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Registered Member #2099
Joined: Wed Apr 29 2009, 12:22AM
Location: Los Altos, California
Posts: 1716
James wrote ...
Klugesmith wrote ...
Patrick wrote ... It allows for feedback too, would that be useful for stabilizing HV, for your Xray stuff?
Could be. But the optoisolator LED current (5 mA?) could be a significant load at x-ray voltages, with significant power in the current-limiting resistor.
That's not a problem. The xray anode current will typically be somewhere in the range of 4-10mA for a dental unit.
Yes, but you can't regulate the high voltage by monitoring anode current. An opto whose LED carries the anode current could be used to regulate the filament supply. But if filament is near GND you don't need the isolation, and if filament is at x-ray high voltage you'll have trouble finding a single-package optoisolator that can stand the voltage.
James wrote ... ...ensure that the filament in the tube is always hot prior to activating the HV. It's easily possible to exceed 120kV with no load.
There's an opposite risk if filament power is regulated by feedback from anode current -- pegging the supply & burning out the filament if there's no HV!
Registered Member #3610
Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506
Sorry I was a little hasty in my reply and got some things switched around. My experience so far is mostly with the Kodak high frequency xray power supplies. These heads have the transformer, multiplier, and a voltage divider with a 200M resistor to monitor the anode voltage. 0-5V on the feedback lead covers a range of 0-72kV, and this is used to regulate the anode voltage. A similar arrangement could be built to work with any HV power supply, just buffer it with an op-amp. Filament voltage will affect the anode current, but in practice if you regulate the anode voltage and run the filament at a reasonable voltage (3.5-3.8V is typical for dental tubes) the anode current will be in the right ballpark.
Schematic is here for reference
C10 is actually a 1kV MOV, otherwise this is correct.
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This is a neat little IC
