JPH11275770A - Power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply device that can stably feed power to various kinds of devices and circuit and also be miniaturized. SOLUTION: A power supply circuit 2 is provided with a switch circuit 30 for conducting and breaking a backup power feed line for feeding power from a first power feed line BATT for constantly receiving power from a battery BT to a second power feed line + B for receiving power fed from the battery BT only during the conduction of a relay RLY. When a power feed voltage VB2 of the second power feed line + B becomes lower than a charge voltage VC of a capacitor 46, that is charged by power feed from the second power feed line + B by an on-voltage Vbe, a changing circuit 50 is operated, thus retaining a power fed voltage VB2 at a value that is lower than a charging voltage VC by the on-voltage Vbe and discharges the capacitor 46, and at the same time feeds a drive current Id to the switch circuit 30, thus allowing a backup power feed line to conduct electricity. When the power feed voltage VB2 becomes lower than the on-voltage Vbe due to the discharging of the capacitor 46, the charging circuit 50 is stopped.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a first power supply line which always receives power from a power supply, and a second power supply which receives power from the power supply only when a switching means provided between the power supply line and the power supply is closed. The present invention relates to a power supply circuit having a line.

[0002]

2. Description of the Related Art Heretofore, a power supply circuit mounted on an electronic control unit (ECU) for performing various controls such as engine control in an automobile has been known as this type of power supply circuit.
That is, in such a vehicle-mounted power supply circuit 100, as shown in FIG. 5, the power supply circuit 100 is connected to a battery BT as a power supply via a connector C of the ECU, and is connected to a power supply terminal T1 which always receives power supply from the battery BT. First power supply line BATT
And a second power supply line + B connected to a power supply terminal T2 receiving power from the battery BT only when a contact of a relay RLY provided between the battery R and the battery BT is closed, and grounded ground terminals T3 and T4. And a ground line G connected thereto. The relay RLY is configured so that the contact is opened and closed according to the operation of the ignition switch IG.

[0003] That is, the first power supply line BATT is used for power supply to devices and circuits that require constant power supply regardless of the operation of the ignition switch IG, while the second power supply line + B is used for power supply of the ignition switch IG. It is used to supply power to devices and circuits whose start and stop are controlled according to the time.

In the power supply circuit 100, constant voltage circuits 10 and 20 are connected to the first power supply line BATT and the second power supply line + B, respectively. Among them, the constant voltage circuit 10 connected to the first power supply line BATT is
The resistor 12 has one end connected to the first power supply line BATT, the other end connected to the output terminal of the constant voltage circuit 10, and the Zener diode 14 having the cathode connected to the output terminal and the anode connected to the ground line G. Is configured.

That is, the output of the constant voltage circuit 10 is normally used as a backup power supply for holding the storage contents of a data holding circuit such as a RAM. This is because it is only necessary to fall within an allowable range in which the operation can be performed quickly, and it is not necessary to perform the control with high accuracy.

On the other hand, a constant voltage circuit 20 connected to the second power supply line + B has a PNP type power transistor having an emitter connected to the second power supply line + B and a collector connected to an output terminal of the constant voltage circuit 20. 22, a permission terminal e connected to the second power supply line + B, a first power supply line BA
Reference power supply terminal f connected to TT, monitor terminal m connected to the collector of transistor 22, transistor 22
And a control terminal b connected to the base of the controller, and a voltage applied to the permission terminal e is set to a preset operation threshold value (for example,
When the voltage is equal to or more than 5.1 V), the transistor 22 is controlled via the control terminal b so that the voltage applied to the monitor terminal m (that is, the output voltage of the constant voltage circuit 20) becomes constant (for example, 5.0 V). Well-known constant voltage control I for controlling base current
C (for example, TA7900 made by Toshiba) 24, and is configured so that the output voltage of the constant voltage circuit 20 can be accurately and constantly maintained.

That is, since the output of the constant voltage circuit 20 is usually used to supply power to a control circuit such as a microcomputer, the voltage value must be accurately and constantly maintained. The constant voltage control IC 24 has a built-in reference voltage generation circuit that generates a reference voltage with almost no temperature fluctuation by using a semiconductor band gap in order to generate a highly accurate constant voltage. A power supply for operating the circuit is obtained from a reference power supply terminal f. The reason why the reference power supply terminal f is connected to the first power supply line BATT which is always supplied with power from the battery BT is that when the power of the reference voltage generation circuit is obtained from the second power supply line + B, the relay RLY This is because the reference voltage is not determined immediately after being closed, and the constant voltage control IC 24 cannot perform control with high accuracy.

