Charging Super Cap w/ a battery
Charging Super Cap w/ a battery
(OP)
I'm working on a pulse power design. The duty cycle is 10%: .1sec ON @ 100mA, 1sec OFF(sleep) @ 0.1mA. The super cap (.47F) will be discharged at startup. What is the best way to combat 'inrush' at startup? My goal in this design is to power the circuit with a 3.6V battery and when the pulses (transients) occur, to power the circuit with the super cap.
So far I have the following options:
1.) using a NTC thermistor in line with a diode
2.) using a resistor in parallel with a schotky
3.) using a current limited voltage reference.
Any suggestions? The simpler the better.
So far I have the following options:
1.) using a NTC thermistor in line with a diode
2.) using a resistor in parallel with a schotky
3.) using a current limited voltage reference.
Any suggestions? The simpler the better.





RE: Charging Super Cap w/ a battery
Another option (if the math works out at all the extremes) is just a simple resistor.
It is possible that the battary could handle the charging surge - if so, then just connect with wire. The user might be offended by the sparks when changing the battery...
All these assume that you want the cap to charge to the battery voltage (less the inevitable drops).
RE: Charging Super Cap w/ a battery
RE: Charging Super Cap w/ a battery
Your bigger problem might be that the series resistor forces the initial charge time to be over 10 seconds and that the 3 time-constants apply to the 1 second available to recharge the capacitor. The largest resistor you can use to met your other requirements is less than 0.7ohm.
This would limit your inrush to about 5A and either the battery can handle it or it'll simply be limited by its ESR.
TTFN
RE: Charging Super Cap w/ a battery
Maybe he needs two super caps - one for the Incredible Pulsating Load From Hell, and another for the rest of the circuit that wants 3.1v min.
...or, maybe just split the circuit and connect the fussy part directly to the battery and the IPLFH part to the supercap side.
RE: Charging Super Cap w/ a battery
It would completely eliminate the inrush problem from killing the battery, and the super-cap could be charged to a regulated voltage independent of battery voltage. It would probably be a lot more energy efficient too.
There are simple switched mode voltage converter chips that contain everything you would need to do this with just a few extra passive components. The average power is only 3.6v at 10mA, not very high.
RE: Charging Super Cap w/ a battery