Protected electric power supply for discharge appts. - uses series resistor normally by=passed by transistor switch opened if overcurrent occurs, increasing circuit resistance

摘要

The supply consists of three sub-units: a power supply (A) delivering a direct or a chopped current, a first (less than 1 millisecond transistor switch (E), and a limiting resistor (R). In normal use the transistor switch (E) by-passes the limiting resistor (R). If an over current condition is detected the transistor switch (E) is opened in less than 1 millisecond, effectively inserting the resistor (R) in the lamp supply. The value of the resistor is calculated to be equal to the lamp resistance during abnormal discharge. The response time of the switch is less than 15 microseconds. The arrangement eliminates the occurrence of arcing and can be adapted to standard power supply systems. The protected supply is for luminescent discharge appts. e.g. for cathodic sputtering.