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Registered Member #7963
Joined: Thu Nov 08 2012, 09:06PM
Location: Maine
Posts: 4
Hello everyone! I am very glad to have found this forum, I am thoroughly enjoying reading and learning from all the previous posts......
I have the guts to a sputter coater system (Vacuum chamber, pump, TC tube, target, etc). The main HV section looks pretty much toasted, and I am just starting a “digital†conversion to allow programmatic control of the unit.
The existing HV section was pretty simple: 120V in through a variac, feeding what looks like a 1:10 step up transformer, bridge rectifier / filter / current limit resistor to give approx -1000v DC out to generate the plasma. There was an output current monitor, and you just tweaked the variac to obtain the desired sputter current once the plasma is struck (and the pressure stabilizes).
My requirements for the output section would be 0 - 1100ish volts (for striking at fairly low pressure), but I want to be able to constant-current the output to be variable from 1-50 mA. Additionally, this unit is going to be around some EMC sensitive equipment, so I’d like to go as low-noise as possible.
I've been looking at various topologies, and was reading with interest the Linear Technologies APP note 118, “High Voltage, Low Noise, DC/DC Convertersâ€, specifically the use of the Resonant Royer topology with soft switching of the transformer drive. I was thinking of using a current sense transformer to provide the feedback regulation. I would like to ask some opinions to the following questions, if I may:
Registered Member #7963
Joined: Thu Nov 08 2012, 09:06PM
Location: Maine
Posts: 4
My thought was that if I had a conduction path to ground other than through the sample being coated (say an arc, or some catastrophic failure in the transformer or HV cable), I would still be able to sense and regulate the current, whereas with a sense resistor between the substrate and ground, the transformer may be forced to maximum output......
Perhaps that is less of a concern than I imagine?
(PS I really appreciate the input and look forward to further discussion!)
Registered Member #7963
Joined: Thu Nov 08 2012, 09:06PM
Location: Maine
Posts: 4
Just to make sure I know what you mean by shunt, do you mean a small current sense resistor, say 10-20 ohms? 20 ohms would give me 1 volt at 50 mA...... Is there a drawback to having either an additional winding on the transformer or a separate, small current transformer with appropriate burden?
Would a current transformer be more robust (less chance of being damaged) in case of an Arc?
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Sputter Coater Resurrection......
