Abstract:
A voltage regulating system is used to regulate the output voltage of an alternating current generator which serves to supply electrical loads on a motor vehicle including a battery. The field winding of the generator is supplied with current through the voltage regulating system operating in a switching mode. 
     The voltage regulating system includes a voltage sensing circuit connected with the battery, a control transistor connected with the voltage sensing circuit for effecting ON-OFF of a field current, and a protection circuit having a PNP transistor and a zener diode connected between an output terminal of the generator and the voltage sensing circuit which becomes operable to effect ON-OFF of the field current when the voltage sensing circuit is disconnected from the battery, whereby the output voltage of the generator is regulated at a lower level than that regulated by the voltage sensing circuit during such a disconnection.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an improvement of a voltage regulating system for controlling an output voltage of a direct current power supply that is utilized not only to supply electrical load on an automotive vehicle but to charge a storage battery installed in the automotive vehicle. 
     2. Description of Prior Art 
     A conventional voltage regulating system, for example, exemplified in the U.S. Pat. No. 3,469,168, comprises a first voltage sensing circuit connected to a storage battery for detecting a voltage thereof applied thereto by a direct current power source, a second voltage sensing circuit connected to said power source at another positive terminal, and a field control circuit connected to said first and second voltage sensing circuit and a field winding, whereby the battery voltage is controlled at a first preset level by the first voltage sensing circuit, and in the event that the first voltage sensing circuit disconnected from the battery, the battery voltage is controlled at a second preset level by the second voltage sensing circuit. 
     However it has a disadvantage that the second preset level is higher than the first one, whereby the battery may be overcharged or the life-time thereof may be shortened due to the overcharge. 
     SUMMARY OF THE INVENTION 
     It is, therefore, a primary object of the present invention to provide a voltage regulting system enabling control of the output voltage of the generator in the event that the battery is disconnected from the generator or the like. 
     It is another object of the present invention to provide a voltage regulating system enabling control of the output voltage of the generator at a lower level than that controlled at a normal condition when the malfunction occurs. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic circuit diagram of a voltage regulating system according to the present invention, 
     FIG. 2 is a partial circuit diagram of FIG. 1 showing circuit constant, 
     FIG. 3 is a graphical representation showing a relationship between a regulated voltage and a current during a normal operation, 
     FIG. 4 is a partial circuit diagram of FIG. 1 showing circuit constant for explanation of the operation thereof when a first malfunction occurs, 
     FIG. 5 is a graphical representation showing a relationship between a regulated voltage and a current during the first malfunction, 
     FIG. 6 is a partial circuit diagram of FIG. 1 showing circuit constant for explanation of the operation thereof when a second malfunction occurs, 
     FIG. 7 is a graphical representation showing a relationship between a regulated voltage and a current during the second malfunction, 
     FIG. 8 is a graphical representation making FIGS. 3, 5 and 7 in a single figure, and 
     FIGS. 9, 10 and 11 are partial circuit diagrams of modified voltage regulating system which may be utilized in place of certain of components shown in FIG. 1. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1 showing a first embodiment of the present invention, the reference numeral 2 generally designates a direct current power source which takes the form of a diode-rectified alternating current generator which is used to supply battery charging current on a motor vehicle and is used to supply other electrical loads on the motor vehicle when the generator is driven by the engine of the motor vehicle. The power source 2 includes an alternating current generator having a three phase Y-connected output winding 5a which is connected to the A.C. input terminals of a three phase full-wave bridge rectifier 3 which provides at one end a positive terminal 2a. The generator includes a field winding 5b which controls the output voltage of the generator. As current through the field winding 5b is increased the output voltage of the generator increases and when this current is reduced the output voltage of the generator decreases. 
     The power source also includes three auxiliary diodes providing another positive terminal 2b and forming another full wave bridge rectifier 4 in combination with a part of the rectifier 3. 
     The positive terminal 2a is connected with a storage battery 1 through a power supply conductor 23, to which an electical load 14 is connected. The other positive terminal 2b is also connected with the battery through a key switch 13 and a charge display circuit 12 including a display lamp 121 and a resistor 122. 
     A series circuit 11 of a resistor 114, a zener diode 113, and resistors 111 and 112 is connected across the battery 1 through a positive conductor 22 and a negative conductor 24, forming a voltage sensing circuit for sensing a battery voltage applied thereto. The resistors 111 and 112 form a voltage dividing circuit 11a, and a junction point A therebetween is connected to a base of a control transistor 8 whose emitter is connected with the negative conductor 24 and whose collector is connected to a base of a input transistor 72 forming a Darlington amplifier 7 in combination with an output transistor 71. The emitter of the output transistor 71 is connected with the negative conductor 24 and the collector thereof is connected with the auxiliary three diodes through the field winding 5b and also with the positive terminal 2b through a diode 6. The collector of the control transistor 8 is connected with the positive terminal 2b through a resistor 9 and also with a junction point B between the resistor 112 and the zener diode 113 through a protection circuit 10 including a PNP transistor 101, a NPN transistor 102, a resistor 104 and a zener diode 105. 
     The operation of this embodiment will be explained. 
     When the key switch 13 is closed an electric current flows through the charge display circuit 12, the field winding 5b and to the output transistor 71. At this stage, the voltage sensing circuit 11 detects less voltage than needed to make the control transistor 8 conductive, so then the output transistor 71 is in the conduction state, whereby the field winding 5b provides initial excitation for the generator 2. 
     When an engine (not shown) of the automotive vehicle starts to rotate and drives the generator 2, the output voltage thereof rises and is regulated at a desired level. 
     As the output voltage of the generator 2 rises above a predetermined level, the zener diode 113 is broken down to make the control transistor 8 conductive. The base current to the Darlington amplifier 7 thereby flows through the control transistor 8. The output transistor 71 is made non-conductive so that the field current may flow through the diode 6 and the control transistor 8 to the negative conductor 24 with a gradual decrease of the output voltage of the generator 2. 
     When the output voltage of the generator 2 decreases below the predetermined level the zener diode 113, and consequently the control transistor 8 are made non-conductive, thereby to make the output transistor 71 conductive in order to flow the field current through the field winding 5b, whereby the output voltage of the generator 2 rises again. Thus, the above described operation is repeated to control and maintain the battery voltage at a desired level. 
     In the event that the power supply conductor 23 is disconnected from the generator 2, or the voltage sensing circuit 11 is disconnected from the battery 1 due to a line failure of the positive conductor 22, the protection circuit 10 is made conductive and nonconductive in response to the output voltage of the generator 2 at its positive terminal 2b to finally switch off and on the field current, thereby to regulate the output voltage of the generator 2 at another desired level determined by the protection circuit 10. 
     The operation in the events of the malfunction described above will be explained more in detail. 
     Assuming each circuit constant as designated in FIG. 2, a voltage V S  applied across the voltage sensing circuit 11, namely an electric potential at a terminal S is introduced by the following equation (1) when both the protection circuit 10 and the control transistor 8 are nonconductive. 
     
