Electronic – Capacitor Inrush Current


I have to filter a power control circuit and as usual I am using lots of capacitors in parallel. Some of these capacitors are Tantalum or Aluminium Polymer types, with ripple current ratings of 3 amps or so… in normal operation the ripple current will be just fine, but when the battery is first attached to the circuit I expect that the capacitors will behave like a short circuit, consuming a huge inrush current that exceeds its ripple current.

Do I have to worry about these and make some sort of slow start circuit to charge the capacitors, or it's just fine?

Example circuit:


simulate this circuit – Schematic created using CircuitLab

Best Answer

An NTC should work fine, as any transients will be supplied from the capacitors at a later time.

However, here is a pretty simple soft start circuit with a small difference from those seen commonly with an RC circuit on the MOSFET gate - I added some negative feedback to the emitter of the NPN to control the rise time more predictably.
Disclaimer - I have not tested this circuit, only quickly thrown together in SPICE, hopefully I haven't missed anything stupid though. Obviously you can alter values to suit your purposes.

enter image description here

EDIT - the MOSFET part number is not a recommendation (thanks Zebonaut) rather just a random SPICE part. Make sure to choose a suitable part for the circuit requirements. The NPN can be any general purpose part (like the 2N3904)


enter image description here