Patent ID: 8872485

Claim:
A circuit for increasing DC power supply hold-up time comprising: an inductor having a first node and a second node, said first node of said inductor coupled to a positive terminal of a DC power source and a negative terminal of said DC power source coupled to ground; a first capacitor having a first node coupled to said first node of said inductor and having a second node coupled to ground; a second capacitor having a first node coupled to said second node of said inductor and having a second node coupled to ground; and a controller operative to direct current to said inductor such that said inductor can serve as a Boost inductor for said second capacitor and a Buck inductor for said first capacitor; wherein said controller has a first input coupled to said first node of said first capacitor to sense a first voltage and a second node coupled to said first node of said second capacitor to sense a second voltage and comprises logic responsive to said first voltage and said second voltage and is operative to develop a first control signal having a first on duty cycle and a second control signal having a second on duty cycle and having a ratio computed as the first on duty cycle divided by the second on duty cycle, said controller being operative in a first mode for adjusting said ratio to maintain said second voltage at a first predetermined voltage, and if said first voltage drops below a predetermined threshold, said controller being operative in a second mode for adjusting said ratio to maintain said first voltage at a second predetermined voltage.