I made a flyback driver which just uses an astable 555 circuit to drive the flyback. The 4 and the 8 pins were connected to the positive rail. 7 pin was connected to the positive rail via a 1K resistor and a 10K pot. The 6 pin was connected to the 7 via another 1K resistor and pot. A 10nF cap was between 2 and the negative rail, which was connected to the 6 pin. I used an IRF540 MOSFET directly connected to the 555 to drive it. I was able to get atleast a centimeter long arcs out my flyback (FKD15A001). As excpected, the MOSFET gets hot, I had already attached a heatsink to it so it was no problem. But, the chip also gets very hot for some reason. I have already lost 3 of my chips because of this. Is there anyway to prevent this? Why is this happening? I am using a 12V power supply.
IC555 flyback driver troubleshooting
555flybackhigh frequencyhigh voltagemosfet
Related Solutions
Wow, where to start...
If you blind yourself from the arc or electrocute yourself, it's your own fault. These sorts of do-it-yourself circuits can produce LETHAL amounts of energy and are easily FATAL.
Now to your questions:
I don't know what this exactly means, but I think it means to wind 5 turns with two separate coils and connect the two middle ones together.
Correct. What you're describing is two windings of 5 turns with the end of the first winding connected to the start of the second winding (technical speak for 'the middle ones').
I used fairly thick magnet wire from a radio shack roll of three thicknesses (i used the thickest). (tell me if i need thicker).
"Fairly thick" is completely relative and not helpful. The 5+5 turn windings are used to source energy to the arc that's formed by the open HV terminals. It's difficult to predict just how much current can flow since (I believe) this sort of self-oscillating, non-controlled design is going to be dominated by parasitic elements and hard-to-control elements like transformer coupling, the resistance of the windings, the layout of the switching devices with respect to the transformer, etc. - so, use the thickest magnet wire that you can fit on the core.
I am planning on winding one myself due to price, so what size toroid core should I buy, is that same magnet wire reasonable for 10 amps or do I have to buy larger, aprox. how many winds do I need to get close enough for the circuit to work!
You should do a complete inductor design. The number of turns on the toroid depends on the core's inductance factor (\$A_L\$) which of course depends on the exact toroid you're going to be using. There's no magic solution here. As for wire, I'd guesstimate 18AWG magnet wire or thicker to minimize DC losses. Go for a toroid that has room for more turns that you calculate, so that you can more easily add more turns if you find you need more inductance.
Third, I have a bunch (like 30) aerovox capacitors. The schematic calls for 6 1μf 270 volt capacitors to make a large bank but I looked and they can get quite pricy especialy when buying 6 of them so I am wondering if these would work.
The idea is to use multiple capacitors to divide up the current, so these in parallel should work. The inductor and capacitor values define the operating frequency (or so a few websites say) so try and keep the same capacitance value as the original schematic as a starting point.
Next, is the flyback itself suitable for a ZVS driver? And is it possible I don't even have to wind my own primary? (maybe it has something like 5+5 turns already built in)
You tell us. It's your transformer, after all. Seriously, "flyback transformer" is a broad term that covers many more devices than those found in CRTs. And I wouldn't trust any windings other than the multi-turn high-voltage one (that's the reason you're recycling a CRT transformer and not building your own transformer, right?)
My main concern is winding the primary of the flyback CORRECTLY and EFFICIENTLY and the capacitor bank and the inductor.
This sort of homebrew work doesn't lead itself to immediate efficiency. You probably won't hit the sweet spot the first few times, especially if you don't have any power electronics knowledge.
The missing resistor (known as a pull-up resistor) was the issue. Without it, there is nothing to define the voltage at the trigger pin, except when the button is pressed. This means that airborne electrical noise can couple in to the pin, which might go low enough to trigger the circuit. Since the circuit then latches on for a long time, it doesn't matter that the random noise might then go to a higher voltage again - one very short low trigger is enough to produce the behaviour you saw.
Long wires will definitely have increased the circuit's ability to pick up this random noise by acting as a better aerial (although not "better" for your circuit).
Best Answer
You should consider interfacing the 555 indirectly to the MOSFET for a couple of reasons: -
There may be other things wrong with your design but I would definitely consider using a high current logic driver to feed the gate. The gate driver should be able to deliver about an amp into the gate in order to charge and discharge the gate's capacitance up quickly.
With a poor driver you might also be getting an instability when the FET switches. When it turns off (gate attempts to go low), the output rises quickly and with the inter-lead capacitance this rising voltage can couple to the gate and cause it to momentarily switch off partially. Again it will warm up the FET and if it happens on the rising edge it will likely happen on the falling edge of the drain voltage.