The power supply circuit 100 includes a diode connected between the first and second power supply lines BATT and + B with the forward direction of current flowing from the second power supply line + B to the first power supply line BATT. 4 and the second power supply line +
And a capacitor 6 connected between B and the ground line G.

The first and second power supply lines B are caused by poor contact between the connector terminals T1 to T4 and chattering of the relay contacts based on vibration of the vehicle during operation of the engine.
For example, when power supply from the battery BT to the first power supply line BATT is interrupted, power is supplied from the second power supply line + B via the diode 4 so as to cope with the second power supply. When the power supply to one power supply line BATT is continued, while the power supply from the battery BT to the power supply line + B is interrupted, the power supply to the second power supply line + B is continued by discharging the charge charged in the capacitor 6. It has been like that. It should be noted that, with respect to the ground line G, the connector terminals T3 and T4 are doubled to cope with such an instantaneous interruption.

[0010]

In recent years, in order to improve the power performance of vehicles and the purifying performance of exhaust gas, etc.,
The types and scales of devices and circuits mounted on the ECU tend to increase. Since these devices and circuits need to supply power by the output of the constant voltage circuit 20 having a stable voltage value, the amount of power supply via the second power supply line + B for supplying power to the constant voltage circuit 20 increases. There is a tendency.

However, when the amount of power supplied on the second power supply line + B increases, a larger capacitor is required to cope with the above-described momentary interruption, and the large-capacity capacitor is very large. Therefore, there is a problem that the power supply circuit is enlarged.

In order to effectively use the space in a vehicle, there is a growing demand for mounting an ECU in an engine room. However, an aluminum electrolytic capacitor generally used as a large-capacity capacitor has a characteristic depending on temperature. When operating in a high temperature environment such as an engine room,
There is also a problem that the reliability of the apparatus is reduced, for example, the capacity is reduced, the length of the instantaneous interruption that can be dealt with is shortened, and the life is shortened.

Further, in order to cope with the contact failure of the connector terminals, the connector terminals T1, T2
However, there is a problem that the size of the connector is increased and the wiring harness for wiring is increased, so that the device is enlarged and the wiring is complicated.

The present invention has been made in order to solve the above problems.
An object of the present invention is to provide a power supply circuit that can stably supply power to various devices and circuits and that can be downsized.

[0015]

According to a first aspect of the present invention, there is provided a power supply circuit comprising: a first power supply line which always receives power from a power supply; A second power supply line that receives power from the power supply only when the power supply is closed, and when the voltage of the second power supply line falls below a preset allowable voltage, the conduction control means includes a path conduction means. Then, the backup power supply path for supplying power from the first power supply line to the second power supply line is made conductive for a preset allowable time.

Therefore, according to the power supply circuit of the present invention, even if power supply from the power supply to the second power supply line is temporarily interrupted due to instantaneous interruption due to chattering of the switching means, the power supply is interrupted for a period of time. If it is within the allowable time, power is supplied through the backup power supply line until power supply from the power supply to the second power supply line is resumed, so that various devices and circuits connected to the second power supply line are supplied. Power supply can be stably continued.

Also, when the power supply from the power supply to the second power supply line is interrupted, the second power supply line
Since power is supplied to the power supply line, there is no need to provide a large-capacity capacitor or multiplex the connector terminals of the second power supply line as in the conventional apparatus, so that the apparatus is not enlarged. .

Further, according to the power supply circuit of the present invention, there is no need to supply power to the second power supply line, and if the switching means is opened, power supply from the power supply to the second power supply line exceeds the allowable time. And the conduction control means causes the path conduction means to cut off the backup power supply path, so that power is not wastefully consumed through the backup power supply path.

Next, in the power supply circuit according to the second aspect, the conduction control means includes a charging means that is charged by receiving power supplied from the second power supply line, and a charging means that is charged when the voltage of the second power supply line becomes equal to or lower than an allowable voltage. And discharging means for discharging the charging means,
After the discharging means starts discharging, the backup power supply path is made to conduct to the path conducting means until the charging voltage of the charging means reaches a preset lower limit voltage.

