US2958033A

US2958033A - Regulating apparatus for generators

Info

Publication number: US2958033A
Application number: US710029A
Authority: US
Inventors: Mittag Hermann; Paule Kurt
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1956-07-14
Filing date: 1958-01-20
Publication date: 1960-10-25
Anticipated expiration: 1977-10-25
Also published as: JPS35818B1; GB835210A; JPS362264B1; DE1132223B; DE1095923B; GB835834A

Description

Oct. 25, 1960 H. MlTTAG ETAL REGULATING APPARATUS FOR GENERATORS Filed Jan. 20, 1958 Fig. 7

2 Sheets-Sheet 1 INVENTORS Oct. 25, 1960, H. MITTAG ETAL 2,958,033

REGULATING APPARATUS FOR GENERATORS Filed Jan. 20, 1958 2 Sheets-Sheet 2 INVENTOR$ United States Patent REGULATING APPARATUS FOR GENERATORS Hermann Mittag, Stuttgart-Botnang, and Kurt Paule, Stuttgart-Oberturkheim, Germany, assignors to Robert Bosch, G.m.b.H., Stuttgart, Germany Filed Jan. 20, 1958, Ser. No. 710,029

Claims priority, application Germany July 14, 1956 23 Claims. (Cl. 322-25) The present invention relates to a regulating arrangement. More particularly, the present invention relates to an apparatus for automatically regulating the voltage output of an electrical generator.

This application is a continuation-in-part of our now abandoned application Serial No. 671,950, filed July 15, 1957, entitled Regulating Apparatus.

The present invention is primarily applicable to electrical generators which are found on motor vehicles for supplying the electrical energy for operating the lights and the other electrical apparatus used on such motor vehicles. It is well known that the conventional voltage regulators all use certain types of contacts which become pitted with use. These pitted contacts tend to stick and provide major maintenance difliculties in the voltage regulation system of the motor vehicles.

It is accordingly an object of the present invention to provide an apparatus which overcomes the disadvantages of the prior art arrangements.

A second object of the present invention is to provide a new and improved apparatus for regulating the voltage output of shunt wound generators.

Another object of the present invention is to provide a voltage regulator for generators used on motor vehicles wherein the voltage regulator uses no movable contacts.

Still another object of the present invention is to provide a new and improved voltage regulator for shunt wound generators, which voltage regulator uses transistors.

A further object of the present invention is to provide a new and improved voltage regulator which regulates the voltage output of shunt wound generators and which controls the current output thereof.

Yet a further object of the present invention is to provide a voltage regulator for electrical generators wherein one transistor is controlled by a second transistor which in turn is varied by the voltage output of the electrical generator.

Still a further object of the present invention is to provide a voltage regulator of the type set forth in which the voltage output of the generator remains substantially constant up to a preselected value of the output current of the generator, while the voltage decreases rapidly whenever the output current exceeds the preselected value.

With the above objects in view, the present invention mainly consists of an apparatus for regulating the voltage output of an electrical generator having a shunt field exciting winding adapted to have exciting current flow therethrough. This apparatus includes variable impedance means in the form-of a first transistor which is connected in circuit with the shunt winding of the electrical generator for adjusting the exciting current flowing through the shunt winding in accordance with the impedance thereof and thereby to adjust the voltage output of the generator. Control means are utilized in the apparatus, the control means including a second transistor and having an input circuit connected in circuit with the output of the generator and having an output circuit connectedin Patented Oct. 25, 1960 circuit with the first transistor to produce an output current. The output current varies the impedance of the first transistor which in turn varies the voltage output of the generator. Accordingly, any change in the voltage output of the electrical generator will change the output current of the second transistor to produce a corresponding change in the impedance of the first transistor and in the exciting current flowing through the shunt field winding to thereby change the voltage output of the generator in a preselected manner.

In a preferred embodiment of the present invention, the generator has a self-exciting field winding so that the variable impedance means is connected between the voltage output of the generator and the shunt field winding to supply exciting current for the shunt field winding.

The variable impedance means can be a first transistor having electrodes connected in circuit with the shunt field winding, which transistor regulates the current flowing through the shunt field winding in accordance with the potential distribution between the various electrodes of the transistor. In such a case, the control means can be a second transistor which is placed in self-oscillating condition when the voltage output reaches a preselected level. The output current of the second transistor changes the potential distribution between the electrodes of the first transistor so that the current through the field winding is changed in a direction to maintain the generator voltage output at the preselected level.

In one embodiment of the present invention, an auxiliary battery is arranged in circuit with the second transistor utilized as the control means.

In still another embodiment, such auxiliary battery is eliminated and a rectifier bridge circuit is used to initiate self-oscillation in the second transistor circuit.

In order to properly allow for the load current taken from the electrical generator, a resistor having a negative temperature coefiicient is used to change the operating range of the control means when necessary.

