I am trying to simulate circuit from link: Nixie power supply, but I have come into some problems. I downloaded MC34063 from this forum and example in package is working perfectly. Below is my circuit in LTspice. But for my circuit there is no oscillation on swe output so Q1 and M1 is constantly in one state. As output voltage I got 3.6 V.

Schematic of DC/DC converter

Output voltage

Here is digital version of my schematic file: circuit + mc34063 model

What am I missing? Not working is caused by wrong components, different from schematic? I don't get something about LTspice?

I am new to electronic and just pick this as exercise.

  • \$\begingroup\$ For the future, sharing a schematic should be done together with all the custom symbols and libraries, since not everybode has them. In your case, you should have also packed the symbol for the MC34063 (the .asy file), and the library (.lib), zipped (since it's quite universal). When in doubt, keep a clean installation of LTspice elsewhere, untouched, and try to open the schematic you're about to send as if you were the receiver. \$\endgroup\$ – a concerned citizen Jan 11 at 8:11
  • \$\begingroup\$ @aconcernedcitizen good point - I have edited my post. \$\endgroup\$ – Nichten Jan 12 at 17:04

You can improve your model by placing the resistance of L1 in series with the inductance. But your real issue is that the BSS123 is rated to only 100 volts and low power, so you will need a higher voltage one. I would aim for about 400 volts as a minimum because your coil will have some high voltage spiking. You need a FET capable of switching at least a few amps so you can't have an SOT-23 package - go with a TO220 or TO263. Good luck!

  • \$\begingroup\$ Yeap, I have changed this transistor and added serial resistance 10 ohm - after all of that I got switching effect on swe output. It was a good beginning, so I edited R5 to 500 kohm - after that everything is working!. The key thing was what you have mentioned! Thanks! \$\endgroup\$ – Nichten Jan 12 at 17:06

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