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Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
There are two likely causes for the TVS heating;
1) each cycle the capacitance of the TVS is charged and discharged, the resultant charging and discharging currents heat up any resistive/lossy parts of the circuit - the TVS and the transistor. This loss/heating can be eliminated by putting a suitable diode in series with the TVS.
2) A more significant source of your TVS heating is probably
Sulaiman wrote ...
One big problem with 555-flyback inverters is what happens when energy is pumped into the primary every cycle but there is no load on the eht output ? (this is important to understand and design for, in my opinion)
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
here's my design I did in 2005 for design comparison if you want.
This was designed for lower power to drive a Crooke's tube without generating too much X-ray for the kids science center. We had a hard time keeping the tube ignited because it was over 80 years old.
If you want lots of power, you need to design for a push-pull, half bridge, or full bridge and use something like the SG3525 or TL494.
Okay thanks for the schematics. I have replaced the IRFP260 with a 600v 50amp mosfet. I tested it and it works great with nearly zero heating of the transistor. I don't need the TVS either (atleast not until 50+ volt input) so I don't have to worry about it melting. BUT when I do run it above 50v I will try putting the diode in series with the TVS to see if that helps. I have yet to try it on a dc flyback. Just my hand wound AC ones. My DIY high frequency XRT works amazing on this driver. There is about 3-4cm of corona coming off the output wire when I run it at 25ish volts. I'll see if I can get a picture of it and post it on the projects section. Thanks for the help!
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"Flyback" Mode Flyback Driver Design