In order to prevent the output current of the generator to increase the values potentially dangerous for the generator, an embodiment of the invention includes conductor means in circuit with the input and output circuits of the second transistor and adapted to be in substantially blocked condition as long as the voltage drop across a resistor in the output circuit is below a preselected value, but to become conductive when this voltage drop exceeds the preselected value. The voltage drop is transmitted by the conductor means to the output circuit of the second transistor so that the voltage output of the generator remains substantially constant as long as the output current does not exceed a predetermined amount corresponding to said preselected voltage drop value, but decreases rapidly as soon as the predetermined current amount is exceeded.

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 drawings, in which:

Fig. 1 is an electrical schematic diagram of a first embodiment-of the present invention;

Fig. 2 is a partial schematic diagram of a second embodiment of the present invention;

Fig. 3 is an electrical diagram of a third embodiment of the present invention; and

Fig. 4 is an electrical diagram of a modification of the embodiment illustrated by Fig. 3.

Referring to the drawings and more particularly to Fig. 1, it can be seen that the generator G is provided with brushes a and b. The a brush is the negative brush and is directly connected to the electrical ground while the b brush is the positive brush and is connected by means of

conductors

51 and 52 to the emitter electrode E1 of a transistor 10. V a V p r The transistor has a collector electrode C1 connected by means of a conductor 53 to one side of the field winding F of the generator G. The other end of the shunt field exciting winding F is connected by means of a conductor 54 directly to ground.

It is apparent that the generator G has a rotatable armature which is coupled to the motor of the motor vehicle and which generates a voltage which is produced between the brushes a and b in the indicated polarity. The voltage generated by the generator G is indicated by the arrow U.

The transistor 10 also has an input circuit including the base electrode B1 which is connected to ground through the resistor 11. Connected in parallel with the resistor 11 is a capacitor 35. I

From the portion of the figure so far described, it is apparent that the generator G has a self-excited shunt field winding F, the exciting current being produced in the Winding F by the voltage produced across the brushes a and b. The magnitude of the current Je which is the exciting current flowing through the field winding F depends upon the potential distribution between the electrodes of the transistor 10.

That is, the exciting current for the field winding F is the output current obtained on the conductor 53 from the collector electrode C1 of the transistor 10. The magnitude of this current depends upon the potential difference between the emitter E1 and the base electrode B1. It is apparent that the emitter electrode will be maintained at the same potential as the voltage output appearing at the brush b. Output current will be obtained at the collector electrode C1 as long as the potential of the base electrode B1 is equal to or smaller than the potential at the emitter electrode E1. As the potential of the base electrode is raised, the magnitude of the output current appearing at the conductor 53 will decrease. Similarly as the potential applied to the base electrode B1 decreases, the magnitude of the output current appearing on the conductor 53 will increase.

It is also clear that the magnitude of the current flowing through the shunt field winding P will determine the voltage output of the generator G for the particular speed at which the generator is being rotated by the motor of the motor vehicle.

To further complete the circuit of Fig. 1, it can be seen that the positive brush b is also connected to the positive terminal of an auxiliary battery H, the negative terminal of which is connected to the emitter electrode E2 of a second transistor 20. The output circuit of the transistor 20 includes the conductor 56 connected to the collector electrode C2 thereof and also connected at the other end to the junction point between

windings

22 and 23.

Windings

22 and 23 are two windings of a transformer T having an iron core 21. The transformer T also has a third winding 24 wound about the iron core 21. That is, the transformer T includes three

windings

22, 23, and 24, each wound about the iron core 21 in the same winding direction.

It can be seen that the junction point between the

windings

23 and 24 is connected to the electrical ground of the apparatus While the distant end of the winding 22 is connected to the base electrode B1 of the transistor 10 by means of the half-Wave rectifier 29. Similarly, the other end of the winding 24 is connected to the base electrode B1 by means of the half-wave rectifier 28.

This end of the winding 24 is also connected to the base electrode B2 of the transistor 20 by means of the series combination of the

resistors

27 and 26. The base electrode B2 of the transistor 20 is also connected to the positive voltage supply conductor 51 by means of an adjustable resistor 25. The

resistors

25, 26 and 27 form a voltage divider circuit between the positive conductor 51 and the electrical ground. The winding 24 has a very low resistance and accordingly does not form a substantial part of the voltage divider arrangement.

The resistor 27 is a resistor having a negative temperature coeflicient so that the resistance thereof decreases as the temperature of the resistor 27 increases. To vary the temperature of the resistor 27 in a predetermined manner to be described subsequently, a heating coil 30 is wound about the resistor 27 and is connected at one of its ends by means of a conductor 31 to the positive supply conductor 51. The other end of the coil 30 is connected by means of a half-wave rectifier 34 to the positive terminal of a battery 32. It is apparent that the battery 32 may be the conventional storage battery utilized in the motor vehicles. Also shown in schematic form is a load 33 which is adapted to be connected across the battery 32 by means of a switch 57. It is clear that when the switch 57 is closed, and voltage is generated by the generator G, current flows through the

conductors

51, 31, the coil 30 and the rectifier 34 to the load 33. This current is also used for charging the battery 32 when the potential of the generator is sufficiently large to carry out this function.

