TL783c phantom problem?

[hitchhiker]

I've been trying to do the TK 24v & 48v circuit here

http://recording.org/users/kev/TKpowersup.pdf

and no luck getting the right voltage. Is it possible that my tl783 parts
are pin 1 out rather than pin 2.

I'm getting 73 volts on pin 3 in,
64.5v out on pin 2,
63v on pin 1 ???

My tl783 regs were bought from Maxwall. Anybody here used these yet?

Lance

 

[Test Point]

Hey Lance....I have used these in the past and I can't imagine that a company would change the I/O pins on a standard part. My guess is that you don't have enough of a load on the output...I don't remember what it's supposed to be (20ma rings a bell) but if you don't have a minimum load on it, it won't be able to regulate.....just a thought.
TP



Lance...I just checked the spec sheet I had in a file at my bench...it needs 15ma minimum output current so if your load isn't sinking at least that much,
you'll have to tie a resistor to ground on the output to help the TL783 along.

Good Luck

 

[alk509]

What Test Point said...

You need to be pulling 15mA or more from the regulator. Stick to the recommended value for R1 (82 Ohm) and adjust R2 for 48V (comes to around 3050 Ohm).

And watch the power dissipation on those resistors!

Peace,
Al.

 

[hitchhiker]

thanks guys,

I was wondering if I should be adding a load . I'll study the
data sheet more and add the 82r.

cheers,
Lance

 

[PRR]

> Is it possible that my tl783 parts are pin 1 out rather than pin 2.

No.

Read the data sheet. As TP and Al point out, these HV regs need a heavy load to keep them alive. If you are SURE your load is heavy enough and will never be disconnected, fine. But for general light-duty work, it is best to build the minimum load into the regulator. And doing it in the voltage divider slightly improves regulation.

Do it like this:

Al's values will work too, but give just-over 15mA dead load. I like to pull a little more just to be sure. Mostly because I threw-out THREE "dead" (not!) TL783s before I figgered this out. I'll never underload a TL783 again.

If it is already built, just add some 10K 1/2W resistors across the output until it regulates, Check with a few more 10K resistors to be sure it does not drop as load increases.

 

[hitchhiker]

thanks, that's great PRR.

I'm racking this stuff up for a friend and so with your info I can feel
better about the stability of the phantom aspect.

cheers,
Lance

 

[Test Point]

I love those regulators but alas; rumor has it that they have been axed by the manufacturer :? ....I have used many of them for regulating plate supplies, screen supplies, 48v supplies, you name it. Fortunately I bought a few extras...I will hoard those like my SAD chips.....I don't even think they've been out all that long...I'll have to go back to using LM317's when my supply is exhausted
TP

 

[rascalseven]

Isn't there a ground connection missing from that drawing in the 48-volt section?

:?:

JC

 

[adrianh]

But the LM317's do not sound good as
a voltage regulator. The TL783
does sound good as a voltage regulator.






Adrian's Law
"If it is a good part and it sounds good
the manufacturer will discontinue it!"