Characterization of the Serial NPN Power Transistor in a Negative Voltage Regulator Operating in Various X-Ray Environments

Negative low-dropout voltage regulator was examined in two various bremsstrahlung X-ray fields. The principal values used to estimate the radiation response of the circuit were variations of the serial power transistor dropout voltage and its base current. In a similar manner as in the previous research, done on low-dropout voltage regulators with lateral PNP power transistors, an effort was made to utilize a method for indirect experimental characterization of the serial transistor’s base current. However, due to the distinction of circuit topology implemented in the negative voltage regulator examined, there were limitations for indirect calculation of the base current of the serial transistor. The main reason for this is the implementation of a coupling diode, connected between the output terminal of the voltage regulator and the collector contact of the driver transistor. The use of a detailed SPICE simulation model made it possible to determine the bias conditions required for the successful implementation of the specified method.