On-state voltage measurement of high-side and low-side power transistors in a half-bridge for in-situ prognostics

An on-state voltage measurement circuit, comprising:

• a first clamping circuit comprising:
• a first high-side voltage clamping circuit coupled across a first high-side switching device of a first half-bridge leg of a converter, the first high-side voltage clamping circuit comprising a first high-side first diode coupled in series with a first high-side second diode, an anode of the first high-side first diode connected to a first source of the first high-side switching device, a cathode of the first high-side first diode coupled to an anode of the first high-side second diode at a first clamped point between the first high-side first diode and the first high-side second diode, wherein the first clamped point is coupled to a positive DC bus via a first Zener diode;
• and
• a first low-side voltage clamping circuit coupled across a first low-side switching device of the first half-bridge leg of the converter, the first low-side voltage clamping circuit comprising a first low-side first diode coupled in series with a first low-side second diode, a cathode of the first low-side first diode connected to a first drain of the first low-side switching device, an anode of the first low-side first diode coupled to a cathode of the first low-side second diode at a second clamped point between the first low-side first diode and the first low-side second diode, wherein the second clamped point is coupled to a negative DC bus via a second Zener diode;
• a first on-state voltage circuit coupled to the first clamping circuit comprising:
• a first high-side voltage measurement circuit configured to provide a first non-isolated high-side on-state voltage based upon the first clamped point voltage and a first forward voltage measured across the first high-side second diode of the first high-side voltage clamping circuit, referenced to the positive DC bus of the converter;
• and
• a first low-side voltage measurement circuit configured to provide a first non-isolated low-side on-state voltage based upon the second clamped point voltage and a second forward voltage measured across the first low-side second diode of the low-side voltage clamping circuit, referenced to the negative DC bus of the converter;
• and
• an output circuit coupled to the on-state voltage circuit comprising:
• a first high-side isolation circuit configured to provide a first isolated high-side on-state voltage with reference to a control ground of the converter from the first non-isolated high-side on-state voltage;
• and
• a first low-side isolation circuit configured to provide a first isolated low-side on-state voltage with reference to the control ground from the first non-isolated low-side on-state voltage.