JPH07123607A - Charging circuit - Google Patents

Abstract

PURPOSE:To lessen voltage loss by providing a diode and a detecting transistor which detect the potential difference between both terminals of a detecting resistor which varies according to charge current, and turn on when the potential difference is large, controlling the current supply of a charge current supply circuit. CONSTITUTION:Setting is so made that a detecting transistor 10 may be biased and turned on when a diode 12 is in the on-state, and the potential difference between both terminals of a detecting resistor 9 becomes larger since current flowing through a rechargeable cell 6 is larger at the time of charge start. Accordingly, the diode 12 connected in parallel is turned on, and along with it a detecting transistor 10 is biased and turned on. Then the detected signal is inputted to a charge control circuit 8 to control a charge-current supply circuit 7, and charge current is supplied to the cell 6. And when the charged capacity increases, the charge current decrease, and when it decreases down to a set value, the diode 12 and the detecting transistor 10 are turned off, and the supply of the charge current is stopped. Consequently, it becomes possible to raise the charged capacity nearly to 100%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging circuit for a rechargeable battery.

[0002]

2. Description of the Related Art Audio equipment such as disk players and tape recorders, which are used by being carried around, is in widespread use. However, since such audio equipment is used outdoors, a battery is used as a power source. In recent years, the number of devices using rechargeable batteries such as NiCd batteries as such batteries is increasing.

The relationship between the charging current and the charging time of a rechargeable battery is that a large current flows at the start of charging, and the charging current decreases as the charging operation is performed and the charging voltage of the battery increases.

A charging circuit is generally used in which the charging operation of a rechargeable battery is controlled by detecting such a change in charging current. As such a technique, for example, Japanese Utility Model Laid-Open No. 64-16143. Some are disclosed in the official gazette.

[0005]

The detection operation of the charging current in the technique described in the above publication is performed by detecting the potential difference between both ends of the detection resistor inserted in the charging current supply path. Be seen.

The charging method in the case where the rechargeable battery is a nickel-cadmium battery is carried out at a constant current, so the resistance value of the detection resistor can be set in accordance with this current value. The rechargeable battery called an ion battery has the following problems.

That is, the charging characteristics of the lithium ion battery are
As shown in FIG. 2, the value of the charging current changes greatly. Therefore, if the resistance value of the detection resistor inserted in the charging current supply path for detecting the charging current is set in accordance with the point where the current is large, it cannot be detected at the point where the current is small. On the contrary, if it is set according to the point that the current is small, there is a problem that the voltage loss increases.

The present invention seeks to provide a charging circuit that improves on this point.

[0009]

SUMMARY OF THE INVENTION A charging circuit according to the present invention is for detection which is inserted and connected in a charging current supply path between a charging current supply circuit for supplying a charging current to a rechargeable battery and the rechargeable battery. Detects a potential difference between both ends of the resistance and the detection resistor, which changes according to the charging current flowing through the detection resistor, and conducts when the potential difference is large, and controls the charging current supply operation of the charging current supply circuit. And a diode connected in parallel with the detection resistor.

[0010]

In the present invention, a diode is connected in parallel to a detection resistor that is inserted and connected in the charging current supply path to detect the charging current, thereby reducing the voltage loss in the state where the charging current is large. Is.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The circuit shown in FIG. 1 is an embodiment of the charging circuit of the present invention. In the figure, 1 is a power supply terminal connected to a commercial AC power supply, 2 is a power supply transformer for stepping down an AC voltage to a predetermined voltage, 3 is a diode bridge circuit for rectifying the AC stepped down by the power supply transformer 2 to DC, Reference numeral 4 is a smoothing capacitor for smoothing the signal rectified by the diode bridge circuit 3, and constitutes a DC power supply circuit 5 together with the diode bridge circuit 3.

6 is a rechargeable battery such as a lithium ion battery,
A charging current supply circuit 7 is supplied with DC power from the DC power supply circuit 5 , and has a function of supplying a charging current to the rechargeable battery 6 based on the control operation of the charging control circuit 8.

