I am designing (simulating in LTSpice and building on a breadboard) a charge pump to power my numitron tube. I need to get ~15-20 V out of 3.3 V. The circuit is as follows:
simulate this circuit – Schematic created using CircuitLab
All diodes are 1N4148, the V1 source comes from a voltage regulator, while CLK1 from an Atmega OSC1 pin (Atmega powered by the same voltage regulator). The NOT gate is made from a NAND gate on a separate IC.
The circuit gives me about 18-20 V on the output without load, but when loaded, it lowers drastically. I measured the effective output resistance of this charge pump to be about 11 kOhm which is way too much for me. I tried simulating the circuit with smaller/bigger capacitances or frequencies, but it didn't change much.
The question is: how can I lower the output impedance of my charge pump?
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