Power-supply control apparatus

A power-supply apparatus is disclosed, which comprises an input terminal, a signal-detecting circuit which receives a drive power from a battery and which detects a signal input to the input terminal, a constant-current-source circuit which receives a drive power from the battery, which is activated by the signal detected by the signal-detecting circuit and which self-holds an operation state, a main power-supply circuit which receives a drive power from the battery and which operates to output a constant voltage, upon receiving a current from the constant-current-source circuit, and a reset circuit which turns off the constant-current-source circuit upon receiving a reset signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-039085, filed Feb. 15, 2002, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a power-supply control apparatus. More particularly, it relates to an apparatus that uses a battery or the like to provide a main power supply. The apparatus is designed for use in, for example, apparatuses for locking and unlocking the doors of automobiles.

2. Description of the Related Art

In conventional apparatuses that use a battery, providing a main power supply and a backup power supply required for controlling the apparatus, the main power supply is turned off in the standby mode in order to save the battery power. Such an apparatus comprises a signal-detecting circuit and a control circuit. The signal-detecting circuit detects a signal that changes the operating mode back to the operation mode from the standby mode to the operation mode. The control circuit activates the main power supply. In the standby mode, both circuits are driven by the backup power supply generated from the battery power supply. Hence, the battery power must be consumed in the standby mode.

A conventional power-supply control apparatus used in apparatuses that lock and unlock the doors of automobiles will be described in detail.

To get into a car, the user first inserts the key into the key slot in the door beside the driver's seat. When the user turns the key, the door-lock motor is driven, unlocking that door. The doors can therefore be opened.

When the door is thus unlocked, the engine remains stopped. So does the generator. Thus the battery is used to drive the motor-lock motor to open the door without supply of an electric current from the generator. The battery is used to drive the door-unlock motor to open the door. Inevitably, the battery power is consumed.

Moreover, power is always supplied from the backup power supply to the signal-detecting circuit so that the circuit may detect a signal for changing the operating mode back to the operation mode from the standby mode to the operation mode, no matter when the signal comes. Also, power is always supplied from the backup power supply to the door-unlock motor control circuit. Hence, the battery power is consumed even when the door-unlock motor is not driven to open the door.

Recently, intra-vehicle LAN (Local Area Network) and the like come into common use. The consumption of the battery power inevitably increases. This is a great problem.

As described above, the conventional apparatus that locks and unlocks the doors of automobiles fast consumes the battery power when the door-unlock motor is driven to open the doors, when the signal detecting circuit operates before the doors are open and when a circuit operates to control the door-unlock motor.

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided a power-supply apparatus comprising an input terminal; a signal-detecting circuit which receives a drive power from a battery and which detects a signal input to the input terminal; a constant-current-source circuit which receives a drive power from the battery, which is activated by the signal detected by the signal-detecting circuit and which self-holds an operation state; a main power-supply circuit which receives a drive power from the battery and which operates to output a constant voltage, upon receiving a current from the constant-current-source circuit; and a reset circuit which turns off the constant-current-source circuit upon receiving a reset signal.

DETAILED DESCRIPTION OF THE INVENTION

An embodiment of this invention will be described in detail, with reference to the accompanying drawings.

FIG. 1shows a power-supply control apparatus that is an embodiment of the invention. The apparatus is designed for use in apparatuses for locking and unlocking the doors of automobiles. The power-supply control apparatus has an electric circuit that is partly or entirely a semiconductor integrated circuit.

AsFIG. 1shows, the power-supply control apparatus comprises an input terminal11, a serial-data-receiving circuit12for receiving and reproducing an external serial data input via the input terminal11, a serial-data-transferring circuit13, and a power supply terminal14. The serial-data-receiving circuit12and the serial-data-transferring circuit13are connected to the input terminal11. A battery15(external power supply), for example, a 13.5 V vehicle battery, is connected to the power supply terminal14.

The power-supply control apparatus further comprises a signal-detecting circuit16, a buffer circuit17, a constant-current-source circuit18, a bypass capacitor19, a main power-supply circuit20, a control circuit21, and a reset circuit22.

