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Project Notes

#147 555Timer/VoltageDoublerChargePump

Test a voltage-doubling charge pump circuit based on a 555 timer.

Notes

See the 555Timer/InvertingChargePump project for similar circuit (but with inverted output) that explores the inners of charge pumps in more detail.

This configuration can theoretically deliver an output voltage that is double the output voltage.

The 555 oscillator is configured with a reasonable larger R1 in order to minimise power loss in the 555 - in this configuration it draws only 5mA with no load. This means the frequency is a little lower that desirable at 13.9kHz.

Flyback and output capacitors could be larger, but only only have on hand 1µF rated for over 16V.

I’m using 1N5819 diodes for their low forward voltage, but as shown in the InvertingChargePump circuit, other rectifiers such as 1N4001 are possible but at the expense of voltage gain.

Here are some measurements:

D1/D2 R1 R2 C1 CF CL RL Vin Iin Vout Iload Pin Pout Efficiency
1N5819 10kΩ 47kΩ 1nF 1µF 1µF 1kΩ 8.52 32.3mA -13.68 13.8mA 275.2mW 188.8mW 68.6%
1N5819 10kΩ 47kΩ 1nF 1µF 1µF 10kΩ 9.25 8.5mA -16.79 1.7mA 78.6mW 28.5mW 36.3%
1N5819 10kΩ 47kΩ 1nF 1µF 1µF 100kΩ 9.27 5.46mA -18.18 182µA 50.6mW 3.3mW 6.5%

Some Conclusions

Pretty much the same as for the InvertingChargePump circuit:

Diode selection:

  • 1N5819 is ideal, maximising the voltage gain
  • but 1N4001 still works, with some loss, and there’s not much benefit in using 1N4148 instead

Frequency:

  • higher frequencies are more robust under varying loads (lower voltage drop at lower output impedences)

Capacitor values:

  • for this circuit and range of loads, CF and CL should be at least 1µF
  • higher values get the circuit closer to unity gain
  • note the need to ensure the capacitors are rated for the voltage generated

Output Impedence:

  • this circuit struggles to maintain voltage for low impedences (under 10kΩ)
  • understandable, since they want to rapidly deplete the output capacitor
  • for low impedence loads, the circuit would need to change so that a heavy charging current could be delivered via a BJT or FET

Oscillator:

  • the 555 chip is an expensive way to drive a low-power charge pump, being responsible for the bulk of conversion losses

Construction

Breadboard

The Schematic

The Build

Credits and References

About LEAP#147 555 TimerPower
Project Source on GitHub Return to the LEAP Catalog

This page is a web-friendly rendering of my project notes shared in the LEAP GitHub repository.

LEAP is my personal collection of electronics projects, usually involving an Arduino or other microprocessor in one way or another. Some are full-blown projects, while many are trivial breadboard experiments, intended to learn and explore something interesting (IMHO!).

The projects are usually inspired by things found wild on the net, or ideas from the sources such as:

Feel free to borrow liberally, and if you spot any issues do let me know. See the individual projects for credits where due. There are even now a few projects contributed by others - send your own over in a pull request if you would also like to add to this collection.