Patent ID: 6239509
Filing Date: 2001-05-29
Classification: H02M

Abstract:
A step-down switched-mode power supply circuit having a transformer including at least one primary winding and at least one secondary winding, a current sensing device for sensing a current through the primary winding of the transformer, a first switch, a second switch, a voltage regulator coupled to the secondary winding of the transformer to produce a regulated voltage on an output line, and control circuitry for generating a pair of complimentary signals controlling the first switch and the second switch, the circuit comprising:a first comparator for determining if the current through the current sensing device exceeds a threshold;a second comparator coupled to the output line of the voltage regulator for determining if the regulated voltage has drooped below an acceptable level; anda counter coupled to the second comparator for asserting a power save disable signal for a fixed number of switch cycles when the second comparator determines that the regulated voltage has drooped below the acceptable level,wherein the control circuitry is responsive to the first comparator to enter a power saving mode disabling the complimentary signals and is responsive to the power save disable signal to temporarily exit the power saving mode while the power save disable signal is asserted.