Browse Prior Art Database

Radiation Modulated Conductivity Switch

IP.com Disclosure Number: IPCOM000075453D
Original Publication Date: 1971-Sep-01
Included in the Prior Art Database: 2005-Feb-24
Document File: 2 page(s) / 24K

Publishing Venue

IBM

Related People

Schrottke, G: AUTHOR

Abstract

Circuits which are used in transient gamma-radiation environment require use of very low-value resistances to negate, as much as possible, the effects of semiconductor photocurrents. Use of these resistors often causes high-bias currents and power dissipation. One way to eliminate this problem is to design circuits to work at high-impedance levels under normal conditions and low impedance during gamma bursts. The circuit discloses a technique for switching the resistances during a gamma burst.

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Radiation Modulated Conductivity Switch

Circuits which are used in transient gamma-radiation environment require use of very low-value resistances to negate, as much as possible, the effects of semiconductor photocurrents. Use of these resistors often causes high-bias currents and power dissipation. One way to eliminate this problem is to design circuits to work at high-impedance levels under normal conditions and low impedance during gamma bursts. The circuit discloses a technique for switching the resistances during a gamma burst.

During normal operation R1 is the required resistor, biased as shown. T1 and T2 are biased off, since the base of T1 is tied to -V (through R3 and R5), and T2 has its base and emitter tied together. The resistance in the circuit is therefore essentially R1.

During transient gamma radiation, photocurrent I(pp) flows as shown in the back-biased collector junctions of T1 and T2. However, R2, R3, R4 and R5 are adjusted so that T1 saturates. When this happens, I(pp1) no longer flows since the collector-base junction of T1 is now forward biased. I(pp2) is limited by R3 and R4. It is fed directly to the base of T1 (less any current through R5), keeping T1 saturated until the radiation transient disappears. At this time, the circuit returns to its original condition.

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