US3263155A

US3263155A - Voltage regulator for generators

Info

Publication number: US3263155A
Application number: US269361A
Authority: US
Inventors: Dietl Franz
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1962-04-07
Filing date: 1963-04-01
Publication date: 1966-07-26
Anticipated expiration: 1983-07-26
Also published as: JPS3926491B1; DE1176752B; GB1035071A

Description

July 26, 1966 F. DlETL 3,263,155

VOLTAGE REGULATOR FOR GENERATORS Filed April 1. 1963 Mum //v VE/V TOR Franz D l Patented July 26, 1966 3,263,155 VOLTAGE REGULATOR FOR GENERATORS Franz Dietl, Stuttgart, Germany, assignor to Robert Bosch, G.m.b.H., Stuttgart, Germany.

Filed Apr. 1, 1963, Ser. No. 269,361 Claims priority, application Germany, Apr. 7, 1962, B 66,709 4 Claims. (Cl. 322-28) The present invention concerns a voltage regulator for a self-excited generator having a shunt exciter winding and being operable at greatly varying speeds as is particularly the case where a generator is operated on a vehicle and with a speed depending upon the traveling speed or on the engine speed of the vehicle.

Essentially the present invention is an improvement of known voltage arrangements of the type set forth. In voltage regulators of this type the ex-citer winding is connected at one of its two ends with the collector electrode of a main transistor forming part of the regulator and is supplied intermittent-1y or periodically with current via the emitter-collector circuit of the main transistor. In order to assure excitation when the generator is started from standstill, the base electrode of the main transistor is connected with the other end of the exciter winding via a baseresistor, and for controlling the main transistor depending upon the varying output voltage of the generator a control transi'stor'is provided the base electrode of which is so connected with an output of the generator that it carries a potential proportional to the output voltage. a .It has been foundthat known regulator arrangements of this type are'exposed to .the danger that a short-circuit develops within the exciter winding whereby the ohmic resistance thereof is reduced to such an extent that the main transistor is overloaded and destroyed. It has been observed that even short-circuits which last only through fractions of a second already cause a breakdown of th main transistor.

It is therefore one of the objects of this invention to electrode and serving to alternatively rendering the main transistor non-conductive when the output voltage of the generator is superior to a predetermined value, and for provided for an improvement of conventional voltage regulators of the type set forth in such a manner that the regulator circuits and particularly its main transistor are protected against overload.

It is another object of the present invention to provide for an improved voltage regulator as mentioned above, the protective circuit means thereof being so constructed that they become active immediatelyupon .the occurrence of a short-circuit as mentioned, however make it possible that after the disappearance of the short-circuit the full operativeness of the regulator and therefore of .the generator is re-established.

It is still another object of the invention to provide for an improved voltage regulator arrangement of the type set forth which is composed of a comparatively small number of entirely reliable and conventional circuit components.

With above objects in view the invention includes a voltage regulator for a self-exoited generator having a shunt exc-iter winding and being operatable at greatly varying speeds which comprises, in the first place, main transistor means having a collector, an emitter, and a base electrode, arranged for controlling the exciter current of the generator, the collector-emitter circuit of the transistor being connected in series with one of the shunt exciter winding. For assuringexcitation upon starting of the generator from standstill a base resistor connected between the base electrode of the main transistor and the other end of the shunt exciter winding is provided. The regulator arrangement further comprises control transistor means having also a collector, an emitter and a base rendering the main transistor conductive when the output voltage is inferior to that predetermined value. For this purpose the base electrode of the control transistor is con nected with one output of the generator so as to carry a potential proportional to the output voltage thereof. For protecting the arrangement as mentioned above the arrangement finally comprises protective circuit means cooperating w-i-th the main and control transistors for shortcirc-uiting said control transistor and for rendering the main transistor non-conductive when the exciter current through the collector-emitter circuit of the main transistor exceeds a predetermined maximum, even when the output voltage of the generator is still inferior .to the above mentioned predetermined value.

