Abstract: A capacitor charging circuit is provided with a primary side output voltage sensing circuit for generating a control signal indicative of whether the output voltage has reached a desired level. The control signal is unaffected by voltage spikes occurring when the main switch is turned off. In one embodiment, the circuit filters the primary side voltage for comparison to a reference voltage in order to provide the control signal. In another embodiment, an AND gate provides the control signal indicating that the output voltage has reached the desired level only in response to the primary side voltage being greater than a reference voltage and the secondary current being discontinuous. In a further embodiment, an AND gate provides the control signal indicating that the output voltage has reached the desired levels only in response to a predetermined delay occurring after the primary side voltage becomes greater than a reference voltage and the secondary current being discontinuous.

Abstract: Apparatus for detecting failure of an isolation device includes a current sensor to sense current through the isolation device and a circuit responsive to the current sensor output signal and to an enable signal that controls the isolation device for providing an Early Failure Warning (EFW) signal indicative of whether the isolation device has failed. The enable signal is at a first logic level when the isolation device is on and is brought to a second logic level to disable and test the isolation device. Also described is a method of detecting a failure of an isolation device including disabling the isolation device, sensing a current through the isolation device, and providing an EFW signal indicating that the isolation device has failed if the current through the isolation device is greater than a predetermined level when the isolation device is disabled.

Abstract: A bias supply circuit and a method of operating a bias supply circuit for use with a switching power supply employing a main switch and an auxiliary switch and having an input voltage and a voltage across a clamp capacitor coupled to a transformer. In one embodiment, the bias supply circuit includes a bias supply winding associated with the transformer and configured to provide a first voltage dependent on at least one of the input voltage and the voltage across the clamp capacitor during a conduction period of the main switch or the auxiliary switch. Additionally, the bias supply circuit further includes a bias supply storage capacitor coupled to the bias supply winding and configured to provide a second voltage dependent on at least another of the input voltage and the voltage across the clamp capacitor during a conduction period of another of the main switch or the auxiliary switch. A sum of the first voltage and the second voltage provides a bias supply voltage.