| 摘要 |
<p>An electrical circuit is connected in series with a lead (13) of an implantable heart pacemaker (10) between the pacemaker and the heart (11) to protect the pacemaker against high voltages and currents produced by defibrillators (17) and other sources. The electrical circuit has a sensing resistor (24) arranged between two normally conducting field effect transistors (FETs) (22, 23) all in electrical series with the pacemaker lead (13). When the voltage drop across the sensing resistor (24) exceeds a predetermined positive or negative amplitude, a transistor becomes conductive and turns off the normal conduction channels of the FETs. An alternate, electrically conductive high-impedance path is switched in to limit the current flow to the pacemaker until the magnitude of the voltage across the sensing resistor drops to a safe level. The transistor then becomes non-conductive and the FETs become conductive re-establishing the normal low-impedance conduction path and effectively switching the alternate high-impendance path out of the circuit. </p> |
