I am helping my son make a mini-Tesla for his science fair project and came across a problem I can't figure out. I am following this diagram (pretty much, but without the LED):

enter image description here

Also, I am not sure of the exact number of windings - around 300 of 27 AWG wire. I have experimented with 2 to 6 primary coil windings and can make this work with 3 windings of the primary coil. My problem is that I have burned up two transistors already - not right away, the circuit works and I can turn a bulb on but the transistor is getting VERY hot. Why? Do I need

  1. fewer or more primary windings?
  2. a different type of transistor?
  3. a heatsink?
  4. a different value resistor or an additional resistor or capacitor (don't ask, but I have seen other versions of this mini Tesla)
  5. just need to buy more tansistors and hope for the best?

Thanks in advance.


  • \$\begingroup\$ Is the switch physical or electronic? \$\endgroup\$
    – vofa
    Jan 21 '18 at 17:22
  • \$\begingroup\$ The switch is a physical switch. \$\endgroup\$ Jan 21 '18 at 18:32
  • \$\begingroup\$ If you wind the transformer the wrong way, does the mini-Tesla still work? \$\endgroup\$ Jan 21 '18 at 21:54

See Understanding the slayer exciter circuit base voltage for a full explanation, but you are basically abusing the transistor in two ways:

  1. By leaving out the diode, you're forcing the B-E junction into reverse breakdown whenever the base tries to go negative.

  2. The 2222 is a small transistor, only good for a few hundred milliwatts of dissipation. It's hard to say what this circuit needs, but it could be considerably more. And issue #1 is only making matters worse.

  • 1
    \$\begingroup\$ So the quick (before Feb 1st) solution is..... \$\endgroup\$ Jan 21 '18 at 17:49
  • 2
    \$\begingroup\$ What is the significance of Feb. 1? The first thing you should do is add the diode, assuming that wasn't totally clear in what I wrote above. If the transistor is still overheating after that, you need a bigger transistor -- one that can be bolted to a heatsink. \$\endgroup\$
    – Dave Tweed
    Jan 21 '18 at 17:55
  • 1
    \$\begingroup\$ So the LED (Light Emitting Diode) will is actually doing something in the circuit other than indicating that the switch is on? Feb 1st is when his project is due and I have been working on this for weeks now - using the wrong transistor and trouble shooting. I just ordered a TIP31C transistor and a heatsink based on the above comments and others I found on this site. I need a solution soon, unfortunately. \$\endgroup\$ Jan 21 '18 at 18:10
  • \$\begingroup\$ Update: Added a bigger transistor T31C NPN and the LED to the circuit. It WORKS! Here is a short video. facebook.com/larry.reiter/videos/10155997926924705 \$\endgroup\$ Jan 25 '18 at 21:55

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