Power Dissipation in MOS Power Transistors for Automotive Applications: System Voltage Considerations

The specific on-resistance (product of chip resistance and chip area) of power MOSFET's increases as a power of the transistor breakdown voltage. The exponent is 1.8 for today's transistors and will be about 2.0 for next generation power MOS power transistors. This dependence results in a relatively small reduction in transistor power dissipation with increasing battery voltage for today's MOS power transistors and no change for the next generation devices. Reducing the safety margin (ratio of breakdown voltage to battery voltage) will significantly reduce power dissipation for all battery voltages but requires regulation of the power bus voltage to protect the transistor from overvoltage.