         V.sub.S = I.sub.S (R.sub.1 + R.sub.2 + R.sub.4) + V.sub.Z  (1) 
    
     wherein 
     R 1 , R 2 , R 4  : resistance values of the resistors 111, 112 and 114 
     V Z  : a voltage drop across the zener diode 113 
     I S  : a value of electric current through the circuit 11. 
     A desired regulated voltage V reg  of the generator is the voltage V S  determined when the control transistor 8 is made conductive, that is, when the base potential I S  R 1  of the control transistor 8 attains to a voltage V BE  across the base-emitter thereof. 
     Therefore, the regulated voltage V reg  is given by the following equation (2). ##EQU1## 
     FIG. 3 shows a relationship between I S  and V S , in which the abscissa shows V S  and the ordinate I S . It is noted from FIG. 3 that no current flows through the voltage sensing circuit 11 until V S  exceeds V Z  of voltage drop across the zener diode 113. When V S  exceeds V Z , I S  begins to increase in proportion to V S  with a gradient given by ##EQU2## and when I S  attains the value of V BE  /R 1  the control transistor 8 is made conductive, whereby the output voltage of the generator 2 is regulated at V reg . 
     In this stage, a voltage V G  appearing at a terminal G to be connected to the positive terminal 2b and for making the protection circuit 10 conductive is given by the following equation (3). ##EQU3## 
     In the normal operation, the system of the present invention should operate in response to the voltage V S  applied to the terminal S. For this purpose, it is required that V G  is larger than V reg , that is, V G  &gt;V reg . Then ##EQU4## 
     When the system of the present invention is fabricated into one-chip integrated circuit, it results in V Z1  = V Z , and thereby the equation (4) is rewritten as follows. ##EQU5## 
     This relationship is shown in FIG. 3. 
     And it is further noted from the equation (5) that 
     
         R.sub.1 &gt; R.sub.4                                          (6) 
    
     since V T  ≈ V BE . 
     When the first malfunction, that is, the voltage sensing circuit 11 is disconnected from both the battery 1 and the generator 2 due to the line failure of the positive conductor 22, occurs, the output voltage of the generator 2 is controlled by the voltage V G  supplied to the terminal G. Assuming the circuit constant in this event as designated in FIG. 4, the following equation (7) is introduced when the control transistor 8 is in the nonconduction state. 
     
