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my oscillator

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jamiee

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hi ev1

I want to build an oscillator, but I'm unsure what circuit and components to use because of the voltages involved. I'm also a relative novice to high voltages and high frequency electronics.

I have two capacitors charged to 200v and -200v.
I have a 555 outputting square at 300 kHz, (0v and 9v).

Additionally, I want to be able to alter the duty cycle of the square output by on-off keying at approximately 100Hz of variable pulse width (5% upto 100%). This will use another 555 or combine into a 556.

I want this to drive an output that oscillates +/-200v. Current drain from the high voltage lines will definitely be under 1A, more likely 100mA.

My first idea was to use a bipolar power rail on the 555 to get it to output at +/-4.5v. Then use that to drive two power transistors; one npn (MJE340); one pnp (MJE350) to switch the two high voltage lines on and off, to a common output.

I'm worried about voltages leaking back into the 555.

I'm also worried that during switch over, if both transistors conduct at the same time, they would bridge the capacitors and blow everything.

A single npn transistor switching between 0v-200v pulses, driving a 1:1 transformer might be better. Maybe that would work better. What winding should be used at these frequencies and power levels? What about harmful self induced voltage spikes from the transformer?

Your suggestions please, but I want to try and keep this project as simple as I can :)


jamiee
 
At 100mA your capacitor won't last for very long.

You're right, you need an isolation transformer between the 555 and the driver transistors.

You're better off using MOSFETs rather than BJTs at that frequency.
 
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