Circuit design aid

I need a circuit that will charge a cap. then allow me to switch over to an output to discharge a 4.3 amp pulse through a 1 ohm resistor for 20 msec. I have to use a 6 vDC power supply. Not sure how to calculate the cap. size I need. Thanks.

Capacity = Current * time / (Vstart - Vend)

Start voltage = 6V, end voltage = 0V?
If so then you need 14333uF.

If you charge the cap to 6V, run a low drop-out 4.3V linear regulator and connect the output to your 1 ohm load, you can only maintain the 4.3A as long as the cap voltage is above the input voltage for the linear regulator. It is realistic to get a linear regulator that will produce 4.3A at an overhead of 500mV. This means the end voltage in the above equation goes to 4.8V:

Cap = 4.3 * 20,000/(6-4.8) = 71,667uF

While doable, that is not exactly a small setup. If you were to use 6.3V caps (way too close for my comfort level), you can get 15,000uF caps in 0.75" x 1.5" package. You will need 5 of those in parallel.

If you wanted a safety margin, I would use 6 of 15,000uF, 10V caps (0.75" x 1.75" size) in parallel, feeding a MIC29502 set to operate at 4.3V. The MIC29502's enable input will enable/disable the output current.

---55p