The regulating function of the circuit of Fig. 1 is carried out in the following manner: It is seen that the emitter electrode E2 of the transistor 20 is arranged to be at a lower voltage than the positive voltage appearing at the conductor 51. This lower voltage is a fixed amount lower than the positive conductor 51 due to the fixed biasing voltage introduced by the battery H. When the motor vehicle starts moving and the generator starts turning and generating voltage, the voltage appearing on the conductor 51 is divided by the voltage divider circuit including the

resistors

25, 26 and 27. Therefore, the base electrode B2 of the transistor 20 has a potential applied thereto depending upon the voltage drop in the adjustable resistor 25. The values of the various components of the circuit'are arranged so that this voltage drop in the resistor 25 will be smaller than the biasing negative voltage introduced by the battery H. Accordingly, initially, the potential of the base electrode B2 will be higher than the potential of the emitter electrode E2. The transistor 20 will then be in blocked condition and no output current J will appear on the output conductor 56 thereof.

Under these conditions, the exciting current Ie flowing through the field winding F will depend only upon the potential distribution between the various electrodes of the transistor 10 connected in circuit with the winding F. As the voltage increases on the conductor 51, the voltage drop across the resistor 25 will increase until it is substantially equal to the amount of biasing potential applied to the emitter electrode E2. At this point, the transistor 20 will change from blocked condition to conductive condition. Therefore, some output current will appear on the output conductor 56 and some base electrode current will flow through the lower portion of the voltage divider.

The output current J appearing on the conductor 56 will flow through the winding 23 to the electrical ground returning to the negative brush of the generator. This will induce a fiux change in the iron core 21 about which the winding 23 iswound. 'This flux change in the core 21 will produce a voltage across the coil 24 in a direction as indicated by the arrow U2.

The polarity of the voltage U2 is in such a direction as to decrease further the potential of the base electrode B2 of the transistor 20. Therefore, the feedback effect will cause a greater output current to appear on the output conductor 56. This large increase in the output current 1 appearing on the conductor 56 ll not p od ce a Corresponding change in the winding 24 since the iron core 21 soon becomes saturated and the increased current flowing through the winding 23 has no substantial effect on the flux in the core 21. Finally, the output current I reaches a maximum value which is predicated on the maximum value of the base current and the other elements of the transistor. When this maximum value is reached, the voltage U2 produced in the winding 24 disappears and the potential of the base electrode B2 quickly rises to a higher value. Accordingly the base current of the transistor 20 can no longer be sustained at its high level. The magnitude of the base current accordingly decreases carrying with it a corresponding decrease in the output current I quickly cutting off such output current.

The winding 23 acts to oppose this rapid change in the magnitude of the output current I and in so doing changes the flux distribution through the core 21 in the opposite direction so that a voltage U2 shown by the dotted arrow in Fig. 1 is induced in the coil 24. It is apparent that the second induced voltage U2 is in the opposite direction from the initial induced voltage. This second induced voltage U2 acts to quickly raise the base electrode above the potential of the emitter electrode E2 of the transistor 20. The transistor 20 therefore changes back to the blocked condition thereof.

At this point the cycle is complete and the transistor 20 can start a new cycle as soon as the preselected level of the voltage appearing on the conductor 51 is again reached. It is apparent that this preselected level is the level wherein the voltage drop across the resistor 25 will equal the negative biasing potential introduced by the battery H.

Since the voltages U2 and U2 induced in the winding 24 in accordance with the changes of the collector current J are applied to the potential of the base electrode B2 which is in the input circuit of the transistor 20, an amplification elfect is achieved which corresponds to a self-excited electrical oscillation. In this self-oscillation, the transistor 20 operates between a conductive condition having a high collector current J and a blocked condition having a low collector current J This is substantially the equivalent of a mouostable blocking oscillator which oscillates at a repetition rate determined by the desired preselected level of the generator voltage and the setting of the resistor 25.

The voltage impulses U2 and U2 are applied by means of the

rectifiers

28 and 29 to the capacitor 35. The value of the capacitor 35 is chosen to have a time constant which corresponds to the particular type of generator being used. Each time the potential impulse is applied across the capacitor 35, the potential of the base electrode B1 of the transistor is raised. This operates to decrease the collector current appearing on the output conductor 53, which collector current is the exciting current Ie for the shunt field winding F. Therefore, the voltage output of the generator is automatically decreased each time that an impulse is applied to the capacitor 35. The decrease of the output voltage of the generator G has the effect of blocking the transistor 20 which will remain blocked until the generator G is able to again reach the preselected level.

In order to avoid overloading the generator G by means of too high a load consumption, the load current obtained from the generator G flows through the

conductors

51 and 31 to the coil 3% wound about the resistor 27. The larger the load current produced by the geneator and consumed by the load 33, the greater will be the amount of heat produced in the coil 30.

As the heat produced by the coil 30 increases, the resistance of the negative temperature coeilicient 27 will decrease. it is apparent that this resistor 27 will then play a smaller part in the voltage divider circuit and have less of a voltage drop thereacross. Therefore, the resistor 25 will have a greater voltage drop in proportion and the base electrode B2 of the transistor 20 6 will reach the potential of the emitter E2 at a lower level of the generated voltage.

