GB1174488A - Improvements relating to Voltage Regulators. - Google Patents

Abstract

1,174,488. Automatic voltage control. ROBERT BOSCH G.m.b.H. Feb.14, 1967 [Feb.15, 1966], No.6952/67. Heading G3R. A voltage regulator for a D.C. generator 10, which may be an alternator with a rectified output, comprises a power transistor 16 which is connected in series with the generator field winding 17 and a resistor 18 across the generator output leads 14, 15; a transistor 28 associated with an output voltage sensing circuit including a potentiometer 35 and a Zener diode 34; a further transistor 25 having its base connected over a circuit including a resistor 22, an N.T.C. resistor 23 and a variable resistor 24 to the junction between resistor 18 and transistor 16, and having its collector/ emitter path connected in series with resistors 36, 37 across the leads 14, 15; and a thyristor 38 which is connected together with a resistor 41 across the leads 14, 15 and which has its control electrode connected to the junction between resistors 36, 37, the junction between the thyristor 38 and resistor 41 being connected over a resistor 39 to the base of transistor 28. In normal operation, transistor 25 is non-conductive and the current in field winding 17 is controlled in known manner by the functioning of transistors 26 and 28 so that the output voltage of the generator is maintained constant at a predetermined value. If, however, the current through transistor 16 should rise to an excessive value the increased voltage drop across resistor 18 will render transistor 25 conductive to fire thyristor 38, whereby a negative potential will be applied to the base of transistor 28 which will conduct to block transistor 16. The power transistor 16 is thus protected against overload conditions which could arise on the occurrence of a fault condition, e.g. a short-circuit, in the field winding 17. The voltage across transistor 25 may be stabilized by a Zener diode Fig.2 (not shown).