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Registered Member #2012
Joined: Sat Mar 07 2009, 10:22AM
Location: Slovakia
Posts: 45
Greetings, I've built the simple one-transistor flyback driver, but wasted two old KD606 NPNs on the circuit, I think it was due to overheating. I've got them from an old TV along with their heatsink. The transistors aren't manufactured nowadays so I'm searching for a replacement, I can "borrow" some old AT/ATX power supplies from my school and take out the high voltage switching transistors from there (on the primary side). What do you think of them? Would it be a good replacement (in general)?
I've already done some searching for old ATX PSU schemes and googled out datasheets for the specific transistors I've found in them, they seem to be pretty "compatible" with the KD606 I've used before (collector current, maximum voltage etc) but I'm not sure.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Cheap high voltage NPN switching transistors like BU208A were good enough for televisions until quite recently, but their incredible appetite for base current makes them unpopular with many experimenters.
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Do not use HOTs or any transistors with >300V Vce for the single transistor driver, they are usually made with different process than the low voltage ones (<180V) and heat MUCH more or even fail to oscillate completely...
Great transistor is the MJ15003, but beware of fakes, I boghut a fake one and it was worse than 2N3055.
I would suggest using a better circuit, at least 555+MOSFET, the "zvs" driver or a half-bridge...
For improved performance, see some of my improvements of the simple circuits:
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
Look for discarded CRT monitors, that always use these transistors (1500 V, ~10 A). Note that they are made to use the normal primary winding of the flyback, and a power supply with at least 50 V for good results. If you will make another primary, you need more current and less voltage. Anyway, if you find a monitor there are many other useful components there, including quite good medium power mosfets, protection devices, and a complete switching power supply with several outputs.
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Switching power NPN's for a flyback driver
