Title of Invention

VOLTAGE REGULATOR HAVING CIRCUIT FOR SUPPESSING INCREASE IN FIELD CURRENT

Abstract

A voltage regulator (1) controls an output voltage of an alternator (2) mounted on an automobile to a predetermined level by controlling a field current of the alternator in an on-and-off fashion. The voltage regulator (1) includes a circuit (14) for suppressing increase in the field current and a circuit (15) for outputting a field current conductive ratio signal to an FR-terminal to be connected to an exterior conductive ratio monitor (41). Operation of the suppressing circuit (14) is allowed or prohibited based on whether or not the exterior conductive monitor (41) is connected to the FR-terminal. Connection or disconnection of the exterior conductive ratio monitor (41) is detected without adversely affecting the function of generating the conductive ratio signal in the voltage regulator (1) .

Full Text

VOLTAGE REGULATOR HAVING CIRCUIT FOR SUPPRESSING INCREASE IN FIELD CURRENT BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage regulator for an alternator mounted on an automotive vehicle. 2. Description of Related Art Various types of alternators are used in recent automotive vehicles. For example, there is an alternator having a device for suppressing a rapid increase in field current when a heavy electric load is connected to the alternator. An alternator in which a regulation voltage is switched between two levels is also known. Further, an alternator having a FR-terminal for transmitting conductive ratio signals of a field current is known. When the alternator having the device for suppressing increase in field current is combined with a C-terminal for switching the regulation voltage between two levels, there is a possibility that a response to the voltage switching is delayed due to operation of the device for suppressing increase in field current. This would be detrimental to voltage regulation of the alternator. To cope with this problem, JP-A-7-46898 proposes an alternator in which operation of the device for suppressing increase in the field current is prohibited when the regulation voltage is switched to the other level. In this manner, the voltage regulator quickly responds to a command for switching the regulation voltage. Further, JP-A-2003-111495 proposes to prohibit operation of the device for suppressing increase in the field current by supplying a voltage higher than a regulation voltage to the FR-terminal. In those conventional alternators, in which operation of the device for suppressing increase in the field current is prohibited when the regulation voltage is switched to the other level, there has been a following problem when the alternator is mounted on an engine having a relatively low torque. That is, a torque required for driving the alternator rapidly increases, when an electric load is connected to the alternator, and accordingly, vibration of the engine increases and the engine may stall in the worst case. In the case where a low idling speed is employed in a small vehicle to improve fuel economy when the field current is low, the following problem is involved in the conventional alternators in which the operation of the device for suppressing increase in the field current is prohibited by supplying a voltage higher than the regulation voltage to the FR-terminal. A low level signal among signals representing a conductive ratio of the field current cannot be transmitted because the voltage supplied to the FR-terminal is too high. Accordingly, the FR-terminal transmits only the high level signal, and a device for monitoring the conductive ratio of the field current erroneously judges that the field current is low, i.e., the engine load is low. Based on such judgment, the idling speed of the engine is set to a low level. However, the engine load, i.e., the amount of the field current is not actually low. Accordingly, the engine vibration increases and the engine may stall in the worst case. SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved voltage regulator having a device for suppressing increase in a field current, operation of which is controlled based on whether an exterior conductive ratio monitor is connected or not. The voltage regulator controls a voltage generated in an alternator mounted on an automobile engine to a predetermined level. The voltage regulator includes a switching element such as a power transistor for controlling a field current of the alternator in an on-and-off fashion. The voltage regulator further includes a circuit for suppressing an increase in the field current and a circuit for outputting a signal representing a conductive ratio of the field current. An output of the conductive ratio signal outputting circuit is supplied to an FR-terminal to which an exterior conductive ratio monitor circuit is connected. Operation of the circuit for suppressing an increase in the field current is controlled to avoid rapid changes in an engine load due to changes in an electric load of the alternator. The voltage regulator further includes a circuit for detecting whether or not the exterior conductive ratio monitor is connected to the FR-terminal. When