 best way to obtain adjustable limited current from my setup?
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Ruskie
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Thu Jan 17 2013, 04:04AM
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Registered Member #9290
Joined: Sat Jan 05 2013, 03:42PM
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Posts: 60
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I am in the process of designing and making a small demonstration x-ray device that will be shielded on all sides. I'll be using a small dental tube, but I'm having trouble deciding on the best/ easiest way to extract filament voltage/ current from my set up for the tube. Although I could use a traditional 60 Hz HV transformer supply like the tube was powered with originally, I am opting for a high frequency DC flyback circuit that is powered by a 12 V ATX PC supply to produce approximately 27-30 KV output from a 3 stage multiplier attached to the hot side of the flyback circuit. The goal voltage and current for the tube is <30KV at 1 mA or less. The PC supply has several outputs available of course and I'm wondering if I could use say the 5V output for the filament of the tube. Of course this would have to have either a resistor or rheostat and I have two questions here: 1) Can this work by having the ATX power the flyback driver on the 12V rail and the tube filament on either the 5 or 3V rails with a rheostat/ resistor in series? and 2) I need a rough idea of the size and resistance of rheostat I would need to start with. I want something with maximum resistance and wattage capability so I can slowly turn up the voltage/ current while monitoring the tube. If memory serves, these tubes usually have a 3V filament at 2-3 amps draw maximum so for safety a 15 watt rheostat but at what resistance? I got in trouble one time because a rheostat I used didn't have enough resistance and burned out a tube filament. Thanks for any help.
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