JPH06335177A - Charge control circuit - Google Patents

Abstract

PURPOSE:To keep the backup battery of an electric apparatus which can be driven by an AC power supply and by a battery and has the backup battery in addition to a driving battery fully charged but not overcharged. CONSTITUTION:An AC adapter 1 through which a required driving voltage is supplied, a circuit 4 which judges ON and OFF of a power supply and a circuit 5 which detects the output from the AC adapter 1 and the judged result of the circuit 4 are provided. The charging current value and the charging current supply source of a backup battery 3 is controlled in accordance with the results of the judging circuit 4 and the detecting circuit 5.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a charge control circuit.

[0002]

2. Description of the Related Art With the recent miniaturization of various electronic components, electronic devices such as personal computers and word processors are so small and lightweight that they are called laptop size, notebook size, and eventually palm size, and are easy to carry. Came. In order to make the most of this advantage, rechargeable batteries such as nickel-cadmium (Ni-Cd) and nickel-hydrogen (Ni-M) can be used as a driving power source.
H) and other secondary batteries are built-in.

In addition, due to the progress in power saving of various electronic parts and the increase in capacity of secondary batteries, even in this kind of portable electronic equipment, the operation of the CPU is temporarily stopped during the execution of processing, and various data at that point in time. After backing up the data, when the operation of the CPU is started again, the so-called Suspend / Re which continues the processing suspended based on the above backup data
The sum function has come to be added.

The secondary battery in the device having such a function is not only for the purpose of operating the device but also for backing up various data at the time of Suspend. Generally, the secondary battery of this type of device is detachable so that it can be charged by a dedicated charger. Considering this attachment / detachment, it is preferable to use a dedicated battery for the backup.

Conventionally, many primary batteries such as manganese batteries and lithium batteries have been used as the dedicated batteries. Recently, however, secondary batteries have been used in response to market needs such as higher capacity. ing.

[0006]

Generally, in this type of device, a part of the output voltage obtained by rectifying a commercial AC voltage with an AC adapter is utilized as disclosed in Japanese Utility Model Laid-Open No. 1-64937. The battery is being charged.

However, when the secondary battery intended for the operation of the device is detachable as described above, the secondary battery is often removed from the device and charged by another dedicated charger. In some cases, the backup battery will not be fully charged.

Further, it is general to charge such a backup dedicated battery simply by a trickle current using a current limiting resistor. The resistance value of such a current limiting resistor is normally set so that the maximum trickle charge current value at full charge can be suppressed within an allowable range (about 1/20 to 1 / 50C) that enables long-time charging. . In order to minimize the charging time, it is preferable to lower the limiting resistance value and increase the trickle charging current value as much as possible. However, if the trickle charge current value is large, charging is continued for a long time when the trickle charge current value exceeds the permissible range and becomes large when the battery is not in a fully charged state,
There is a possibility of overcharging.

On the other hand, it is possible to prevent overcharging by increasing the limiting resistance value and lowering the trickle charging current value, but there are cases where it takes a long time to reach full charge and the full charge state is not reached. Since the number of backups increases, backup performance deteriorates.

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and features thereof include a first battery for supplying a drive current to the entire device and a drive current to a part of the device. A rechargeable second battery, an AC adapter for converting a commercial AC voltage into a desired voltage and outputting the same, a status signal indicating an operation status of the device indicates an ON state of the device, and A detection circuit that outputs a control signal when it detects that there is no output, a first charging path for supplying the output of the AC adapter to the second battery, and a first charging path connected in parallel with the first charging path. Two charging paths, a first switching means disposed on the second charging path, which makes the second charging path conductive only when the status signal indicates an ON state of the device, and an output of the first battery. Up A third charging path for connecting the first battery and the first switching means for supplying to said second battery through the first switching means,
The second switching means is arranged on the third charging path and makes the third charging path conductive only when the control signal is output from the detection circuit.

[0011]

According to this structure, when the first battery has a sufficient charge amount, the second battery is charged using the first battery, and the trickle charge to the second battery is not overcharged. Can always be suppressed.

[0012]

FIG. 1 is a partial block circuit diagram showing an embodiment of a charging control circuit of the present invention applicable to electronic equipment such as a personal computer.

In the figure, (1) is an AC adapter, which converts a commercial AC voltage into a DC voltage of 15.5 V and outputs it. (2) is a first battery that supplies a drive voltage to all circuits (not shown) of the electronic device, and the first battery is, for example, a secondary battery composed of Ni-cd or Ni-MH and has a capacity of 2200 mAh. 1 with charge capacity
Generate a standard voltage of 2V. The first battery (2) can be attached to and detached from the electronic device body.
(3) is a second battery for always backing up some circuits (not shown) such as a memory and a clock circuit in the electronic device, and the second battery is, for example, a Ni-Cd secondary battery. It has a charging capacity of 600mAh and generates a standard voltage of 4.8V.

(4) is a state determination circuit, which outputs a state signal SS based on the state of the power switch (not shown) of the equipment. Specifically, a high level (H) signal is output as a status signal when the power switch is on, and a low level (L) signal is output when the power switch is off.

(5) is a detection circuit, and the detection circuit is A
It is determined whether a voltage is output from the C adapter (1), that is, whether the device is connected to a commercial AC power source, and the determination result and the status signal SS output from the status determination circuit (4) are used. Based on this, the control signal CS is output. Specifically, the control signal is output only when the voltage is not output from the AC adapter (1) and the status signal SS is the L signal (that is, the power switch is on). (6) is A
A first charging path for supplying the output of the C adapter (1) to the second battery (3), and a diode D1 for backflow prevention and a resistor R1 for current limiting are arranged on the path.
The value is set so that the current value flowing through the first charging path (6) is 30 mA.

