JPH0522877A - Power control device - Google Patents

Abstract

(57) [Summary] [Object] To provide a power supply control device that does not need to consider the voltage drop when a direct current is supplied to a load from a direct current supply means. A direct current is supplied from a direct current supply means (battery) 13 to a load 12 through a first switch means (first transistor) 18 when the load 12 is on, and a first direct current when the load 12 is off. The switch means 18 is turned off, the direct current is supplied to the load 12 through the diode (second diode) 14, and the external direct current is input from the external direct current supply means (external (direct current) power supply) 10. At this time, the second switch means (second and third transistors) 19 and 20 are turned off to supply the external DC current to the load 12 regardless of whether the load 12 is on or off.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply control device used in electronic equipment and the like.

[0002]

2. Description of the Related Art FIG. 2 is a circuit diagram of a conventional power supply control device. In the figure, 1 is an external (direct current) power supply which is an external direct current supply means, and the external direct current is the first diode 2
Is supplied to the load 3 via. 4 is a battery which is a DC current supply means, and the DC current is supplied to the load 3 via the second diode 5. Reference numeral 6 denotes a charging circuit, which charges the battery 4 via the third diode 7. A switch 8 turns the load 3 on and off.

The operation of this conventional power supply control device is as follows. When the external DC current is not input from the external (DC) power source 1, the DC current of the battery 4 is the second diode 5
Is supplied to the load 3 via. In this state, when an external DC current is input from the external (DC) power supply 1, its output voltage is set sufficiently higher than the voltage of the battery 4. As a result, the external DC current of the external (DC) power supply 1 is supplied to the load 3 via the first diode 2, and the DC current of the battery 4 is not supplied to the load 3.

Charging of the battery 4 is performed by the charging circuit 6 via the third diode 7 while the external DC current is being supplied to the load 3. Further, when the capacity of the load 3 is large, the battery 4 can be used as an auxiliary circuit of the external (DC) power source 1.

[0005]

However, in this conventional power supply control device, when only the DC current of the battery 4 is supplied to the load 3, the first diode 5 causes a voltage drop of the forward voltage VF. Occurs, the voltage at point A in the figure is B
There is a problem that the voltage becomes lower than the voltage at the point by the forward voltage VF.

This is because the voltage of the battery 4 (particularly the discharge end voltage) is higher than the voltage required by the load 3 in the forward voltage V.
If it is high enough not to be affected by F, it does not matter, but if it is not, the original capacity of the battery cannot be used up and shallow discharge will be repeated. Therefore, there is a problem that a memory effect of the battery occurs.

The battery voltage is determined by the type and number of batteries, which is often determined by the characteristics of the load, and the voltage is usually selected only by the number of batteries.

However, increasing the number of batteries in order to increase the voltage causes a problem in that the shape of electronic equipment is made compact and the cost is reduced.

The present invention has been made in order to solve the above-mentioned conventional problems, and provides a power supply control device which does not need to consider the voltage drop when a direct current is supplied from a direct current supply means to a load. The purpose is to do.

[0010]

In order to achieve the above object, a power supply control device according to the present invention provides an external DC current supply means for supplying an external DC current to a load, and a DC current to the load via a diode. DC current supply means for supplying,
Connected in parallel with the diode and turning on the load;
First to turn on / off the diode according to an off state
Switch means, the external DC current supply means, and the first
A second switch means connected to the switch means and forcibly turning off the first switch means when the external direct current is supplied from the external direct current supply means to the load. To do.

[0011]

When the load is on, the direct current is supplied to the load through the first switch means.

As a result, the current is not supplied to the load through the diode provided between the DC current supply means and the load, and it is not necessary to consider the voltage drop.

When the load is off, the first switch means is off.

Therefore, when the load is off, a small-capacity direct current may be needed for memory backup. In that case, the direct current supply means supplies the direct current to the load through the diode. Will be possible.

Furthermore, when an external DC current is input from the external DC current supply means, regardless of whether the load is on or off,
The second switch means forcibly turns off the first switch means, and the output voltage thereof is set sufficiently higher than the battery voltage, whereby the current supply from the battery to the load is cut off.

Therefore, the external DC current is supplied from the external DC current supply means to the load.

[0017]

1 is a circuit diagram showing an embodiment of a power supply control device according to the present invention.

