Self running coil?

[gotoluc]

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

--
NextGen67

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

Luc

[gotoluc]

@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]

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

--
NextGen67

MAXIMUM OPERATING FREQUENCY 1.2 MHz
-Nice-

LightRider

[gotoluc]

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]

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