Patent ID: 7541694
Filing Date: 2009-06-02
Classification: H03K

Abstract:
1. A circuit connectable between a pair of input lines and a pair of output lines, comprising: a primary battery connected across a pair of input lines; at least one hold-up battery connected in parallel with said primary battery and connected across said pair of input lines; an RC circuit comprising a first resistor connected in parallel with a first capacitor, said RC circuit connected in parallel with said primary battery and isolated from said hold-up battery by at least one unidirectional current valve which has a very low reverse leakage current; a comparator having a first input coupled to said RC circuit and a second input coupled to a voltage reference; a switching device controlled by an output of said comparator, said switching device connecting said hold-up battery to at least one of said output lines in a first state and disconnecting said hold-up battery from at least one of said output lines in a second state; wherein said at least one unidirectional current valve prevents a reverse leakage current from said hold-up battery from charging said first capacitor during a discharge period of said RC circuit.