Author Options:

Flyback transformer broke in two days Answered

Hi, I made a flyback driver from a 555 timer 2 days ago and now its not working. I think the flyback broke but i dont know. I ran the driver with 6 volts at first but got tired of the 1 cm sparks so I used 12 volts instead and it stopped working. I left it alone for a while, and when i tested it again, it worked again. Now its not working again and i think the flyback broke this time but im not sure.



Best Answer 7 years ago

Why do you think it's the transformer and not the driver?


This circuit is junk without the use of a decoupling capacitor for the 555 and a clamping network for the MOSFET. Back EMF will eventually kill the MOSFET and/or the 555, but as stated by steveastrouk the back emf spike is what causes the HV on the output so you will be sacrificing performance in turn for circuit protection.

The flyback is most probably fine, I have abused mine with a couple hundred watts and it still works fine.

Ah, you have taken too much current through it and killed the 555. Add an external transistor to run the transformer next time

I followed this schematic http://tacashi.tripod.com/elctrncs/555sstc/555sstc.htm
I did add a transistor and the 555 timer still works

Try the transistor then, since you didn't say you had one in the original question. If you increase the voltage too much on the primary, then the current in the transformer shoots way to high, as the transformer's core saturates.

Also put a diode across the coil primary with the cathode (band end) at the top, otherwise you'll be getting a large back EMF into the circuit which could damage the 555 or transistor.

Ah - So I see!
I always assumed that it was the current pulse into the Xformer which caused the HV in the secondary.  I see now it's the collapsing field.
Obvious when you think about the name - flyback transformer.

Precisely. Its an energy exchanger, you wind up the energy in the field around the core, that energy is delivered when it collapses into the secondary.

The original point of course was that you wanted the lovely linear current ramp for other things, and the HT generation was a free benefit. Very clever.


Hmm.... With the demise of the CRT telly I'd forgotten all about the original use of the line output transformer #;¬)