DE1090295B - Circuit arrangement for the supply circuit of electric motors, especially small shunt motors - Google Patents

Description

GERMAN

The invention relates to a circuit arrangement for regulating the supply circuit of electric motors, especially small shunt motors, where a voltage regulating, with the power source series-connected resistor element is used.

When operating a shunt motor with constant speed or speed with fluctuating Load and constant field current, the rotor current changes in direct proportion to the load, while the rotor voltage increases with increasing current, by the increasing voltage drop across the To compensate for rotor resistance. Therefore, if a constant speed is to be maintained, then the must Runner can be connected to a power source that allows either negative regulation or has a series resistance which is negative and approximately equal to the equivalent series resistance of the Rotor is so that the effective total resistance of the rotor circuit is practically zero and the induced Voltage or counter-electromotive force in the rotor winding is kept constant.

The invention is based on the object of creating a circuit arrangement which makes it possible to small shunt motors with fluctuating load with very simple means with constant Speed to operate.

The invention is based on a circuit arrangement with a voltage-regulating current source series-connected negative resistance element and solves the problem in that the A protective device is assigned to the WMstand element, which is activated when a value falls below a certain value lying, occurring at the motor terminals impedance the size of the resistor element lying voltage is limited.

In a preferred circuit arrangement according to the invention, the negative resistance element is a Transistor to which an auxiliary circuit is assigned, which reduces the impedance of the transistor in accordance with the Changes in the current consumption of the electric motor controls, the protection device in the auxiliary circuit lies.

In small regulated power systems, the use of transistors for regulation results and control have obvious advantages, especially with regard to the space requirements or the compact ones Design, efficiency and simplicity of the circuit, however, occur with the usual Circuits of this type damage the transistors, especially when starting and when overloaded due to overvoltages on the transistor or excessive power dissipation or - inclusion in the transistor or for both reasons.

Circuit arrangement

for .the supply circuit

of electric motors, in particular

small shunt motors

Applicant:

Minnesota Mining

and Manufacturing Company,

St. Paul, Minn. (V. St. A.)

Representative: Dr.-Ing. H. Ruschke, Berlin-Friedenau,

and Dipl.-Ing. K. Grentzenberg,
Munich 27, Pienzenauer Str. 2, patent attorneys

Claimed priority:
V. St., v. America June 17, 1958

Chester Conrad Shaw, Burbank (V. St. A.),
has been named as the inventor

One embodiment of the invention provides a control circuit with transistors with effective protection of the transistor against overvoltages and excessive power dissipation.

In short, in this embodiment the rotor of the motor is in series with a power source and a current regulator circuit which has a negative resistance of such a value that the total or actual series resistance of the circuit is practically zero. Hence the power source that is out a voltage source and the control loop, an ideal constant voltage source in series with a negative resistance equivalent. The current control loop has two transistors that look like this are connected so that the base of one transistor is connected to the collector of the other. The first of these two transistors has its emitter and collector in series with the armature of the Motor and a power source. Also in this circle lies between the collector of the first Transistor and a power source a small series resistor, so that there is a voltage drop proportional to the rotor current. This resistance also forms part of the base-emitter circuit of the second transistor, whereby the currents

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by the second transistor and in particular its Collector current change directly with the rotor current. Because the collector of the second transistor is on the base of the first transistor is connected, the conductivity of the first transistor changes also directly with the rotor current, whereby the voltage on the first transistor is reversed with changes with the current and the resistance characteristic is negative.

The Zener voltage of the collector-base connection of the first transistor protects the first Transistor, but additional protection may be required and a zener diode between the Base and collector of the first transistor are connected.

This is evident from the following explanatory description and the drawings, among other things. This shows

Fig. 1 is a schematic circuit diagram of an embodiment of the invention,

2 shows a schematic circuit diagram of a further embodiment and

Figure 3 is a schematic circuit diagram of yet another embodiment of the invention.