Preferably, the protective circuit means mentioned above comprise a series-resistor connected at one of its ends in series with the emitter electrode of the main transistor for producing a voltage drop depending upon the exciter current flowing through the main transistor, and a controllable semiconductor rectifier having a control electrode and an anode-cathode circuit, the latter being connected between a junction point located between the base resistor mentioned above and the base electrode of the main transistor, on one hand, and the other end of the series resistor, on the other hand, the control electrode of the semiconductor rectifier being connected with the series-resistor for causing the voltage drop thereacross to control the semiconductor rectifier in such a manner that the control transistor is shor-t-circuited and the main transistor is rendered non-conductive when the exciter current through the main transistor exceeds a predetermined maximum, even when the generator output'voltage is inferior to the predetermined value thereof.

It is advisable to connect the semiconductor rectifier in parallel with the emitter-collector circuit of the control transistor. In this case it is also advisable to choose the breakdown voltage of the controllable semiconductor rectifier to be substantially higher than the output voltage of the generator to be kept at a. predetermined constant value by means of the regulator arrangement. For instance, if the operating voltage of the generator is higher 'than about volts, then according to a further feature of this invention it would be advisable to connect, in series with the anode-cathode circuit of the semiconductor rectifier, a semiconductor diode or unidirectional conductor passing the current in the same direction as the rectifier, and to connect this diode directly with the collector of the control transistor while additionally the junction point between the semiconductor rectifier and the diode is connected with the intermediate point of a voltage divider, consisting of at least two resistors in series connect-ion and connected as a whole across the generator so as to produce at said intermediate point afraction of the output voltage of the generator.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing, in which:

FIG. 1 is a diagrammatic elevational view of a lighting generator adapted to be used on a railroad car and combined with a regulator and with a storage battery connected in parallel with the generator;

FIG. 2 is a schematic circuit diagram of anarrangemerit according to FIG. 1, including one embodiment of a regulator arrangement according to the invention; and

FIG. 3 is a schematic circuit diagram illustrating a modification of the regulator arrangement according to FIG. 2.

The generator of the arrangement according to FIG. 1 contains in its housing a direct current armature (indicated at in FIG. 2) carried by an armature shaft 12 and rotatable by means of a V-belt pulley 11, while a shunt ex-citer winding 16 is mounted inside the housing 10 and is connected at one of its ends with the positive terminal 17 of the generator via the corresponding positive output line 18. A storage battery 21 is connected at its positive terminal via a rectifier 22, conductive in the appropriate direction, with the positive output line 18, while the negative terminal of the battery 22 is connected via the negative output line with the negative terminal 19 of the generator. In a well known manner the arrangement is such that the battery 21 can be charged and at the same timeother current consumers can be supplied with energy when the output voltage of the generator available between the

lines

18 and 20 rises above 110 volts.

In order to prevent this output voltage to increase beyond the above mentioned predetermined value when the rotary speed of the generator shaft 12 is very considerably increased, an electronic voltage regulator 25 is provided which may be mounted on the housing 10 of the generator as shown in FIG. 1 and whose circuit arrangement is illustrated in FIG. 2 within the dotted frame 25.

In particular, the voltage regulator 25 comprises a main transistor 26 which has a collector electrode connected with the other end of the exciter winding 16, and additionally a control transistor 27 which has the function of changing the main transistor 26 from conductive to nonconductive condition every time when the output voltage of the generator tends to exceed a predetermined value thereof. However, in order to assure, when the generator is started from standstill, that the main transistor 26 is in conductive condition so that the generator can excite itself, a series-combination of a base resistor 28 of, e.g., 160 ohms, a resistor 29 of 40 ohms and a rectifier 30 passing current from the positive line 18 toward the base electrode of the main transistor 26 is provided between the positive output line 18 and the base electrode of the main transistor 26. The control transistor 27 has a collector electrode which is connected with the junction point between the

resistors

28 and 29. Between the base electrode of the main transistor 26 and the collector electrode of the control transistor 27 a capacitor 31 is placed of about 0.1 ,uf. The emitter of the control transistor 27 is directly connected to the negative output line 20.