Reference numeral (7) is a second charging path connected in parallel with the first charging path (6), on which a backflow prevention diode D2 and a current value flowing through the second charging path (7). A resistor R2 is provided to limit the current to 20 mA. Further, the first switching element Q1 composed of a PNP type transistor is arranged between the diode D2 and the resistor R2 of the second charging path (7). The base of the element Q1 is grounded via a second switching element Q2 composed of an NPN transistor and a voltage dividing resistor R3. Further, the status signal S is applied to the base of the second switching element Q2.
S is supplied. Therefore, when the high level state signal SS is applied to the base of the second switching element Q2, the element Q2 becomes conductive and the first switching element Q1 also becomes conductive.

(8) is a third charging path for guiding the output of the first battery to the first switching element Q2 in the second charging path (7), and the backflow prevention diode D is provided on the third charging path.
3 and a third switching element P including a MOSFET are arranged. The switching of the third switching element P is controlled according to the control signal CS output from the detection circuit (5). Specifically, while the control signal CS is being output, the third switching element P is in a conductive state, and the output of the first battery (2) passes through the third charging path (8) to the second charging path (7). ) Can be supplied to.

Next, the operation of the circuit of this embodiment will be described in the following (a).
The cases (1) to (d) will be described separately.

(A) The power switch is on and A
Case in which C adapter (1) output is present In this case, the status signal SS becomes H and the control signal CS is not output. Therefore, the output of the AC adapter (1) passes through the first and second charging paths (6) and (7). And is supplied to the second battery (3). Therefore, the charging current for the second battery (3) is 5
0 mA current is supplied. This charging current value is 1 / 12C with respect to the charging capacity (600mAh) of the second battery (3).
However, since the power switch is turned on in this case, the second battery (3) is used at the same time, and the battery (3) is not overcharged. You can always maintain a state close to full charge.

(B) The power switch is off, and A
Case with C Adapter (1) Output In this case, the status signal SS becomes L and the control signal CS is not output. Therefore, the first to third switching elements Q1, Q2, P are all in the non-conducting state. As a result, the AC adapter (1) is connected to the second battery (3) only through the first charging path (6).
A charging current of 30 mA is supplied. This charging current value becomes 1/20 C with respect to the charging capacity (600 mAh) of the second battery (3), and continuous charging for a long time becomes possible.

(C) The power switch is on, and A
Case without C Adapter (1) Output In this case, the status signal SS becomes H. Further, since there is no output from the AC adapter (1), the detection circuit (5) outputs the control signal CS. As a result, the first to third switching elements Q1, Q
Both 2 and P are in a conductive state, and the output of the first battery (2) is supplied to the second battery (3) via the third charging path (8) and the second charging path (7). That is, the charging current of 20 mA is supplied to the second battery (3).

For example, the total current value required for operating a portable personal computer is usually about 800 mA.
Therefore, when the current switch is turned on and the device is driven by the first battery (2), a part of the driving current is
Even if it is used for charging the battery (3), its charging current value is about 1/40 of the operating current value of 800 mA. Therefore, the second battery (3) can be charged by the first battery (2) without making the user aware of the decrease in the drivable time of the device by the first battery (2). Specifically, when the first battery (2) is fully charged and only the device is driven without charging the second battery (3), the continuous driveable time is 2200 mAh ÷ 800 mA.
= 2.75 hours. On the other hand, when the second battery (3) is charged at the same time, 2200 mAh ÷ 820 mA =
It will be 2.68 hours. That is, the difference is only about 4 minutes.

(D) The power switch is off, and A
C Adapter (1) No Output Case In this case, the status signal SS becomes L and the control signal CS is not output. Therefore, all the switching elements Q1, Q2, P are in a non-conducting state, and as a result, no charging current is supplied to the second battery (3).

This means that when the power switch is on, the first
When the device is driven using the battery (2) (case (C) above), it is considered that the charge amount of the first battery (2) has a sufficient value. Is off, the charge amount of the first battery (2) is unknown, and the second battery (3) is charged in consideration of the case where the first battery (2) itself is not attached to the device. This is a prohibition measure.

[0025]

According to the present invention, AC drive and battery drive are possible, and in addition to the drive battery (first battery), a separate backup battery (for realizing the Suspend / Resume function) is provided. Second battery), and switches the charging current for this backup battery so that it will not be overcharged according to the usage condition of the equipment and uses this battery when the driving battery has a sufficient charge amount. Since the backup battery can also be charged, the battery can be maintained in a nearly fully charged state unless it is connected to an AC power source and left unused for a long period of time.

[Brief description of drawings]

FIG. 1 is a partial block diagram showing an embodiment of a charge control circuit of the present invention.

[Explanation of symbols]

 1 AC Adapter 2 1st Battery 3 2nd Battery 5 Detection Circuit 6 1st Charging Path 7 2nd Charging Path 8 3rd Charging Path Q1 1st Switching Element Q2 2nd Switching Element P 3rd Switching Element

Claims (1)

[Claims] 1. A first battery for supplying a drive current to the entire device, a rechargeable second battery for supplying a drive current to a part of the device, and a commercial AC voltage to a desired voltage. An AC adapter to output, a detection circuit that outputs a control signal when it is detected that the status signal indicating the operation state of the device indicates the ON state of the device and that there is no output from the AC adapter, and the AC adapter A first charging path for supplying an output to the second battery, a second charging path connected in parallel with the first charging path, and a second charging path disposed on the second charging path, and the status signal of the device. A first switching means for bringing the second charging path into a conductive state only when it shows an on state, and for supplying the output of the first battery to the second battery via the first switching means. A third charging path connecting the first battery and the first switching means, and a third charging path disposed only on the third charging path when the control signal is output from the detection circuit. A charging control circuit comprising: a second switching unit that is in a conductive state;