The DEI1028 is a control circuit for a 28VDC power bus voltage clamp. It is designed for use as the front end to a 28VDC input power supply to provide transient voltage protection. It controls the gate drive of a P-Channel power MOSFET to linearly clamp the output during over-voltage transients. The output voltage is maintained below the clamping threshold of 35V (max) which is adequate to protect most Commercial-Off-The-Shelf switching supplies, linear regulators, and op amps.