Between the output lines 18 and 20 a series-combination of a resistor 33 and of a potentiometer 34 is arranged. A Zener diode 35 is connected with one of its terminals with the movable tap 32 of the potentiometer 34, while the other terminal of the Zener diode 35 is connected with the base electrode of the control transistor 27 and additionally with one end of a resistor 36 of about 200 ohms, the other end whereof is connected with the negative output line 20. The breakdown voltage of the Zener diode is so chosen that the latter becomes conductive when the output voltage of the generator as available between the two

output lines

18 and 20 exceeds the predetermined value of, e.g., 110 volts. When this occurs a control current can flow from the tap 32 via the Zener diode to the base electrode of the control transistor 27 and from there through the emitter to the negative output line 20, this current rendering the emitter-collector circuit of the control transistor 27 conductive whereby the main transistor 26 is rendered non-conductive as will be described further below.

As long as the predetermined value of the output voltage is not reached the control transistor 27 remains in non-conductive condition and consequently the main transistor 26 is fully conductive. When this is the case the base current of the main transistor 26 flowing through the resistor 29 produces across the latter a voltage drop of about 20 volts. Under this condition that electrode of the capacitor 31 which is connected with the collector of the control transistor 27 is charged to a voltage differing from that of the other electrode of the capacitor 31 which is connected with the base electrode of the main transistor 26. When now the output voltage of the generator exceeds the predetermined value of, e.g., 110 volts the control transistor together with the Zener diode 35 becomes conductive. The collector current of the control transistor 27, flowing through the base resistor 28 produces across the latter a voltage drop of about volts to which is now added the existing charge of the capacitor 31 whereby the potential at the base of the main transistor 26 is reduced to a value which is about 10 volts lower than the potential of the negative output line 20. Hereby the main transistor 26 is rendered completely non-conductive and the exciter current which up to this moment could flow through the exciter winding 16 is interrupted. The inductive voltage peak generated at the moment of the current interruption is substantially taken care of and diverted by a rectifier 37 which is conductive in the proper direction and connects the collector of the main transistor 26 with the positive output line 18. The remainder of the inductive voltage peak is applied via a resistor 38 and a series-connected capacitor 39 in such a manner to the base electrode of the control transistor 27 that the latter is kept in conductive condition through a period of time which is determined by the charging time constant of the capacitor 39.

Due to the now lacking exciter current the output voltage of the generator drops rapidly below the above mentioned predetermined value thereof. As a result, the control current for the transistor 27 which up to this moment was flowing through the Zener diode 35 cannot be maintained any longer so that the control transistor 2 27 now returns to its non-conductive condition. Consequently, the main transistor 26 is now able to return to its original conductive condition and will carry an exciter current flowing through the exciter winding 16 until the output voltage again reaches the predetermined value thereof whereafter the cycle repeats.

In order now to protect the main transistor 26 against the danger that in the case of a short-circuit occurring in the field winding 16 the full amount or at least a substantial portion of the voltage existing between the