It can therefore be seen that the effect of the coil 30 which is a heating coil, is to displace the voltage zone of operation in which the regulating apparatus operates.

The rectifier 34 arranged between the coil 30 and the battery 32 is provided in order to prevent a discharge from the battery 32 to the generator G when the respective potentials might so dictate. In one embodiment of the apparatus constructed in the manner of Fig. l, the following values for the elements are used. The resistor 11 had a resistance of 100 ohms; the center winding 23 of the transformer T had approximately windings and an inductance of 20 millihenries; the voltage introduced by the negative biasing battery H was in the order of 2 volts; the adjustable resistor 25 had a resistance of approximately 10 ohms while the resistor 26 had a resistance of between 40 and 50 ohms; the negative temperature coefiicient resistor 27 had a resistance of 10 ohms in its cold state while the resistance of the winding 24 was substantially negligible; and the capacitor 35 had a capacitance of 50 microfarads.

Additional elements can be added to the circuit of Fig. 1 as shown in dotted lines. For example in order to avoid undesired voltage peaks being introduced in the field winding F when the transistor 10 may be in blocked condition, a rectifier 36 can be arranged in parallel with the winding F. This rectifier will have practically no current flowing therethrough during the constant excitation of the field winding. If a crystal diode is used as the rectifier 36 a limiting resistor 37 can be arranged in series therewith. With generators of very heavy load capacity it might be advantageous to arrange a damping resistor 38 in parallel with the field winding F,

Referring now to Fig. 2, a modification of the arrangement shown in Fig. 1 will be described wherein no separate auxiliary battery H is needed. In Fig. 2, only that portion of the circuit which is different from the portion of Fig. 1 is indicated. Otherwise the circuit remains the same.

In this circuit arrangement of Fig. 2, it can be seen that the positive supply conductor 51 is connected to the emitter electrode E of the transistor 40 by means of two series-connected

rectifiers

41 and 42. The transistor 40 takes the place of transistor 20 of the arrangement in Fig. 1. Arranged between the power supply conductor 51' and the ground conductor is a voltage divider consisting of a variable resistor 44, a resistor 45 and the low resistance winding 24. As before, the base electrode B of the transistor 40 is connected to the junction point of the resistor 44 and the resistor 45. The emitter electrode E of the transistor 40 is connected to ground by a resistor 43.

The remainder of the circuit of Fig. 2 includes the rectifier 49, the battery 32 and the load 33'.

It can be seen that the circuit of Fig. 2 provides a bridge circuit wherein the voltage applied from the generator G is applied across a diagonal of the bridge to the

terminals

61 and 62 thereof. The remaining two terminals of the bridge include the terminals 63' and 64. It can be seen that the transistor 40 is connected in this diagonal of the bridge.

Accordingly, in operation, the potential of the base electrode B will decrease to the potential of the emitter electrode B when the voltage of the generator G increases to the preselected level and provides a substantially large increase in the adjustable resistor 44. This voltage drop across the resistor 44 must equal the voltage drop across the rectifiers 41 and These rectifiers have sharply curving characteristics and accordingly the equalizing preselected level is reached in accordance with the adjustment of the resistor 44. When this occurs, the transistor 40 changes from its blocked condition to its conductive condition. Therefore an output current is provided on the output conductor 66 thereof taken from the collector electrode C. This conductor 66 corresponds to the conductor 56 of Fig. 1 and accordingly is connected between the coils of the transformer T in the same manner, namely between

coils

22 and 23. Therefore the circuit of Fig. 2 functions in the same manner as the circuit of Fig. 1 but requires no auxiliary battery.

In order to produce the equalized voltage between the base electrode B and the emitter electrode E of the transistor 40, a crystal diode 46 can be used which has a substantially rectilinear characteristic in the blocking zone thereof. One such crystal diode is called a Zener diode and is shown in dotted lines in Fig. 2. This crystal diode 46 can be used in place of the

rectifiers

41 and 42. The advantage of utilizing the diode instead of the

rectifiers

41 and 42 is that a resistor 47 can be arranged in series therewith to have a much higher resistance than the resistor 43.

In order to produce a lower preselected level at which to regulate the voltage of the generator with increasing load in the arrangement of Fig. 2, it is advantageous to arrange a resistor 48 as shown in the power supply conductor 51 in dotted form in Fig. 2. This resistor can have a resistance in the order of milliohms, for example. The junction point between the resistor 48 and the resistor 44 is utilized for the output current going via a semiconductor diode 49 to the load 33' and the battery 32. As the magnitude of the output current of the generator G flowing through the conductor 51' increases, the voltage drop across the resistor 48 will also increase. In this manner, the transistor 40 will be changed from its blocked condition into its conductive condition at a lower value of the generator voltage. Therefore the regulating efiect of the self-excited transistor 40 following a linear characteristic will be introduced to maintain the voltage output of the generator G at such lower preselected level.