         I.sub.R = I.sub.G                                          (7) 
    
     a base current I B  of the transistor 101, namely, current flowing through the resistor 112 is a negligibly small quantity in comparison with I R , since ##EQU6## wherein  the amplification factor h FE  is the product of the amplification factor h 1  of the transistor 101 by that h 2  of the transistor 102. 
     Accordingly,, 
     
         I.sub.R &gt;&gt; I.sub.B                                         (8) 
    
     therefore, the voltage V G  appearing at the terminal G is introduced from the above equations (7) and (8) as follows. ##EQU7## 
     A desired regulated voltage V N  of the generator in this event is the voltage V G  determined when the control transistor 8 is made conductive, that is, when the base potential I R .sup.. R 1  of the control transistor 8 reaches to the voltage V BE  across the base-emitter thereof. 
     Therefore, the regulated voltage V N  is given by the following equation (10). ##EQU8## 
     FIG. 5 shows a relationship between I G  and V G , in which the abscissa indicates V G  and the ordinate I G . 
     It is noted that I G  begins to increase with a gradient given by ##EQU9## when V G  exceeds the value of V Z1  + V T . 
     When the second malfunction, that is, the power supply conductor 23 is disconnected from the generator 2, occurs, the voltage sensing circuit 11 senses the battery voltage V O  which is less than that V G  generated at the generator 2. 
     Assuming the circuit constant in this event as designated in FIG. 6, V S  and V G  respectively appearing at the terminals S and G are given by the following equations (11) and (12). ##EQU10## since I.sub. B is a negligibly small quantity. ##EQU11## since I B  is a negligibly small quantity. 
     A desired regulated voltage V N , of the generator in this event is the voltage V G  determined when the control transistor 8 is made conductive, that is, when the base potential I R .sup.. R 1  of the control transistor 8 attains to the voltage V BE  across the base-emitter thereof. 
     Because of ##EQU12## the regulated voltage V N   &#39;  is given by the following equation (14). ##EQU13## since from the above equations (11), (12) and (13), the following equations (15), (16) and (17) are introduced. ##EQU14## 
     Substituting the above equations (15) and (16) for I S  and I G  in the equation (12), the equation (14) is introduced. 
     On the other hand when the transistor 101 is in the nonconduction state, no current flows therethrough, that is I G  = 0. 
     Accordingly, 
     
         V.sub.O = I.sub.S (R.sub.1 + R.sub.2 + R.sub.4) + V.sub.Z  (18) 
    
     fig. 7 shows a relationship between I R  and V G , in which the abscissa indicates V G  and the ordinate I R . 
     A voltage V X  where I R  begins to increase, namely where the transistor 101 becomes conductive, is introduced as follows. 
     From the equation (18), ##EQU15## since I S  = I R  when the transistor 101 is nonconductive. Then substituting the equation (18)&#39; for I R  in the equation (14), ##EQU16## And above the voltage X V , I R  increases with a gradient of ##EQU17## 
     FIG. 8 shows the relationship between I R  and V G  shown in FIGS. 3, 5 and 7 in one drawing. 
     According to this drawing, it is noted that the protection circuit 10 becomes inoperative during the normal condition, that is, the condition of no malfunction, by selecting R 1  to be larger than R 4  as indicated by the equations (4), (5) and (6), whereby the regulated voltage V reg  is determined by V S , and further that the regulated voltage V N  or V N   &#39;  in the malfunction can be selected not only to be larger than the voltage V reg  by arranging R 2  and R 5  but also to be less than the voltage V reg . 
     FIGS. 9, 10 and 11 show modified embodiments according to the present invention, in which the zener diodes 105 and 113 form various connections as shown. That is, diode 105 in FIGS. 9 and 10 is connected in different places than in FIG. 1 and in FIG. 11 diode 113 is differently connected than in FIGS. 1, 9 and 10.