Current regulator with differential amplifier esp for telephones - has differential amplifier controlling variable conductor which connects to base of bipolar transistor having diode across collector base.

摘要

The telephone line (1) has connections (2) to a d.c. conversion circuit (3). The differential amplifier (5) regulates the variable conductor (4), which is pref. a DMOS transistor, according to a reference current, which generates a d.c. voltage (7), and a measured current, which generates a voltage across a resistor (6). The variable conductor connects to the transistor base (10) via a low value resistor of about 100 ohms. An energy dissipating resistor (9) is connected to the collector is parallel with the variable conductor and a high value resistor (13) of several tens of kilohm is connected between the base and emitter. The total line resistance (6,9,3) is chosen to equal the maximum voltage to current ratio. ADVANTAGE - Easily integrated into i.c. at minimum cost, avoids transistor breakdown at high supply voltages.