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Author Topic: Self running coil?  (Read 302273 times)

gotoluc

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Re: Self running coil?
« Reply #165 on: March 19, 2010, 04:39:14 PM »
Hi Luc,

From the waveform data your scope shot shows we can approximate pretty well how much driving power goes INTO the MOSFET at its gate source input.
The current flowing across the 100 Ohm carbon resistor is I=.3438V/100=3.438mA.  Here I considered the RMS value of the peak to peak waveform of 3.44V (yellow trace).
This is the current actually flowing into the gate source path (and this path of course includes all the loading effects coming from the output side of the FET i.e. from the drain side).

So the input power to the gate source of the MOSFET is Pinp=4.5V*3.438mA=15.47mW
(I used half of the 9.06V peak to peak value of the gate source voltage (green trace) because for a regular square wave the RMS value is half of the peak to peak value and I took your wave form as a regular one to simplify things.)
We have to add to this the power dissipated in the 100 Ohm series resistor, which is about 1.18mW (.34382/100).

So your signal generator provides about 15.47 + 1.18=16.65mW input to the MOSFET.  Now I cannot tell you how much from this leaks through to the tank circuit, maybe others can help here too. Will think about it.

rgds, Gyula

Thanks Gyula for taking the time to calculate and post this data.

My local supplier has a CMOS version of the 555 timer and I'll pick one up today. I'll go this direction for now, as it seems to be the easiest answer. I'll power it from the capacitor bank so this way we can compare accurately what is drawn to what is produced by the pickup coil.

Luc

NextGen67

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Re: Self running coil?
« Reply #166 on: March 19, 2010, 04:40:02 PM »
Luc,

Would this not be a good solution ? Then no need for a seperate opto at all, as it is build in the mosfet.

http://pdf1.alldatasheet.com/datasheet-pdf/view/139498/TELEDYNE/TC4804.html

EDIT: Attached PDF

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NextGen67

wattsup

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Re: Self running coil?
« Reply #167 on: March 19, 2010, 04:53:06 PM »
@gotoluc

Do you have any germanium diodes. You mentioned somewhere you were using a half bridge and I am wondering if you are not better to make one with germanium diodes. They may leak back somewhat but they only need .2 volts and may just add a new effect.

Also, please make sure you will always be able to go back to square one and get the original effect, while you play around these other ideas.

gyulasun

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Re: Self running coil?
« Reply #168 on: March 19, 2010, 05:03:45 PM »
Hi Luc,

I attach a circuit schematic for you to test the opto coupler, first with still your signal generator output. Use a series 1.5-2 kOhm resistor between the generator and the opto diode input to confine forward current to 10mA or even below for the input diode in the opto coupler, ok?

Your 4N35 opto coupler has 7us (microsecond) rise and fall times so it should work up to about 70kHz (1/7+7).
If you still find it cannot switch at 40-50 kHz, than you may use CNY17-3 from Active Tech,
http://www.active123.com/eng/storeSection/redirect.cfm?sectionID=b2c/search/productSearchResults.cfm&itemCategoryLevel2=43754&itemCategoryLevel1=43746&number_results=12   it has 5us rise and fall times, hence should go up to 100kHz, see data sheet:
http://skory.gylcomp.hu/alkatresz/CNY17%20-1-4.pdf

The 10kOhm resistor between the gate source of the IRF640 could be increased to reduce current taken from the electrolytic capacitor, and do not let the voltage in this cap higher that 20V because this is the maximum limit for the gate source voltage for this MOSFET.

rgds, Gyula

EDIT: The output transistor in the opto coupler has a floating base pin, do not connect it to anything, leave it open.

If you can reach higher than 20V in the electrolytic cap, then use another 10kOhm in series with the collector of the opto transistor, this way you divide the higher than 20V into just half of it, now within safe voltages for the gate-source.  Now the upper limit is the collector emitter maximum voltage allowed for the opto transistor, this is 30V.

NextGen67

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Re: Self running coil?
« Reply #169 on: March 19, 2010, 05:10:55 PM »
@gyula,

Just send you a PM.

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NextGen67

gotoluc

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Re: Self running coil?
« Reply #170 on: March 19, 2010, 05:11:09 PM »
Luc,

Would this not be a good solution ? Then no need for a seperate opto at all, as it is build in the mosfet.

http://pdf1.alldatasheet.com/datasheet-pdf/view/139498/TELEDYNE/TC4804.html

EDIT: Attached PDF

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NextGen67

I don't know?  maybe Gyula can comment on this!

Luc

gotoluc

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Re: Self running coil?
« Reply #171 on: March 19, 2010, 05:13:02 PM »
@gotoluc

Do you have any germanium diodes. You mentioned somewhere you were using a half bridge and I am wondering if you are not better to make one with germanium diodes. They may leak back somewhat but they only need .2 volts and may just add a new effect.

Also, please make sure you will always be able to go back to square one and get the original effect, while you play around these other ideas.