In the operation of the embodiments shown in Figs. 1 and 2, it is clear that the second transistor, either transistor 20 or transistor 40, operates to control the potential distribution of the electrodes of the transistor which is connected in circuit with the field winding F of the generator. As the controlling transistor oscillates between blocked and conductive conditions, the exciting current flowing through the winding F is changed in a direction to regulate the voltage output of the generator G at its preselected level.

In Fig. 2 it is clear that the

rectifiers

41 and 42 or the crystal diode 46 are arranged to provide the desired non-linear resistance characteristics to achieve the proper potential distribution of the electrodes of the transistor 40 to change the transistor from is blocked condition to its conductive condition.

Referring now to Figs. 3 and 4, modified embodiments of the invention are based on the idea to provide in the input or control circuit of the means producing a selfexcited oscillation a resistor connected in the current output circuit of the generator and to apply the voltage drop appearing across that resistor to said means by way of conductor means adapted to be in substantially blocked condition as long as the voltage drop is below a preselected value, while said conductor means are conductive when the voltage drop exceeds that preselected value.

Suitable conductor means for this purpose are active or passive diode means to which a negative bias voltage is applied, or which have a linear V-I characteristic which has however a distinct break at a point corresponding to a critical voltage-current ratio. A particularly simple arrangement is obtained by using as a conductor means a crystal diode adapted to produce the so-called Zener effect. Figs. 3 and 4 illustrate two embodiments incorporating the above-mentioned features. Figs. 3 and 4 are generally quite similar to the above-described Figs. 1 and 2 so that hereinafter only those portions of these diagrams will be described in detail which differ from those shown by Figs. 1 and 2. Reference numerals and letters of parts that are substantially identical and have the same function as those illustrated in Figs. 1 and 2 are the same as in Figs. 1 and 2.

Referring specifically to Fig. 3 it can be seen that the transformerT has a (fourth winding 27:: which is connected in series with conductor means 59, 51a as will be described below. Connected in the main line 51" leading from the generator G, positive terminal 1;, to the battery 32 or load 33, is a resistor R in such a manner that the potential at the emitter E is lower than existing at the terminal b when the generator voltage U is higher than that of the storage battery 32 so that an output or charging current 1;, flows from the positive terminal 12 to the positive pole of the battery through said resistor R. From a point S beyond the resistor R, i.e. on the side remote from the generator, a branch line leads to a silicon rectifier 42 which, together with a series connected resistor 43 constitutes a voltage divider to which is connected the emitter E of the transistor 2%. On the input side of the transistor 20 the base electrode B is connected on one side via a variable resistor 25 to the resistor R, and on the other hand also to the minus terminal a of the generator via a resistor 26 and the series-connected winding 24.

By way of example it may be stated that in a preferred embodiment as illustrated the resistor 11 is of the magnitude of 100 ohms, the winding 23 has approximately turns and 20 mh., the resistor R is of the magnitude of 40 milli-ohms, the variable resistor 25 is of the magnitude of approximately 10 ohms, the resistor 26 is of the magnitude of approximately 40 to 50 ohms and the winding 24 has comparatively low resistance.

The

resistors

25, 26 and the ohmic resistance of the winding 24 constitute one branch, and the rectifier 42 of the resistor 43 constitutes the other branch of a bridge circuit which has a non-linear characteristic. The voltage appearing in the diagonal of the bridge is bound to change more than in proportion to changes of the generator voltage U from its preselected or nominal value, because of the pronounced curvature of the characteristic of the rectifier 42.

The operation of the whole arrangement is easily understood if one starts from considering that the voltage U appearing at the terminals a and b of the generator G is increasing and that the resistor 25 is so adjusted that at the moment when the voltage U reaches a preselected value, the voltage drop across the resistor 25 causes the base B to have the same potential as the negatively biased emitter E of the transistor 2e. On account of this the transistor 20 becomes conductive and causes a collector current 1 to flow which induces in the winding 24 a potential indicated by the arrow U This potential U is so directed that the base B of the transistor 20 is made even more negative with respect to the emitter E with the result that a rapidly increasing base current (the maximum value of which is determined by the magnitude of the induced voltage U and by the magnitude of the resistors 26 and 27) and consequently also a rapidly increasing a collector current I is produced. The voltage U induced by the collector current I during its increase changes but little. The collector current, however, reaches very soon its maximum which is determined by the maximum value of the base current J and by the structural characteristics of the transistor. As soon as this maximum value is reached, the voltage U induced in the winding 24 practically disappears and the potential of the base B returns abruptly to a higher level so that the base current I cannot be maintained on its preceding level. Consequently, also the collector current J is reduced. The inductivity of the winding 23 opposes such a change of the collector current and therefore generates a voltage impulse. which is symbolized in Fig. 3 by the broken line arrow U' The transistor 20 is rendered completely nonconductive by this voltage im- 9 pulse and remains in this condition until the voltage impulse U' is completely terminated. Then, the whole cycle described above can start again as soon as the output voltage U of the generator G reaches again the preselected value.

