Power current circuitry e.g. for DC motor - uses controllable resistor in branch circuit to detect load current regulated in output stage

摘要

The circuitry comprises a load current circuit consisting of the electrical appts. (V) supplied and an output stage regulating the load current (IL). A shunt resistor (RS) is placed in the load current circuit to detect the load current in association with a controllable resistor (T1) with a control terminal (5) and a resistor (R1) coupling one terminal (1) of the shunt resistor to one terminal (3) of the controllable resistor. A first circuit branch (6) couples one input of an operational amplifier (OP) to the other terminal (2) of the shunt resistor. A second circuit branch (7) couples the other input of the amplifier to the first terminal (3) of the controllable resistor. The output of the amplifier is coupled to the control terminal of the latter. A further resistor (R2) delivers a voltage (VA) proportional to the load current. This resistor is connected to earth and the second terminal (4) of the controllable resistor. The ratio of the values of the shunt (RS) and first (R1) resistors is lower than one. The value of the second resistor (R2) is large compared with the ratio RS/R1. ADVANTAGE - Detects load current without inflicting inacceptable loss, i.e. produces proportional voltage sufficiently high for control purposes yet uses a shunt resistance of low value.