MC34063 output voltage

[rankot]

Your C3 value is too small.   Use a large value like 22uF.

You should also add a Cap across the 555 power.   Maybe 100uF.

Maybe checkout this one,  (no max current given)

I noticed the timing resistors on you original ckt are too low.  Generally no need to use less than about 2k2.

I'll try with bigger value fo C3, and I have an 220uF cap across power, just didn't put it on schematic.

This schematic can go upto 22.4V in LTspice, with 22mA of load, or 24V@14mA. I'll give it a try.

I wanted to have higher switching frequency (80kHz), that's why I went with small resistors, and it also allow smaller switching capacitors.

[rankot]

After tweaking those circuits in LTspice for a little bit more, I have finally arrived to this:



I already had this PCB made, so only changed few components and it gives 24.2V@14mA, tested with real preamp. Very nice! I will try to add LC filter at the end, but it is already quite hissless.

[Rob Strand]

I already had this PCB made, so only changed few components and it gives 24.2V@14mA, tested with real preamp. Very nice! I will try to add LC filter at the end, but it is already quite hissless.

The switched cap converters tend to be inherently low noise provided you have a cap on the input supply.  The down side is poor regulation and the final voltage depends on just about every part.

Your original circuit was LC so if you use another LC circuit you might *have to* solve whatever problem it had.   I've built 3A switchmodes (LC based) which give off very little noise - so you can get them to work.

I wanted to have higher switching frequency (80kHz), that's why I went with small resistors, and it also allow smaller switching capacitors.

In theory you can keep increasing the frequency and decreasing the caps.   However,  once you choose the caps there is a frequency where they work best.   Lower ESR caps let you operate at higher frequencies.   I've seen generic 10uF electrolytics  giving very poor performance past 10kHz to 20kHz in those circuits.