BREAKDOWN PROTECTION CIRCUIT USING HIGH VOLTAGE DETECTION

摘要

A high voltage circuit includes a first switching device for supplying one of a high voltage (Vpp) and a low voltage (Vcc) to a controlled path that includes a series connection of a control p-channel transistor and a protection p-channel transistor. A high voltage detector is utilized to determine whether Vpp or Vcc is applied to the controlled path. The high voltage detector also establishes a protecting condition for the protection p-channel transistor during Vpp operation. On the other hand, the detector establishes a non-protecting condition during Vcc operation, thereby rendering the protecting p-channel transistor transparent to circuit performance. A signal input switches the control p-channel transistor between on and off states. When the control transistor is in an off state and the protection transistor is in a protecting condition, the voltage drop along the controlled path will cause the protection transistor to turn off, so as to limit the voltage across the control transistor. A second controlled path is preferably in series connection with the first controlled path. The second controlled path includes n-channel transistors, with one of the transistors fixed at Vcc in order to guard against gate-aided junction breakdown of the other transistor. In this embodiment, the high voltage circuit is preferably an inverter circuit.