In the power supply circuit of the present invention thus configured, when power is supplied from the power supply to the second power supply line, the charging means is charged, and power supply from the power supply to the second power supply line is interrupted. The discharging means gradually discharges the charge charged in the charging means. In other words, the conduction control means can be easily configured by setting the time constant of the discharge so that the time required for the charging means to reach the lower limit voltage from the fully charged state of the charging means becomes the above-mentioned allowable time. can do.

Since the charging means does not use the electric charge for power supply to the second power supply line, a small-capacity charging means can be used without increasing the size of the device. Further, the power supply circuit of the present invention uses a vehicle-mounted battery as a power supply, and the switching means is configured to be opened and closed in response to an operation of an ignition switch. It can be suitably used as a power supply circuit mounted on an electronic device for electronic devices.

By the way, in the power supply circuit according to the first to third aspects, the opening / closing control of the switching means provided between the second power supply line and the power supply is performed outside the power supply circuit. According to the power supply circuit according to claim 4, the power supply command for instructing whether or not power supply by the second power supply line is input, and a power supply command from the control line, Switch control means for controlling switching of the switching means may be provided so that the power supply circuit controls opening and closing of the switching means.

In this case, when the power supply command input through the control line indicates that the power supply is permitted, the conduction control means causes the path conduction means to conduct the backup power supply path, and the power supply command is set in advance. If the power supply is stopped for more than the allowed time, the path conducting means can be configured to cut off the backup power supply path.

That is, in the power supply circuit of the present invention, the necessity of power supply by the second power supply line is not indirectly confirmed from the power supply state of the second power supply line as in the above-described power supply circuit. The path conduction means may be controlled by directly confirming with a power supply command input through the device.

Even in the case of the power supply circuit configured to control the opening / closing of the switching means, the vehicle-mounted battery is used as the power supply, and the ignition switch is provided in the control line. When a power supply command corresponding to the above operation is input, the power supply circuit can be suitably used as a power supply circuit mounted on a vehicle-mounted electronic device.

[0026]

Embodiments of the present invention will be described below with reference to the drawings. [First Embodiment] FIG. 1 is a circuit diagram showing the configuration of a power supply circuit of the first embodiment and its peripheral circuits.

Note that the power supply circuit 2 of the present embodiment first
Since only a part of the configuration is different from the conventional power supply circuit 100 described above, the same components have the same reference characters allotted, and detailed description thereof will be omitted. The description will focus on the parts.

That is, like the conventional power supply circuit 100, the power supply circuit 2 of this embodiment includes a first power supply line BATT connected to the power supply terminal T1 of the connector C, and a power supply terminal T
2, a second power supply line + B, a ground line G also connected to the ground terminals T3, T4, a constant voltage circuit 10 connected to the first power supply line BATT, and a second power supply line + B. Constant voltage circuit 20 and first and second
A diode 4 connected between the power supply lines BATT and + B.

In the power supply circuit 2 according to the present embodiment, the switch circuit 30 and the switch circuit 30 are used instead of the capacitor 6 (see FIG. 6).
A backup circuit including a charging circuit 40 and a discharging circuit 50 is provided. The switch circuit 30 includes a PNP transistor 32 having an emitter connected to the first power supply line BATT, a collector connected to the second power supply line + B, a first power supply line BATT at one end, and a transistor 32 at the other end.
And a resistor 34 connected to the base of the
4, when a drive current Id described later flows through the transistor 32,
Is turned on, and the second power supply line BATT
It is configured as path conducting means for conducting a backup power supply path for supplying power to the power supply line + B.

The charging circuit 40 includes a diode 42
One end is the second power supply line + B, and the other end is the diode 42
And a capacitor 46 having one end connected to the cathode of the diode 42 and the other end connected to the ground line G. Power is supplied from the second power supply line + B to the resistor 44 and the diode 42. And charging means for charging the capacitor 46 via the.