The signal-detecting circuit16receives power from the battery15that is connected to the power supply terminal14. The circuit16detects a pulse signal (in this example, serial data COM for data communication) supplied from an external device to the input terminal11, as an input signal “set”.

The buffer circuit17is driven by power supplied from the battery15that is connected to the power supply terminal14. Thus driven, the circuit17amplifies the output of the signal-detecting circuit16.

The constant-current-source circuit18receives power from the battery15that is connected to the power supply terminal14. Once activated by the output of the buffer circuit17, it self holds the operation state. The bypass capacitor19is provided between, and connected to, the ground node and the activating input node DINa of the current-source circuit18. The capacitor19absorbs an instantaneous input to the constant-current-source circuit18.

The main power-supply circuit20receives power from the battery15that is connected to the power supply terminal14. When activated by the output current of the constant-current-source circuit18, the circuit20outputs a constant voltage VREG of, for example, 5 V. The constant voltage VREG is lower than the voltage VCC that the battery15has.

The constant voltage applied from the main power-supply circuit20drives the control circuit21. The control circuit21includes a logic circuit or a microcomputer. When the control circuit21receives data RXL (containing a door-unlock command) from the serial-data-receiving circuit12, it generates a door-unlock signal and outputs a reset signal “reset” after generating the door-unlock signal. The opening signal is supplied to a door-opening motor (not shown). The control circuit21generates data TXL, which is supplied to the serial-data-transferring circuit13.

The reset circuit22turns off the constant-current-source circuit18when it receives the reset signal from the control circuit21. The main power-supply circuit20is therefore turned off.

A part of the apparatus shown inFIG. 1will be described in greater detail.

The signal-detecting circuit16comprises resistors R0to R3and an NPN transistor Q1. In the circuit16, the input signal is supplied via the resistor RO to the base of the NPN transistor Q1. The base of the transistor Q1is connected to the ground node by the resistor R1. The collector of the transistor Q1is connected to the power supply terminal14by the resistors R2and R3that are connected in series to each other.

While the power-supply control apparatus stays in the standby mode, the signal detected by the signal-detecting circuit16remains at such a low potential as would not turn on the NPN transistor Q1. Hence, the NPN transistor Q1consumes no power at all. As the signal rises from 0 V to a higher potential, the potential of the base of the NPN transistor Q1rises, too. As a result, the NPN transistor Q1is turned on. Note that the conventional signal-detecting circuit comprises a comparator and a CMOS Schmidt trigger buffer and uses a backup power supply to drive the comparator or the trigger buffer.

The buffer circuit17comprises a PNP transistor Q2and resistors R4to R6. The PNP transistor Q2has its base connected to the node of the resistors R2and R3that are provided in series in the signal-detecting circuit16. The emitter of the PNP transistor Q2is connected to the power supply terminal14. The PNP transistor Q2is one of multi-collector structure and has two collectors in this example. The first collector is connected to the ground node by the resistors R4and R5that are connected in series. The second collector is connected to one end of the resistor R6.

The constant-current-source circuit18comprises NPN transistors Q3and Q4, PNP transistors Q5to Q10, and resistors R7-R14. The NPN transistor Q3is an input transistor for activation. The NPN transistor Q3is connected to the other end of the resistor R6. The resistor R6connects the base of the NPN transistor Q3to the second collector of the transistor Q2incorporated in the buffer circuit17. The resistor R7is provided between and connected to the emitter of the NPN transistor Q3and the ground node. The PNP transistor Q4has its collector-base path connected to the base-emitter path of the NPN transistor Q3in parallel, and its emitter connected to the ground node.

The resistor R8is connected at one end to the power supply terminal14and at the other end to the emitter of the PNP transistor Q5. The collector of the transistor Q5is connected to the collector of the NPN transistor Q3. The resistor R9is provided between and connected to the base of the PNP transistor Q5and the power supply terminal14. The resistor R10connects the emitter of the PNP transistor Q6to the base of the PNP transistor Q5. The PNP transistor Q6has its collector connected to the ground node and its base connected to the collector of PNP transistor Q5.

The PNP transistor Q7constitutes a feedback circuit that achieves self-hold of the constant-current-source circuit18. More specifically, the PNP transistor Q7has its base connected to the base of the PNP transistor Q5, its emitter connected by the resistor R11to the power supply terminal14, and its collector connected to the base of the NPN transistor Q3.

