| 摘要 |
An excess voltage input protection circuit comprises first 18 and second 20 metal oxide semiconductor field effect transistors (MOSFET) having common sources 18b,20b. The drain 18a of first MOSFET 18 is connected to an input voltage 12 and a voltage sensor 26 turns off the second MOSFET 20 upon sensing that the input voltage exceeds a threshold. Each MOSFET 18,20 may comprise an intrinsic body diode 21,23 that allows conduction in one direction only so that if the input voltage is reversed the first MOSFET diode 21 prevents the first voltage being transmitted to a load connected to output 14. MOSFETS 18,20 may be P-type for positive voltages at input 12 or N-type for transmission of negative voltages. Voltage sensor 26 may comprise a transistor (fig 2, 30), a resistor (fig 2, 32) and a zener diode (FIG 2,28) and may short circuit the source and gate 20c of the second MOSFET 20. The protection device may be used to protect the supply to a load which may be a ratiometric transducer such as a potentiometer. |