Further, the discharge circuit 50 has a diode 52 having an anode connected to the second power supply line + B, a resistor 54 having one end connected to the cathode of the diode 52 and the other end connected to the ground line G, and a collector grounded. , A PNP-type transistor 56 whose base is connected to the cathode of the diode 52, and an NPN transistor whose emitter is connected to the emitter of the transistor 56 and whose collector is connected to the base of the transistor 32.
Transistor 58, and a resistor 59 having one end connected to the base of the transistor 58 and the other end connected to the cathode of the diode 42, and discharges the capacitor 46 in accordance with the power supply voltage VB2 of the second power supply line + B. And a discharging means for controlling the ON / OFF state of the transistor 32. That is, the charging circuit 40 and the discharging circuit 50
Corresponds to the conduction control means.

In the discharging circuit 50, the base voltage Vb of the transistor 56 is changed from the power supply voltage VB2 of the second power supply line + B to the forward voltage Vf (≒
0.7V) (Vb = VB2-Vf). When the transistor 56 is on, the emitter voltage Ve is higher than the base voltage Vb.
be (≒ 0.7V) (Ve = Vb + Vbe = VB)
2-Vf + Vbe), and the forward voltage Vf and the ON voltage Vbe
(Vf ≒ Vbe), the end result is that the emitter voltage V
e becomes substantially equal to the power supply voltage VB2 of the second power supply line + B (Ve ≒ VB2).

Further, when the transistor 58 is turned on, its base voltage, that is, the charging voltage V
C must be higher than the emitter voltage Ve (that is, the power supply voltage VB2) by the ON voltage Vbe (VC> Ve +
Vbe ≒ VB2 + Vbe). In addition, transistors 56 and 58
Are turned on, both transistors 56,
In order to secure the ON voltage (Vbe + Vbe) of the transistor 58, the base voltage of the transistor 58, that is, the charging voltage VC of the capacitor 46 must be at least twice the ON voltage (VC ≧ 2Vbe).

That is, the discharge circuit 50 determines that the power supply voltage VB2 of the second power supply line + B is equal to or higher than the ON voltage Vbe and is smaller than the charging voltage VC of the capacitor 46 by the ON voltage Vbe (Vbe <VB2 <VC- Vbe), the operation state (the transistors 56 and 58 are turned on), the capacitor 46 is discharged, and the drive current Id flows through the resistor 34 of the switch circuit 30.

When the discharging circuit 50 discharges the capacitor 46, the power supply voltage VB2 of the second power supply line + B is maintained at a value lower than the charging voltage VC of the capacitor 46. In this case, no charging is performed, and only discharging is performed. The discharging speed of the capacitor 46 can be arbitrarily set by appropriately adjusting the capacity of the capacitor 46 and the resistance value of the resistor 59.

Here, the overall operation of the power supply circuit 2 of this embodiment will be described with reference to FIG. As shown in FIG. 2, first, before time t1 when the relay RLY is in the cutoff state, only the first power supply line BATT receives power supply from the battery BT. At this time, the capacitor 46 that receives power supply via the second power supply line + B is in an uncharged state (charge voltage VC = 0 V), and the discharge circuit 50
Is also stopped (the transistors 56 and 58 are off), the drive current Id does not flow through the switch circuit 30, and the backup power supply path is cut off. As a result, power is not supplied from the first power supply line BATT to the second power supply line + B via the backup power supply path of the switch circuit 30, so that the power supply voltage VB2 of the second power supply line + B becomes 0V. As a result, the output voltage VDD of the constant voltage circuit 20 connected to the second power supply line + B also becomes 0V.

When the ignition switch IG is operated and the relay RLY is turned on (time t1),
Power supply from the battery BT to the second power supply line + B is started, and the power supply voltage VB2 of the second power supply line + B increases.
When the power supply voltage VB2 exceeds the operating threshold value Vth (5.1 V in this embodiment) of the constant voltage control IC 24, the constant voltage circuit 20 outputs a constant voltage (5 V in this embodiment).
Start output of

The charging voltage VC of the capacitor 46 is gradually increased by the power supply from the second power supply line + B.
At this time, since the power supply voltage VB2 is always higher than the charging voltage VC, the discharging circuit 50 does not change from the stop state to the operating state, only the charging is performed, and finally, the capacitor 46 substantially stores the power supply voltage VB2. Charged until (VCm
ax ≒ VB2).