The PNP transistor Q8has its base connected to the base of the PNP transistor Q5, its emitter connected by the resistor R12to the power supply terminal14and its collector connected to the drive-current input node of the serial-data-receiving circuit12. The NPN transistors Q9and Q10have their bases connected to the base of the PNP transistor Q5. The PNP transistor Q9has its emitter connected by the resistor R13to the power supply terminal14. Similarly, the NPN transistor Q10has its emitter connected by the resistor R14to the power supply terminal14.

The main power-supply circuit20has a band-gap voltage source201, a regulator circuit202, and a NPN transistor Q11for constant voltage output. The band-gap voltage source201generates a band-gap voltage from the constant current supplied from the collector of the PNP transistor Q9incorporated in the constant-current-source circuit18. The regulator circuit202is driven by the constant current supplied from the collector of the PNP transistor Q10provided in the constant-current-source circuit18. The regulator circuit202generates a constant voltage of, for example, 5 V from the band-gap voltage applied from the band-gap voltage source201.

The regulator circuit202is connected to the constant voltage output terminal23. The circuit202detects the emitter output of the NPN transistor Q11, the collector-emitter path of which is provided between and connected to the power supply terminal14and the constant voltage output terminal23. In accordance with the emitter output of the NPN transistor Q11, the circuit202controls the base potential of the NPN transistor Q11in a feedback manner. Note that a voltage-stabilizing capacitor24is connected to the constant voltage output terminal23.

The reset circuit22has NPN transistor Q12and Q13and resistors R15and R16. The transistor Q12functions as a reset switch, and the transistor Q13as a reset-invalidating switch.

A base of the NPN transistor Q12receives a reset signal via the resistor R15from the control circuit21. The transistor Q12has its emitter connected to the ground node and its collector connected to the base of the NPN transistor Q3incorporated in the constant-current-source circuit18. The resistor R16is provided between and connected to the base of the transistor Q12and the ground node. The NPN transistor Q13has its collector-emitter path provided between and connected to the base of the transistor Q12and the ground node. The base of the transistor Q13is connected to the node of the resistors R4and R5of the buffer circuit17.

In the reset circuit22, the NPN transistor Q13, or reset-invalidating switch, is turned on by the potential at the node of the resistors R4and R5while the buffer circuit17is operating. When the transistor Q13is turned on, the NPN transistor Q12, or reset switch, is turned off.

While the buffer circuit17is not operating, the NPN transistor Q13remains off due to the potential at the node of the resistors R4and R5. Hence, the NPN transistor Q12is turned on when the reset signal is input (that is, when the reset signal rises from low level L to high level H). As a result, the NPN transistor Q3of the constant-current-source circuit18is turned off.

In the standby mode, the input signal from outside is at a potential that is too low to turn on the NPN transistor Q1of the signal-detecting circuit16. Hence, the signal-detecting circuit16, buffer circuit17, constant-current-source circuit18, main power-supply circuit20and control circuit21remain off. InFIG. 2, “VCC” is the output voltage of the battery15.

When the door-unlock command COM, for example, is input to the input terminal11, the signal-detecting circuit16detects this command COM in the form of a set signal “set”. This detection is transferred as signal DINa to the constant-current-source circuit18through the buffer circuit17, and the circuit18starts operating (comes out of the standby mode) and a constant current flows in the constant-current-source circuit18. Owning to the constant current, the circuit18self-holds the operation state. The constant current output from the circuit18drives the main power-supply circuit20. When the main power-supply circuit20is driven, it outputs a constant voltage VREG, e.g., 5 V that is lower than the output voltage of the battery15. The constant voltage is applied to the serial-data-receiving circuit12, serial-data-transferring circuit13and control circuit21, which are driven.

On the other hand, the control circuit21receives data RXL containing the door-unlock command from the serial-data-receiving circuit12and controls the door-unlock motor (not shown) to be driven. Upon finishing the control on the motor, the control circuit21outputs a reset signal “reset”, which is supplied to the reset circuit22, and thus the operating mode is back from the operation mode to the standby mode.

