for sure.

As far as running a 12 volt relay from 15 volts, we do this frequently in our antenna couplers. Running them at a higher voltage makes them switch more quickly, which speeds up tuning. They dissipate slightly more heat, but no big deal.

 

[Pars]

Thanks for all the responses. In case anyone hadn't guessed, this is for a muting relay on an IV board. I think I will allow for a current limiting resistor... I can always jumper it. The zener was in the correct way (assuming it was marked correctly... never checked that). It did smoke a bit

I was doing things quickly for this portion, and should have looked at the datasheet... DOH!

 

[cetoole]

Quote:

Originally Posted by beerguy0 /img/forum/go_quote.gif Um, actually he does need a current limiting resistor for the zener. The schematic shows it directly from +15 to ground. A smoke recipe for sure. As far as running a 12 volt relay from 15 volts, we do this frequently in our antenna couplers. Running them at a higher voltage makes them switch more quickly, which speeds up tuning. They dissipate slightly more heat, but no big deal.

Exactly, the zener diode is being used as a very simple shunt regulator, so some sort of current source or current limiter is absolutely required. A resistor fills this requirement nicely, as a CCS would be overkill here. It is still overkill, but I would be tempted to use a lone LM7812 regulator here.

I am curious to see if that relay is fast enough to prevent pops on the output. I had been looking more at reed relays for this.

 

[DanPash]

Sorry, I didn't view the pic to spot the diode. I thought use a small reg as its tiny and would cut down on parts.