Thereafter, due to chattering of the relay contact or poor contact of the connector terminal T2, the second power supply line +
When an instantaneous interruption (time t3) occurs at B, the power supply voltage VB2
Is lowered by the ON voltage Vbe, the discharge circuit 50 enters the operating state. Then, the power supply from the first power supply line BATT to the second power supply line + B is started via the backup power supply path of the switch circuit 30, and thereafter, while the power supply from the battery BT is interrupted, the capacitor 46 is turned off.
The supply voltage VB2 gradually decreases in accordance with the decrease in the charging voltage VC.

If the period of the instantaneous interruption is sufficiently shorter than the allowable time Td required for the power supply voltage VB2 to decrease to the operation threshold Vth of the constant voltage control IC 24, the output voltage VDD of the constant voltage circuit 20 Is maintained at a constant value even during this momentary interruption, and power supply to various devices and circuits is stably continued.

On the other hand, when an instantaneous interruption occurs in the first power supply line BATT due to a contact failure of the connector terminal T1 (time t4), the second power supply line + B is passed through the diode 4 to the first power supply line BATT. Is supplied, the power supply voltage VB1 of the first power supply line BATT is reduced by the forward voltage Vf of the diode 4 while the power supply from the battery BT is interrupted.

Thereafter, when the ignition switch IG is operated and the relay RLY is turned off (time t4),
Similarly to the momentary interruption at the time t3, when the power supply voltage VB2 of the second power supply line + B decreases by the ON voltage Vbe, the discharge circuit 50 enters an operation state, and the first discharge circuit 50 is connected via the backup power supply path of the switch circuit 30 to the first circuit. Second from feed line BATT
Since power is supplied to the power supply line + B, the power supply voltage VB
2 gradually decreases as the charging voltage VC of the capacitor 46 decreases.

When the power supply voltage VB2 reaches the operation threshold value Vth of the constant voltage control IC 24, that is, when the allowable time Td elapses after the power supply from the battery BT to the second power supply line + B is stopped (time t5). ), Constant voltage circuit 2
0 means that the output voltage VDD cannot be kept constant (5 V), and thereafter, the output voltage VDD decreases as the power supply voltage VB2 decreases.

Thereafter, when the discharge of the capacitor 46 proceeds and the power supply voltage VB2 reaches the ON voltage Vbe (time t6),
The discharge circuit 50 is stopped, the backup power supply path of the switch circuit 30 is cut off, and the first power supply line BATT
Supply to the second power supply line + B from the
Both the power supply voltage VB2 of the power supply line + B and the output voltage VDD of the constant voltage circuit 20 become 0 V, and the charging voltage VC of the capacitor 46 is maintained at the voltage (<2 Vbe) at the time when the discharging circuit 50 stops.

As described above, in the power supply circuit 2 of the present embodiment, the second power supply line + B
When the power supply to the power supply is interrupted, the charge previously charged in the capacitor 46 by the power supply from the second power supply line + B is discharged by the discharge circuit 50, and the charged voltage of the capacitor 46 is necessary for operating the discharge circuit 50. Low limit voltage (2
Vbe) or more from the first feed line BATT to the second
The backup power supply path for supplying power to the power supply line + B is made conductive.

Therefore, according to the power supply circuit 2 of the present embodiment,
Even if the power supply from the battery BT to the second power supply line + B is temporarily interrupted, the power supply via the second power supply line + B can be stably continued, and the relay RLY
, The power supply to the second power supply line + B can be reliably stopped.

In addition, the power supply circuit 2 of the present embodiment does not require the large-capacity capacitor 6 (see FIG. 6) unlike the conventional power supply circuit 100, and can deal with such instantaneous interruption. Since the operation is performed without increasing the number of terminals C, the ECU in which the power supply circuit 2 is mounted can be reduced in size.

The switch circuit 30, the charging circuit 40,
Since the discharge circuit 50 can be easily integrated into a circuit, and can be incorporated in the constant voltage control IC 24, the power supply circuit 2 itself, and further, the ECU can be further downsized. In the power supply circuit 2 of the present embodiment, the capacitor 46 is used for the charging circuit 40. However, unlike the capacitor 6 of the conventional power supply circuit 100, the power supply circuit 2 is not used for power supply to the second power supply line + B and therefore has a low capacity. Since it is not necessary to use an aluminum electrolytic capacitor which is weak in a high-temperature environment, it can be suitably used as a power supply circuit of an ECU used in a high-temperature environment such as being disposed in an engine room. [Second Embodiment] Next, a second embodiment will be described.