it is detected that the exterior conductive ratio monitor is connected to the FR-terminal, operation of the circuit for suppressing an increase in the field current is prohibited. When the exterior conductive ratio monitor is not connected, the operation of the suppressing circuit is allowed. Detection of the exterior monitor connection is performed without adversely affecting the function of generating the conductive ratio signal. The operation control of the suppressing circuit may be reversed according to a function of the exterior conductive ratio monitor. The conductive ratio signal outputting circuit may be composed of a switching element that is turned on or off according to the conductive ratio of the field current and an amplifier circuit for amplifying a Lo-level voltage appearing when the switching element is turned on. The amplifier circuit may be constituted by a resistor or a diode or both. Two or more diodes may be connected in series. According to the present invention, the operation of the circuit for suppressing an increase in the field current is controlled based on whether or not the exterior conductive ratio monitor is connected to the FR-terminal of the voltage regulator without adversely affecting the function for generating the conductive ratio signal. The rapid changes in the engine load due to changes in the electrical load of the alternator are avoided. Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiments described below with reference to the following BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing an entire structure of a voltage regulator according to the present invention; FIG. 2 shows an FR-terminal voltage together with other associated voltages when an exterior conductive ratio monitor is connected to the FR-terminal; FIG. 3 shows the FR-terminal voltage together with other associated voltages when the exterior conductive ratio monitor is not connected to the FR-terminal; FIG. 4 shows various waveforms in the voltage regulator when the exterior conductive ratio monitor is not connected to the FR-terminal; FIG. 5 shows various waveforms in the voltage regulator when the exterior conductive ratio monitor is connected to the FR-terminal; FIG, 6 is a circuit diagram showing a modified form 1 of a conductive ratio signal outputting circuit used in the voltage regulator; FIG. 7 is a circuit diagram showing a modified form 2 of the conductive ratio signal outputting circuit; FIG. 8 is a circuit diagram showing a modified form 3 of the conductive ratio signal outputting circuit; FIG. 9 is a circuit diagram showing an entire structure of a voltage regulator as a second embodiment of the present invention; FIG. 10 shows various waveforms in the voltage regulator shown in FIG. 9 when the exterior conductive ratio monitor is connected to the FR-terminal; FIG. 11 is a circuit diagram showing a modified form 1 of a conduction detector circuit used in the voltage regulator shown in FIG. 1; and FIG. 12 is a circuit diagram showing a modified form 2 of the conduction detector circuit used in the voltage regulator shown in FIG. 1. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIGS. 1-5. A voltage regulator 1 connected to an alternator 2 controls an output voltage of the alternator 2 to a predetermined range. The alternator 2 is composed of a stator having an three-phase armature winding 31, a rotor having a field winding 32, and a rectifier 33 that rectifies a three-phase alternating current output from the armature winding 31. The output voltage of the alternator 2 is controlled by adjusting an amount of field current supplied to the field winding 32. An output terminal B (referred to as a B-terminal) of the alternator 2 is connected to a battery 3 and an electric load 4 to supply electric current thereto. Referring to FIG. 1, the voltage regulator 1 will be described in detail. The voltage regulator 1 includes: a field current control element 11 (such as a power transistor) connected in series to the field winding 32 for controlling the field current in an on-and-off fashion; a diode 12 connected in parallel to the field winding 32 for circulating current through the field winding 32 when the field current control element 11 is turned off; a voltage control circuit 13 that controls the output voltage at the B-terminal to a predetermined level by turning on and off the field current control element 11; a control voltage switching circuit 19 for switching the control voltage between two levels based on a signal fed from a control voltage switching commander 42; a suppressing circuit 14 for suppressing a speed of increase in the field current supplied to the field winding 32; a conductive ratio signal outputting circuit 15 for outputting a signal indicating a conductive ratio of the field current control element 11; a connection detector circuit 16 for detecting whether or not an exterior conductive ratio monitor 41 (located outside of the voltage regulator 1) is connected to an FR-terminal that is connected to the connection detector circuit 16; an OR circuit 17 for calculating a logic sum of outputs from the suppressing circuit 14 and the connection detector circuit 