The reset circuit22turns off the constant-current-source circuit18upon receiving the reset signal if the externally input signal is invalid. The control circuit21is thereby turned off. The power-supply control apparatus is therefore set into the standby mode. If the externally input signal is valid, the NPN transistor Q13, which is a reset-invalidating switch, is on. In this case, the reset circuit22does not turn off the constant-current-source circuit18when it receives the reset signal.

While the power-supply control apparatus remains in the standby mode, the signal-detecting circuit16requires no backup power supplies and can yet detect a signal that changes the operating mode back to the operation mode from the standby mode. In addition, the power consumed is less than in the conventional power-supply control apparatus, because the signal-detecting circuit16, buffer circuit17, constant-current-source circuit18, main power-supply circuit20, control circuit21and reset circuit22are off.

Once the signal-detecting circuit16detects the signal that changes the operating mode back to the operation mode from the standby mode, the constant-current-source circuit18is driven to generate a constant current and self-holds the operation state owing to the generated constant current. Thus, the circuit18needs no backup power supplies to hold the operation state and can drive the main power-supply circuit20.

In the constant-current-source circuit18, the PNP transistor Q7serves to accomplish the self-hold of the circuit18. Instead, a constant voltage source using the PNP transistor Q10may be used to achieve the self-hold. Still alternatively, a circuit including a logic circuit using a constant voltage source using the PNP transistor Q10as may be used to achieve the self-hold.

<Modification of the Embodiment>

FIG. 3shows a modification of the power-supply control apparatus illustrated inFIG. 1.

This power-supply control apparatus differs from the embodiment shown in ofFIG. 1in that a control input terminal31, a manual switch32and a control input detecting circuit33are provided. It is identical to the embodiment in any other respects. The components identical or similar to those shown inFIG. 1are denoted at the same reference numerals and will not be described in detail.

The control input detecting circuit33has a similar structure to the signal-detecting circuit16, but has no components equivalent to the resistors R2and R3. Specifically, the control input detecting circuit33comprises resistors R17and R18and an NPN transistor Q14. The resistors R17and R18are provided between and connected to the control input terminal31and ground node. The NPN transistor Q14has its base connected to the node of the resistors R17and R18. The collector of the NPN transistor Q14is connected to the node of the resistor R2and the collector of the NPN transistor Q1of the signal-detecting circuit16. The emitter of the NPN transistor Q14is connected to ground node.

The control input detecting circuit33performs almost the same function as the signal-detecting circuit16. Specifically, when the manual switch32is operated, a control voltage is applied from external to the control input terminal31. The control input detecting circuit33detects the control voltage. In accordance with the control voltage, the circuit33activates the signal-detecting circuit16.

The power-supply control apparatus attains the same advantage as the apparatus illustrated inFIG. 1. Moreover, its operating mode can be switched back to the operation mode from the standby mode when the manual switch32is operated and the control voltage is applied from external to the control input terminal31.

In the embodiment described above, the NPN transistor Q2provided in the buffer circuit17and provided to receive the output of the signal-detecting circuit16may be replaced with a PNP transistor. Further, an N-channel MOS transistor may replace the NPN transistor Q1that receives externally input signals in the signal-detecting circuit16. Still further, MOS transistors can replace the bipolar transistors in the buffer circuit17, constant-current-source circuit18, and main power-supply circuit20and reset circuit22.

This invention is not limited to the embodiment and the modification thereof, both described above. Rather, various changes and modifications can be made within the scope and spirit of the invention.

The embodiment and its modification, both specified above, are designed for use in apparatuses that lock and unlock the doors of automobiles. As indicated above, the battery15is, for example, a 13.5 V vehicle battery and the main power-supply circuit20outputs a constant voltage of 5 V. Nevertheless, the battery15and the circuit20may output 5 V and 2 to 3 V, respectively.

As has been described, the power-supply control apparatus according to this invention need not have a backup power supply that enables the signal-detecting circuit to detect a signal for changing the operating mode back to the operation mode from the standby mode to the operation mode. When the apparatus receives such a signal, the main power supply is automatically used. This saves the power of the battery. The power-supply control apparatus is therefore fit for use in apparatuses for locking and unlocking the doors of automobiles.