Nixie Power Supply MK.II Schematic?

[Luka C]

Reading about the power supplies for the clock, I found the MK 1.5 power supply (schematic: https://threeneurons.files.wordpress.com/2011/08/mc34063_mk15cm1.gif) and have already built a clock based on it, but the coil seems to be buzzing pretty noticeably, especially when all the tubes turn OFF -> ON or change numbers at the same time, you can hear the buzzing frequency change at those moments. I suppose that changing the inductor could fix it so I'll give it a try. But, on multiple threads I saw people mentioning MK.II version of the power supply but wasn't able to find the schematic for it. So, does anyone have the schematic for it and would be kind to share it or was it never even made publicly available?

Thanks in advance :)

[threeneurons]

The MK I (one), MK1.5 (one-point-five), and MK II (two), refer to ways of driving the FET, in a MC34063 based switching supply. Here is a drawing showing some preliminary tests done years ago:

The MKI, is the oldest and only actively pulls up the FET gate. Turning it off is passive thru a resistor. MK1.5, uses the MC34063 to turn ON the FET, thru the diode, then actively turns it off by way of a PNP. MKII uses a complimentary NPN/PNP buffer to both actively turn ON and OFF the FET.

After a bit of tweeking, I managed to get 80% efficiency out of the MK1.5 design.

The buzzing is coming off the coil, and will be a problem with all these designs. Its just the way the MC34063 works. It may be improved by choosing a different coil, or even potting one in epoxy resin. Usually, I find the worst buzzing under light loads. If you draw more current, you will get a continuous pulse train, as opposed to a burst of pulses here and there, creating the audible buzz.