Reference numeral 9 is a detection resistor that is inserted and connected in the charging current supply path between the charging current supply circuit 7 and the rechargeable battery 6, and 10 is for detecting the potential difference between both ends of the detection resistor 9. A detection transistor whose emitter is connected to the power source side of the resistor 9 and whose base is connected to the rechargeable battery 6 side of the resistor 9 via the resistor 11;
Its collector is connected to the charge control circuit 8.
Reference numeral 12 denotes a diode whose anode is connected to the power source side of the detection resistor 9 and whose cathode is connected to the rechargeable battery 6 side of the resistor 9.

In such a circuit configuration, the diode 12
The value and the like of the resistor 11 are set so that the detection transistor 10 is biased to be in a conductive state when is in a conductive state. Further, when the detection transistor 10 is inverted from the conductive state to the non-conductive state, the control operation of the charging control circuit 8 stops the supply operation of the charging current from the charging current supply circuit 7 to the rechargeable battery 6. There is.

The charging circuit of the present invention is configured as described above. Next, the operation of such a circuit will be described. The commercial AC power input from the power terminal 1 is the power transformer 2
Is stepped down and supplied to the DC power supply circuit 5 to be rectified and smoothed. When a DC voltage is output from the DC power supply circuit 5, a charging current supply circuit 7 by a charging control circuit 8
The control operation is performed, and the charging current is supplied from the charging current supply circuit 7 to the rechargeable battery 6.

At the start of the charging operation, since the charging current flowing through the rechargeable battery 6 is large as is apparent from the charging characteristic diagram shown in FIG. 2, the potential difference across the detection resistor 9 becomes large. Therefore, the diode 12 connected in parallel to the detection resistor 9 becomes conductive and the detection transistor 10 is biased to become conductive.

When the detection transistor 10 is turned on, a detection signal is sent from the collector to the charging control circuit 8,
That is, a signal indicating that the charging current is larger than the predetermined value is input. As a result, the charge control circuit 8
Judging that the capacity of the rechargeable battery 6 is low,
Since the control operation for the charging current supply circuit 7 is performed, the operation for supplying the charging current to the rechargeable battery 6 is performed.

As described above, the charging current is supplied from the charging current supply circuit 7 to the rechargeable battery 6 to perform the charging operation.
When the charging current is large, the charging current is supplied to the rechargeable battery 6 through the detection resistor 9 and the diode 12. That is, in such a charging state, the diode 12 is in a conducting state, so that the potential difference across the detection resistor 9 is suppressed to 0.7 to 1.0 V which is the forward voltage of the diode 12. . Therefore, the voltage loss can be reduced even if the charging current is large.

Although the charging operation is performed in such a state, if the charging capacity is increased by charging the rechargeable battery 6, the charging current decreases as apparent from the charging characteristic diagram of FIG. Then, when the value of the charging current decreases to the set value I, that is, when the charging is performed until time T, the diode 12 and the detection transistor 10 are inverted to the non-conducting state.

When the detection transistor 10 is inverted to the non-conducting state, the level of the detection signal input to the charge control circuit 8 is inverted. As a result, the charge control circuit 8
When it is determined that the capacity charged in the rechargeable battery 6 has reached a predetermined value, the charging current supply circuit 7 is controlled to stop the charging current supply operation to the rechargeable battery 6.

The charging operation according to the embodiment shown in FIG. 1 is performed as described above. However, since the potential difference across the detection resistor 9 is determined by the forward voltage of the diode 12, the detection resistor 9 is charged. The resistance value can be increased. That is, by increasing the resistance value of the detection resistor 9, the value of I, which is the detection value of the charging current, can be decreased, and thus the charging capacity of the rechargeable battery 6 is reduced to 1
It can be close to 00%.

The operation of the embodiment shown in FIG. 1 is performed as described above. Next, the embodiment shown in FIG. 3 will be described.
3, the same parts as those in FIG. 1 are designated by the same reference numerals.

In FIG. 3, reference numerals 13 and 14 denote a first detection resistor and a second detection resistor which are connected in series in the charging current supply path between the charging current supply circuit 7 and the rechargeable battery 6. The resistance value of the second detection resistor 14 is set larger than the resistance value of the first detection resistor 13.