The power supply circuit 2a of this embodiment is different from the first embodiment only in the configuration of the discharge circuit. Therefore, the description will focus on the differences in this configuration. That is, in the power supply circuit 2a of the present embodiment, as shown in FIG. 3, the discharge circuit 60 includes a PNP transistor 62 whose emitter is connected to the cathode of the diode 42 and whose base is connected to the second power supply line + B.
An NPN transistor 64 having a collector connected to the base of the transistor 32 and an emitter connected to the ground line G;
A resistor 66 has one end connected to the collector of the transistor 62 and the other end connected to the base of the transistor 64, and one end includes a resistor 68 connected to the base of the transistor 64 and the other end to the ground line G.

In this discharge circuit 60, the second power supply line +
B is equal to the charging voltage VC of the capacitor 46.
If the ON voltage Vbe is lower than the
Is turned on. At this time, if the divided voltage obtained by dividing the charging voltage VC by the resistors 66 and 68 (that is, the base voltage of the transistor 64) is equal to or higher than the on-voltage Vbe, the transistor 64 is turned on. The drive current Id flows. Further, while the discharging of the capacitor 46 via the transistor 62 is performed, the power supply voltage of the second power supply line + B is maintained at a value lower than the charging voltage VC of the capacitor 46 by the ON voltage Vbe.

That is, in the power supply circuit 2a of the present embodiment including such a discharge circuit 60, the charge voltage V of the capacitor 46 when the discharge circuit 60 changes from the operating state to the stopped state.
C is not twice the on-voltage (2 Vbe), and resistances 66, 6
The operation is exactly the same as that of the power supply circuit 2 of the first embodiment, except that the power supply circuit 2 has an arbitrary value equal to or higher than the on-voltage Vbe determined by the division ratio of 8.

As described above, the power supply circuit 2a of the present embodiment operates in the same manner as the power supply circuit 2 of the first embodiment, so that the same effects can be obtained. In particular, according to the power supply circuit 2a of the present embodiment, when the discharge circuit 60 is stopped,
That is, since the time at which the backup power supply path of the switch circuit 30 is cut off can be arbitrarily set, for example, the power supply voltage VB2 of the second power supply line + B falls below the operation threshold Vth of the constant voltage control IC 24, and If the discharge circuit 60 is immediately stopped at the time when the data cannot be held (see time t5 in FIG. 2), wasteful power consumption can be reduced. Third Embodiment Next, a third embodiment will be described.

In the present embodiment, since only a part of the configuration is different from that of the first embodiment, the same components are denoted by the same reference numerals, and detailed description thereof will be omitted. Will be described. In the first and second embodiments, the relay RLY connected to the second power supply line + B is turned on and off.
The ignition switch IG is directly controlled, and the ECU is configured as a power supply circuit applied when the drive control of the relay RLY is not performed. Here, the ECU detects the operation state of the ignition switch IG, and detects the detection state. An embodiment configured as a power supply circuit applied to the case where the drive control of the relay RLY is performed in accordance with the embodiment will be described.

For this reason, as shown in FIG. 4, in addition to the terminals T1 to T4, an ignition switch IG is connected to the connector C of the ECU on which the power supply circuit 2b of this embodiment is mounted.
And a drive terminal T6 connected to the battery BT via the exciting coil of the relay RLY.

The power supply circuit 2b according to the present embodiment includes the first
And the first power supply line BATT connected to the power supply terminal T1 of the connector C, similarly to the power supply circuits 2 and 2a of the second embodiment.
And the second power supply line also connected to the power supply terminal T2 +
B, a ground line G also connected to the ground terminals T3 and T4, a constant voltage circuit 10 connected to the first power supply line BATT, a constant voltage circuit 20 connected to the second power supply line + B, And a diode 4 connected between the first and second power supply lines BATT and + B, and a switch circuit 30 similarly connected between the first and second power supply lines BATT and + B.
And

