One popular approach to producing a variable EHT supply with an output range of a few kilo-volts is via control of the input voltage to the EHT transformer's primary using SCEs or triacs. During the development of such a supply for the thin-film coating unit, it was observed that the control of the EHT voltage could be done fairly accurately by controlling the angle of firing. However, it was difficult to regulate such a supply over load conditions.
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