Dual LM317/337 supply sequencing

[bdivi]

Hello,

I am building a bench power supply and I am using +/- 15V auxiliary supply for the high side control circuitry. That aux supply is based on LM317/337.

As I am finalizing the project it turned out that were are random spikes from the main supply when I turn it on because of the aux supply - in order to fix that I need to delay the +15V rail by 100-200ms relative to the -15V rail.

Any ideas how to do that without going digital ?

[MrAl]

Hi,

I am not entirely sure what problem you have having, but it sounds like a large capacitor might work.

Maybe you could explain the problem a little better too.

[void_error]

As I am finalizing the project it turned out that were are random spikes from the main supply when I turn it on because of the aux supply - in order to fix that I need to delay the +15V rail by 100-200ms relative to the -15V rail.

Any ideas how to do that without going digital ?

LM393. Half of it is a comparator to detect that the negative rail has reached 15V, the other half a delay circuit. Use a TL431 or a zener as the reference for the comparator. Some extra transistors might also be needed.

[C]

see figure 36 in
ti's datasheet

http://www.ti.com/lit/ds/symlink/lm117.pdf

C

[bdivi]

see figure 36 in
ti's datasheet

http://www.ti.com/lit/ds/symlink/lm117.pdf

C

That would not work for me - it is slow start from 1.25V and not from 0. Should be something that do not rely on the output to charge a capacitor.