Testing device for generator output voltage regulators
LIST OF PRIOR ART REFERENCES (37 CFR 1.56 (a)) 
     The following reference is cited to show the state of the art: Japanese Utility Model Application Laid-Open No. 58211/&#39;75 
     BACKGROUND OF THE INVENTION 
     This invention relates to a testing device for semiconductor voltage regulators, and more particularly to a testing device suitable for testing such a semiconductor voltage regulator as is incorporated in a generator assembly having an AC generator. 
     Conventionally, it was the practice to conduct a test for checking failures of a semiconductor voltage regulator incorporated in a generator assembly including an AC generator by rotating the AC generator or disconnecting the regulator from the generator assembly. This conventional testing method, however, it disadvantageous in that a device for rotating the AC generator is needed or it takes a long time to conduct the test. Therefore, there is a demand for a testing device with which the test can easily be effected without taking the incorporated regulator out of the generator assembly. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide a testing device for a semiconductor voltage regulator incorporated in a generator assembly having an AC generator, with which a test for checking failures of the semiconductor voltage regulator can easily be conducted without taking the regulator out of the generator assembly and without rotating the AC generator. 
     To accomplish this and other objects a DC power source is coupled to means for applying a variable voltage to the input of the regulator, and a resistor is connected between the DC power source and the field coil of the AC generator to conduct a voltage from the DC power source to the field coil with a predetermined voltage drop. The input voltage to the voltage regulator is gradually increased, so that the presence or absence of failures of the regulator may be judged from a magnitude of the input voltage and a change in voltage at a junction between the field coil and the resistor. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a circuit diagram showing an embodiment of the invention. 
     FIG. 2 is a graphic representation useful to explain judging failures from the change in voltage in the embodiment of FIG. 1. 
     FIG. 3 is a circuit diagram of an example of variable voltage generator circuit used in the embodiment of FIG. 1. 
     FIG. 4 is a circuit diagram showing another embodiment of the invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to FIG. 1 showing an embodiment of the invention, a generator assembly 1 comprises a semiconductor voltage regulator 11 incorporated in the assembly, an AC generator with an armature 12 and a field coil 13, three-phase rectifier diodes D 1  to D 6 , and auxiliary rectifier diodes D 7  to D 9 . 
     The generator assembly, which is carried on an automobile, for example, is adapted to generate a DC voltage to charge a battery 3 carried on the vehicle. When a key switch SW 1  is thrown on, a base current is fed from the battery 3 through a terminal L and a resistor R 1  to a transistor TR 1 , thereby turning on the transistor TR 1  and allowing a current to flow through the field coil 13. At the same time, a charging pilot lamp L 1  is turned on. As the number of revolutions of the armature 12 increases in synchronism with the rotation of the vehicle engine, an AC voltage is included in the armature coil 12. This AC voltage is, on the one hand, rectified through the diodes D 1  to D 6  in a full-wave rectification fashion into a DC voltage which in turn charges the battery 3 through a terminal A, and, on the other hand, rectified through the diodes D 7  to D 9  so as to increase the current flowing through the field coil 13. When the voltage of the battery 3 increases until it reaches the voltage at the terminal A, the charging pilot lamp L 1   is turned off. 
     At a voltage detecting terminal S, which is an input terminal of the voltage regulator 11, the voltage of the battery 3 is detected. When voltage of the battery 13 i.e., the output voltage of the generator assembly 1 exceeds a predetermined value, 00 and hence a division of the voltage of the battery 3 produced by a resistor divider consisting of resistors R 2  and R 3  exceeds a Zener voltage of a Zener diode ZD 1 , the Zener diode ZD 1  and a transistor TR 2  are turned on and the transistor TR 1  is turned off. This decreases the current of field coil 13 to reduce the output voltage of the generator assembly. In this manner, controlling of output voltage is accomplished. A diode D 10  is a fly-wheel diode and a terminal E is grounded. 
     As described above, the generator assembly incorporating the semiconductor voltage regulator is provided with output terminals A and E, the initial exciting and charging pilot lamp terminal L and the voltage regulator input terminal S standing for the voltage detecting terminal. Terminals other than the above ones are normally dispensed with. The invention utilizes the terminals L, S and E to which a testing device is connected, so that a test for checking failures of the regulator 11 can easily be made without the necessity of rotating the armature 12. 
