HV Linear Regulator Outputting 0.4V

Hey everyone,

I assembled a couple of the same PCB for testing and it seems that the high voltage linear regulator is outputting 0.4V on both boards. Does anybody have any idea why this would be?

The linear regulator being used as per the schematic on page 9 except the input capacitance is 1uF 250V X5R and the output capacitance is 10uF or 30uF (I tried both) 25V X5R:
https://www.onsemi.com/pub/Collateral/NCP785A-D.PDF

This is the 15V version of the regulator where the minimum input voltage is 60V and I tested it between 65VDC to 73VDC. The only load on the regulator is an IC that consumes 1-2mA.

Problem found. Must have mixed up the pins with some other datasheet.

dknguyen said:

The only load on the regulator is an IC that consumes 1-2mA.

Click to expand...

are you sure of that figure?

Funny I was just looking at the data sheet in a different window. How do you know what pin is "In". I can see "1,2,3" and "In, Gnd, Out" but not together.

ronsimpson said:

Funny I was just looking at the data sheet in a different window. How do you know what pin is "In". I can see "1,2,3" and "In, Gnd, Out" but not together.

Click to expand...

table 1 page 2

unclejed613 said:

are you sure of that figure?

Click to expand...

As sure as the manufacturer's datasheet for that IC.

ronsimpson said:

Funny I was just looking at the data sheet in a different window. How do you know what pin is "In". I can see "1,2,3" and "In, Gnd, Out" but not together.

Click to expand...

Yeah. I have no idea how I ended up with the pin out I used. When laying it out, I remember thinking that it was a bit strange that the tab was not ground since that would be most convenient for the heatsink plane.