Comments on: 2n3055 flyback driver

By: Daniel

Daniel — Tue, 01 Nov 2011 12:55:04 +0000

Hello, I have made a similar driver to the one shown above but with MJ15003 transistor and a P600M diode, schematic from (By Dr Kilovolt) http://4hv.org/e107_plugins/forum/forum_viewtopic.php?37658
the 25V capacitor doesn’t seem to charge and therefore I get not HV OUT. i then tested the transistor with a different circuit, it worked fine….any help?
thanks v. much

PS. you can checkout the video of the circuit in action in first chat by Dr Kilvolt

By: Alex

Alex — Wed, 08 Jun 2011 09:55:55 +0000

Thanks, just what I wanted to know ( :

By: Mads Barnkob

Mads Barnkob — Tue, 07 Jun 2011 16:32:52 +0000

The capacitor will absorb most of the high voltage transients occuring doing switching of the load.

By: Alex

Alex — Tue, 07 Jun 2011 10:48:05 +0000

Thanks, I meant I have the diode in place and know it is to protect the transistor but what is the small capacitor for? isn’t the diode enough on its own to protect the transistor.

I have the diode but not the capacitor.

Thanks

Alex.

By: Mads Barnkob

Mads Barnkob — Tue, 07 Jun 2011 04:05:43 +0000

Hi Alex

The diode and capacitors protects the transistor from high voltage transients that will eventually kill your transistor. The circuits works fine without, but it might die faster than if it had protection.

Kind regards
Mads

By: Alex

Alex — Mon, 06 Jun 2011 10:48:27 +0000

What purpose does the small capacitor across the protection diode serve? I have mine set up with the diode but without the capacitor and it works fine.

Thanks.

By: Bill whitw

Bill whitw — Wed, 17 Nov 2010 16:31:00 +0000

As strange as it sounds this design is more flexible that it appears superficially. I worked with several transistors and found that a MJE13009 and similar along with much higher filter cap (50v 4000uf) ; higher wattage resistors will bring this to a workable level. not as efficient as the ZVS but not too poor either. The small TO-220 transistor must be efficiently heat-sinked – yet is does not appear to warm up at
5 amps and 18v. I pushed it higher for short periods and it survived and gave surprising performance.
The real problem with this design (aside from it basically being less efficient than the Mazzelli) is that the transistor should really never be a 3055 & the resistors should always be higher wattage than 2 and 5 watts.
(IMO) The Mazelli drivers that occasionally fail are generally due to people not using heat sinks or poorly made one as well.