โ Scribed by Tomasz Durakiewicz
No coin nor oath required. For personal study only.
A novel circuit has been invented for the versatile and safe stabilization of the electron emission current (le) produced by a hot filament in mass spectrometers or in ionization gauges. The voltage signal, which is directly proportional to le, is provided to the inverting input of a comparator, whereas the noninverting input is connected to the reference voltage. In addition to the commonly used negative feedback loop, a positive feedback loop was introduced by siting a resistor between the noninverting input and the output of the comparator, which results in a pulsation of the filament voltage. The pulses are rectangular, so that the power dissipated by the transistor in the filament power supply circuit is radically reduced. To refine the switching action of the transistor, the output of the comparator is connected through a capacitor to the transistor gate.
A concise discussion of the phase shift between le, the filament temperature Tf, and the filament voltage Vf, including time constants for different modes of power dissipation, is included.
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