Circuits and methods for secondary-side rectified voltage sensing in isolated switched-mode power converters

A voltage sensor for tracking a secondary-side voltage of an isolated switched-mode power converter, the voltage sensor comprising:

• a first sense terminal for connection to an input node having a first sense voltage corresponding to the secondary-side voltage;
• a first level shifter for shifting the first sense voltage, thereby providing a first level-shifted voltage;
• a first input buffer configured to input the first level-shifted voltage, and to provide a first buffered output having a voltage corresponding to the first level-shifted voltage and having a first buffered current which is higher than a current at the input of the first input buffer;
• and a tracking analog-to-digital converter (ADC) having an ADC input coupled to the first buffered output and configured to output a present digital value corresponding to the secondary-side voltage at a present sample instant, wherein a previous digital value output at a previous sample instant serves as an initial estimate for determining the present digital value.

A method for sensing a secondary-side voltage within an isolated switched-mode power converter, the method comprising:

• sensing a first sense voltage at a first sense terminal, the first sense voltage corresponding to the secondary-side voltage;
• shifting the first sense voltage, thereby providing a first level-shifted voltage;
• buffering the first level-shifted voltage, so as to provide a first buffered output having a voltage corresponding to the first level-shifted voltage and having a first buffered current, which is higher than a current at the input of the first input buffer;
• and digitizing the first buffered output using a tracking analog-to-digital converter (ADC), so as to provide a present digital value corresponding to the secondary-side voltage at a present sample instant, wherein a previous digital value output at a previous sample instant serves as an initial estimate for determining the present digital value.