Uhf mosfet
datacps
Posts: 139
My next project involves a Propeller and I need to know if there is a MOSFET or any High Voltage ,, Like 1000 V device that can go upto 30Mhz.· I may be asking too much from a MOSFET .. I also did a search but most of the JFET went to 1Mhz.. Thanks
Comments
Leon
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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle
Unless you have something up your sleeve, you will need to regulate more than 1000V. A typical Neon transformer puts out 15,000 Volts and can require almost twice that as a starting voltage. Also, if you are planning on running DC, then you need to take extra precautions against the potential of thermal runaway destroying your tube. This is also seen with florescent tubes as well running on DC, but not as severe, since the starting voltage is around 400V. Thermal runaway can occur when the gas in the tube is in steady plasma. Electrically this plasma state looks like a short circuit, so the contacts can overheat and burn up, not to mention the tube itself under severe circumstances. An AC or pulsed DC stream provides a mechanical means to "break" the short circuit and prevent a thermal runaway condition.
What you should see by altering the frequency are standing waves producing illuminated "bands" within the tube, dependant on tube length, and the chemistry of the gas within the tube.
When I was in high school, I had the opportunity to help with the construction of a few exhibits at the science museum. One of which was very similar to what you are trying to do, although I don't know that the frequency went that high. Instead of powering a Neon transformer directly off of the mains we had a variable speed Dynamotor driving the Neon transformer. A Dynamotor is basically a motor/generator in one device. The motor was powered by the mains and could be easily varied in speed. Because of this, the output frequency could also be varied... I think 10 kHz was the max.
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
"What you should see by altering the frequency are standing waves producing illuminated "bands" within the tube, dependant on tube length, and the chemistry of the gas within the tube."
Beau, this experiments is in that range of study. As you stated it has to do with standing waves. The tube is only 12 inches long. I just have to take the frequencies up to 30Mhz to meet my Max target range. I can get the bulb to light I just need to see if there is a driver capable of that freq range. Thanks again guys for your help
At first I looked for 1000V Mosfets, and found this one... http://www.datasheetcatalog.com/datasheets_pdf/I/R/F/P/IRFPG30.shtml·...The rise and fall times look ok, but the turn Off delay would limit you to 11MHz
Then I searched for 500V Mosfets.... Several of these had worse delays for rise time and fall time ... I found one that looks like it might work...
http://www.alldatasheet.co.kr/datasheet-pdf/pdf_kor/68303/IRF/IRF820.html
...The rise/fall and on/off times look good on these...
Note:·· You can place mosfets in parallel to decrease RdsON, and to increase the current capability.
RdsON = 3 Ohms Id = 2.5Amps Gate Threshold Voltage = 2 to 4 Volts Rise Time = 8.6nS Fall Time = 16nS Turn On Delay = 8.0nS Turn Off Delay = 33nS...The bottle neck is the Turn Off Delay of 33nS = which places you right at 30.3MHz
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Beau Schwabe
IC Layout Engineer
Parallax, Inc.
-Phil
You can request samples from the link below:
http://www.microsemi.com/catalog/part.asp?PARTNO=DRF1200
Regards,
Bruce Bates
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Veni, Vidi, Velcro! - I came, I saw, I stuck around!
Haven't looked at the datasheet....but would be usefull if it could do the job of the switching.
James L
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James L
Partner/Designer
Lil Brother LLC (SMT Assembly Services)
Radars that use the same antenna for transmit and receive (monostatic) have something called a TR Cell or LImiter (TR being Transmit/Receive).
Because you are using the same path to transmit and receive, there's always the risk of transmitting directly in to your receiver...200kW in to something that's looking for mW won't survive!
So there's something called a Transmit/Receive Cell or Limiter (TR Cell)....this is an enclosed piece of waveguide that has a radioactive (below regulatory levels) gas inside that will ionize upon large power levels. (Ever see those gas charged lightning arrestors...same idea)
So, when transmitting this little guy ionizes and essentially blocks (not perfectly, but good enough) the transmit pulse from going down the receiver path.
The caveat to this device, is that it's not instant on/instant off! There's a rise/fall time to it's operation.
If you look at your local NexRad image, you might see a little donut in the center of the screen (essentially where the radar is)....this is, in part, caused by the TRcell being active and blocking any energy before the receiver.
If you see the donut getting bigger, it's a sign that the cell is starting to have problems....if the cell fails, well, there won't be any data on the image as you've already blown your receiver!
Anyhow, to the point....the roll off time for these things are differently from device to device (assuming different gases inside).
I'd suspect a similar thing using a neon tube!
What's your duty cycle and pulse width? I suspect a longer tube would have a longer 'turn off time'....
Are you trying to put a 30Mhz carrier on top of a 60Hz drive signal?
Cheers
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<FONT>Steve
What's the best thing to do in a lightning storm? "take a one iron out the bag and hold it straight up above your head, even God cant hit a one iron!"
Lee Travino after the second time being hit by lightning!
I am running a 50% duty cycle and no carrier wave it just a straight DC·pulse or freqout signal through the tube. I had my 10 inch bulb working upto 5Mhz but I need to go upto 30Mhz.· I have to test the output when I get it working and see what effects it will have on the lenght of the wires and the bulbs.
Thanks again
How big does your tube need to be? IF the length changes things, you might have to shorten your tube a bit....will be neat to see!
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<FONT>Steve
What's the best thing to do in a lightning storm? "take a one iron out the bag and hold it straight up above your head, even God cant hit a one iron!"
Lee Travino after the second time being hit by lightning!