In the figure, 10 is an external (DC) power source as an external DC current supply means, and the external DC current is supplied to the load 12 via the first diode 11. The first diode 11 rectifies the external DC current. Reference numeral 13 denotes a battery as a direct current supply means, and the direct current is supplied to the load 12 via the second diode 14. Second diode 1
4 rectifies the direct current. A charging circuit 15 charges the battery 13 via the third diode 16. The third diode 16 prevents the reverse flow of current from the battery 13 to the charging circuit 15. Reference numeral 17 is an on / off terminal for applying an on / off signal to the load 12, and 18 is a first transistor as a first switch means. This first transistor 18 has a second
An on / off terminal 17 connected in parallel with the diode 14.
The second diode 14 is turned on / off in accordance with the turning on / off of.

Reference numerals 19 and 20 denote second and third transistors as second switch means. These second and third transistors 19 and 20 are connected to the load 1 from the external (DC) power source 10.
The second transistor 18 is forcibly turned off when an external direct current is supplied to the second transistor 18. The base of the second transistor 19 is connected to the external (DC) power source 10, the collector is connected to the base of the third transistor 20 and the on / off terminal 17, and the emitter is grounded. Further, the collector of the third transistor 20 is connected to the base of the first transistor 18, and the emitter is grounded. The collector of the first transistor 18 is the second
The cathode of the diode 14 is connected to the anode of the second diode 14 and the “+” side of the battery 13 to the emitter.

Next, the operation of the power supply control device having the above configuration will be described. When there is no power supply from the external (DC) power supply 10 and the load 12 is in an operating state, that is, when the load capacity is large,
The on / off terminal 17 becomes the "high (H)" level. Therefore, the third transistor 20 and the first transistor 18
Are turned on, and current is supplied to the load 12 from the battery 13 through the first transistor 18. When the load 12 is off, that is, when the capacity of the load 12 is small, the on / off terminal 17 is off, that is, "low (L)".
As a result, the third transistor 20 and the first transistor 18 are both turned off. Therefore, current is supplied to the load 12 through the second diode 14.

When the external (DC) power supply 10 is input, the second transistor 19 is turned on, the first and third transistors 18 and 20 are forcibly turned off, and the voltage of the external (DC) power supply 10 is changed to the battery 13 When the voltage is set sufficiently higher than the voltage of, the current does not flow in the second diode 14, and the current is supplied to the load 12 from the external (DC) power source 10 through the first diode 11. Further, the battery 13 is charged from the charging circuit 15 through the third diode 16. Normally, it is necessary to consider the operating voltage only when the on / off terminal 17 is on, that is, at the “high (H)” level. At this time, the charging current is supplied to the load 12 via the third transistor 20. Therefore, it is not necessary to consider the drop of the power supply voltage corresponding to the forward voltage (VF) of the second diode 14.

If the first transistor 18 is not turned off when the on / off terminal 17 is off, the battery 1
3 to the first transistor 18 and the third transistor 20
Direct current is supplied to the load 12 via the. The power supply via this path is used only as a backup, and the voltage supplied to the load 3 is no longer affected by the forward voltage VF.

When the external DC current of the external (DC) power source 10 is input, the second transistor 18 is turned off as described above because the external DC current from the external (DC) power source 10 is the same as above. , So as not to flow into the battery 13 via the second transistor 18.

[0024]

As described in detail above, according to the present invention,
Only when the load is on, the forward voltage VF of the diode can be neglected, so that the number of batteries as the direct current supply means only needs to satisfy the voltage required by the load. Further, the battery can be used up to its full capacity, and further, the shape of electronic equipment using this power supply control device can be made compact and the cost of the power supply control device can be reduced.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of a power supply control device according to the present invention.

FIG. 2 is a circuit configuration diagram showing a conventional power supply control device.

[Explanation of symbols]

10 External (DC) power supply (external DC current supply means) 12 load 13 Battery (DC current supply means) 14 Second diode 15 Charging circuit (charging means) 18 first transistor (first switch means) 19 Second transistor (second switch means) 20 Third transistor (second switch means)

Claims (2)

[Claims] 1. An external direct current supplying means for supplying an external direct current to a load, a direct current supplying means for supplying a direct current to the load via a diode, and a diode connected in parallel to the diode and turning on the load. An external DC current is connected to the first switch means for turning on / off the diode according to the OFF state, the external DC current supply means and the first switch means, and an external DC current is supplied from the external DC current supply means to the load. And a second switch means for forcibly turning off the first switch means when being supplied. 2. A charging unit connected to the DC current supply unit and charging the DC current supply unit when the external DC current supply unit supplies the external DC current to the load. The power supply control device according to claim 1.