Reverse current throttling of a MOS transistor

A circuit coupled to an output transistor of a first conductivity type including a gate, a drain coupled to a power supply terminal having a rail voltage thereon, and a source coupled to an output terminal having an output voltage thereon, the circuit to ensure current flow in one direction and to throttle current flow in a reverse direction, comprising:

• a first circuit coupled to the gate of the output transistor to progressively turn off the output transistor as the output voltage reaches a first threshold voltage and approaches the rail voltage;
• and
• a second circuit coupled to the gate and source of the output transistor to turn off the output transistor as the output voltage reaches a second threshold voltage, the second threshold voltage being less than the rail voltage.

A method of ensuring current flow in one direction and throttling current flow in a reverse direction in an output transistor having a gate, a drain coupled to a power supply terminal having a rail voltage thereon, and a source coupled to an output terminal having an output voltage thereon, comprising:

• turning off the output transistor progressively as the output voltage reaches the first threshold voltage and approaches the rail voltage such that an electrical resistance of the output transistor increases in inverse proportion to the difference between the output voltage and the rail voltage as the output voltage approaches the rail voltage;
• and
• turning off the output transistor as the output voltage reaches a second threshold voltage, wherein the rail voltage is at a voltage between the first threshold voltage and the second threshold voltage.