Temperature monitoring pilot transistor

Abstract

A load transistor is integrated into a region of a semiconductor layer. The load transistor has an on-resistance which passes the load current. One or more drain pilot transistors are also integrated into the same region of the semiconductor layer such that the load transistor substantially surrounds the pilot transistor(s). Consequently, as the load transistor heats-up due to the load current, the heat from the load transistor conducts to the pilot transistor(s) and heats the pilot transistor(s) to substantially the same temperature as the load transistor. If more than one drain pilot transistor are provided, then they are located adjacent to each other to ensure that all the pilot transistors exhibit substantially the same temperature as each other. The pilot transistor(s) are scaled models of the load transistor such that an on-resistance of each of the pilot transistors varies proportionally to the on-resistance of the load transistor with temperature. Current sources supply fixed currents to the on-resistances of the respective pilot transistors. Consequently, voltage(s) developed across the pilot transistor(s) are accurate references with which to set a drive voltage for the load current or an overcurrent or undercurrent detector, which reference voltages are temperature compensated.