16; and an AND circuit 18 for calculating a logic product of outputs from the OR circuit 17 and the voltage control circuit 13, and for driving the field current control element 11. The voltage control circuit 13 is composed of resistors 131, 132, and a voltage comparator 133. The resistors 131, 132 constitute a voltage divider circuit that divides the B-terminal voltage. The divided voltage is fed to a minus terminal of the voltage comparator 133. The voltage comparator 133 compares the divided voltage with a reference voltage Vreg fed to its plus terminal. When the divided voltage becomes lower than the reference voltage Vreg , i.e., when the B-terminal voltage becomes lower than a control voltage, the voltage comparator 133 outputs a high level signal (referred to as a Hi-level signal). On the other hand, when the divided voltage becomes higher than the reference voltage Vreg, i.e., when the B-terminal voltage becomes higher than the control voltage, the voltage comparator 133 outputs a low level signal (referred to as a Lo-level signal). The control voltage switching circuit 19 is composed of resistors 191, 195, a switching element 192, and a voltage comparator 193. A series circuit of the resistor 191 and the switching element 192 is connected in parallel to the resistor 132 in the voltage control circuit 13. A C-terminal connected to the control voltage switching commander 42 is connected to a minus terminal of the voltage comparator 193, and a reference voltage VI is connected to its plus terminal. The switching element 192 is driven by an output of the voltage comparator 193 which is obtained by comparing two inputs fed to the voltage comparator 193. The resistor 195 is set to a value so that the C-terminal voltage becomes higher than the reference voltage VI when the C-terminal is open. Accordingly, when the C-terminal is open or a switching element 421 in the control voltage switching commander 42 is turned off, the voltage comparator 193 outputs a Lo-level signal that turns off the switching element 192. A voltage at a junction of the resistors 131 and 132 becomes a high side. On the other hand, when the C-terminal voltage is lower than the reference voltage VI, the voltage comparator 193 outputs a Hi-level signal that turns on the switching element 192. The voltage at the junction of the resistors 131 and 132 becomes a low side because the resistor 191 is connected in parallel to the resistor 132. The conductive ratio outputting circuit 15 is composed of a resistor 151, a switching element 152 and an amplifier circuit 153. The resistor 151 is connected to an output terminal of the AND circuit 18, and the amplifier circuit 153 is connected in series to the switching element 152. The switching element 152 is turned on when the output from the AND circuit 18 is Hi-level and turned off when the output from the AND circuit 18 is Lo-level. In other words, the conductive ratio signal outputting circuit 15 supplies the conductive ratio signals consisting of Hi- and Lo- levels to the FR-terminal in synchronism with operation of the field current control element 11. The connection detector circuit 16 is composed of a voltage comparator 161. A reference voltage V2 is supplied to a minus terminal of the voltage comparator 161, and the FR-terminal voltage is supplied to its plus terminal. The voltage comparator 161 outputs a Hi-level signal when the FR-terminal voltage is higher than the reference voltage V2, and outputs a Lo-level signal when the FR-terminal voltage is lower than the reference voltage V2. The conductive ratio monitor 41, which is located outside of the voltage regulator 1 and connected to the FR-terminal, is composed of a voltage comparator 412 and a resistor 411. One end of the lesiscor fill is connected to the battery 3 via a key switch 5, and the other end is connected to a minus terminal of the voltage comparator 412. A reference voltage V3 is fed to a plus terminal of the voltage comparator 412. The reference voltage V3 is set to a level between an FR-terminal voltage appearing when the switching element 152 is turned off and an FR-terminal voltage appearing when the switching element 152 is turned on. The voltage comparator 412 detects a signal which is in synchronism with operation of the switching element 152. Referring to FIGS. 2 and 3, the FR-terminal voltage will be explained in relation to the reference voltage V2 and outputs of the connection detector circuit 16 and the AND circuit 18. The FR-terminal voltage appearing when the conductive ratio monitor 41 is connected to the FR-terminal is shown in FIG. 2. The output of the connection detector circuit 16 is at Hi-level as shown with a solid line in (a) , and the output of the AND circuit 18 changes as shown in (b) . The FR-terminal voltage changes as shown in (c) . That is, when the switching element 152 is turned on, the FR-terminal voltage becomes VFR-L2 that is equal to a sum of voltage drops both in the amplifier circuit 153 and in the switching element 152. The voltage drops are caused by current supplied through the resistor 411. If the amplifier circuit 153 is not used, the FR-terminal voltage becomes VFR-L1. When the