### Author Topic: VIC-PICK UP SECTION  (Read 7732 times)

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##### VIC-PICK UP SECTION
« on: March 08, 2011, 11:46:27 am »
Hey guys has anyone figured out how the pick up coil works with the over all circut?

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##### Re: VIC-PICK UP SECTION
« Reply #1 on: March 08, 2011, 18:37:14 pm »
If by pick up coils you mean the pulse indicator coil, o tell you how it can work. The VDD 12v forms with the resistors a voltage divider that maintain a predefined voltage in the + and - comparator inputs, The diodes limit the voltage difference between the pins to 0,7 volts, and the other resistor determine the gain and the other the load.

I think the resistors should form a 1:5 voltage divider so two resistors of 500 on each side and a 100 ohm resistor going to ground seems ok... The current would be 20ma and the power dissipated 24milliwatts if using 12v as vdd and there would be 2v in the inputs of the comparator (relative to ground). I think that the gain transistor could be something like 5k ohms...

Well this are some values i'm working on to test here...

The pulse indicator coil i would put in a separated coil in series with the resonant coil, so it can get a purer resonant signal... I think a current transformer could also be used. But voltage is ok too. just need to limit the current...

I'm still trying to find witch is the best signal that the pll wants, i mean the voltage of the signal cause the kind of signal is a 50/50% square wave. I just don't know if must be 0-5v or maybe from 2 to 3v square wave-.

If anyone know please... I all ear.

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##### Re: VIC-PICK UP SECTION
« Reply #2 on: March 10, 2011, 16:56:19 pm »
Quote
I just don't know if must be 0-5v or maybe from 2 to 3v square wave-.

Lol, well, it just has to get to the voltage which will be interpreted as high from your PLL-Chip (4046). The exact value, you can get from a datasheet.
E.g. if you let the 4046 run on 12volts, then you best put out 0/12V signals from your pickup-OpAmp. Sure the OpAmp is not able to put out a 12V signal if feed with 12V, but e.g. 10V would surely still be OK.
About the resistors. I think 20mA at 12V is a bit much. That much current is IMHO not needed. E.g. Stan used two 10kOhm resistors, which is about the size I would have taken too. I would have gone a bit smaller, not to be influenced too much by induced currents (noise).
You also have to remember, that if there's a resonance in the VIC, the voltage of the pickup-coil will be much larger than 12volts.
And if you wanna use a current transformer, then the PLL gets a problem. For the current has 90° offset. Then you would have to take the first comparator of the PLL, instead of the 2nd. But the first has the problem, that it also locks on harmonics, as it doesn't use a flip-flop.
BTW: Just for informational purposes, he used a 1MOhm in series with a 100KOhm for the feedback. The feedback is responsible for the hysteresis.
It does looks, like he additionally added, a capacitor. IMHO I already thought this is strange before, as I designed additional filter capacitors to my Pickup-circuit. You just don't wanna have some high frequency noise on the pickup-voltage.
« Last Edit: March 10, 2011, 19:15:11 pm by Kali_ma_Amar »

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##### Re: VIC-PICK UP SECTION
« Reply #3 on: March 10, 2011, 19:25:19 pm »
Thanks for the input man. I'm having many problems here, i just blowed three mosfets...

I only have 1 now.

I'm going to wind more turns on the primary cause i think i wounded not many turns.. I found that when the duty cycle is 0 even being no pulse there the mosfet stay on so i think that when the inibit pulse leaves maybe a high logic.. i need to solve that. Don't know what is happening, my oscilloscope don't measure dc. Seems some kind of avalanche effect. I think that i'm going to add a diode in parallel with the mosfet and with the coil too. maybe the mosfet is not able to turn off correctly because of the impedance of the driver, i'm going to take out the 100 ohms resistor and connect the driver to the source, and not to the ground...

the problem is that my money finished...also the credit.. hehehe

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##### Re: VIC-PICK UP SECTION
« Reply #4 on: March 10, 2011, 19:59:30 pm »
Well, what kind of protection do you have? IMHO a varistor or transil-diode is an absolute must have in such a prototype circuit, where you never know, what you will get (the integrated Z-diode of the FET cannot handle much energy). And, as always surely some z-diode(s) for the protection of the gate (the gate is quite sensitive to overvoltage). And last but not least you certainly need a fuse, to protect the FET, if anything goes wrong in the driver circuit, so that not too much current can flow, if the FET stays too long ON.

This is how I made my driving circuit. And then you don't so easily kill it. If something is going wrong, you will usually first see this, by the fact, that one of your protection devices are getting hot. then you know. Immediately switch off, and look why.

What FETs do you use? What driver?

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##### Re: VIC-PICK UP SECTION
« Reply #5 on: March 10, 2011, 20:59:56 pm »
Yes I have figured out the Pulse Indicator circuit. When the circuit is out of resonance the output of the Op Amp will be high and when this High signal is sent to pin 14 of the PLL circuit and this lets the PLL circuit know that resonance hasnt been found. When the feedback coil senses  resonance, the output of the Op Amp will produce 50% square waves at the same frequency as sensed by the feedback. Very simple I might say :-) I will let you guys know more about this when i finished up building the circuit and testing.

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##### Re: VIC-PICK UP SECTION
« Reply #6 on: March 10, 2011, 21:15:47 pm »
Thanks for the description.

I'm using the ir4427 driver and was using irfp460 mosfets, all died including a driver and one section of the other driver...

Don't know what to do..

I need something that rocks solid up to 250v 3 amps...

Could you help me design it? maybe you can make a schematic?

I tried all that i could but could not keep the mosfets from blowing.

Tomorow i'm going to get this mosfets and some resistors

irf740    x3
irf840    x2
Irfp460LC   x1
Irfpg50     x1

If you know any part numbers you recommend for working at this voltages...

I still have some IGBTS modules here so i will still working until i have components to blow...

The igbts are more solid... i hope...

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##### Re: VIC-PICK UP SECTION
« Reply #7 on: March 10, 2011, 21:19:05 pm »
Yes I have figured out the Pulse Indicator circuit. When the circuit is out of resonance the output of the Op Amp will be high and when this High signal is sent to pin 14 of the PLL circuit and this lets the PLL circuit know that resonance hasnt been found. When the feedback coil senses  resonance, the output of the Op Amp will produce 50% square waves at the same frequency as sensed by the feedback. Very simple I might say :-) I will let you guys know more about this when i finished up building the circuit and testing.

Nice one thanks very much this explain manythings... but if so then the resonant scaning circuit is a must have not an option. when i tried it two years ago i didn't figured out to it work the way you describe. would you have a diagram with the resistors values?