Isolated power supply with input voltage monitor

An isolating power converter circuit, comprising:

• a rectifier circuit;
• an input node configured to be coupled to a voltage source;
• a transformer having first and second windings, wherein a first tap of the first winding is coupled to the input node using a first switch and to a reference node using a second switch, and wherein a first tap of the second winding is coupled to a voltage output node that provides an output signal that is substantially proportional to an input signal at the input node, and a different second tap of the second winding is coupled to a sense node and the rectifier circuit;
• and
• wherein the different second tap of the second winding is configured to provide, at the sense node and to a pulse generator circuit, an input voltage monitor signal that is the same polarity as the input signal at the input node and is substantially proportional to the input signal at the input node and substantially independent of the output signal at the voltage output node, wherein the input voltage monitor signal is provided over a switching period that includes switching both the first and second switches.

A power converter system, comprising:

• an input voltage node;
• a control signal generator circuit;
• a first power stage converter, including:
• a first transformer including a first transformer primary side configured to receive a voltage signal from the input voltage node, and a first transformer secondary side having a first power stage output node configured to provide an output voltage signal;
• and.
• a first switch that is switchable to update the output voltage signal according to a modulation signal received from the control signal generator circuit;
• and
• a second power stage converter, configured to provide a voltage supply signal to the control signal generator circuit, the second power stage converter including:
• a second transformer including a second transformer primary side circuit with a second transformer primary winding and second and third switches, and a second transformer secondary side with a second transformer secondary winding, wherein the second transformer primary side circuit is configured to provide a voltage across the second transformer primary winding that is a function of a signal at the input voltage node and of a duty cycle of a switching period of the second switch relative to the third switch;
• and
• wherein the second transformer secondary winding includes first and second taps respectively coupled to an input voltage monitor node and a second power stage output node, wherein the second power stage output node is configured to provide the voltage supply signal to the control signal generator circuit, wherein the voltage supply signal is substantially proportional to the voltage signal at the input voltage node, and wherein the input voltage monitor node is configured to provide an input voltage monitor signal that is substantially proportional to the voltage signal at the input voltage node and wherein the input voltage monitor node provides the input voltage monitor signal over the switching period.