switching element 152 is turned off, the FR-terminal voltage becomes VFR-H that is equal to the battery voltage imposed via the resistor 411. On the other hand, when the FR-terminal is not connected L-O uiie cunuuctive ratio monitor 41, the FR-terminal voltage is zero volt as shown in FIG. 3(c) . The output of the connection detector circuit 16 is at Lo-level as shown with a solid line in (a) , and the output of the AND circuit 18 changes as shown in (b) . The reference voltage V2 is set to a level that is higher than zero volt and lower than VFR-L2. As understood from the foregoing explanation, the output of the connection detector circuit 16 becomes Hi-level when the conductive ratio monitor 41 is connected to the FR-terminal, and thereby the Hi-level signal masks the output signal from the suppressing circuit 14 fed to the OR circuit 17. Accordingly, operation of the suppressing circuit 14 is prohibited. On the other hand, when the conductive monitor 41 is not connected to the FR-terminal, the output of the connection detector circuit becomes Lo-level, and thereby operation of the suppressing circuit is allowed. Now, operation of the suppressing circuit 14 will be explained with reference to FIG. 4 and 5. FIG. 4 shows various waveforms in the voltage regulator 1 when the conductive ratio monitor 41 is not connected to the FR-terminal and the operation of the suppressing circuit 14 is allowed. FIG. 5 shows those waveforms when the conductive ratio monitor 41 is connected to the FR-terminal and the operation of the suppressing circuit 14 is prohibited. In FIG. 4, the output voltage of the alternator 2 is stably controlled within a predetermined range between a lower limit VL and a upper limit VH up to time tl, as shown in (a) . An average conductive ratio at an F-terminal (an average conductive ratio of the field winding 32) is about 60%, for example. In this situation, the suppressing circuit 14 outputs a signal having a duty ratio of 70% which is higher than the average conductive ratio at the F-terminal as shown in (b) . When a high electric load is connected to the output terminal (B-terminal) at time tl, the output voltage sharply drops up to a level below the lower limit VL, as shown in (a) . Accordingly, the output of the voltage control circuit 13 maintains Hi-level after the output voltage becomes lower than the lower limit VL, as shown in (e). In this situation, the OR circuit 17 outputs the same output signal (shown in (d) ) as the suppressing circuit 14 (shown in (b) ) because the connection detector circuit is maintained at Lo-level. The AND circuit 18 outputs the same signal (shown in (f) ) as the OR circuit 17 because the output of the voltage control circuit 13 is maintained at Hi-level. Accordingly, the field current control element 11 is driven with a duty ratio of 70%, for example, which is higher than its average conductive ratio. Thereafter, the duty ratio for driving the field current control element 11 is gradually increased as shown in (b) . In this manner, the output voltage of the alternator 2 is gradually increased as shown in (a) . This means that the average conductive ratio of the field current control element 11 does not drastically increase when the high electric load is connected to the output terminal B. Instead, it gradually increases, and therefore, it is avoided that the engine load is drastically increased. Thus, vibration of the engine is suppressed and the engine stall is avoided. With reference to FIG. 5, the operation of the suppressing circuit 14 when the conductive ratio monitor 41 is connected to the FR-terminal will be explained. The output of the connection detector circuit 16 is always at Hi-level because the FR-terminal voltage is higher than the reference voltage V2, as shown with a solid line in FIG. 5(c). The operation of the circuit 14 for suppressing increase in the field current 14 (the suppressing circuit 14) is prohibited because the Hi-level signal from the connection detector circuit 16 is supplied to the OR-circuit 17. This means that the operation of the suppressing circuit 14 is prohibited when the exterior conductive ratio monitor 41 is connected. The conductive ratio signal outputting circuit 15 shown in FIG. 1 may be modified in forms exemplified in FIGS. 6, 7 and 8. In a conductive ratio signal outputting circuit 15A shown in FIG. 6, a resistor 153A is used in place of the amplifier circuit 153. By using the resistor 153A in place of the amplifier 153, the amplifier circuit can be made at a low cost. In a conductive ratio signal outputting circuit 15B shown in FIG. 7, the amplifier circuit 153 is replaced with a circuit including at least one diode 153B. The circuit may include two or more diodes 153B connected in series. By using the diode, it is possible to maintain the FR-terminal voltage at a substantially constant level even when current supplied from the conductive ratio monitor 41 varies. In a conductive ratio signal outputting circuit 15C shown in FIG. 8, a circuit including a diode 153B and a resistor 153A connected in series is used in place of the amplifier circuit 153. Two or more diodes 153B may be connected in series- By using the