Electro-motor current supply - has circuit with resistance network to give rectified AC to apply dynamic limit to motor current

摘要

The circuitry to supply an electro-motor with rectified AC, such as in a sewing machine, to give a dynamic limit to the motor current, a measurement resistance (35) in the motor current circuit (33,16,2,14) is coupled to a switch (66) to take the drop-out voltage as a control voltage. The switching path is bridge-connected to the charging current of the condenser (49) and is linked to a point (69) in the resistance network (64,47,51,52), and is operative if the control voltage at the switch (66) exceeds the nominal motor current value. The resistance (44) is between the tap (40) of the ohmic branch (39,44) of the voltage distributor (39,44,46) and the zener diode (46). It has a lower ohm rating than any other part (64) of the resistance network, between the zener diode and the connection (69) of the switch (66), and on its part has a lower ohm rating than the remainder of the resistance network (47,51,52) in series. ADVANTAGE - The system gives a dynamic limit to the motor current, without narrowing the action of the motor limit, in a simple operation.