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Help! Need advice choosing proper resistor value.

Discussion in 'General Electronics Discussion' started by Rahulk70, Feb 14, 2017.

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  1. Rahulk70


    Feb 14, 2017
    Hi guys, I made a simple inverter circuit for a neon lamp using the parts I salvaged from an old power ATX PC Power supply. So, I had two 13007-H2 NPN transistors and the power transformer from the ATX supply and I decided to use it to make the circuit as shown in the below circuit diagram.
    R1&R2=240Ohm &100 Ohm

    Those resistor where also salvaged from the ATX itself.
    So, I managed to get the inverter running but the issue is that the inverter runs only for a a few seconds since the neon bulb dims and fades out and I need to wait sometime before I can reconnect it. The transistors heat up and I doubt it is some kind of thermal shutdown in the transistor is shutting it down. It does get pretty hot too if I try to run it long. What do I need to fix in this circuit?

    Last edited by a moderator: Feb 14, 2017
  2. duke37


    Jan 9, 2011
    You will need a more complicated circuit than this.
    1. The frequency is determined by the transistors running out of steam. This can work but puts them under stress. The limit will be when the current provided by the transistor does not drive the inductance which may have saturated.

    2.The bases are driven from +/- 12V. When positive the resistor will limit the current, when negative there will be little current and the base will be be overvoltaged and perhaps running into Zener area. I do not know what collector current this would give. You could try a diode from each base and a 4.7V Zener diode to limit the reverse voltage.

    I have used a two transformer circuit where a small base drive transformer is run into saturation and fet transistors driven by an oscillator. In both cases, the main transformer runs in linear mode.
  3. Rahulk70


    Feb 14, 2017

    Thanks. I'll try to add a diode from both the bases and see how it runs. I have Power MOSFET FS7KM with me.Maybe I should try one with them .
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