Overvoltage Protection Circuit
Original Publication Date: 1988-May-01
Included in the Prior Art Database: 2005-Feb-15
By detecting an overvoltage condition and self-biasing transistor terminals to voltage levels in the 3-volt range, voltage stress and reliability degradation of 3-volt circuits is avoided. This circuit maintains reliability protection whether the voltage supply Vcc is operational or not. Referring to the figure, with high voltage supply Vcc on and equal to 3 volts, node A is a threshold voltage Vt drop below the input voltage at IN but always equal to or greater than 0.0 volts. Input voltage at IN may vary from 0 to 6 volts. Node B is clamped to the 3- volt Vcc by p-type transistor T6. Node C is clamped to ground by n-type transistor T8. Transistor T7 is off.