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-   -   LM317 tracking pre-regulator and current regulator (http://www.diyaudio.com/forums/power-supplies/220720-lm317-tracking-pre-regulator-current-regulator.html)

yagoolar 30th September 2012 03:46 PM

LM317 tracking pre-regulator and current regulator
 
Based on tracking pre-regulator circuit form National and this link I expect to achieve 1A regulated current. But in reality ripple voltage is around 0.2V RMS.
The voltage across second reg is around 2V and does not change if one or two red LEDs are connected between Vout2 and Vadj1.
Sims in LTspice are ok.

yagoolar 30th September 2012 03:51 PM

1 Attachment(s)
Two setups were tested - same result.
Below there are LT1086, just for comparison - LM317T were used for both

peranders 30th September 2012 04:03 PM

Do you plan to built it also?

yagoolar 30th September 2012 04:31 PM

I have built it already. "Reality" is the key.
I added 8mF+8mF to voltage doubler (VD), so results in 12,7mF+12,7mF . There is visible improvement in ripple. So I should go 20mF+ for VD, I think.

yagoolar 30th September 2012 04:32 PM

Here it is. On the left there is the load resistance of 4 33ohm in parallel

http://img.tapatalk.com/d/12/10/01/vy8aba7a.jpg

sofaspud 30th September 2012 04:44 PM

Quote:

The voltage across second reg is around 2V and does not change if one or two red LEDs are connected between Vout2 and Vadj1.
Are you sure about that?

yagoolar 30th September 2012 04:52 PM

Quote:

Originally Posted by sofaspud (Post 3185018)
Are you sure about that?

When 4,7mF caps were in the doubler - 100%. And it was odd. Changing R7 did not help.

sofaspud 30th September 2012 05:01 PM

1 Attachment(s)
The drop across reg2 should be 1.25V + the voltage drop across the LEDs. So it should definitely change 1 LED vs 2 LEDs. Unless something is wrong.
This topic hits close to home, because the below circuit is next in my circuit build queue:

yagoolar 30th September 2012 05:12 PM

"Unless" is the keyword. :)

sofaspud 30th September 2012 05:20 PM

OK. So if the drop is 2V across reg2, what is the drop across R7?


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