Methods and apparatus for auxiliary trickle power supply

Abstract

Circuit arrangements and methods are disclosed for providing trickle voltages and currents when a main power supply is unavailable or, alternatively, for providing auxiliary power. In one embodiment, a trickle power supply consists of a bilaterally conducting semiconductor diode device such as a SIDAC receiving an unregulated DC input voltage through a resistor. The SIDAC is contemplated to have a specified breakover voltage V.sub.bo and current carrying capability chosen according to designer preference. A first capacitor is coupled between the SIDAC and a primary side of a step-down pulse transformer providing a specified reduction in voltage from a secondary side relative to the voltage applied to the primary side. The resistor, the first capacitor, and the SIDAC together form a modified RC resonant circuit oscillation characteristic. When the unregulated DC input voltage is applied, the first capacitor will charge up to the breakover voltage V.sub.bo of the SIDAC, whereafter the SIDAC becomes strongly conducting and charge is rapidly discharged to ground from the first capacitor through the SIDAC. When the stored charge has been depleted, the SIDAC becomes nonconducting, and charge is thereafter again accumulated in the first capacitor. The alternate charging and discharging of the first capacitor according to the V.sub.bo of the SIDAC produces an oscillating pulse waveform. The pulse waveform is subsequently reduced in magnitude by the pulse transformer, and thereafter routed through voltage regulating means to adjust the reduced voltage and current of the oscillating pulse waveform to an output trickle voltage and current of specified magnitude.