No germanium diodes :(

Yes, I'm careful with the coil.

Luc

LightRider

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Re: Self running coil?
« Reply #172 on: March 19, 2010, 05:16:32 PM »
Luc,

Would this not be a good solution ? Then no need for a seperate opto at all, as it is build in the mosfet.

http://pdf1.alldatasheet.com/datasheet-pdf/view/139498/TELEDYNE/TC4804.html

EDIT: Attached PDF

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NextGen67

MAXIMUM OPERATING FREQUENCY 1.2 MHz
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LightRider

gotoluc

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Re: Self running coil?
« Reply #173 on: March 19, 2010, 05:20:01 PM »
Hi Luc,

I attach a circuit schematic for you to test the opto coupler, first with still your signal generator output. Use a series 1.5-2 kOhm resistor between the generator and the opto diode input to confine forward current to 10mA or even below for the input diode in the opto coupler, ok?

Your 4N35 opto coupler has 7us (microsecond) rise and fall times so it should work up to about 70kHz (1/7+7).
If you still find it cannot switch at 40-50 kHz, than you may use CNY17-3 from Active Tech,
http://www.active123.com/eng/storeSection/redirect.cfm?sectionID=b2c/search/productSearchResults.cfm&itemCategoryLevel2=43754&itemCategoryLevel1=43746&number_results=12   it has 5us rise and fall times, hence should go up to 100kHz, see data sheet:
http://skory.gylcomp.hu/alkatresz/CNY17%20-1-4.pdf

The 10kOhm resistor between the gate source of the IRF640 could be increased to reduce current taken from the electrolytic capacitor, and do not let the voltage in this cap higher that 20V because this is the maximum limit for the gate source voltage for this MOSFET.

rgds, Gyula

Hi Gyula,

thanks for the schematic. That's exactly how I had the 4N35 connected last night and I also had the 10K between the gate and source to shut the mosfet off.

I don't understand why it was only working at low frequencies ??? I'll see if they really have the CNY17-3 in stock when I pickup the CMOS 555

Thanks for your help.

Luc

UPDATE

I just checked and they have the CNY17-3 in stock

mikestocks2006

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Re: Self running coil?
« Reply #174 on: March 19, 2010, 05:27:03 PM »
To everyone

One way to Isolate the signal generator is to use an OPTO Isolator and connect the switching side of the OPTO to the capacitor bank to feed the mosfet gate. I do have a 4N35 and a H11D1 which I both tried last night but they are way too slow to shut off. At 1KHz they were at 95% duty and to full on with frequencies over that. My signal generator is fixed at 50% duty. So these are not working or I don't know how to connect them correctly. If someone with electronic knowledge can recommend an Isolator which could A a up to 50KHz and still keep the 50% duty cycle using a component that I can pickup locally please look at the two suppliers in my city for stock: http://www.resetelectronics.com/VALUE/index.asp  or http://www.active123.com/

The other way is using the pickup coil to trigger the mosfet. This is complicated because the pickup coil is a sine wave that it peaks are out of phase with the mosfet pulses. So again I'm at a loss of how to use this energy or build a circuit that could create the very exact frequency, gate drive voltage and current that is needed.

I'll see if I can pickup a CMOS 555 locally and try to power it from the cap bank by keeping it in the 10vdc range.

AT EVERYONE If you know how to close the loop please provide a complete drawing of how to build it. Please do not just say do this and that. I am willing to do everything I can and I think I have done all I can with my minimal electronic knowledge I have.

Thank you for your time
Hi Luc
The  4N35 you are using appears to be slow, TurnOn, TurnOff times of 2 microseconds typical with max of 10 microseconds. So total rise plus fall would be 4 typical and 20 max allowable per their specs. This equates to frequencies of 250Khz but also within the specs as low as 50 Khz. And this allows for No Flat on the pulse, just rise and fall. Then the flat part of the cycle needs to be accounted for (the post indicates 50% of the total pulse length) Most likely to be safe, something much faster maybe needed if you are routinely operating at 50Khz or more.
Something to possibly look at
OPI2000MK specs claim up to 2Mb/sec with propagation times of 800 nanosecs.
http://www.bot.co.uk/UserDocs/OPI2000MK.pdf
Maybe even something faster
AgilentHCPL-0708  15Mb
Output rise and fall times in the 20-25 nanosecond ranges,
max propagationtimes of 60 ns
http://www.datasheetcatalog.org/datasheet2/1/0351i6kp2qlj3sqzoc47hh3yespy.pdf

I hope this helps
Mike
« Last Edit: March 19, 2010, 06:11:40 PM by mikestocks2006 »

gyulasun

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Re: Self running coil?
« Reply #175 on: March 19, 2010, 05:32:29 PM »
Hi Gyula,

thanks for the schematic. That's exactly how I had the 4N35 connected last night and I also had the 10K between the gate and source to shut the mosfet off.