The power supply circuit 2b of this embodiment has the following configuration instead of the charging circuit 40 and the discharging circuits 50 and 60 of the first and second embodiments. That is, the power supply circuit 2b of the present embodiment includes a low-pass filter 70 including resistors r1 and r2 and a capacitor c1 and connected to the detection terminal T5;
A low-pass filter 7 includes a microcomputer (hereinafter referred to as “microcomputer”) 72 for taking the output of the low-pass filter 70 into the input port IN via the resistor 80, and a pair of diodes d 1 and d 2 whose cathodes are connected in common.
An OR circuit 74 for generating a drive signal SD that goes high when at least one of the output from the output port 0 and the output from the output port OUT of the microcomputer 72 is high; a drive terminal T6 for the collector and a ground for the emitter. An NPN-type transistor 76 connected to the line G and driving the exciting coil of the relay RLY in accordance with a drive signal SD applied to the base via the resistor 82, a collector connected to the base of the transistor 32, and an emitter connected to the ground line G And the drive signal S applied to the base via the resistor 84
D, the drive current Id flows through the switch circuit 30 in accordance with D.
And a PN transistor 78.

Although not shown, the microcomputer 72 is connected so as to be supplied with a constant voltage VDD via the constant voltage circuit 20. The power supply circuit 2b thus configured
The output of the low-pass filter 70 is at the low level when the ignition switch IG is in the off state, and at the high level when the ignition switch IG is in the on state. The output is also taken into the microcomputer 72 through the input port IN.

When the drive signal SD is at a low level, that is, when both the output of the low-pass filter 70 and the output from the output port OUT are at a low level, the transistor 7
6 and 78 are both turned off, the relay RLY is cut off, and the backup power supply line of the switch circuit 30 is cut off. For this reason, neither the power supply from the battery BT to the second power supply line + B nor the power supply from the first power supply line BATT to the second power supply line + B is performed, so that the constant voltage circuit 20 is in a stopped state.

Conversely, when the drive signal SD is at the high level, that is, when either the output of the low-pass filter 70 or the output from the output port OUT is at the high level, both the transistors 76 and 78 are turned on, and the relays are turned on. While RLY conducts, the backup power supply path also conducts. Therefore, the second power supply line + B
To the second power supply line + B from the first power supply line BATT to the second power supply line + B.
Is also in the operating state.

The setting process of the output port OUT executed by the microcomputer 72 will be described with reference to the flowchart shown in FIG. This process is started when the ignition switch IG is turned on and the power supply to the microcomputer 72 via the constant voltage circuit 20 is started.

As shown in FIG. 5, when this process is started, first, in S110, the output port OUT is set to the high level. In the following S120, it is determined whether or not the signal level of the input port IN is at the Low level. If a negative determination is made, the process waits by repeatedly executing S120. If an affirmative determination is made in S120, in S130 that follows, a predetermined allowable time Td is set.
After waiting for (in this embodiment, 2 ms), in S140, the signal level of the input port IN becomes low, as in S120.
Determine whether it is at the low level.

If a negative determination is made in S140, the process returns to S120 and the above-described processing is repeatedly executed. On the other hand, if a positive determination is made, the process proceeds to S150, where the output port OUT is set to the low level. After the setting, the process ends. That is, when this process is started, it is known that the ignition switch IG has been closed. Therefore, by setting the output port OUT to the high level (S110), the drive signal SD is reliably held at the high level. As a result, even if a momentary interruption occurs in the control line connected to the connector terminal T5 due to chattering of the ignition switch IG or poor contact of the connector terminal T5, the instantaneous interruption immediately changes the relay RLY to the cutoff state. Is prevented.

If the instantaneous interruption is sufficiently short, the signal level of the input port IN is reduced by the operation of the low-pass filter 70.
Although the signal is held at the high level, if the instantaneous interruption becomes longer to some extent, the effect cannot be removed by the low-pass filter 70, so that the signal level of the input port IN is temporarily low
Level. In addition, even when the ignition switch IG is intentionally opened, the signal level of the input port IN is at the low level.

Therefore, the signal level of the input port IN becomes
When the low level is detected (S120-YE
S), it is determined whether this is due to the opening of the ignition switch IG or the instantaneous interruption of the control line even if the signal level of the input port IN has passed the allowable time Td.
It is determined whether the level remains (S130, S1)
40).

