Circuit for sustaining output power during input power interruption

A circuit for sustaining output power during input power interruption, comprising:

• an input terminal for receiving an input voltage;
• first current flow control means connected to the input terminal for providing a voltage at a level lower than the input voltage, said first current flow control means including a blocking diode, with the voltage provided by the blocking diode being at a level lower than the input voltage by the forward voltage drop across the blocking diode;
• first means for sensing the input voltage and including a voltage divider connected to the input terminal and second current flow control means connected to the voltage divider and maintained in an "on" state;
• third current flow control means connected to the first current flow control means and to the second current flow control means so as to be rendered in an "off" state;
• second means connected to the third current flow control means and including energy storage means, said energy storage means being a capacitor, with the energy stored in the capacitor being equal to one-half of the capacitance of the capacitor times the square of the voltage across said capacitor, and the size of said capacitor being directly proportional to said capacitance times a DC voltage rating product, whereby the energy stored in the capacitor is maximized and the size of said capacitor is minimized, and the voltage across the capacitor is maximized;
• third means connected to the first current flow control means and including fourth current flow control means connected to the second means, whereby the energy storage means in the second means stores a peak voltage for application to the third means during an interruption of the input voltage, said third means providing a primary regulated output voltage;
• a return terminal;
• the voltage divider in the first means including a first resistor connected to the input terminal and a second resistor connected to the first resistor and to the return terminal;
• the second current flow control means connected between the first and second resistors;
• a fifth current flow control means connected to the second current flow control means and to the return terminal, said fifth current flow control means being a zener diode and the voltage provided by the first current flow control means being larger than the avalanche voltage across said zener diode;
• the second current flow control means being an NPN bipolar transistor having base, collector and emitter elements;
• the base element is connected between the first and second resistors, the collector element is connected to the third current flow control means and the emitter element is connected to the zener diode;
• the collector element being at a voltage which is the difference between the avalanche voltage across the zener diode and the collector element to emitter element voltage across the NPN bipolar transistor, whereby the NPN bipolar transistor is maintained in the "on" state;
• the third current flow control means is an N channel enhancement MOSFET having source, gate and drain elements;
• the source element is connected to the blocking diode, the gate element is connected to the collector element of the NPN bipolar transistor and the second means is connected to the drain element;
• the gate element is at the NPN transistor collector voltage, the source element is at the voltage provided by the blocking diode, and the gate to source voltage is equal to the NPN transistor collector voltage minus the blocking diode voltage;
• said gate to source voltage being in a negative sense, since the blocking diode voltage is larger than the NPN transistor collector voltage, whereby said N channel enhancement MOSFET is in the "off" state;
• and
• means connected to the blocking diode, to the energy storage capacitor and to the N channel enhancement MOSFET for minimizing power dissipation when said N channel enhancement MOSFET is conducting.