Okay, you got me on that one.about the diode bridge the diodes do not all point in the same direction. the bottem is like a 'V' and the top is like a '^'
If the catodes join they do not point in the same direction
So I was wrong.
Do any of these coils have a natural resonant frequency of around 680kHz? You will have to drive the coil at resonance if you are replicating MIT's experiment.Yes the 555 will (should output around 680kHz) work. It worked fine with a smaller setup.
What is Ciss and how is it 6.6nF?
I have an LCR meter I can mesuer L but whats Ls?
I have 3 coils i might use.
1. Short wrapped evenly around 7 Screws. .002mH
2. the green coil from the 3 pack at radio shack 1.2mH
3. a long coil wrapped around a big ceramic(i think) cup .25mH
I think the best coil is the one with 1.2mH but the short one also worked. so did the cup.
I ran a sim on a bipolar 555 driving the IRF540, with the 10 ohm gate resistor. The 555 dissipated around 460mW, and the 10 ohm resistor dissipated about 170mW. This is with a 12V supply. It looks to me like a 1/8 watt resistor would burn your fingers, or a 1/4 watter would get pretty warm. The 555, according to the datasheet (thermal resistance is 106deg C/watt), will reach around 75C, which is above the 70C max operating temperature.If the gate resistor is getting hot, it is carrying too much current. This is probably why your 555s are burning up. Your FET, at the speeds you are driving it, needs more gate current than the 555 can source. I'll bet your FET is not turning all the way on or off. Such would severely limit power to your coil.
You'll need to put a FET driver between the 555 and your FET. The best tutorial I've seen on FET drivers is here: http://focus.ti.com/lit/ml/slup169/slup169.pdf
Well, a driver would certainly help if he sticks with the IRF540. The sim shows that the gate voltage is reaching the rails with time to spare, but it also shows the bipolar 555 going all the way to the rails, which it won't do, and it shows transient gate current to be +/- 400mA, when the datasheet says it can source or sink 200mA. As I said though, I think a smaller FET would solve all the problems.That's only half the problem, Ron. He still needs to turn the FET fully on and fully off. He needs a driver!
(Good call on dropping Vcc for the 555, though!)
If he leaves the 100 ohm resistor in series with the drain, the Rds(on) is irrelevant. He could reduce it to 10 ohms and still get away with a much smaller FET.If he's trying to replicate the MIT experiment, wouldn't less power be counterproductive?
by Jake Hertz
by Jake Hertz
by Jake Hertz