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Charging large capacitor banks with an LDO regulator

  1. Jul 10, 2011 #1
    I'm trying to see if charging large capacitor banks with a limited current LDO is feasible.

    If the capacitors draw current past the maximum current of the LDO, will the LDO become unstable or will it be current limited?
  2. jcsd
  3. Jul 11, 2011 #2


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    I suppose it depends on the LDO and the proposed input to the LDO.

    I think most just turn off when they hit the current limit (not what you want). Others just stay fixed current until the strong load is removed (this is what you want).

    Another option might be to use an adjustable LDO that takes an external reference. You can then slowly ramp up the reference with a dv/dt that limits max I for your C. You have to be careful with this though because at the beginning there will be lag on the output and the error signal could cause the LDO pass element to saturate, which would likely blow it out (depending on how much C were talking about).

    What were you planning on using as the input to the LDO, about how much C is in the bank?

    Another, possibly better option (assuming the reason you want the LDO is to make a precise voltage on the cap) would be to over charge the caps on purpose, then remove that power source, and finally slowly bleed off the excess charge with a weak parallel R. Remove the R when the right voltage has been obtained.
  4. Jul 11, 2011 #3


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    Oh ya, even more simply... You can also just put a power resistor in series with the output of the LDO to limit max I into the caps. Ipeak = Vout/R. The LDO feedback point needs to be the input to the series R to keep it stable. Then make sure the R can handle Ipeak*Ipeak*R Watts.

    This assumes you don't need a good transient response on the LDO (and presumably you don't since there is a lot of output C).
  5. Jul 14, 2011 #4
    Thanks so much for the responses
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