35results about How to "Good overvoltage protection" patented technology

An open drain driver ( 7 ) selectively switches a MOSFET switch (MN 1 ) which is passively held in the conducting state into the non-conducting state. The MOSFET switch (MN 1 ) switches an AC analogue input signal on a main input terminal ( 3 ) to a main output terminal ( 4 ) and the gate of the MOSFET switch (MN 1 ) is AC coupled by a capacitor (C 1 ) to the drain thereof. The open drain driver ( 7 ) comprises a first MOSFET (MN 2 ) and a second MOSFET (MN 3 ) through which the gate of the MOSFET switch (MN 1 ) is pulled to ground (Vss). The gate of the first MOSFET (MN 2 ) is coupled to the supply voltage (VDD) for maintaining the first MOSFET (MN 2 ) in the open state. A control signal is applied to the gate of the second MOSFET (MN 3 ) for selectively operating the open drain driver ( 7 ) in the conducting state for operating the MOSFET switch (MN 1 ) in the non-conducting state. When the second MOSFET (MN 3 ) is in the non-conducting state, the first MOSFET (MN 2 ) remains in the conducting state until the voltage on a coupling node ( 9 ) between the first and second MOSFETs (MN 2 ,MN 3 ) equals the difference between its gate voltage and its threshold voltage, at which stage, any over-voltages applied to the gate of the MOSFET switch (MN 1 ) are divided between the first and second MOSFETs (MN 2 ,MN 3 ). A coupling diode (D 1 ) coupling the coupling node ( 9 ) to the supply voltage (VDD) clamps the voltage on the coupling node ( 9 ) at the supply voltage (VDD) plus the conducting voltage of the diode (D 1 ), in the event of the voltage on the coupling node ( 9 ) rising after the first MOSFET (MN 2 ) has gone into the non-conducting state. The coupling node ( 9 ) may be capacitively coupled to the supply voltage (VDD) by a coupling capacitor instead of or as well as the diode (D 1 ) for limiting the voltage on the coupling node ( 9 ).