| 摘要 |
<p>It should not be possible to overdrive a transistor, the collector-emitter path of which is connected in series with a variable load resistance and an emitter resistor to a voltage source and the base of which is connected to a source of constant reference voltage, due to increased load resistances even outside the constant current range so that, seen from the load resistance, the high impedance of the circuit arrangement is retained. For this purpose, an overdrive protection device is provided which monitors the collector voltage and below a minimum collector voltage still providing for the nominal constant current forms a base series resistance increasing from zero. The invention can be advantageously used in balanced feed circuits for telephone subscriber lines. <IMAGE></p> |
