Is there a better or best adj. voltage regulator??

[ENS Audio]

Just wondering, this is like the 1000th time that I have to replace the LM 317 for the phantom voltage section on my green PSU. Is there something that Im probably doing to cause this to short??? I mean, my soldering is pretty decent (dont see any signs of bridging of any kind) what gives? :? So as I was saying, what adj regulator should I get?


Thanks,

 

[Svart]

are you using the LM317HV version? It can go up to 60v.

The regular LM317 can only do 37V.

 

[ENS Audio]

[quote author="Svart"]are you using the LM317HV version? [/quote]

Yeah, and the voltage is around 60v (possibly Im forgetting something very obvious or somehow the reg shorted out again.

 

[Svart]

how is it isolated? I had trouble with Sil-pads and plastic isolators eventually allowing a short...

 

[ENS Audio]

[quote author="Svart"]how is it isolated? I had trouble with Sil-pads and plastic isolators eventually allowing a short...[/quote]


What do you mean by plastic isolators? Dont mean to be so dense, just a little out of it atm.

 

[Svart]

is it attached to a heatsink? if you have 60V on the input and are regulating down to 48v then that regulator is dissipating 12V at some current. If we say that it's .25A then that's P=VI or P=12*.25. That's 3 watts. That would overheat and shut down.

I assume that it's heatsunk and you must have used some kind of isolating device since the tab of the to-220 LM317 is connected to the output, not to ground. If you hooked the tab straight to ground then it would short out immediately.

The isolator I speak of is the little plastic piece that goes between the screw and the tab of the to-220 part. The sil-pad is a silicone pad that goes between the tab and the heatsink so that you don't short the tab to ground.

sometimes when you tighten the sil-pads or mica isolators they crack and allow *slight* shorts that get worse over time.

It's just an idea. Otherwise, I don't have a clue..

:shock:

 

[ENS Audio]

[quote author="Svart"]is it attached to a heatsink? if you have 60V on the input and are regulating down to 48v then that regulator is dissipating 12V at some current. If we say that it's .25A then that's P=VI or P=12*.25. That's 3 watts. That would overheat and shut down.

I assume that it's heatsunk and you must have used some kind of isolating device since the tab of the to-220 LM317 is connected to the output, not to ground. If you hooked the tab straight to ground then it would short out immediately.

The isolator I speak of is the little plastic piece that goes between the screw and the tab of the to-220 part. The sil-pad is a silicone pad that goes between the tab and the heatsink so that you don't short the tab to ground.

sometimes when you tighten the sil-pads or mica isolators they crack and allow *slight* shorts that get worse over time.

It's just an idea. Otherwise, I don't have a clue..

:shock:[/quote]

What kind of heatsink(s) do you use for the lm317?

 

[dale116dot7]

Make sure you add all of the protection diodes specified in the application notes for the regulator. If you don't have them, it'll eventually short out, usually when you either turn the power on, or when you turn it off. I've used the LM317HV for phantom and no problems so far. Also, make sure you have the correct capacitors around the regulator as well.

-Dale

 

[ENS Audio]

[quote author="dale116dot7"]Make sure you add all of the protection diodes specified in the application notes for the regulator. If you don't have them, it'll eventually short out, usually when you either turn the power on, or when you turn it off. I've used the LM317HV for phantom and no problems so far. Also, make sure you have the correct capacitors around the regulator as well.

-Dale[/quote]

ok, then the protection diodes that your talking about do you have a mouser part #?? currently I have the 4007 diodes, what do I need to consider?


Thanks,

 

[Svart]

he's talking about the flyback diode that is reverse biased between the IN and the OUT pins. When you shut off the unit, the output side of the regulator might see 48v for a few seconds while the input side might go straight to ground. This forces voltage/current back into the device, damaging it. This happens unless you have a diode that allows an easier path for the voltage to follow, which biases the input side at roughly the same potential as the output side while it drops to 0 volts, amongst other things.

A 4007 would be fine for this.

 

[Svart]

check out D1. That's a recirculation/flyback/protection diode.

 

[AudioJohn]

Another regulator to consider - is the LM783 - which is pin compatible with the LM317. It is widely used as the Phantom regulator in commercial mixer PSU's and can stand a much higher input/output differential voltage.

With the LM317 - the input/output differential is 40 volts - so connecting, say a 36 volt zener diode in place of D1 would protect the regulator. In the event of a short to earth on the output side, the zener must operate within its ratings, so the current on the input side of the regulator must be limited.

If the Phantom is only required to feed a couple of channels, this isn't too difficult to achieve and probably worthwhile.

 

[CJ]

Would the LM317 reject the extra ripple caused by removing the big filter caps on the input?

If so, then you may realize a smaller in/out delta.

Easy to try, just clip the leads.
Then listen.
Then measure the input voltage drop.

 

[peterc]

LM 783 will work fine in this application.

Maxwall here on the forum was selling them at a good price.

Peter

 

[Svart]

I have lm317s in a couple phantom applications. They've been running for years with no issues. i think ENS has a problem with the circuit. I'd hate to send him to another part without figuring out what the issue is to begin with. For all we know, he might end up with the same problem only with a more expensive and harder to get part...

 

[ENS Audio]

[quote author="Svart"]I have lm317s in a couple phantom applications. They've been running for years with no issues. i think ENS has a problem with the circuit. I'd hate to send him to another part without figuring out what the issue is to begin with. For all we know, he might end up with the same problem only with a more expensive and harder to get part...[/quote]

Wow, thanks for being so concerned about the dilemma im in Im using the Green PSU PCB as my PSU (most recent revision I received a few months ago from peter)

I dont have the schematic infront of me atm but, I think that I found the problem when you started talking about "rev diode protection" and in reference to the diode thats positioned towards the middle end (near the 4 way connector, I dont have the most recent layout/schematic)


I suspect that its positioned the wrong way (its in parallel/same direction as the other diodes) So, should the diode im referring to be facing the opposite way???

When I get home from work later on, i'll be able to give more info if needed.


Thanks,

 

[peterc]

The diode to protect the 48v reg is at the top left of the board (1N4007). You could try a zener diode in there, 20v would work.

Peter

 

[Svart]

or a power schottky. they have even lower forward voltage drops than zeners.

 

[Dan Kennedy]

I've used 317l's as phantom regulators for years, in thousands of units with no problems, but you do need to limit the voltage differential from in to out, so a zener in the D1 position takes care of the problem.

I think I'm using a 28v part in the current units, whatever a 1N4750 is. I'm not where I can look at a parts list right now, and the memory is only so good.

 

[PRR]

> I think I'm using a 28v part in the current units, whatever a 1N4750 is.

Nominal 27V.

A '317 is awful hard to kill. Heat won't do it. Overvoltage and reverse-voltage are the likely culprits.