Electronic – Voltage Doubler stops ‘Doubling’

circuit analysisvoltage measurementvoltage-doubler

I constructed a simple voltage doubler on a bread-board. Here's the schematic.

schematic

simulate this circuit – Schematic created using CircuitLab

The output across the 100kΩ resistor was the following. (middle waveform is input, top is output)

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Now when I scaled the resistance and capacitance (for the elements on the right) proportionally – resistance went to 1kΩ, capacitance went to 1mF – the output changed as follows.

enter image description here

Why does the output voltage go down so much? I can't seem to analyze the circuit and see why this would happen. Might I have mixed something up?

Best Answer

Keeping the left hand cap at 1uF is the problem. Just do the math - it has an impedance of 398 ohms at 400Hz and in your original circuit you had a 100k load. No problem here but, dropping the load to 1kohm means you should increase the left hand capacitance appropriately in order to counter the loading effects. Or increase the operating frequency in order to reduce the 1uF reactance.

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