Importance

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Abstract

A dc power supply circuit for supplying simultaneously dc voltages to a dc load and to a standby battery employed to power the load upon a loss of dc power to the load. The load is adapted to draw varying amounts of current. The dc power supply circuit in accordance with the invention includes a capacitor which is arranged to retain a dc voltage derived from an ac voltage. A fixed voltage regulator circuit coupled to the capacitor operates to supply a fixed dc voltage to the load and to maintain this voltage as the current drawn by the load varies. An adjustable voltage regulator circuit coupled to the capacitor operates to supply a varying dc voltage to the battery as the current drawn by the load varies. The varying voltage of the adjustable voltage regulator circuit is achieved by a current sensing resistor which senses the current drawn jointly by the load and the battery and which causes control circuitry coupled to the adjustable voltage regulator circuit to vary the dc voltage thereof in accordance with variations in the current sensed by the current sensing resistor. In accordance with the invention, the current drawn jointly by the load and battery is limited to a predetermined maximum amount, for example, one ampere, with the load being supplied first and at all times with its needed current and the difference between the current drawn by the load at any given instant and one ampere being made available to the battery.

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First Claim