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Circuit to keep power during micro-cuts.

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joeka

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Hi,

I'm currently working on a project where I need to keep power during micro-cuts. In order to validate the power supply card, this one must supply a camera during 300-400ms.

To do this, I'm using 3 high caps 3.3F 2.7V (REF : NICHICON - JUMT1335MPD. - CAPACITOR DBL LAYER, 3.3F, 2.7V) as shown in the following schematics : schematic_powersupply.png

However, I tested it and I got this when I switched off the power :test2.jpg

Blue : Input Power (12V)
Red : terminal voltage High Caps
Green : Output Power (12V) (PowerIntern on schematics)

I think that current is too high on DC ouput, so coupled to high Cap ESR, it generates these oscillations.

I' d like to solve this problem. I may need to use higher capacitors to reduce ESR ? but I'd like to know if there are other solutions ?

Thank You
 

Hi Joeka

It's difficult to see what's going on in your graphs as it looks like they don't all have the same vertical scale. I don't know about the oscillation, but I see a couple of other problems.

Firstly the caps are rated at 2.7V each, so for three in series the maximum safe voltage is 8.1V. Putting 12V across them seems to be asking for trouble.

I don't know about these supercaps but when you overvolt a normal electrolytic, it works fine until it explodes.:shock: After it explodes, you remember not to do that again. (I might have learned this the hard way.:smile:)

Also, the datasheet for the LT1510 says the input voltage must be at least 3V higher than the battery voltage, so I'm not sure how you're charging the caps to 12V with only 12V input.

Regards - Godfrey
 

Hi godfreyl,

There is only 8V at the ouput of LT1510 (BAT pin 11) so capacitors won't be overvolted and the input voltage is about 4V higher than the battery voltage, so it's fine.

Regards
 
Last edited:

OK, but then the output voltage should drop by about 4V when the input power is switched off. I think the plots on your graph must be mixed up - you said green is the output voltage, but that's the only one that doesn't drop. :???:

I'm also still not sure how to compare them. At the bottom of the graphs, it says the red trace is a different scale and offset to the others. If that is the capacitor voltage (as you said) then it shouldn't start higher than the others, but it also shouldn't drop so much.

Could you maybe post plots with everything at the same scale and both axis clearly marked. As is, I can't make out the frequency of the ringing or figure out what any of the voltages are.
 

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