output lines

18 and 20 has to be carried by the emittercollector circuit of the main transistor 26, the invention provides a protective arrangement as follows. The protective arrangement according to the invention comprises a series resistor 40 connected between the main transistor 26 and the negative output line 20, and preferably a potentiometer 41 connected in parallel with the series resistor 40. Moreover a controllable semiconductor rectifier 42 is provided the anode whereof is connected with the collector of the control transistor 27 while its cathode is directly connected with the negative output line 20. The semiconductor rectifier has a control electrode 43 which is connected with the movable tap 44 of the potentiometer 41 so that, depending upon the setting of the tap 44, the semiconductor rectifier is rendered conductive as soon as a voltage drop of more than 10 volts appears between the emitter electrode of the main transistor 26 and the negative output line 20. This will occur when the emitter current of the main transistor 26 exceeds a maximum permissible value of, e.g., 1.5 amperes. When the semiconductor rectifier 42 is rendered conductive then it constitutes a low resistance short-circuit for the control transistor 27 and carries a current flowing through the base resistor 28 and having so large an amplitude that the main transistor 26 is returned to its nonconductive condition even when the output voltage of the generator should have dropped already below the above mentioned predetermined value thereof. Only when the excitation of the generator has almost entirely vanished and when its output voltage has droped to a very low value, the semiconductor rectifier 42 automatically returns to its non-conductive condition. In case that the short-circuit in the exciter winding hasbeen eliminated or has vanished in the meantime, then the excitation of the generator will start again and the regulator arrangement will operate in the manner described further above. However, should upon the new excitation of the generator the short-circuit still exists and apply to a great portion of the exciter winding, then the generator cannot be excited again. On the other hand, if the shortcircuit applies only to a very small portion of the exciter winding 16 then the generator will be able to excite itself again. In any case however, as soon as the above mentioned critical value of 1.5 amperes of the exciter current flowing through the series resistor 40 is reached the semiconductor rectifier 42 is again rendered conductive and causes in the above described manner non-conductive condition of the main transistor 26.

e FIG. 3 illustrates only theregulator portion of a generator arrangement as described above. The modified regulator arrangement shown within the dotted frame 50 may be used in the same manner as the regulator arrangement according to FIG. 2 in the lighting installation of a vehicle. FIG. 3 contains elements identical or equivalent to those of the arrangement according toFIG. 2, the same reference'numerals have been used in the drawing. The main difference between the arrangements of FIGS. 2 and 3 consists in the provision of a plain not controllable rectifier or diode or unidirectional conductor 53 in series with the controllable semiconductor rectifier 52, both connected as a series-combination in the connection between the collector of the control transistor 27 and the negative output line 20. The rectifier or diode 53 is connected with its anode directly with the collector of the control transistor 27. Since the controllable rectifier 52 can carry only a comparatively low breakdown voltage between its anode and its cathode which is connected with the nega tive output line 20, and in order to make it possible to utilize the rectifier 52 also in a regulator arrangement operating with comparatively high voltages, a voltage divider comprising at least two resistors 54 and 55 is arranged between the positive output line 18 and the negative output line 20. The intermediate point A of the voltage divider, located between the resistors 54 and 55 is connected with the anode of the controllable rectifier 52 as Well as with the cathode of the series-connected. noncontrollable rectifier 53. The control electrode of the rectifier 52 is connected as in the previous example with the movable tap 44 of the potentiometer 41 which is again connected in parallel with the series resistor arranged in the emitter connection of the main transistor 26. The voltage divider resistors 54 and 55 are so dimensioned that the potential at the intermediate point A is always higher than the potential of the collector of the control transistor 27.

In this arrangement the controllable rectifier 52 remains in non-conductive condition until the exciter current flowing through the series resistor reaches a maximum permissible value which is predetermined by the setting of the movable tap 44. Whenever this occurs the controllable rectifier 52 by becoming conductive constitutes a short-circut for the resistor 55 and consequently causes the collector of the control transistor 27 to assume a potential which is substantially equal to that of the negative output line 20 because under this condition the rectifier 53 constitutes only a low resistance connection to the controllable rectifier 52 which is also in highly conductive condition.

The not'controllable rectifier 53 has the additional As far as the arrangement according to function to prevent during lator the voltage available at the intermediate point A between the voltage divider resistors 54 and 55 from influencing the base electrode of the main transistor 26. In this manner it is assured that the main transistor 26 is sufiiciently rendered non-conductive when the control transistor 27 assumes conductive condition at the moment when the output voltage of the generator exceeds its predetermined value.

