Luminous gas discharge tube supply - measures discharge tube current to generate error signal which varies duty cycle of primary voltage of step up transformer

摘要

The supply is regulated to maintain the tube current constant by measuring the DC component of voltage developed over a capacitor (C2) bypassed resistor (R2) in the cathode circuit of the discharge tube and applying this voltage to the base of a transistor (T1) which has a reference voltage (VR) at its emitter, developed over a zener diode (D1). The amplified error voltage is further amplified by a second transistor (T1) to give an error signal Ve which is applied to one timing circuit of an astable multivibrator circuit (3) to give a variable duty cycle ON-OFF waveform. The ON-OFF waveform is fed to the base of a buffer transistor (T5) which drives a transistor (T6) to switch the primary of a transformer (T) having a high voltage secondary. The duty cycle of the ON-OFF waveform applied to the transformer primary determines the level of the high voltage output of the transformer which is rectified and filtered by a diode and capacitor chain (6), then applied to the anode of the gas discharge tube (1).