Battery Powered Power Supply

[gregfox151@gmail.com]

Hello all, I took Dave’s power supply, and added a front end that allows a single push button for on and off, and will shut down when the battery reaches a predetermined level (12V in my case). In addition I increased the power supply to ~16v hoping to get out ~14.5V.  The Power/Auto cutout circuit works perfectly, but the power supply is a dud.
I took the schematic right from Dave’s video and I just can’t get more than 8 volts out. I played with R17 and R20 but no luck. In addition, if I put more than 10mA load, the voltage goes to zero. I can’t seem to find out what is causing the problem.
Can anyone tell me why it doesn’t work?
Thanks!

[skrap]

You may want to check out this thread:
https://www.eevblog.com/forum/projects/lt3080-wierdness-dave's-power-supply-(eev224)-gone-mad/

Turns out the LT3080 has few quirks which might be related to your problem.

[gregfox151@gmail.com]

Oh, do you know what they may be?

[skrap]

Well it's explained in detail in the other thread so I won't repeat it all here but the main problem is with the internal design of the SET-pin of the LT3080. It's connected to the output through internal clamping diodes and can't take any more than a maximum of +- 10mA. This will result in a latch-up if the voltage difference between the output pin and the set pin become too large.

[gregfox151@gmail.com]

thank you, I'll check it out... Do you know the thread?

[gregfox151@gmail.com]

never mind, got it.

[_Steven_]

the 3080 gives you this problems.

[gregfox151@gmail.com]

I found the 3080 wasn't properly seated, and after I seated it again and after charging R17 & R20 get 14.8V out, but it only goes down to 2.2V. Anybody have any ideas?

[mcbmcb0]

at a quick glance:

• why is r27 1K? does the voltage at ic1 pin 7 get down to 0v? if it does then the problem may be the 1k after the voltage amp - dave's plan had 100 ohm so r27 and c4 are a low pass filter to help get the current limit stable.
• is c5 a low ESR? the lt3080 needs it to be.
• failing that have you put a scope on it to make sure its not oscillating?
• if not the above maybe its the dreaded lt3080 weirdness (as per other thread) where it appears driving v-set hard down in current limit can exceed to max v-set to v-out allowed and maim it. it appears to regulate tho v-set to v-out much more than the almost 0v its supposed to be.

unless you really need down to 0v, how about the good old lm317 - they are hard to kill and do get to 1.2v - if you can get them to current limit with stablity.

[gregfox151@gmail.com]

HI, Where did you see R27 as 100 ohm? I got R23 and R27 as 1K in Dave’s video EEVBlog #224.
C5 is low ESR, and my scope depicts no oscillation. I think it is the IT3080 weirdness. I spoke to Linear, and they had me ground SET, which should cause the output to be “0” instead I got 2.21V.
Three out of five are in my opinion bad, so I sent them to Linear for evaluation, and should heare from them shortly.
I would like to go down to 0 volts because sometimes one may like to simulate a 1.2v battery in it’s after life.