As is apparent from Fig. 1, a common shunt motor has a rotor 1 and one separately excited field winding 2. There is a constant excitation of the field winding 2 by any suitable Power source 3. Since the field is constant, the induced voltage or counter-electromototic Force in rotor 1 proportional to the speed of the motor shaft. Therefore the induced voltage remains or counter electromotive force constant as long as the speed remains constant, and vice versa. However, the total voltage across the rotor does not generally remain constant because of this voltage in addition to the induced voltage or back EMF, the voltage drop across the equivalent resistance of the rotor, which is proportional to the rotor current. Because the torque delivered by the engine is proportional to the rotor current, the rotor current must be directly related to the load on the motor shaft change. Consequently, if there is an increased load on the motor shaft, both the rotor current as well as the voltage on the rotor increase to a constant back EMF and motor shaft speed maintain.

The motor rotor 1 is in a circuit in series with a switch 4, a voltage source 5 and a control loop with a negative resistance characteristic. The control loop has two Surface transistors 6 and 7, which are connected as shown in the circuit diagram. Every transistor has the usual emitter, the base and the collector, as indicated by the usual symbols in the Drawings are shown. For example, the transistor can be a 2 N 174 PNP power transistor and the transistor? a 2N95 ~ NPN germanium transistor be. It should be noted that the collector of transistor 7 is directly connected to the base of transistor 6 and that the base of the transistor 7 is connected to the collector of the transistor 6 through a resistor 8 of about 390 ohms is connected.

The emitter and the collector of the transistor 6 are connected in series with the rotor 1 and the voltage source 5. As can be seen from the drawing, the emitter of the transistor 6 is connected directly to the rotor 1, while the collector of the transistor 6 is connected to the current source 5 via a small series resistor 9, which is approximately 1 ohm. Since the resistor 9 is part of the circuit with the motor rotor, there is a voltage across the resistor 9 which is proportional to the rotor current.

The variable resistor 10 is, as can be seen from the drawing, between the negative terminal of the current source 5 and the emitter of the transistor 7. The base-emitter circuit of the transistor 7 contains the resistors 8, 9 and 10 in series, whereby the voltage drop The resistor 9 produces an input signal to the transistor 7 and regulates the currents which flow as a result, so that these currents and in particular the collector current of the transistor 7 change directly with the rotor current. Since the collector of transistor 7 is connected directly to the base of transistor 6, the base current of transistor 6 increases with each increase in the collector current of transistor 7, and consequently the conductivity of transistor 6 changes directly with the rotor current. The relationship between the change in conductivity and the change in the rotor current can be adjusted by adjusting the current parameters, and in particular the resistor 10, so that either a positive or negative resistance of adjustable magnitude is obtained. In general, increasing resistor 10 will decrease the ratio, making the circuit resistance more positive or less negative, and vice versa. Therefore, the value of resistor 10 can vary widely depending on the desired operating conditions and the values of the other circuit components.

The speed of the motor can also be controlled in that a control signal dem Emitter-base current of the transistor 6 is supplied. As can be seen from the drawing, there is a resistor 11 of about 470 ohms between your emitter and the base of transistor 6 and a resistor 12 of several thousand ohms between the base of the Transistor 6 and the positive side of the rotor 1. The speed of the motor can be adjusted by setting various switching elements can be set, in particular the resistor 12 or the voltage the power source 5 or both. In a typical application of the invention using of a shunt motor, the voltage of the power source 5 fluctuates to adjust the motor speed between 50 and 2SOVoIt.

The resistor 10 is set so that the negative resistance between the emitter and the collector of the transistor 6 approximately compensates for the positive resistances of rotor 1, current source 5 and resistor 9, so that the effective resistance of the series circuit is approximately zero. With this setting of the circuit, the motor speed remains practically constant over a tenfold range, for example from 50 to 500 mA, despite changes in the load on the motor shaft and similar fluctuations in the rotor current. Because of its positive resistance, the voltage supplied by the current source 5 falls and the voltage across the rotor 1 increases when the rotor current increases. Both voltage changes are compensated for by a falling voltage on transistor 6, for example from about 30 volts at 50 mA to about V2 volts at 500 mA. This decrease in the voltage drop across the transistor 6 with increasing current results in the required negative resistance for the circuit.

For the invention, the way is characteristic in which the transistor 6 against "overvoltages and

Protected against excessive power dissipation or consumption during starting and overload will. This protection is partly due to the described automatic operation, through which the The conductivity of the transistor 6 is automatically increased and the voltage drop across the transistor is reduced becomes when the transistor current increases. Therefore, at relatively high voltages across the transistor the current is low and, with relatively high currents, the voltage is low, so that the energy dissipation not equal to the product of voltage and current in normal operation is never excessive. However Under certain circumstances, such as those that occur when starting, additional protection is necessary. this is described below.