series circuit including the diodes 153B and the resistor 153A, the FR-terminal voltage VFR-L2 (shown in FIG. 2 (c) ) can be raised in a relatively inexpensive manner. Advantages attained in the embodiment described above will be summarized below. The operation of the circuit for suppressing increase in the field current (the suppressing circuit 14) can be allowed or prohibited in response to whether or not the exterior conductive ratio monitor 41 is connected to the FR-terminal without adversely affecting the function of outputting the conductive ratio signals. By using the amplifier circuit 153 in the conductive ratio signal outputting circuit 15, a difference between the reference voltage V2 and the Lo-level FR-terminal voltage VFR-L2 can be made large, thereby avoiding erroneous judgments in the connection detection circuit 16. The amplifier circuit 153 may be constituted by a resistor 153A, a diode 153B or a series circuit of the resistor 153A and the diode 153B. More than two diodes may be connected in series. By using the resistor, the conductive ratio signal outputting circuit 15 can be made at a low cost. By using the diode, the FR-terminal voltage VFR-L2 at the Lo-level can be stabilized. A second embodiment of the present invention will be described with reference to FIGS. 9 and 10. A voltage regulator 1A as the second embodiment of the present invention is shown in FIG. 9, and various waveforms in the voltage regulator 1A when the exterior conductive ratio monitor 41 is connected to the FR-terminal are shown in FIG. 10. In this second embodiment, the followings are modified from the first embodiment: a holding circuit 20 and a reset circuit 21 are additionally used; a reference voltage V2' in the connection detector circuit 16 is set to a level between VFR-H (FR-terminal voltage at Hi-level) and VFR-L (FR-terminal voltage at Lo-level) ; and a resistor 153A is used in place of the amplifier circuit 153 in the conductive ratio signal outputting circuit 15A. Other structures are the same as those in the first embodiment described above. As shown in FIG. 10, the output of the connection detector circuit 16 changes between the Hi-level (H) and the Lo-level (L) as shown in (a) in response to the output of the AND circuit 18 shown in (b) . That is, when the switching element 152 in the conductive ratio signal outputting circuit 15A is turned on, the FR-terminal voltage becomes VFR-L (Lo-level), and when the switching element 152 is turned off, the FR-terminal voltage becomes VFR-H (Hi-level) , as shown in (c) . The reference voltage V2' in this embodiment is set to a level between VFR-H and VFR-L, and the output of the connection detector circuit 16 becomes an inversed signal of the output of the AND circuit. The output of the AND circuit 18 is fed to the reset circuit 21, and the reset circuit 21 outputs a reset signal shown in (e) to the holding circuit 20. The reset signal is generated every time when the output of the AND circuit 18 is switched from Hi to Lo. The output of the connection detector circuit 16 and the reset signal from the reset circuit 21 are fed to the holding circuit 20. The output of the holding circuit 20 is supplied to the OR circuit 17. The holding circuit 20 outputs the same signal as the connection detector circuit 16 when the reset signal is fed. The output of the holding circuit 20 is maintained at the previous level when no reset signal is fed. Therefore, the output of the holding circuit 20 is always at Hi-level as shown in (d) . Since the holding circuit 20 does not respond to the output of the connection detector circuit 16 when the FR-terminal voltage is at Lo-level (VFR-L) but keeps the previous level, the reference voltage V2' can be set to a level higher than VFR-L as shown in FIG. 10 (c) . Therefore, erroneous detection due to noises in the connection detector circuit 16 is suppressed, and the operation of the suppressing circuit 14 is surely prohibited when the exterior conduction ratio monitor 41 is connected to the FR-terminal. The connection detector circuit 16 shown in FIGS. 1 and 9 may be modified to forms shown in FIGS. 11 and 12. In a connection detector circuit 16A shown in FIG. 11, an inverter 163 is additionally connected to the output terminal of the voltage comparator 161. Other structures are the same as those of the connection detector circuit 16 previously described. In this modified form, the connection detector circuit 16A outputs a Lo-level signal when the conductive ratio monitor 41 is connected to the FR-terminal. That is, the operation of the suppressing circuit 14 is allowed when the conductive ratio monitor 41 is connected to the FR-terminal while its operation is prohibited when the conductive ratio monitor 41 is not connected. The operation of the suppressing circuit 14 is controlled in response to connection or disconnection of the conductive ratio monitor 41 without adversely affecting the function of generating the conductive ratio signals. In a connection detector circuit 16B shown in FIG. 12, the FR-terminal voltage is fed to a minus terminal of a voltage comparator 161A and the reference voltage V2 is fed to its plus terminal. In other