TL783: TL783

R1 is 82 ohms, output voltage is 50 to 70 volts.

Yes the pots have an accurate value.

Thank you

Hi Michael,

Would you mind sharing your circuit and the components used?

Thanks,

Good Morning JCHK,

Below you should find the regulator section of the design.

Given; Vin = 70V filtered, Vout = 60V, and Iout = 2 Amps.

This is my second attempt to insert my schematic, your email app. is dumping what I paste into it.

Hi Michael,

I put together a very simple model to see what could be going on and it does look than when changing the potentiometer, there is a point where the power dissipation could exceed the power rating:

 As with all simulations, they are not including all parasitics and the model I put together for the TL783 is crude at best. I have attached the Tina model used if you want to play around with it.

TL783 figure 15.TSC

I hope this helps.

John,

Yes, I agree with your assessment. I have conducted a few tests with an amp meter in the adj. leg, and found that when the pot’s value is low it can draw 28 ma or more the closer it gets to ground.

Two questions;

1. Is this normal for this circuit to do this?

             If it is normal, what is my recourse for adjustment, say 10V to 70V without this issue.

        2. This circuit does not adjust the voltage as described in the data sheet.

The In and Out voltage diff. is about 1.3 volts, no matter what voltage is on the input.

Example: 70 v in with 68.7 V out. It appears to regulate at a fixed voltage only.

I suspect TL783 device is defective. Is it possible to get a couple samples of the TL783 with the KTT (TO-263) PACKAGE ?

Thank You for all your help

Mike Andrasko