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I have a DC-to-AC inverter circuit that isn't working. It takes 12V DC input and is being used to power a CCFL. The circuit looks remarkably similar to the one labelled "Conventional CCFL inverter" on https://en.wikipedia.org/wiki/CCFL_inverter .

As far as I can tell with my limited electronics skills, the problem was in one of the transistors. I have unsoldered it OK, and measuring it with a multimeter, I'm seeing a short between two of the pins, which I assume isn't supposed to be the case. Before I removed the transistor, I was seeing a short across the two DC input pins, which I assume is due to the dodgy transistor.

So I need to source a replacement transistor, but I don't know enough about transistors to know what to look for. The dead transistor has written on it:

H.   A
3669
89(something)Z

Web searching for HA3669 I find http://www.hsmc.com.tw/pdf/HA3669.pdf which sounds like what I have.

Does anyone know an equivalent transistor that I can obtain easily in the UK, e.g. from a Maplin store, or online.

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You'll have a tough time finding an NPN transistor that meets all the specifications of that one in the same package, but you may not need that. The particular transistor you linked to has a relatively high beta (min 240 at 500mA) and a relatively high breakdown voltage (80V) without resorting to a darlington structure.

A BC639 can do 100V but it doesn't have the same beta (typ ~80 at 500mA) so the transistors will burn a little more current. This shouldn't be a problem, however, if the output power is not much. I'de try that one (it should be very easy to find) first. If you find it's getting too hot, try a FET or a darlington NPN.

Alternatively, the 80V rating may be overkill. If you can test an operating version of the circuit / find a schematic / reverse engineer it, then you could find something in 60V operating range which is more common...

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