A power converter circuit includes a transformer. The transformer includes a primary winding and a secondary winding. A primary circuit is coupled to the primary winding. A secondary circuit is coupled to the secondary winding. The primary circuit and the secondary circuit are referenced to different ground voltage potentials that may vary with respect to each other. During operation, the primary circuit controls input of energy to the primary winding of the transformer. The secondary circuit receives the energy through the secondary winding and uses it to produce an output voltage to power a load. The secondary circuit receives and/or generates state information at one of multiple different levels. The secondary circuit controls a flow of current through the secondary winding to convey the state information as feedback to the primary circuit. The primary circuit analyzes a voltage at a node of the primary winding to receive the feedback.