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I've come across circuits that utilize MOSFETs to drive a center-tapped transformer, but unfortunately, I don't have any MOSFETs on hand. Since I'm working on a circuit for a Geiger-Muller tube, I don't require a high-power setup. I've considered using NPN and PNP transistors as an alternative, but I'm unsure of how to incorporate them with a center-tapped transformer. Transformers are not my strong suit, and I could use some guidance.

I would greatly appreciate any suggestions or recommendations on how to properly connect the transistors to the center-tapped transformer. If possible, it would be incredibly helpful if you could provide a schematic as well since I'm not particularly knowledgeable in this area.

Additionally, if you have any suggestions for making the circuit more power efficient by reducing the current, I'm all ears. I'm limited to using common components, salvaged parts, or affordable components due to budget constraints. Thank you in advance for any assistance you can provide!

In addition to my previous request, I wanted to mention the components I already have on hand for the circuit:

Transistors:

BC547 BC557

Transformer: Center-tapped transformer

Resistors: I have plenty of resistors and a variety of potentiometers available.

Capacitors: I have capacitors with the following values: 100nF 10nF 2.2uF rated at 500V

Diodes: I have the following diodes: 1N4002 BYV95C BY133

OPAMP: NE555

If you have any ideas on how to incorporate these components into the circuit to drive the center-tapped transformer efficiently, please let me know. Your insights and suggestions are greatly appreciated!

Not finished circuit

Doobalo
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  • In this application you need a flyback circuit, not a center tapped forward converter. – Jens Jun 23 '23 at 18:24
  • I wrote a short comment at bottom [here](https://electronics.stackexchange.com/q/671437/330261) that may help a little if you can find and read the article I linked. 555 and TL494. I've another circuit that could easily generate 400 V with just a BJT, though. But you'd need to wind (or find) an appropriate transformer. (It would need regulation of some kind -- even a string of NE-2's could do that, though not as efficiently as you may want. I've used NE-2's before because they can be selected from a batch to target the Geiger-Miller plateau which should be at least 100 V wide.) – periblepsis Jun 23 '23 at 18:29
  • This appears to be an [XY problem](https://xyproblem.info/) to me. Are you required to use a 555 or could you use a different circuit you might happen to find with a google search that works? – Andrew Morton Jun 23 '23 at 18:36
  • Show the MOSFET circuit you are trying to modify please. Forward converters usually have a bridge rectifier on the output. – Andy aka Jun 23 '23 at 18:46
  • @Andyaka Here is the circuit https://electronoobs.com/eng_circuitos_tut14_2.php – Doobalo Jun 23 '23 at 18:58
  • @Jens Another possibility I'm considering is building a flyback transformer. I happen to have a transformer salvaged from an old LED bulb, which has only two pins. I could potentially wind a few turns to create the primary coil and repurpose it as a step-up transformer or flyback transformer. Could it be a cost-effective solution to achieve the desired voltage boost? – Doobalo Jun 23 '23 at 19:05
  • With the mentioned components it is hard to solve. The diodes are too slow, the breakdown voltage of the transistors is too low and the transformer parameters are unknown. Do you have two identical, small classic transformers with mains input and 6..24 VAC output? – Jens Jun 23 '23 at 19:22
  • @Jens I do not have two identical small classic transformers with mains input and 6..24 VAC output. But I can try and look for a transistor from an old power supply maybe. – Doobalo Jun 23 '23 at 19:51
  • @Doobalo go to their forum (they have one because there's a tab for it) and check to see what folk say about it and whether it needs modifications just to make the basic circuit work. No comments or recommendations would lead me to examine the style of the schematic and, dismally it is rather poor and amateurish meaning, if I were a noob I wouldn't rely on it at all. Sorry, but it looks a joke circuit to me. – Andy aka Jun 23 '23 at 19:55
  • @Doobalo If it has only two pins, it's an inductor, not a transformer. Why can't you get some FETs? – Hearth Jun 24 '23 at 02:23
  • @Doobalo This really sounds like you are needing to scrounge and not buy value-added parts. When you are considering parts scavenged from an old LED bulb, that means you are seriously on your own. I've been there when a young teenager, no family support of any kind, and pretty much on my own. (And I still find myself tempted strongly to scavenge parts when there's little need now. Old habits...) You can strip the inductor down and extract the magnet wire from it. And you can find a core somewhere, as well. So it's all possible. (Just most here aren't in that mindset.) – periblepsis Jun 24 '23 at 09:29
  • @Doobalo The two-wire 'transformer' is really an inductor, typically in the small mH range (3 mH is common.) This is your source of magnet wire. But it will take effort to unbox and then finally unwind it carefully. The coating on the wire will be thin and easily damaged when unwinding (it's barely sufficient to save cost.) So be very careful with it. The remaining core may or may not be salvageable. Regardless, the window area is likely too small to be helpful and you may want a different kind of core, anyway, due to frequency differences in your needs. There is a HV BJT usually. Some diodes. – periblepsis Jun 24 '23 at 09:36
  • @Doobalo For example, [this *was* a commonly used NPN](https://cdn.sparkfun.com/assets/home_page_posts/1/8/2/1/D4251T_Datasheet.pdf) in these LED bulbs. (Might be different now.) You'll need to carefully think the flyback transformer design and scavenge what you need, build something, and then test it out before using it. All of this will take time and care and thought. You also seem to have a limited supply of other parts. So start tearing down other stuff for parts. I used to simply walk into a place with a dumpster in back with electronics in it -- local phone central office, for example. – periblepsis Jun 24 '23 at 09:41

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