It is assumed that the engine is at a standstill and the switch 4 has just been closed to start the engine At this moment there is no back EMF in the rotor of the motor, and one A large part of the supply voltage would occur at the transistor 6 and with great probability lead to severe damage to the transistor, if no protection by the circuit described in the Way would exist. For this purpose, the advantage of a transistor property or property is used exploited: the Zener voltage of the collector-base path. For example, suppose that the transistor? a 2N95 germanium transistor is, as already mentioned. With these transistors, the Zener voltage lies in the base-collector path between 30 and 50VoIt, and every time the collector is positive with respect to the base by an amount greater than the Zener voltage, the base-collector path is so highly conductive that the applied voltage practically corresponds to the Zener voltage is limited. Since the collector of transistor 7 is connected to the base of transistor 6 is, an increasing collector current of the transistor 7 also generates an increasing base current across it Transistor 6, what the immediate increase in conductivity of transistor 6, and in this way the voltage across transistor 6 lowered. Due to this effect, the maximum voltage on the transistor 6 is approximately the Zener voltage of the Base-collector connection of the transistor 7 is limited and thus excess and harmful voltages prevented at transistor 6.

On the other hand, transistor 7 is protected in that transistor 6 becomes more conductive as soon as considerable current flows to the collector of transistor 7 So , after which most of the rotor current flows through transistor 6 and not through transistor 7. Therefore, the current flowing through the transistor 7 is always so small that there is little or no possibility of conditions occurring which could lead to the transistor 7 being damaged.

In addition to the parts already described, a capacitor 13 can be parallel to the resistor 8 and a capacitor 14 in parallel with the resistor ΙΟ, as shown. Both capacitors can have a value of around 25 microfarads to have. The purpose of the two capacitors is to make the amplification transistor 7 respond to improve high frequency or transmission properties and thereby regulate the circuit to improve with respect to voltage fluctuations and to change the rotor current quickly.

There are typical germanium junction transistors, such as the type 2 N 95, base-collector lines with Zen er voltages have, which are often only 30VoIt, the circuit shown in Fig. 1 is on a control area limited by about 30 volts of the voltage on transistor 6. For some purposes this is enough Completely. For other purposes, a larger control range, for example 50VoIt, is desirable. In the latter The circuit shown in FIG. 2 can be used more advantageously.

As can be seen from FIG. 2, the same parts as in FIG. 1 are provided with the same reference numerals, and parts that are similar but not identical are provided with the same reference numerals with the addition of an index (') to denote those in the circuit 2 differentiate parts used. By and large, the circuit of FIG. 2 operates in a manner similar to that shown in FIG. 1 and as previously described, with the exceptions discussed below. In the circuit according to FIG. 2, the transistor T is a silicon NPN junction transistor. In the case of these transistors, the Zener voltage of the base-collector connection is significantly above 50VoIt, and therefore the transistor 7 ′ does not limit the voltage range which can be formed across the power transistor 6.

However, other means must now be used to protect the transistor 6 against overvoltages during starting and the like can be found. In this version, this is achieved by a 50-volt Zener diode 15, which is provided between the base and collector of the transistor 6 as shown. the Diode 15 becomes: highly conductive when the base of the transistor 6 is about 50 volts positive and thereby limits the maximum voltage that is passed through the transistor 6 can be fed. Therefore, in the circuit of Fig. 2, the Zener diode 15 is practical the same function as the characteristic of the Zener voltage of the connection of the collector and base from transistor 7 in the circuit of Fig. 1, but with the advantage of the circuit of Fig. 2, a higher and more precisely fixed Zener voltage.

It will be apparent that the use of different transistors in the circuits of FIG and 2 may make it desirable to make certain adjustments to other circuit values. For example, in the circuit according to FIG. 2, it may be desirable to set the value of the ballast resistor 9 ' something to increase, for example to 2 to 100hm.