I don't understand why it was only working at low frequencies ??? I'll see if they really have the CNY17-3 in stock when I pickup the CMOS 555

Thanks for your help.

Luc

UPDATE

I just checked and they have the CNY17-3 in stock

Well, then probably the 10kOhm slows down switching, unfortunately. But if you reduce it to 1-2 kOhm or lower to increase speed, then power consumption from the capacitor goes sky high.

Yes I would agree with using the TC4804-05 opto MOSFET driver in itself, no need for the IRF640 then.  IF the TC4804 or 05 does not include the body diode for its output FET, you can connect a fast diode there instead.

rgds,  Gyula

gyulasun

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Re: Self running coil?
« Reply #176 on: March 19, 2010, 05:51:20 PM »
Luc, I agree with Mike, I did not consider the flat on and off parts of the pulses, sorry.  This means that you would not have higher frequency success with the CNY17-3 either, maybe to as high as 10-15kHz.
Also the speed depends on the opto diode input forward current too. The higher the current is the speedyer the device is, up to the data sheet limits of course. And here we cannot spend current for speed.

Thanks, Gyula

gyulasun

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Re: Self running coil?
« Reply #177 on: March 19, 2010, 06:03:00 PM »
Gyula,

Would it not be possible to simply attach only the signal generator to the mosfet and then connect the Cap to the source and drain, and just observe what goes into the cap ?

Actually a [known] voltage/amperage could be supplied to get it at the correct working point, but this can with a calculation be subtracted from the cap value later again?

EDIT: No need to attach battery I guess, since the signal generator can easily deliver enough voltage ?  Anyhow, after say 5 minutes of charge, one could see how much the cap collected.

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NextGen67

Hi,

After your message I have reconsidered what you suggested and I think a test would be worth doing as per your schematic in your above post.
I cannot forecast what the voltage might be in the cap.

If I recall correctly, Luc measured the drain source peak to peak AC voltage as about 3V in one of his videos. And then his input AC voltage was about 9V peak to peak across the gate source.  This would mean that just due to the gate source interelectrode capacitor (some hundred pF, voltage dependent) the 9V couples through 3V to the drain source side from the 9V but this is a guess from here because the schematic was the full circuit, not what you drew above.

Now that the high speed TC4804 or 05 MOSFET driver would make the IRF 640 obsolote in this circuit, maybe the question you pose is not a question any more? 

Thanks,  Gyula

NextGen67

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Re: Self running coil?
« Reply #178 on: March 19, 2010, 06:06:53 PM »
Luc, I agree with Mike, I did not consider the flat on and off parts of the pulses, sorry.  This means that you would not have higher frequency success with the CNY17-3 either, maybe to as high as 10-15kHz.
Also the speed depends on the opto diode input forward current too. The higher the current is the speeder the device is, up to the data sheet limits of course. And here we cannot spend current for speed.

Thanks, Gyula

So, that means we are left over using the TC4804-05 opto MOSFET driver in itself (or similar types, this was the first one coming in mind).

It has a wide enough range for Frequency (up to 1.2Mhz), but you might want to take a look at the specs in the data sheet if there is no other obstacle... It's maximum voltage is also 20 volt.

The data sheet is attached in my message about the TC4804 earlier.

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NextGen67

NextGen67

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Re: Self running coil?
« Reply #179 on: March 19, 2010, 06:11:09 PM »
Hi,

After your message I have reconsidered what you suggested and I think a test would be worth doing as per your schematic in your above post.
I cannot forecast what the voltage might be in the cap.

If I recall correctly, Luc measured the drain source peak to peak AC voltage as about 3V in one of his videos. And then his input AC voltage was about 9V peak to peak across the gate source.  This would mean that just due to the gate source interelectrode capacitor (some hundred pF, voltage dependent) the 9V couples through 3V to the drain source side from the 9V but this is a guess from here because the schematic was the full circuit, not what you drew above.

Now that the high speed TC4804 or 05 MOSFET driver would make the IRF 640 obsolote in this circuit, maybe the question you pose is not a question any more? 

Thanks,  Gyula

For me personally, I definitely would still like to do the test.  But it is up to Luc of course. It is a step that *could* be skipped using the Opto mosfet.  It is just that it would help me in estimating how great are the chances on success ;)

EDIT: About the cannot forecast what the voltage might be in the cap, is exactly what I am searching for also, and this test would [likely] give some conclusions about that. Given a 5 minute time frame of loading or so, would give a really good indication of what is going on at the Gate side, and would help me to determine if my theory is correct.

[optionally, a voltage could also be supplied -together with the generator, to *simulate* a CAP charge-, as I mentioned in the previous message with the drawing, but then this *must* be a sharply defined voltage/amperage, so it can -calculative wise- later on be subtracted from the charge in the cap].

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NextGen67
« Last Edit: March 19, 2010, 06:36:05 PM by NextGen67 »