words, the input terminals of the voltage comparator 161A are reversed, compared with the voltage comparator 161 previously described. Other structures of the connection detector circuit 16B are the same as those of the previously described detector circuit 16. The connection detector circuit 16B shown in FIG. 12 operates in the same manner as in the connection detector circuit 16A shown in FIG. 11. While the present invention has been shown and described with reference to the foregoing preferred embodiments, it will be apparent to those skilled in the art that changes in form and detail may be made therein without departing from the scope of the invention as defined in the appended claims. WHAT IS CLAIMED IS: 1. A voltage regulator (1) for controlling an output voltage of an alternator (2) for use in an automotive vehicle, the alternator including a field winding (32) generating a rotating magnetic field according to rotation of an engine, an armature winding (31) generating alternating current in the rotating magnetic field and a rectifier (33) for rectifying the alternating current into direct current, the voltage regulator comprising: means (13) for controlling the output voltage of the alternator to a predetermined voltage; means (14) for suppressing an increase in a field current supplied to the field winding; means (11) for controlling the field current in an on-and-off fashion based on outputs from the output voltage controlling means (13) and the suppressing means (14); means (15) for outputting a conductive ratio signal in response to a conductive ratio of the field current controlling means (11), the conductive ratio signal being composed of a Hi-level signal and a Lo-level signal; means (16) for detecting whether an exterior conductive ratio monitor (41) is connected to an output terminal (FR) of the outputting means (15) by comparing a voltage of the output terminal (FR) with a reference voltage (V2); and means (17) for prohibiting operation of the suppressing means (14) when the detecting means (16) detects that the exterior conductive ratio monitor (41) is connected, wherein: the reference voltage (V2) is set in a range higher than zero volt and lower than a voltage (VFR-L) corresponding to the Lo-level signal of the conductive ratio signal, 2. The voltage regulator as in claim 1, wherein: the outputting means (15) includes a switching element (152) which is turned on or off according to the conductive ratio of the field current controlling means (11) and means (153) for amplifying a voltage (VFR-L) corresponding to the Lo-level signal appearing when the switching element is turned on. 3. The voltage regulator as in claim 2, wherein: the amplifying means (153) is a resistor (153A). 4. The voltage regulator as in claim 2, wherein: the amplifying means (153) is a circuit in which one or more diodes (153B) are connected in series. 5. The voltage regulator as in claim 2, wherein: the amplifying means (153) is a circuit composed of a resistor (153A) and one or more diodes (153B) connected in series . 6. A voltage regulator (1) for controlling an output voltage of an alternator (2) for use in an automotive vehicle, the alternator including a field winding (32) generating a rotating magnetic field according to rotation of an engine, an armature winding (31) generating alternating current in the rotating magnetic field and a rectifier (33) for rectifying the alternating current into direct current, the voltage regulator comprising: means (13) for controlling the output voltage of the alternator to a predetermined voltage; means (14) for suppressing an increase in a field current supplied to the field winding; means (11) for controlling the field current in an on-and-off fashion based on outputs from the output voltage controlling means (13) and the suppressing means (14); means (15) for outputting a conductive ratio signal in response to a conductive ratio of the field current controlling means (11) the conductive ratio signal being composed of a Hi-level signal and a Lo-level signal; means (16) for detecting whether an exterior conductive ratio monitor (41) is connected to an output terminal (FR) of the outputting means (15) by comparing a voltage of the output terminal (FR) with a reference voltage (V2); means (17) for prohibiting operation of the suppressing means (14) when the detecting means (16) detects that the exterior conductive ratio monitor (41) is connected; and means (20) for holding a result of detection by the detecting means (16) when the conductive ratio signal is the Hi-level and for feeding the result held therein to the prohibiting means (14). 7. The voltage regulator as in any one of claims 1-6, wherein: means for switching operation of the suppressing means (14) is used in place of the prohibiting means (17), the switching means prohibiting operation of the suppressing means (14) when the detecting means (16) detects that the exterior conductive ratio monitor (41) is not connected and allowing operation of the suppressing means (14) when the detecting means (16) detects that the exterior conductive ratio monitor (41) is connected.

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