Since the voltages U and U' induced in the winding 24 on account of the changes of the collector current J influence the potential of the base B and consequently the input circuit of the transistor 26 in such a manner that said changes of J are intensified, a self-excited electrical oscillation is generated while the transistor 29 alternates between a state of high and a state of low collector current I in a manner similar to that of a monostable blocking oscillator, whenever the increasing generator voltage U has risen up to the preselected value determined by the setting of the variable resistor 25.

The voltage impulses U and U are transmitted through the rectifiers 28 and 2? to a charging condenser 35 the size of which is chosen in conformity with the time constant of the generator. The size of the. condenser is prferably approximately 25 to 50 2F and the condenser is connected in parallel with the base resistor 11 to the base B of the first transistor 10. Each one of the voltage impulses has the effect that the potential of the base B is briefly raised and the transistor substantially reduces the exciter current I whereby the output voltage of the generator is reduced. If the generator voltage U decreases below the preselected value, the transistor 20 remains in blocked condition and no impulses tending to lower the output voltage are transmitted to the transistor 10, until the generator has excited itself so as to reach again the predetermined value of its output voltage. This procedure repeats in rapid sequence as described, as long as the output current J is either equal to zero or has a constant value.

The special feature of the embodiments illustrated by Figs. 3 and 4 consists in the fact that for preventing the generator to be overloaded, the output current is caused to flow through the resistor R. Ahead of the resistor R the above-mentioned branch line including line a diode 50 and in series therewith a transformer winding 27 is connected to the main line 51, the diode 50 being of a type which possesses a distinct break in its linear characteristic at a point corresponding to a certain voltagecurrent ratio. In the preferred embodiment according to Fig. 3 a diode consisting of a crystal diode 51a adapted to produce the so-called Zener effect has been found particularly useful an eifective.

In the embodiment according to Fig. 3 the Zener diode 51a together with the series-connected transformer winding 27a is connected in parallel with the terminals :1 and b of the generator G, and obtains therefore practically the full voltage U. As long as no output or charging current I flows, no voltage drop appears across the resistor R. As the current, however, increases the voltage drop across the resistor R increases and the transistor 20 is so controlled by the

non-linear bridge circuit

42, 43; 25, 27, 24 that the generator voltage U rises by an amount equal to the voltage drop across R. In this manner, the potential at the point S is kept practically constant. The magnitude of the resistor R is so chosen that the portion of the generator voltage U applied to the Zener diode 51a reaches its critical amount when the current 1;, exceeds the maximum value permissible as a load for the generator. In that moment, the Zener diode 51a that had been in blocked condition up to then, is rendered conductive so that a current flows through the transformer winding 27a whereby in the other windings of the transformer T voltage impulses are generated by induction, these impulses having the same polarity as the voltage U shown by an arrow for the winding 24. On account of these additional voltage increments the potential of the base B of the transistor 20 is reduced and the transistor 20 transmits to the transistor 10 through the winding 23 a blocking impulse with the eifect that the generator voltage decreases. At the same time the partial voltage applied to the Zener diode 51a decreases below the critical value of this diode so that also the output current is reduced.

The modified embodiment according to Fig. 4 advantageously differs from the embodiment according to Fig. 3 because the limitation of the maximum current 1;, is independent to the value of the generator voltage output.

According to Fig. 4 the shunt field winding F of the generator G is also connected to the collector C of a transistor 10 whose emitter E is connected to the posi tive terminal b of the generator while its base B is connected through a resistor 11 with the minus terminal a of the generator 4. The base B is likewise influenced by a control transformer T comprising three series-connected

windings

22, 23 and 24 through

rectifiers

28 and 29. The transformer is supplied by the transistor 20 whose emitter-base circuit constitutes the one diagonal of a bridge circuit having non-linear characteristic. The bridge circuit is constituted on one hand by the variable resistor 25 and the fixed resistor 26 and the negligibly small ohmic resistance of the winding 24, on the other hand by the fixed resistor 43 and the silicon rectifier 42 which serves as a bridge component having a non-linear characteristic.

In contrast with the arrangement according to Fig. 3, the embodiment according to Fig. 4 is characterized by the fact that the voltage drop appearing across the resistor R depending upon the current I is introduced into the non-linear bridge circuit which serves to control the preselected value voltage output. A non-linear voltage divider consisting of a crystal diode 51a and a fixed resistor 52a of approximately .5 ohm is connected in parallel with the load resistor R. At a point between the just-mentioned components of the voltage divider a variable resistor 25 is connected in circuit. As long as the voltage drop across the resistor R is small, the crystal diode has a comparatively great resistance; how ever, when the voltage drop is large the resistance of the crystal diode is comparatively small.

On account of this characteristic of the diode 51a as a function of the applied voltage the output voltage U of the generator is kept approximately constant as long as the current I rises only up to a predetermined value, however the voltage U decreases rapidly when the current exceeds the predetermined value.

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 regulating apparatus differing from the type described above.

