My first time trying the LT3080.
I want to use it to power a precision 10v voltage reference, so eventually it might be battery powered (+18v).
I need about 15v out of it.
(note: my drawing shows the pins the way they look visually, from overhead: 3 pins protrude out, 2 pins straight down, bottom pin is not connected "NC".)
I can't find out why it's not working. It's fresh out of the package (digikey).
Caps are installed with the correct polarity.
I tried 2 different lab PSU's to power the 3080, just to be sure. Their current limit lights are not flashing. Almost no current is flowing anywhere.
The 3080 outputs will "barely" power an LED.
With no load, "Set resistor" is 34.6k for 15v.
With a 100k load resistor applied to the 3080 outputs, voltage output drops to around 12v, and varies greatly with other load values applied.....
Something is not right........right ?
I want to use it to power a precision 10v voltage reference, so eventually it might be battery powered (+18v).
I need about 15v out of it.
(note: my drawing shows the pins the way they look visually, from overhead: 3 pins protrude out, 2 pins straight down, bottom pin is not connected "NC".)
I can't find out why it's not working. It's fresh out of the package (digikey).
Caps are installed with the correct polarity.
I tried 2 different lab PSU's to power the 3080, just to be sure. Their current limit lights are not flashing. Almost no current is flowing anywhere.
The 3080 outputs will "barely" power an LED.
With no load, "Set resistor" is 34.6k for 15v.
With a 100k load resistor applied to the 3080 outputs, voltage output drops to around 12v, and varies greatly with other load values applied.....
Something is not right........right ?
Last edited:
...and that is why something is not right.
Trying to find the reason.
15/0.00001=1,500,000
...I'm not getting that Vout with a 1.5M ohms as the set resistor.
.....with that set resistor, I get 17.2v out.....I tried it.
Maybe the 3080 part is bad ?
Does my schem seem correct ?
Last edited:
I doubt you got a bad LT3080. With 17 V in, the IC should have no trouble regulating.
With the low Iset, you have to watch out for leakage paths. You could force a higher current though the feedback path by using the circuit shown in the last figure on page 17 of the datasheet. This is similar to what I'm doing in my 21st Century Maida Regulator.
You also need to beware that the IC needs low ESR caps for stability. Find a good X7R or X5R ceramic cap.
Based on your description, I bet the issue is your choice of capacitors. Tantalum caps tend to be relatively high ESR. This can make the regulator unstable, hence, give poor load regulation.
~Tom
With the low Iset, you have to watch out for leakage paths. You could force a higher current though the feedback path by using the circuit shown in the last figure on page 17 of the datasheet. This is similar to what I'm doing in my 21st Century Maida Regulator.
You also need to beware that the IC needs low ESR caps for stability. Find a good X7R or X5R ceramic cap.
Based on your description, I bet the issue is your choice of capacitors. Tantalum caps tend to be relatively high ESR. This can make the regulator unstable, hence, give poor load regulation.
~Tom
...hmmmm tried all these caps, plus a nichicon "PL series" 'electrolytic.
(this is all the caps I have in stock)
No luck....all give me just over 17v out with a 1.5M set resistor.
I thought this was supposed to be an "easy to implement" part ? (LT3080).
Wouldn't a bit high ESR effect stability.....and not give a completely different stable Vout ?
(I have some lower ESR ceramic caps in lower values.....does paralleling them increase the ESR, or reduce the ESR ?)
Last edited:
I think that's it RJM...!!
....I get 14.92v with different loads under 27k.....(air wired for testing...better performance likely when connections are placed properly.)
I was testing with not enough load !
Thanks everybody...very much !!!!!!
I will order the proper caps as well.
Last edited:
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.