As can be seen from FIG. 3, it represents a circuit which is essentially the same as the circuit of FIG with the differences that are explained below. In Fig. 3 are the same parts as in Fig. 2 with the same reference numerals, while similar, but not the same parts with the same Reference numerals with the addition of a double index (") are designated in order to distinguish the parts of FIG.

In this third embodiment, the PNP transistor 6 of FIG. 2 has been replaced by an NPN transistor 6 "and the NPN transistor T by a PNP transistor 7". In accordance with this change, the polarity of the current source 5 at position 5 "has been reversed, while the polarity of the Zener diode 15 at 15" has been reversed. It is evident that this change is a mere reversal of all values in the entire circuit and has no effect on the operation of the circuit other than reversing the direction of current flow and reversing the polarity of the voltage.

Another difference in the circuit according to FIG. 3 is the insertion of two silicon diodes 16

1 09Q

and 17 in series with resistor 10, just like it is shown. Both Siikon diodes form a non-linear impedance, which is proportionate to the current opposes high resistance until the voltage drop reaches about 0.7 volts forward is whereupon the diodes form a low impedance. The effect of these diodes is that they have the Keep transistor 7 'in a highly non-conductive state until the voltage drop across resistor 9 " exceeds about 1.5 volts, and then the inactivity of transistor 7 "in the previously described Way allows. The value of the resistor 9 "is chosen so that, for example, at about 1.5 ohms The voltage drop across the resistor 9 "is usually less than the 1.5 volts under normal operating conditions of the shunt motor is. Therefore, under normal engine operating conditions, the The circuit shown in Fig. 2 essentially as if the transistor 7 "were not present and the Rotor voltage is regulated by transistor 6 ". However, during starting and others exceptional circumstances when the transistor 6 "needs to be protected, the voltage across the Resistor 9 "greater than 1.5 volts, and diodes 16 and 17 will have small impedances during the Transistor 7 "protects the transistor 6" in the manner described.

Claims (9)

Claims: 30 1. Circuit arrangement for the supply circuit of electric motors, especially small ones Shunt motors, with a voltage regulating, connected in series with the power source negative resistance element, characterized in that the resistance element has a protective device is assigned, which is below a certain value, at the motor terminals occurring impedance the size of the voltage applied to the resistance element limited. 2. Circuit arrangement according to claim 1, characterized in that the negative resistance element is a transistor to which an auxiliary circuit is assigned, which reduces the impedance of the The transistor controls in accordance with the change in the current consumption of the electric motor, and that the protection device is in the auxiliary circuit. 3. Circuit arrangement according to claim 2, characterized in that the transistor via the The emitter and the collector are connected in series to the power source and the auxiliary circuit is connected the base of the transistor is connected. 4. Circuit arrangement according to claim 2 or 3, characterized by one with the power source and the transistor in series resistor, which is switched on in the circuit, that it is a measure of the strength of the Stn> absorbed by the motor for the auxiliary circuit mes there. 5. Circuit arrangement according to claim 2, 3 or 4, characterized in that the auxiliary skreis has another transistor, one of which is an NPN and the other a PNP transistor is and the base and collector of the second transistor to the collector and the Base of the first transistor and the emitter of the second transistor connected to the current source are. 6. Switching arrangement according to claim 1, characterized in that the negative resistance element comprises a transistor whose emitter is connected to one of said terminals and whose collector is connected to the voltage source, that at least a second transistor forms part of the device for protecting the negative resistance element and a transistor one is NPN and the other is a PNP transistor and the base and collector of the second transistor to the collector or the base of the first transistor and the emitter the junction of the power source and the resistor are connected, whereby the Voltage across the resistor is the current flowing through the second transistor and therefore the Controls voltage on the first transistor. 7. Switching arrangement according to claim 6, characterized in that the collector of the second Transistor directly to the base of the first transistor and the base of the second transistor the collector of the first transistor is connected through a resistor and that into the Emitter line of the second transistor, a series resistor is switched on. 8. Switching arrangement according to claim 6 or 7, characterized in that the device for protecting the negative resistance element (first transistor) additionally has a diode which is between the base and the collector of the first transistor. 9. Switching arrangement according to claim 6, 7 or 8, characterized in that it also has a contains non-linear impedance which is in the emitter line of the second transistor. 1 sheet of drawings © 009 610/292 9.60