A particular advantage of the above described protective arrangement according to the invention resides in the following facts: Whenever the controllable rectifiers 42 or 52 are rendered conductive on account of a shortcircuit occurring in the field or exciter winding, the controllable rectifier remains in this condition even in the absence of a control voltage at its control electrode 43 as long as a voltage difference exists between the

output lines

18 and 20 of the generator. Even if the shortcircuit is immediately eliminated, the excitation of the generator must first disappear almost completely and the voltage of the generator must drop to a value amounting almost to zero, before the rectifier assumes non-conductive condition and thereby again renders the main transistor 26 conductive. In this manner -it is assured that the main transistor cannot be overloaded. As a matter of fact, this would soon cause a breakdown between its collector and its emitter whereby this collector-emitter circuit would be rendered permanently conductive. If this should occur in the presence of a short-circuit concerning only a portion of the exciter winding 16, this would entail a great increase of the generator output voltage and result no only in a rapid destruction of the control transistor 27 and of the Zener diode 35, but also of the storage battery 21 and the generator itself.

It will be understood that each of the elements described above, or-two or more together, may also find a useful application in other types of voltage, regulator for a self-excited generator differing from the types described above.

- While the invention has been illustrated and described as embodied in voltage regulator for a self-excited gene-rator having a shunt exciter'winding and being operatable at greatly varying speeds, it is not intended to be limited to the details shown, since various-modifications and structherefore, such adaptations should and are intended-to be comprehended within the meaning and range of equivalence of the following claims. I

- What is claimed as new and desired to be secured by Letters Patent is:

. 1. Voltage regulator for a self-excited generator having a shunt exciter winding and'being operable at greatly varying speeds, comprising, in combination, main transistor means having collector, emitter and base electrodes, -respectively, for controlling the exciter current of the generator, the collector-emitter circuit of said transistor means being connected in series with one end of the shunt exciter winding; base resistor means connected between said base electrode and the other end of said shun-t exciter winding for assuring excitation upon starting the generator from standstill, control transistor means having collector,-

emitter and base electrodes, respectively, for alternatively rendering said main transistor means non-conductive when the output ofvoltage of the generator is superior to a predetermined value, and for rendering said main transistor means conductive when said output voltage is inferior to said predetermined value, said collector electrode of said control transistor means being connected both with a normal operation of the regujunction point between said base resistor means and said base electrode of said main transistor means, said base electrode of said control transistor means being connected with one output of the generator so as to carry a potential proportional to said output voltage; series-resistor means connected .at one of its ends in series with said emitter electrode of said main transistor means for producing a voltage drop depending upon said exciter current flowing through said main transistor means; and controllable semiconductor rectifier means having a control electrode and an anode-cathode circuit, the latter being connected between a junction point located between said base resistor means and said base electrode of said main transistor means, on one hand, and the other end of said series resistor means, on the other hand, said control electrode of said semiconductor rectifier means being connected with said series-resistor means for causing said voltage drop thereacross to control said semiconductor rectifier means, in such a manner that said control transisitor means is short-circuited and said main transistor means is rendered non-conductive when said exciter current through said main transistor means exceeds a predetermined maximum, even when the generator output voltage is inferior to said predetermined value thereof.

