beginner help with a voltage regulator

I'm looking at how to setup this voltage regulator. Should the adjustment be connected directly to ground? that seems funny to me. Please take a look at the schematic and let me know what you think. It is a power supply for 48V phantom power.

http://www.bigfootranch.com/schem.jpg

Thanks for your help!

-mike

The Adj should definitely not be shorting to Gnd. For most applications this should be an electrolytic cap, 10uF or so.

The output voltage is set by 1.25(1+R2/R1). If you use a 220R / 8k2 resistor pair, this gives 47.8 volts without the need for a trimpot.

Peter

Thanks Pete.

By all means correct me if I'm wrong, but off the top of my head, I don't think the TL783 wants a cap on the adjust pin. One of the attributes that makes it a bit unusual. Go find the data sheet and have a look at the application circuits. I know data sheets can seem intimidating at first, and admittedly I only understand about 3% or so, but the basic application information should be there and intelligible. You'll also find loads of graphs showing performance and specs, but probably nothing to worry about at this stage.

Bjorn

Just break the connection between ADJ and ground. The way the circuit is drawn, PR2 has no use as all three leads are at ground potential.

Here's the spec sheet.
http://focus.ti.com/lit/ds/symlink/tl783.pdf

yeah that's the same spec sheet that I had which promted me to ask the origional question. I didn't see how P2 would do anything...

so anyway, in regards to the cap, it says you can use one if your placing it far from the input filter. well what is considered far??

-mike

If you place a cap on the adjust pin to ground it will slow the response of the regulator feedback.

"Far" is probably in another box, or in a console with a power buss.

After reading the spec sheet, it does not seem necessary to include the cap.

Peter

thanks for clearing that up!