How can fully charge a capacitor without having it prematurely discharge?
This is an incomplete answer and may not be suitable for one or many reasons but it is simple and give you some ideas.







simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. SCR (thyristor) latching switch.

How it works:


SCR1 is normally off.
As the voltage on C1 rises above about 4.7 V Zener diode, D1, begins to conduct in reverse-breakdown.
When the voltage across R1 gets high enough (about 0.7 V) the SCR will trigger and turn on. "Circuit" will now be powered. SCRs, once triggered, remain on until the current through them falls below the holding current (mA).
When C1 is discharged sufficiently the SCR will turn off and the process can begin again.
The OFF switch allows you to interrupt the circuit to reset it early, if required.


Someone else may be able to correct the values for D1 and R1. It's bedtime for me.