Power switch circuitry for electrically isolating the power switch from a power supply

A power switching circuit for turning on and off a power supply, the power supply including a power transformer having a primary and a secondary inductor, wherein the primary inductor is coupled to an unregulated DC input voltage and a pulse width modulation circuit for transferring power to an output circuit coupled to the secondary inductor of the power transformer, wherein the output circuit provides a feedback signal to a feedback compensation circuit, which develops a vital signal for controlling the pulse width modulation circuit, and wherein the power supply is turned off upon grounding the vital signal, but otherwise operates normally, said power switching circuit comprising:

• a voltage regulator coupled to the unregulated DC input voltage for developing a low power DC signal;
• an oscillator coupled to said voltage regulator for generating an oscillating signal;
• means coupled to said oscillator for converting said oscillating signal to a DC voltage while said oscillator is providing said oscillating signal;
• means coupled to said converting means for discharging said DC voltage while said oscillator is disabled;
• a small signal transformer having a primary inductor and a secondary inductor, wherein said secondary inductor of said small signal transformer is coupled to the output of said oscillator;
• a rectifier circuit coupled to said primary inductor of said small signal transformer for developing a DC power signal from an AC voltage developed across said primary inductor due to the oscillating signal applied to said secondary inductor of said small signal transformer;
• a first switch coupled to said primary of said small signal transformer and receiving a pulse signal, wherein said first switch shorts said primary inductor of said small signal transformer while said pulse signal is asserted;
• a multivibrator circuit coupled to said rectifier circuit receiving power from said DC power signal, wherein said multivibrator provides said pulse signal having a predetermined duration upon receiving a trigger signal;
• a power switch coupled to said multivibrator providing said trigger signal when pressed;
• a comparator coupled to said converting means providing a clock signal when said DC voltage is momentarily discharged and then recharged;
• a flip-flop circuit coupled to said comparator, wherein said flip-flop circuit changes state upon receiving said clock signal;
• and
• a second switch coupled to said flip-flop circuit and for coupling to the vital signal, wherein said switch grounds the vital signal when said flip-flop is in a first state and wherein said switch releases the vital signal when said flip-flop is in a second state.