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can anyone tell me what is wrong with this circuit? Answered

i keep on burning my 555 each time. checked the circuit intallations more than ten times.
voltage using is 12v from a car battery. 

however i am using irfp 450. i don't think that this is a problem.
my ammeter say 5 amps of current passing but no ark to the transformer.

first i thought that the transformer was not good. so i changed it. problem was still not solved. 

then i thought that the winding was not goof. i rewound it but no success.

the mosfet just get hot. 

so i think i will bring my driver to school monday so that i can know if the circuit works.

i removed the mosfet and put a led instead i also change to capacitor with a 10uf cap. the led blinks. therefore the problem is not with the circuit if the led blink.

what can the problem be. i used different kind of mosfets also. still not getting the arcs. 


What frequency are you working at ?

If you see the LED blink, there is NO way it will work

If you think this is a flyback circuit, it isn't. To make it one, make the output DC by adding a high voltage diode

What's happening is you have saturated the core, so the inductance drops to zero, so what happens to the current ? Yep, it soars off to the limiting case of the resistance of your coil/ Vin.

When you apply a voltage to an inductor (the primary of the transformer), the current RAMPS linearly, at a rate of V/L UPTO the point that the magnetic material can accept no more H to turn into B.



no i changed the capacitor to see if is working and then replaced it by the original capacitor.

my operating frequency is 6-70kHz. s3o what should i do?

Yes. Autotransformer designs send a kickback on the trailing edge (switch off). That's what's killing your 555.

Connect the driver circuit to a separate power supply from the autotransformer and use an optoisolator to combine the two circuits.

Also, even 6KHz is pretty fast. I'd suggest reducing the switching speed range to a sub KHz to ~5Khz. 70KHz is really really fast, and doesn't give such a simple design time to recover.

1)To be specific, make it adjustable from ~1-200Hz to ~5KHz max.
2) decouple the 555-based driver from the autotransformer using an optoisolator.

That's not IN autotransformer connection Sean.

There are two problems, his primary saturation is killing the FET, so faster is better, and the absence of the diode in the secondary means that energy isn't transferring to the load in the right way - ie as efficiently as a flyback can.


Fair enough. I stand corrected.

It looked very similar at first to a circuit I used for igniting combustion experiments base4d on a 1970's style car coil (which I do believe is an autotransformer, though I may have the idea wrong), where I used a P chan hexfet for the interface and an opto to isolate. In my case, I found that it was the trailing edge that was kerboffing my 555 due to kickback on field collapse. No other circuitry was adversely affected. (I also used a 2n2222 at first until I replaced it with an optoisolator.

i am using a flyback transforme which aperates at about 25khz