Switched capacitor voltage boosters

[pyrohaz]

Hey guys, i've recently designed myself a simple switched capacitor voltage booster, just using the simple 4069 inverter chip. I was wondering though, can you give me any simple information on increasing the efficiency of my switched capacitor booster? I will include a schematic of what mine looks like :)

The reason is, im only using a 4 stage booster (2 of the inverters for an oscillator, the rest for voltage boosting.) And im using it to drive my tube preamp :) After I tested it, I got an output of 58v (68k load) and a frequency of 42khz. Now obviously, the calculated voltage should be 60v but im sure the combined voltage drop of 4 diodes is about 2 v (0.6*4=2.4 so actually, a little less)

Are there any tips you can give me to improve this circuit?

After having a quick look with my multimeter, it said it was only consuming about 7.4mA which actually seems a tad low for a voltage booster IMO. I calculated the efficiency of the current circuit at a mere 55%!

Im using 63v Axial 1uF capacitors, they have a blue plastic coating on the outside if that helps :)
1N4148 diodes and a PI filter on the output may be a bit of an overkill but its feeding the preamp audio stage so I want as little noise as possible.

[Hero999]

Using Schottky diodes would reduce the voltage drop to 0.3V per diode.

CMOS gates have a high output impedance so you can't expect great efficiency.

If you use the 74C14 you can make an oscillator using a single gate and use a fizv stage booster.

[pyrohaz]

The 74C14 is the same as the 40106 isn't it? I'm happy with the voltage it is at (the capacitors I have are only rated to 63v, hence why I only used the 4 stages). Would adding another stage not decrease the current I could supply? I was thinking of using one of these switched capacitor boosters in a guitar pedal.

For a schottky diode, would the BAT46 be suitable? Afaik, they're rated up to 100v aren't they?

Any other tips you can give me?

Cheers