Patent GB-1254718-A (GB)
Title: Voltage regulator circuit
Inventor: FREDERIKSEN THOMAS MARINUS
IPC: G05F1/575
Filed: 1968-12-05
Abstract: 1,254,718. Automatic voltage control; automatic current regulation. MOTOROLA, Inc. Dec.5, 1968 [Jan.29, 1968], No.57717/68. Headings G3R and G3X. A voltage regulator of the type wherein a series transistor 26 is connected between D.C. input and output terminals 27, 29 to maintain a constant output voltage, comprises a differential amplifier formed by transistors 20, 22 whose bases are respectively connected to a reference voltage and to the output terminal 29, the latter connection thereby providing a feedback to the amplifier of 100% of the output voltage. Transistors 24, 26 form a Darlington current gain output stage between the amplifier and the output terminal 29, the collector of the transistor 20 being connected to an intermediate point in this stage to ensure transistor current gain at low values of load current. A discussion is given of the advantages of the described arrangement over a known differential amplifier, Darlington stage voltage regulator, Fig. 1 (not shown). The reference voltage for transistor 20 is supplied by a circuit 51 having emitter-coupled transistors 32, 34 in a Darlington type connection with transistors 36, 38, to whose bases are respectively applied a reference voltage V REF IN  and a fraction of the reference voltage applied to the base of transistor 20. The circuit 51 acts as a further voltage regulator to control a transistor 54 connected to the input terminal 27, so that the voltage applied to the base of transistor 20 is maintained at a reference value V REF   OUT . The reference voltage V REF  IN is obtained from a bias circuit 49 having a constant current source 65 supplying a Zener diode 43a so that the ripple feedthrough from input 27 is reduced. The voltage drop across the resistor 61 establishes a reference voltage for constant current sources 65, 67, 25 having a common current sink formed by transistor 52. The arrangement of the source 65 is such that variations in the current gain of transistor 42 are automatically compensated, the transistor 42 having a high output impedance which reduces the effect of input voltage ripple on the Zener diode 43a and the differential amplifiers biased by the sources 67, 25. The circuit 49 also includes a temperature compensating network formed by members 46, 48, 50, 73, 75, 77, of which the emitter current of transistor 46 establishes the bias levels for the current sinks 52, 86, 92 and the collector current of transistor 46 sets the current levels in the sources 65, 67, 25. The transistor 46 is chosen so that the emitter and collector currents are equal and thus all the current sinks and sources are referenced by the same current, which has a zero temperature co-efficient due to the network 46----77 previously mentioned. Since the circuit 49 is independent of the input voltage, application thereof will not start the regulator by biasing the Zener diode 43a into conduction. Hence a circuit 47 is provided which responds to the application of the input voltage to activate the source 65 and cause Zener diode 43a to conduct, thereby providing the reference voltage V REF   IN . To "shut-down" the regulator, a positive voltage is applied to terminal 96 causing a clamping transistor 100 to conduct and all the current sources and sinks to "zero", the only bias drain remaining being the current through the resistor 83. Overcurrent protection is provided by a current sensing resistor R sc , which "thresholds" diodes 97, 98, 99 to by-pass the transistors 24, 26 and drive the transistor 45 into conduction, these two actions causing the output voltage and the reference voltage V REF   OUT  at point 35 to fall to zero. Components 47, 49, 51, 53 may be combined into a monolithic form and externally connected to capacitors 87, 89, which perform stabilizing and noise limiting functions.