     A testing device 2 embodying the invention comprises a DC power source 4, a circuit 21 connected to the DC power source 4 to generate a variable voltage, a voltage detector 22 for indicating the output voltage of the variable voltage generator circuit 21, a resistor R connected between the field coil 13 and the DC power source 4 through the terminal L of the generator assembly 1 and a terminal L&#39; of the testing device 2, and a voltage change detector circuit 23 for detecting a change in voltage at the junction between the field coil 13 and the resistor R, that is, at the terminal L. As the DC power source 4, the battery 3 may be used with a suitable booster. A terminal S&#39; is connected to the terminal S of generator assembly 1 while a terminal E&#39; is grounded. 
     When testing the regulator 11, a switch SW 2  is thrown on and a voltage adjuster 30 (FIG. 3) of the variable voltage generator circuit 21 is then adjusted so that the voltage applied to input terminal S of the regulator 11 is increased gradually. If the regulator 11 is normal, the transistor TR 1  is turned on because of the base current flowing through the resistor R, terminal L and resistor R 1  before the output voltage V O  of the variable voltage generator circuit 21 reaches the aforementioned predetermined value i.e., an operation voltage V p  of the regulator (about 13 to 16 volts). Accordingly, a voltage V L  at terminal L can be expressed as, ##EQU1## where R represents the resistance of the resistor R, r the DC resistance of the field coil 13, and V i  the voltage of the DC power source 4. Subsequently, in the case of the regulator 11 being normal, when the output voltage V O  reaches the operation voltage V p  of the regulator 11, the transistor TR 1  is turned off and the voltage V L  at the terminal L is increased to substantially the same level as the voltage V i  of the DC power supply 4 (the resistance of the resistor R 1  is far larger than that of the resistor R). The increase in voltage V L  causes a Zener diode ZD 2  of the voltage change detector circuit 23 and a transistor TR 3  to turn on. This causes a lamp L 2  connected through the transistor TR 3  between the output terminals of the variable voltage generator circuit 21 to turn on, thereby indicating the normal state of the regulator 11. 
     FIG. 2 shows the change in voltage V L  when the regulator 11 is normal. The operation voltage of the regulator 11 is set to 13 to 16 volts, for example, with a tolerance of about ±0.3 volts in consideration of the irregularity of the Zener diode ZD 1  and the other circuit elements. As one mode of failure of the regulator 11, it is assumed that the transistor TR 1  is accidentally turned off. In this case, even with a voltage V O  of zero, the voltage V L  is in the high level substantially equal to the voltage V i . Therefore, as soon as the voltage V O  increases up to a value sufficient to turn on the lamp L 2 , this lamp L 2  lights. In another mode of failure, such that the transistor TR 1  is accidentally turned off before the voltage V O  reaches the operation voltage V p , the lamp L 2  is caused to turn on at a level of voltage V O  lower than the range of the set operation voltage. In another mode of failure in which the transistor TR 1  remains turned on, the lamp L 2  will not turn on even when the voltage V O  is increased to its maximum value. In still another mode of failure in which the transistor TR 1  is turned off when the voltage V O  exceeds the operation voltage V p , the lamp L 2  will turn on at a level of voltage V O  higher than the range of the set operation voltage. 
     The voltage detector 22 serves to indicate a voltage at which the regulator 11 operates and a D.C. voltage meter may be used as the detector. The voltage change detector circuit 23 is described by way of example as being comprised of the Zener diode, transistor and lamp, but instead it may be formed by a comparator and a meter in combination, for example. Also, in place of the lamp, a buzzer may be used. 
     Testing accuracy depends on a ratio of the resistance R and the DC resistance r of the field coil 13. Assuming now that the maximum leakage current of transistor TR 1  is 1 mA and the voltage V i  of the DC power source 4 is 13 volts, the resistance value between the terminal L and ground is 13K ohms with the transistor TR 1  turned off. This value is considered for determining the upper limit of the resistance R. The testing device of this embodiment detects the change in voltage V L  at the terminal L by means of the detector circuit 23. Accordingly, it suffices that a change in voltage is obtained at the terminal L such as to either cause or not cause the avalanche breakdown of the Zener diode ZD 2 . About 1 volt may be sufficient for such a change in voltage. This means that a necessary voltage drop across the resistor R is about 1 volt. The field coil 13 usually has a resistance, as its internal resistance, of several ohms, which is about 4 ohms, for example, so that the resistance R necessary for causing a voltage drop of 1 volt thereacross is: ##EQU2## However, if this resistance is too small, loss in the resistor R becomes unnecessarily large. Practically, power consumption in the resistor R is preferably less than 2 watts. In consideration of this condition and the aforementioned upper limit of resistance, the resistance value of the resistor R is preferably 150 Ω to 300 Ω. 
