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2n3055 flyback driver?

is there a better transistor to use instead of the 2n3055 because those things break easily and are somewhat expensive. 

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Three possibilities immediately come to mind.

1. As Rick Harris said, heat sinking is probably not up to snuff. Make sure it runs cool enough.

2. Inductive kickback is killing the 2N3055. When the transistor stops conducting and the energy field collapses in the transformer, a reverse polarity high voltage spike comes back at the transistor. Use a diode to safely bypass this spike around the transistor.

3. You are using a voltage higher than the 2N3055 is rated for. Use no more than 60 volts (total) across the transistor.

Steveastrouk makes a great point about the different saturations. Both situations cause excessive heat which will kill the circuit.

Qa

The point of the single switch flyback though, is that the energy in the collapsing field is pumped into the SECONDARY load, and NOT into raising the primary voltage.
"steveastrouk says:
The point of the single switch flyback though, is that the energy in the collapsing field is pumped into the SECONDARY load, and NOT into raising the primary voltage. "

Understood, but we don't know just what circuit he is using, or if it is constructed correctly with the correct parts. All very real unknowns, so the basic possibilities must be mentioned along with basic theory so that the OP may make an informed decision as to what information is useful.

Just my take on answers.

Qa
Granted !
Jimmy Proton (author) 6 years ago
turns out there is a better transistor, NTE284, has an output of up to 18kv, but i just bought 10 3055's
AS Rick says, you are doing something wrong ! I suggest you check that the transistor IS fully saturated in use, and that you AREN'T saturating the flyback transformer.
rickharris6 years ago
The I would suggest your using or driving the 3055 incorrectly as they can pass at least 15 amps for ever.

Check heat sinking

or look for a higher rated device than 15 amps collector current.