GB1201368A - Improvements relating to control devices for inductive loads - Google Patents

Abstract

1,201,368. Automatic current control. ROBERT BOSCH G.m.b.H. Oct.18, 1967 [Oct.20, 1966], No.47351/67. Heading G3R. [Also in Division H2] A series motor 10 is supplied from battery 12 through parallel-connected transistors 13, 14, 15, associated with equalizing resistors 16, 17, 18, and free-wheeling diodes 21, 22, 23. The voltagedrops across the equalizing resistors are added by means of resistors 37, 38, 39, and the resultant voltage is fed to comparator 27 connected to pulse amplifier 24 which responds to the difference between a reference voltage derived from potentiometer 28 and the voltage representing the mean current of the motor to control the duty ratio of the transistors 13, 14, 15. The tapping 29 of the potentiometer 28 is connected to the comparator 27 through a delay network 33, 34, 35, and an integrating network 42, 43, 45, is connected between the junction of the resistors 37-39 and earth. The pulse amplifier has a feedback circuit comprising capacitor 25 and resistor 26. If the transistor 13, for example, is short-circuited, the associated resistor 37 is connected directly to the negative pole of the battery so that a high potential is developed at summing-point 36 for blocking the pulse amplifier and protecting the other transistors. When the reference potentiometer 28 is set to zero, the motor 10 is stationary, transistor 60 being conductive and transistor 64 being blocked. Feedback capacitor 25 is charged, and transistor 65 is conductive to block the transistors 66, 67, and 13, 14, 15. If the reference voltage is increased, the motor receives current and starts to rotate until the feedback derived from resistors 16, 17, 18, reduces the potential at junction 27 sufficiently to block the transistor 64. The transistors 66, 67, are reliably blocked by the charge on capacitor 99 so that the transistors 13, 14, 15, change abruptly from the conductive to the non-conductive state. Current flowing through the motor and the diodes 21, 22, 23, decreases exponentially until the transistor 60 is blocked again and the cycle is repeated. When the motor voltage across capacitor 84 exceeds the Zener voltage of diode 78, the pulse amplifier is blocked. A current-limiting arrangement comprises rectifier 105 and resistor 106 which restrict the gain of the pulse amplifier.