2. Voltage regulator for a self-excited generator having a shunt exciter winding and being operable at greatly varying speeds, comprising, in combination, main transistor means having collector, emitter and base electrodes, respectively, for controlling the exciter current of the generator, the collector-emitter circuit of said transistor means being connected in series with one end of the shunt exciter winding; base resistor means connected between said base electrode and the other end of said shunt exciter winding for assuring excitation upon starting the generator from standstill, control transistor means having collector, emitter and base electrodes, respectively, for alternatively rendering said main transistor means nonconductive when the output voltage of the generator is superior to a predetermined value, and for rendering said main transistor means conductive when said output voltage is inferior to said predetermined value, said collector electrode of said control transistor means being connected both with a junction point between said base resistor means and said base electrode of said main transistor means, said base electrode of said control transistor means being connected with one output of the generator so as to carry a potential proportional to said output voltage; series-resistor means connected at one of its ends in series with said emitter electrode of said main transistor means for producing a voltage drop depending upon said exciter current flowing through said main transistor means; voltage divider means connected across the generator for furnishing at a predetermined intermediate point a reference voltage being a predetermined fraction of the generator output voltage; and a series-combination of a unidirectional conductor means and of a controllable semiconductor rectifier means having a control electrode and an anode-cathode circuit, said series-combination being connected between a junction point located between said base resistor means and said base electrode of said transistor means, on one hand, and the other end of said series resistor means, on the other hand, the junction point between said unidirectional coduct-or means and said semiconductor rectifier means being connected with said intermediate point of said voltage divider means, and said control electrode of said semiconductor rectifier means being connected with said series-resistor means for causing said voltage drop thereacross to control said semiconductor rectifier means, in such a manner that said control transistor means is short-circuited and said main transistor means is rendered non-conductive when said exciter current through said main transistor means exceeds a predetermined maximum, even when the generator output voltage is inferior to said predetermined value thereof.

3. Voltage regulator for a self-excited generator having (3 0 a shunt exciter winding and being operable at greatly varying speeds, comprising, in combination, main transistor means having collector, emitter ad base electrodes, respectively, for controlling the exciter current of the generator, the collector-emitter circuit of said'transistor means being connected in series with one end of the shunt exciter Winding; base resistor means connected between said base electrode andthe other end of said shunt exciter winding for assuring excitation upon starting the generator from standstill, control transistor means having collector, emitter and base electrodes, respectively, for alternatively rendering said main transistor means non-conductive when the output voltage of the generator is superior to a predetermined value, and for rendering said main transistor means conductive when said output voltage is inferior to said predetermined value, said collector electrode of said control transistor means being connected both with a junction point between said base resistor means and said base electrode of said main transistor means, said base electrode of said control transistor means being connected with one output of the generator so as to carry a potential proportional to said output voltage; seriesresistor means connected at one of its ends in series with said emitter electrode of said main transistor means for producing a voltage drop depending upon said exciter current flowing through said main transistor means; and contr-ollable semiconductor rectifier means having a control electrode and an anode-cathode circuit, the latter being connected between a junction point located between said base resistor means and said base electrode of said main transistor means, on one hand, and the other end of said series resistor means, on the other hand, potentiometer means being connected in parallel with said series-resistor means, and said control electrode of said semiconductor rectifier means being connected with an intermediate tapping point of said potentiometer means for causing a predetermined fraction of said voltage drop across said seriesresistor means as available atsaid tapping point to control said semiconductor rectifier means, in such a manner that said control transistor means is short-circuited and said main transistor means is rendered non-conductive when said exciter current through said main transistor means exceeds a predetermined maximum, even when the generator output voltage is inferior to said predetermined value thereof.

4. Voltage regulator for a self-excited generator having a shunt exciter winding and being operable at greatly varying speeds, comprising, in combination, main transistor means having collector, emitter and base electrodes, respectively, for controlling the exciter current of the generator, the collector-emitter circuit of said transistor means being connected in series with one end of the shunt exciter Winding; base resistor means connected between said base electrode and the other end of said shunt exciter winding for assuring excitation upon starting the generator from standstill, control transistor means having collector, emitter and base electrodes, respectively, for alternatively rendering said main transistor means non-conductive when the output voltage of the generator is superior to a predetermined value, and for rendering said main transistor means conductive when said output voltage is inferior to said predetermined value, said collector electrode of said control transistor means being connected both with a junction point between said base resistor means and said base electrode of said main transistor means, said base electrode of said control transistor means being connected with one output of the generator so as to carry a potential proportional to said output voltage; series-resistor means connected at one of its ends in series with said emitter electrode of said main transistor means for producing a voltage drop depending upon said exciter current flowing through said main transistor means; voltage divider means connected across the generator for furnishing at a predetermined intermediate point a reference voltage being a predetermined fraction of the generator output voltage;