While the invention has been illustrated and described as embodied in apparatus for regulating the voltage output of shunt wound generators, either self-excited or separately excited, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended Within the meaning and range of equivalence of the following claims.

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

1. In an apparatus for regulating the voltage output of an electrical generator having a shunt field exciting winding adapted to have exciting current flow therethrough, in combination, a first and a second transistor circuit and transformer means operatively connecting said transistor circuits, said first transistor circuit including a first transistor connected in circuit with the shunt winding of the electrical generator for adjusting the exciting current flowing through the shunt winding in accordance with the impedance of said first transistor; and said second transistor circuit including a second transistor having an input circuit connected in circuit with the output of the generator and having an output circuit connected in circuit with said first transistor for producing an output current which varies the impedance of said first transistor, at least a portion of said output circuit of said second transistor being connected to said input circuit thereof so that at least a portion of said output current is fed back to the input thereof to produce self-oscillation in said second transistor for varying the impedance of said first transistor in a selected manner in accordance with the magnitude of the voltage output of said electrical generator.

2. In an apparatus for regulating the voltage output of an electrical generator having a shunt field exciting winding adapted to have exciting current flow therethrough, in combination, a first and a second transistor circuit and transformer means operatively connecting said transistor circuits, said first transistor circuit incuding a first transistor having a plurality of electrodes connected in circuit with the shunt winding of the electrical generator for adjusting the exciting current flowing through the shunt winding in accordance with the difference of potentials between said electrodes of said transistor and thereby adjusting the voltage output of the generator; means for producing an initial difference of potential distribution between said electrodes to thereby produce a predetermined amount of exciting current in the shunt field winding; and said second transistor circuit including a second transistor having an output circuit connected in circuit with the output of the generator and having an output circuit connected in circuit with said first transistor for producing an output current which varies said potential distribution between said electrodes of said first transistor, at least a portion of said output circuit of said second transistor being connected to said input circuit thereof so that at least a portion of said output current is fed back to the input thereof to produce self-oscillation in said second transistor after the voltage output of the generator reaches a preselected level, whereby any change in the volt-age output of the electrical generator after said preselected level is reached changes the output current of said second transistor to produce a corresponding change in said potential distribution of the electrodes of said first transistor and in the exciting current flowing through the shunt field winding, thereby changing the voltage output of the generator to maintain the same at said preselected level.

3. In an apparatus for regulating the voltage output of an electrical generator having a shunt field exciting winding adapted to have exciting current flow therethrough, in combination, a first transistor connected in circuit with the shunt winding of the electrical generator for adjusting the exciting current flowing through the shunt winding in accordance with the impedance of said first transistor; a second transistor having an input circuit connected in circuit with the output of the generator and having an output circuit connected in circuit with said first transistor for producing an output current which varies the impedance of said first transistor; and a transformer connected in circuit with said output circuit of said second transistor and having a winding connected in circuit with said input circuit of said second transistor sothat at least a portion of said output current is fed back to the input thereof to produce self-oscillation in said second transistor for varying the impedance of said first transistor in a preselected manner in accordance with the magnitude of the voltage output of said electrical generator.

4. Apparatus as claimed in claim 3 wherein said transformer has three windings connected in series, one of said windings being connected in circuit with said output circuit of said second transistor, the second of said windings being connected in circuit with the input circuit of said second transistor and the third of said windings is connected in circuit with said first transistor.

5. Apparatus as claimed in claim 15, wherein said bridge circuit arrangement includes at least one non-linear resistor.

6. Apparatus as claimed in claim 5 wherein said nonlinear resistor is a rectifier.

7. Apparatus as claimed in claim 5 wherein said nonlinear resistor is a Zener diode.

8. In an apparatus for regulating the voltage output of an electrical generator having a shunt field exciting winding adapted to have exciting current flow therethrough, in combination, a first transistor having a plurality of electrodes connected in circuit with the shunt winding of the electrical generator for adjusting the exciting current flowing through the shunt winding in accordance with the difference of potentials between said electrodes of said transistor and thereby adjusting the voltage output of the generator; means for producing an initial difference of potential distribution between said electrodes to thereby produce a predetermined amount of exciting current in the shunt field winding; a second transistor having an input circuit connected in circuit with the output of the generator and having an output circuit connected in circuit with said first transistor for producing an output current which varies said potential distribution between said electrodes of said first transistor; and a transformer connected in circuit with said output circuit of said second transistor and having at least one winding connected in circuit with said input circuit of said second transistor so that at least a portion of said output current of said second transistor is fed back to the input thereof to produce self-oscillation in said second transistor after the voltage output of the generator reaches a preselected level, whereby any change in the voltage output of the electrical generator after said preselected level is reached changes the output current of said second transistor to produce a corresponding change in said potential distribution of the electrodes of said first transistor and in the exciting current flowing through the shunt filed winding, thereby changing the voltage output of the generator to maintain the same at said preselected level.

