Unijunction transistor circuit for detecting weak magnetic field - comprises transistor without metallic case and, insulated from ambient light and operating as negative resistance oscillator

摘要

A unijunction transistor (1) of the double base diode type is formed without the metallic cover and has been mounted on a plexiglass support. This transistor acts as the magnetic field sensor when the field is applied transversely w.r.t. the semiconductor bar. A capacitor (2) is mounted in parallel between the emitter (E) and the first base (B1). A resistor (3) is connected to the end of the capacitor (A) connected to the emitter while its other end is connected to a polarising power supply (5) for the emitter and base circuit. A second polarising supply (6) is connected to the two base circuits to control the emitter current and frequency of oscillation characteristic. It also permits accentuation of the negative resistance characteristic to adjust its sensitivity.