9 and a series-combination of a unidirectional conductor means and of a controllable semiconductor rectifier means having a control electrode and an anode-cathode circuit, said series-combination being connected between a junction point located between said base resistor means and said base electrode of said transistor means, on one hand, and the other end of said series resistor means, on the other hand, the junction point between said unidirectional conductor means and said semiconductor rectifier means being connected with said intermediate point of said voltage divider means, potentiometer means being connected in parallel with said series-resistor means, said control electrode of said semiconductor rectifier means being connected with an intermediate tapping point of said potentiometer means for causing a predetermined fraction of said voltage drop across said series-resistor means as available at said tapping point'to control said semiconductor rectifier means, in such a manner that said control transistor means is short-circuited and said main transistor means is rendered non-conductive when said exciter current through said main transistor means exceeds a predetermined maximum, even when the generator output voltage is inferior to said predetermined value thereof.

References Cited by the Examiner UNITED STATES PATENTS 3,098,964 7/ 1963 Hetzler 322-28 3,179,874 4/ 1965 Guennou 32225 3,193,755 7/1965 Zelina 322-28 3,201,681 8/1965 Van Wilgen et a1. 322-25 X MILTON O. HIRSHFIELD, Primary Examiner. J. J. SWARTZ, Assistant Examiner.

Claims

1. VOLTAGE REGULATOR FOR A SELF-EXCITED GENERATOR HAVING A SHUNT EXCITER WINDING AND BEING OPERABLE AT GREATELY VARYING SPEEDS, COMPRISING, IN COMBINATION, MAIN TRANSISTOR MEANS HAVING COLLECTOR, EMITTER AND BASE ELECTRODES, RESPECTIVELY, FOR CONTROLLING THE EXCITER CURRENT OF THE GENERATOR, THE COLLECTOR-EMITTER CIRCUIT OF SAID TRANSISTOR MEANS BEING CONNECTED IN SERIES WITH ONE END OF THE SHUNT EXCITER WINDING; BASE RESISTOR MEANS CONNECTED BETWEEN SAID BASE ELECTRODE AND THE OTHER END OF SAID SHUNT EXCITER WINDING FOR ASSURING EXCITATION UPON STARTING THE GENERATOR FROM STANDSTILL, CONTROL TRANSISTOR MEANS HAVING COLLECTOR, EMITTER AND BASE ELECTRODES, RESPECTIVELY, FOR ALTERNATIVELY RENDERING SAID MAIN TRANSISTOR MEANS NON-CONDUCTIVE WHEN THE OUTPUT OF VOLTAGE OF THE GENERATOR IS SUPERIOR TO A PREDETERMINED VALUE, AND FOR RENDERING SAID MAIN TRANSISTOR MEANS CONDUCTIVE WHEN SAID OUTPUT VOLTAGE IS INFERIOR TO SAID PREDETERMINED VALUE, SAID COLLECTOR ELECTRODE OF SAID CONTROL TRANSISTOR MEANS BEING CONNECTED BOTH WITH A JUNCTION POINT BETWEEN SAID BASE RESISTOR MEANS AND SAID BASE ELECTRODE OF SAID MAIN TRANSISTOR MEANS, SAID BASE ELECTRODE OF SAID CONTROL TRANSISTOR MEANS BEING CONNECTED WITH ONE OUTPUT OF THE GENERATOR SO AS TO CARRY A POTENTIAL PROPORTIONAL TO SAID OUTPUT VOLTAGE: SERIES-RESISTOR MEANS