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Registered Member #4081
Joined: Wed Aug 31 2011, 06:40PM
Location: UK
Posts: 139
I've been trying to make a 2no3055 circuit (as on the 4HvWiki) but with the NPN transistors from CRT televisions. But as soon as I switch on the power supply, the transistor instantly blows, leaving a hole in the casing between pin 1 and 2. These transistors are rated for 15A so I don't see why this is happening. Any help or advice would be greatly appreciated, thanks, Harry. http://www.datasheetcatalog.com/datasheets_pdf/B/U/H/5/BUH517.shtml Is one that I used, the others are very similar.
Registered Member #3343
Joined: Thu Oct 21 2010, 04:06PM
Location: Toronto
Posts: 311
HArry:
When a new circuit is beguining to be tested we shall be careful... Sometimes the bias is not corect, sometimes we have made a wrong connection, etc etc
To avoid burn the circuit, connect a auto bulb 12V 20V between the power supply + and the circuit + terminal.
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Yes. Resistor, light bulb, whatever, the idea is to limit the current and keep your circuit intact long enough to scope it and figure out the problem.
Are you sure you got the transistor pinout right? :(
Also, those transistors are designed to work with one of the existing windings on the flyback, and a 50-150V supply, depending on the screen size. They probably won't perform well with a 12V supply and the traditional hand-made winding that has very few turns.
Registered Member #4081
Joined: Wed Aug 31 2011, 06:40PM
Location: UK
Posts: 139
Not too sure, I assumed the transistors go Base, Collector, Emitter, but I didn't check on the datasheets, so I could well be wrong. I only have one more transistor so I'll make sure to check this time.
Registered Member #4081
Joined: Wed Aug 31 2011, 06:40PM
Location: UK
Posts: 139
So I would be better off buying a 2N3055? Also I'm using a 33 Ohm resistor instead of the 27 Ohm on the diagram, will it make a significant difference?
Registered Member #834
Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644
The high-voltage transistors usually found in TVs ou CRT monitors have very low HFE (current gain), and may not oscillate in that usual 2N3055 circuit. The resistor values must be changed. That simple oscillator found everywhere in the Internet is very far from being safe. Even with the quite robust 3055 the probability of a disaster is very high.
Registered Member #4081
Joined: Wed Aug 31 2011, 06:40PM
Location: UK
Posts: 139
Well the point of this project was to make a high voltage supply to learn the dangers of HV. I had an MOT but rewound it because it was too dangerous. So longetivity is not really an issue, it needs to work for around one hour I guess, but not constantly (i.e. left on for one hour. Maybe enough time to make a jacobs ladder). Then I was thinking of building Plasmanas' TL494 plasma speaker.
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Trouble with 2n3055 flyback circuit.
