No high voltage, no help from the seller...

I only have a 331 value capacitor, which comes out a 330pf, would that be okay?
Can I add 2 values together to get to 360pf?

Sorry for all these messages.
Everything seems to be connected to the right places.
I have found another difference though.
The build manual says that L1 the inductor is 150uh, but the schematics show that to be a 150uh, will this make much difference?
Thanks soooo much for your patience with me.

Hi to all,
just out of curiosity I've taken a look into the Schematics of the HV converter Ian published in this earlier post.

There are some things I don't understand:

First of all, what shall the 220uF at the Ipk pin achieve? The effect is that the peak current limit is now dynamic and a mixture of the voltage drop caused by the current through R1 and the current through the ESR of the 220uF capacitor. And what's missing in the schematics is a bypass capacitor for Vin.

The driving stage for the IRF640 is the second thing - the 2N3906 is working in common collector configuration, so without a negative helper voltage for the pull down resistor it cannot pull down the gate of the IRF 640 to 0V.

As far as i've read through the data sheet the MC34063 has a minimum on time defined by the size of the timing capacitor. I've not yet gone through the formulas given in the data sheet as it makes no sense without knowing the exact parts used (actual capacitance, the operation and the saturation currents of the inductor).

What would also be interesting (but not too easy to measure) would be if there is any ringing on the gate of the IRF640 that could lead to unwanted effects. You can't seriously measure this with a standard probe because you catch more noise and interference through the loop you build up with the ground cable of the probe.

Regards,
Torsten

Hello Ty,
I believe that this capacitor is simply connected wrong. The threeneurons PSU also doesn's have any bulk and/or bypass capacitors on Vin. As mentioned, the peak current through the inductor is determined by the voltage drop over Vin and Ipk. With (in the threeneurons schemantics) C1 mounted at Vin this would simply be (R1|R2)*I_L1. With 300mV Ipk voltage drop this would roughly be 1.2A. But with the wrongly connected capacitor C1 will additionally deliver current, the voltage drop compared to Vin then depends on the discharging of C1 and its ESR. And the ESR highly depends on the capacitor chosen and can be anywhere between 20mOhm (Polymer type) to several hundred mOhm (higher ESR electrolyte types). So the result is highly dynamic and no longer clearly predictable.

With a correctly connected capacitor Ian's circuit would have been set to roughly 135mA peak current on the Vin side which could closely sufficient for a clock with four small Nixie tubes (At 12V Vin: Iout_max = 135mA*12V/170V*x < 10mA with x somewhat smaller than 1 due to losses).

BTW, I found a blogspot article for another boost circuit which uses the same driver stage as Ian's and the threeneurons circuitry where the bulk capacitor is placed correctly.

Regards,
Torsten

P. S. As often I believe someone first introduced this error (perhaps in the threeneurons article, perhaps somewhere else) and then it was simply copied and copied again without questioning the schematics or checking the values.

P. P. S. Another thing to point out: The IRF640 has the typical V_GS of +/-20V. The MC34036 will drive the gate nearly up to Vin. The HV converter circuitry doesn't protect the gate in any way. I haven't seen the whole schematics of the clock, but Ty, I remember that you received them. Is the input voltage limited in any way e. g. by a TVS diode?