Zero cross detection circuit for phase measurement

Abstract

Induction heating systems and methods for induction cooking appliances are provided with inverters and resonant converters. Phase angle through the resonant tank is determined by measuring delay between respective zero crossings of applied voltage and induced current. A current measurement transducer outputs a negative voltage with respect to ground and a comparator capable of accepting an input voltage a few tenths of a volt below ground. An optimized current signal is used for phase only, resulting in reduced variation in phase measurement for different current magnitudes. One of a passive or active differentiator circuit connected to the resonant capacitors of the inverter connects to a clipping and scaling circuit. The clipping allows for an arbitrary gain for the current signal, while protecting the inputs of the comparator. The divider further reduces the voltage. The tank voltage signal initiates phase measurement by reducing the maximum signal presented to the comparator input.

Dependencies are inferred from the claim text.