Minimum dropout voltage on a serial pnp transistor of a moderately loaded voltage regulator in a gamma radiation field

Abstract

The main examined value in an experiment performed on moderately loaded voltage regulators was the serial pnp transistor’s minimum dropout voltage, followed by the data on the base current and forward emitter current gain. Minimum dropout voltage decreased by up to 12%, while the measured values of the forward emitter current gain decreased by 20-40% after the absorption of a total ionizing dose of 500 Gy. The oxide trapped charge increased the radiation tolerance of the serial lateral pnp transistor owing to the suppression of interface trap formation above the base area. Current flow through the serial transistor of the voltage regulator had an influence on the decrease in the power pnp transistor’s forward emitter current gain. Due to the operation with a moderate load of 100 mA, loss of emitter injection efficiency was not as important as during the operation with high current density, thus eliminating the negative influence of emitter crowding on the radiation hardness of the voltage regulator. For a moderate load, gain in the negative feedback reaction was enough to keep output voltage in the anticipated range. Only information procured from tests of the minimum dropout voltage on the moderately loaded voltage regulators were not sufficient for unequivocal determination of the examined integrated circuit’s radiation hardness. [Projekat Ministarstva nauke Republike Srbije, br. 171007: Physical and functional effects of the interaction of radiation with electrical and biological systems

Comparative Study of Gamma Radiation Effects on Solar Cells, Photodiodes, and Phototransistors

“…Figures 1 to 3 show that gamma radiation caused the greatest damages in phototransistors and the smallest in solar panels. Vukić [17] shows that the measured values of the forward emitter current gain decreased by 20-40% after the absorption of a total dose of 500 Gy. The gain of the phototransistor is directly proportional to the minority carrier lifetime in the base region, and since this is strongly affected by radiation, these devices are comparatively radiation sensitive.…”

“…Enhanced hole injection into the emitter is manifested through the accumulation of the surface of the base, caused by the negative oxide charge trapped in the oxide over the emitter-base junction. Forward bias of the base junction would cause many holes to be injected into the emitter, thus increasing the base current [17]. The collector current changes significantly with the total dose.…”

An LTspice Simulation Model of Gamma-radiation Effects and Annealing in a Voltage Regulator With a Lateral Serial PNP Transistor With Round Emitters

“…The maximum output current was detected for an in-put voltage of 8 V DC, when output voltage declined to 4.7 V DC [12,13]. Minimum dropout voltage (for I OUT = 100 mA) was determined for a constant output current and the output voltage of 4.9 V [12,15]. For the second operation point, when I OUT was 400 mA, most of the performed measurement output voltages did not reach 4.9 V. Accordingly, results were recorded for the maximum available output voltage [16].…”

“…Therefore, according to the previous analysis, as well as the published data [12][13][14][15][16], it was assumed that the elements of the control circuit would have constant values, while the values of two power transistors (serial and driver PNP transistors) were changed for every control point. Comparison of the experimental and simulation data for the base current of the serial PNP power transistor, I B12 , are presented in figures 3 -6.…”

“…During the previous years, detailed research was conducted in order to define the topologies of cheap, commercial-off-the-shelf (COTS) low-dropout voltage regulators suitable for implementation in radiation environments instead of specially designed "rad-hard" components [12][13][14][15][16][17]. Among these candidates was a LM2940CT5 voltage regulator, an automotive circuit with lateral PNP power transistors with round emitters.…”