A half-bridge configuration of IGBTs is illustrated on this slide. The half bridge is the building block for inverters and three-phase motor controls. The IGBT driver circuits must have high isolation power supplies for two reasons. First, the high side IGBT emitter will see the full value of the high-voltage DC source. This will then also be impressed on the secondary common lead of the converter, which must be isolated effectively continuously from the primary. This is where the “rated” isolation value of 1500 V comes into play. Secondly, both the high-side and low-side IGBTs can see high voltages induced by the high switched currents and stray inductance of the negative DC bus. Thus it is important that the converter be designed to withstand continuous exposure to the high bus voltage, typically requiring that it be qualified at twice the operating HV, plus 1000 V. This is where the isolation test voltage of 5.2 kV is derived. In addition, given the fast voltage transients, low barrier capacitance is necessary to keep transient voltages on the secondary side from getting through to the otherwise unprotected primary side control circuits.