Needing a higher output current in a voltage doubler, we can connect inverters in parallel, as shown in the figure. In this circuit, the current capacity doubles, but is still in the order of microampers. The operating frequency is determined basically by the capacitor of 2.2 nF and by the resistor of 4.7 k ohm. These components can be altered in order to obtain the best performance. Other input voltages can be used by switching the zener diode to one having twice the input voltage. The diodes D1 to D3 are of type 1N4148 or equivalent.