9. In an apparatus for regulating the voltage output of an electrical generator having a shunt field exciting winding adapted to have exciting current flow therethrough, in combination, a first and a second transistor circuit and transformer means operatively connecting said transistor circuits, said first transistor circuit including a first transistor connected in circuit with the shunt winding of the electrical generator for adjusting the exciting current flowing through the shunt winding in accordance with the impedance of said first transistor; and said second transistor circuit including a second transistor having an input circuit connected in circuit with the output of the generator and having an output circuit connected in circuit with said first transistor for producing an output current which varies the impedance of said first transistor, a resistor connected in said input circuit of said second transistor for producing a voltage drop across said resistor depending upon the output current of said generator, and conductor means connected in circuit with said input circuit of said second transistor for transmitting said voltage drop to said input circuit, said conductor means being in substantially blocked condition as long as said voltage drop is below a preselected value, but becoming conductive when said voltage drop exceeds said value, at least a portion of said output circuit circuit of said second transistor being connected to said input circuit thereof so that at least a portion of said output current is fed back to the input thereof to produce self-oscillation in said second transistor for varying the impedance of said first transistor in a preselected manner in accordance with the magnitude of the voltage output of said electrical generator, said voltage output remaining substantially constant as long as said output current remains below a predetermined valve corresponding to said preselected voltage drop value, said voltage output decreasing rapidly when said output current exceeds said predetermined value.

10. An apparatus as set forth in claim 9, wherein said conductor means is a diode device having a V-I characteristic which possesses a distinct break at a critical voltage-current ratio.

11. An apparatus as set forth in claim 9, wherein said conductor means is a diode device and includes means for applying a negative bias potential thereto.

12. An apparatus as set forth in claim 10, wherein said diode device is a crystal diode adapted to produce the Zener effect.

13. An apparatus according to claim 9, including transformer means having at least one coil connected in series with said conductor means and being connected in circuit with said first transistor for applying to the latter impulses capable of blocking it.

14. An apparatus according to claim 9, wherein said resistor is connected in the output circuit of said generator and said conductor means is connected to said generator output circuit at a point beyond said resistor remote from said generator; said apparatus further including an auxiliary resistor in series connection between said conductor means and one pole of said generator; and a bridge circuit of non-linear characteristic comprising two voltage-divider circuits respectively connected with one end jointly to the other pole of said generator, while the other ends of said voltage dividers are respectively connected to the opposite ends of said auxiliary resistor, said input circuit of said second transistor being connected as one diagonal of said bridge circuit.

15. An apparatus as claimed in claim 3, including a bridge circuit arrangement, said second transistor being connetced in the diagonal of said bridge circuit, said bridge circuit having two input terimnals connected in circuit with the output of said generator.

16. An apparatus as claimed in claim 3, including impedance means connected in circuit with said second transistor and with the voltage output of said generator for controlling the rate at which the impedance of said first transistor is varied.

17. An apparatus as claimed in claim 3, wherein impedance means are connected in circuit with said second transistor and said voltage output of said generator for changing the level of said voltage output in accordance with the magnitude of the current ouput of said generator.

18. An apparatus as claimed in claim 16, wherein said impedance means have a negative temperature coefficient.

19. An apparatus as claimed in claim 17, wherein said impedance means have negative temperature coefiicient.

20. An apparatus as claimed in claim 3, including means for applying to said second transistor a bias potential between its emitter and base electrodes of such a magnitude that said second transistor becomes conductive only when the voltage output of said generator surmounts a predetermined value, the frequency of said selfoscillation depending mainly on the inductivities of said transformer.

21. An apparatus as claimed in claim 3, including a non-linear bridge circuit comprisnig as one bridge arm, in circuit, an auxiliary source of direct current potential, the emitter-collector circuit of said second transistor and a winding of said transformer, and as a second bridge arm, in circuit, resistive voltage divider means and another winding of said transformer, the base electrode of said second transistor being connected to a junction point within said voltage divider means, and the output of said generator being connected as a diagonal of said bridge circuit to the respective junction points of said bridge arms.

22. An apparatus as claimed in claim 3, including a non-linear bridge circuit comprising as one bridge arm, in circuit, rectifier means having a curved current voltage characteristic, the emitter-collector circuit of said second transistor and a winding of said transformer, and as a second bridge arm, in circuit, resistive voltage divider means and another winding of said transformer, the base electrode of said second transistor being connected to a junction point within said voltage divider means, and the output of said generator being connected as a diagonal of said bridge circuit to the respective junction points of said bridge arms.

23. An apparatus as claimed in claim 9, wherein said resistor is connected in the output circuit of said generator, and said conductor means is connected to a junction point in said generator output circuit between said generator and said resistor, said apparatus further including transformer means having one coil connected in series with said conductor means, and having at least one other coil connected with the input circuit of said second transistor for causing the latter to produce selfoscillation when said voltage drop exceeds a predetermined value.

References Cited in the file of this patent UNITED STATES PATENTS 2,740,086 Evans et al Mar. 27, 1956 2,809,301 Short Oct. 8, 1957 2,866,944 Zelina Dec. 30, 1958 2,886,763 Zelina May 12, 1959