That is, if the low level is maintained after the elapse of the permissible time Td, the output port OUT is returned to the low level (S150) instead of the instantaneous interruption, assuming that the ignition switch IG is opened (S150). As a result, the operation of the constant voltage circuit 20 is stopped by stopping the power supply to the second power supply line + B by shutting off the relay RLY and the backup power supply path.

As described above, according to the power supply circuit 2b of the present embodiment, the second power supply line + B
When the power supply to the switch circuit 30 is interrupted, the backup power supply path of the switch circuit 30 is made conductive only during the allowable time Td,
Since the power is supplied from the power supply line BATT to the second power supply line + B, the same effect as in the first embodiment can be obtained.

In particular, in the power supply circuit 2b of the present embodiment, the allowable time Td is set by the program of the microcomputer 72, so that the setting of the allowable time Td can be easily and appropriately changed according to the use environment. In this embodiment, a signal generated by the logical sum of the output of the low-pass filter 70 and the output from the output port OUT is used as the drive signal SD.
Although the transistors 76 and 78 are commonly used, the output of the low-pass filter 70 is used as a drive signal to the transistor 76, and the output of the output port OUT is used as a drive signal to the transistor 78.
8 may be configured to be driven by different drive signals.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating a configuration of a power supply circuit according to a first embodiment.

FIG. 2 is a waveform diagram showing the operation of each part of the power supply circuit.

FIG. 3 is a circuit diagram illustrating a configuration of a power supply circuit according to a second embodiment.

FIG. 4 is a circuit diagram illustrating a configuration of a power supply circuit according to a third embodiment.

FIG. 5 is a flowchart illustrating a process executed by the microcomputer.

FIG. 6 is a circuit diagram illustrating a configuration of a conventional power supply circuit.

[Explanation of symbols]

2, 2a, 2b Power supply circuit 4, 42, 52 Diode 6, 46 Capacitor 10, 20 Constant voltage circuit 12, 34, 44, 54, 59, 66, 68, 80, 8
2, 84 ... resistor 22, 32, 56, 58, 62, 64, 76, 78 ... transistor 14 ... zener diode 24 ... constant voltage control IC
REFERENCE SIGNS LIST 30 switch circuit 40 charging circuit 50, 60 discharging circuit 70 low-pass filter 72 microcomputer 74 OR circuit G
... ground line BATT ... first power supply line + B ... second power supply line
BT: Battery IG: Ignition switch RLY: Relay C
... Connectors T1, T2 ... Power supply terminals T3, T4 ... Ground terminals T
5 ... Detection terminal T6 ... Drive terminal

Claims (5)

[Claims] 1. A first power supply line that constantly receives power supply from a power supply, and a second power supply line that receives power supply from the power supply only when switching means provided between the power supply is closed. A power supply circuit comprising: a path conduction unit that conducts or cuts off a backup power supply path that supplies power from the first power supply line to the second power supply line; and a voltage of the second power supply line being equal to or less than a predetermined allowable voltage. A power supply circuit, comprising: a conduction control means for conducting a backup power supply path to the path conduction means for a preset allowable time when the power supply circuit drops. 2. The continuity control unit includes: a charging unit that is charged by receiving power from the second power supply line; and a discharge that discharges the charging unit when a voltage of the second power supply line becomes equal to or lower than an allowable voltage. Means for conducting a backup power supply path to the path conducting means until the charging voltage of the charging means reaches a preset lower limit voltage after the discharging means starts discharging. Item 2. The power supply circuit according to item 1. 3. The power supply circuit according to claim 1, wherein the power supply is a vehicle-mounted battery, and the switching means is opened and closed in response to an operation of an ignition switch. A first power supply line that constantly receives power supply from a power supply; a second power supply line that receives power supply from the power supply only when switching means provided between the power supply is closed; A control line to which a power supply command for instructing whether or not power supply by the second power supply line is input is provided; and a switch control means for opening and closing the switching means in response to the power supply command from the control line. In the power supply circuit of the control device, a path conduction unit that conducts or cuts off a backup power supply path that supplies power from the first power supply line to the second power supply line; When the power supply command indicates that the power supply is stopped for a preset allowable time or longer, the backup power supply path is connected to the path conductive means. A power supply circuit, comprising: a conduction control unit that cuts off a power supply path. 5. The power supply circuit according to claim 4, wherein the power supply is a vehicle-mounted battery, and the power supply command is input in response to an operation of an ignition switch.