     The variable voltage generator circuit 21, as shown in FIG. 3, is adapted to produce a DC voltage of up to about 16 volts from the DC power source 4 (6 to 12 volts) and constituted by a so-called DC-DC converter. The voltage adjuster 30 for producing the variable voltage is simply shown as a variable resistor, but, instead may be constituted by a semiconductor circuit which changes the output voltage. 
     A multivibrator comprised of transistors TR 4  and TR 5 , resistors 33 and 34, and a transformer 35 drives divided coils of the primary winding of the transformer 35 alternately so as to generate an AC voltage across the secondary winding of transformer 35 in accordance with the winding ratio. Capacitors 31 and 32 are effective to improve and stabilize oscillating waveforms, and the resistors 33 and 34 determine optimum currents of the transistors TR 4  and TR 5 . The AC voltage developing across the secondary winding is rectified into a DC voltage through a rectifier circuit of diodes D 11  to D 14 . The DC voltage is gradually increased and delivered, through the variable resistor 30, and applied to the voltage detector 22, the voltage change detector circuit 23, and the input terminal S of the regulator 11. 
     Another embodiment of the invention will be described with reference to FIG. 4, in which the same members as those in FIG. 1 are designated by the same reference numerals or symbols. In this embodiment, the battery 3 carried on a vehicle is used as the DC power source for the testing device 2. A DC-DC converter 40 is connected to the battery 3 through the switch SW 2 . The output voltage of the DC-DC converter 40 is set to be 1.5 to 2 times the operation voltage (set voltage) of the regulator 11. To the output terminal of the DC-DC converter 40, a transistor TR 7  is connected through resistors R 5  and R 7 , a capacitor 42 and a voltage detector 43 in the form of a voltmeter are connected through the resistor R 5  and a diode D 15 . The output terminal of the DC-DC converter is also connected to the input terminal S of the regulator 11 through the resistor R 5  and the diode D 15 . The resistor R, similarly to the embodiment of FIG. 1, is connected between the DC power source 3 and the terminal L through the switch SW 2 . Between the junction of the resistor R and the field coil 13 i.e., the terminal L and the base of transistor TR 7 , a Zener diode ZD 3  is connected through a resistor R 6 . 
     When the switch SW 2  is thrown on for checking failures of the regulator 11, the voltage V L  at the terminal L assumes the value of r/(R+r)×V i , as described above. If this voltage value is set lower than the Zener voltage of the Zener diode ZD 3  by determining the resistance value of the resistor R in the same manner as above, the transistor TR 7  is rendered off. As a result, the capacitor 42 is charged with the output voltage of the DC-DC converter 40 and the voltage at the terminal S&#39; is gradually increased. When the voltage at the terminal S reaches the operation voltage of the regulator 11, the voltage V L  is increased and becomes approximately equal to the voltage V i  of the battery 3 as in the first embodiment so that the Zener diode ZD 3  and transistor TR 7  are both turned on, thereby to cease charging of the capacitor 42. Thus, charge stored in the capacitor 42 is discharged through resistors R 2  and R 3  and the voltmeter 43. When the voltage at the terminal S falls below the operation voltage of the regulator, the above operation is repeated. Accordingly, the voltmeter 43 indicates the operation voltage of the regulator 11. 
     In one mode of failure of the regulator 11 in which the transistor TR 1  remains turned on, the transistor TR 7  will remain turned off with the result that the voltmeter 43 indicates a voltage which is approximately equal to the output voltage of the DC-DC converter 40. In another mode of failure in which the transistor TR 1  remains turned off, the transistor TR 7  will remain turned on and hence the voltmeter 43 indicates a voltage which is a division of the DC-DC converter output voltage produced by a resistor divider consisting of the resistors R 5  and R 7 . As will be seen from the above, in the other mode of the failure, the voltmeter 43 indicates a voltage other than the operation voltage of the regulator 11.