A Technical question, my second builds primary is a quarter the wire length of my first build, is this why my circuit is drawing a lot more current or is it because i am not using the correct component values to bias and drive the gate properly.
I notice my gate has a slightly larger sine on it than build one, i did try a pot and to get consistent oscillation it did require the resistor values i choose, maybe the pickup coil is still too much at 3/4 of a turn.
Hi Peterae Your circuit has a resonant tank as the main coil. This will not perform as a blocking oscillator. It will perform as a nice class C oscillator. If you want this circuit to perform as a blocking oscillator, you will need more gate drive, not less. Also you would need to operate it without the tank capacitors. From the earlier pics, it looked like you barely had enough drive to force the gate high and low enough. looks like your FET is operating closer to Class A, hence the high power dissipation. If your output is a sine wave, you are not hitting the gate of the FET hard enough. The more you reduce the gate drive coil turns, the less drive you will have until it stops oscillating. Better to have a little extra drive, but adding resistance in series with the gate coil slows the circuit down. With the existing circuit arrangement, and at 1 MhZ there may be a limit to how fast you can charge and discharge the gate of the FET. The 47nF is sucking up all your drive current. I prefer a slightly different circuit arrangement with the drive coil not grounded. The coil instead is inserted between the gate and the bias network. This eliminates the 10nF cap. The placement of the 47nF is slowing the gates ability to swing. By re-arranging the circuit the gate will not "see" the 47nF except as part of a stiff bias supply. Keep the protection diodes close to the gate. If this is not clear, I'll try to supply a schematic. Sorry I didn't catch that 47nF problem before. Edit: OK posted the schematic. This is what I was getting at. Now the 47nF is in the proper place and not sucking base drive. Note: designators in my circuit are arbitrary and do not conform to yours.
« Last Edit: 2010-11-03, 22:51:59 by ION »
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Topic: 1 Mhz Resonant Coil Setup (Read 38996 times)
