So why don't we use NE555 for voltage doubling and negative voltages?

[demym]

Hi,

i know it's an old post... but... i tried this NE555 80V, and i'm getting only 58.5V (without a load)... When i connect a load (and in this case it was a valvecaster), i get only 35V.....

Though, i have few differences in schematic:

- the capacitor from pin4 of 555 to ground is 47uF instead of 100uF;
- the last capacitor on HV out is 22uF instead of 10uF (always at 100V);
- diodes are 1N4007;

Do these differences justify my voltages (with and without load) ?

Thanks

[Rob Strand]

I doubt the cap changes will have a large effect, although keeping the cap across the rails (pin 4) large helps.

The 555 contributes a lot to the sag.  Another issue is running the 555 at too high a frequency for the filter caps.  Normal electos are the best choice in this circuit.  Try increasing the 100pF Cap,  say to the 680p to 3.3nF region.  You can tune the cap for least amount of drop under load.

[demym]

Thanks very much, i'll try tonite or tomorrow.

Cheers

[earthtonesaudio]

The output resistance is a function of both the oscillator frequency and the capacitor size.  Frequency up or cap size up translates to higher output current.  I would say the issue is most likely related to the smaller caps.

[defaced]

1n4007 might be too slow for this application.  You'll have to look at the datasheets to see. 

[StephenGiles]

There was an article in either Practical Electronics or Everyday Electronics (perish the thought ) in the 1980s I should think, called something like Super Tone Control, which contained a photo of Pete Townsend - this used a 555 to generate a negative voltage. I may have posted this at some point in time.

[Rob Strand]

Normal electos are the best choice in this circuit.

I made a typo here,  normal electro's are *NOT* the best choice for this circuit.