Reference numeral 15 denotes a Schottky diode, the anode of which is connected to the power source side of the second detection resistor 14 and the cathode of which is connected to the rechargeable battery 6 side of the second detection resistor 14. Further, the emitter of the detection transistor 10 in this embodiment is connected to the power source side of the first detection resistor 13, and the base is connected to the rechargeable battery 6 side of the second detection resistor 14 via the resistor 11. There is.

In such a circuit configuration, when the Schottky diode 15 is in the conducting state, the detection transistor 10 is biased to bring it into the conducting state.
The value of the first detection resistor 13 and the like are set. Further, when the detection transistor 10 is inverted from the conductive state to the non-conductive state, the control operation of the charging control circuit 8 stops the supply operation of the charging current from the charging current supply circuit 7 to the rechargeable battery 6. There is.

The charging operation in such a circuit is performed in the same manner as in the embodiment shown in FIG. 1, but since the charging current flowing in the rechargeable battery 6 is large at the start of the charging operation, the first detection resistor 13 and The potential difference between both ends of the second detection resistor 14 increases and the potential difference between both ends of the second detection resistor 14 increases. Therefore, the Schottky diode 15 connected in parallel to the second detection resistor 14 becomes conductive and the detection transistor 10 is biased to become conductive.

Although the charging operation is performed in such a state, when the charging current is large, the Schottky diode 15 is in a conducting state, so that the first detection resistor 13 and the second detection resistor 14 are connected to each other. A charging current is supplied to the rechargeable battery 6 through a parallel circuit of the Schottky diode 15. That is, when the Schottky diode 15 is in the charged state, the Schottky diode 15 is in the conductive state, so that the potential difference across the second detection resistor 14 is 0.3 to 0. It is suppressed to about 5V. Therefore, even if the resistance value of the second detection resistor 14 is increased, the potential difference between both ends of the second detection resistor 14 does not increase, and the voltage loss during the charging operation can be reduced.

When the charging operation is performed and the charging capacity of the rechargeable battery 6 increases, the charging current decreases as described above.
Then, when the value of the charging current is reduced to the set value I, that is, when the charging is performed until the time T, the Schottky diode 15 and the detection transistor 10 are inverted to the non-conducting state.

When the detection transistor 10 is turned off, the charging control circuit 8 judges that the capacity charged in the rechargeable battery 6 has reached a predetermined value, and the charging current supply circuit 7 charges the battery. The operation of supplying the charging current to the battery 6 is stopped.

The charging operation according to the embodiment shown in FIG. 3 is performed as described above, but since the potential difference across the second detection resistor 14 is determined by the forward voltage of the Schottky diode 15, the second operation is performed. The resistance value of the detection resistor 14 can be increased. That is, the second detection resistor 14
The value of I, which is the detected value of the charging current, can be reduced by increasing the resistance value of 1, and thus the charging capacity of the rechargeable battery 6 can be made close to 100%.

Further, in FIG. 3, the first detection resistor 13
Is inserted and connected because the forward voltage of the Schottky diode 15 is smaller than the voltage value required to make the detection transistor 10 conductive. That is, the conductive state of the detection transistor 10 described above is determined by the potential difference across the first detection resistor 13 due to the Schottky diode 1.
The voltage of the first detection resistor 13 is equal to the value of the Schottky diode 1 because the forward voltage of 5 is applied.
It is set in consideration of the forward voltage of 5 and the operating point of the detection transistor 10.

In the embodiment shown in FIGS. 1 and 3, the charging current supply circuit 7 supplies the charging current to the rechargeable battery 6 when the decrease of the charging current to a predetermined value is detected by the detection transistor 10. Although the operation is stopped, a timer circuit may be provided to stop the charging current supply operation after a predetermined time.

That is, when a decrease in the charging current to a predetermined value is detected by the detection transistor 10, the timer circuit incorporated in the charging control circuit 8 performs the timer operation, and the charging current supply operation is started after a predetermined time. Configure to stop.

The timer operating time by the timer circuit is set based on the charging characteristic diagram shown in FIG. The detection operation of the charging current by the detection transistor 10 is performed when the current value becomes I, but since this current value I cannot be made zero, the charging current rechargeable battery 6 is charged at this point. If the supply operation of No. 2 is cut off, the charge capacity of the rechargeable battery 6 cannot be made 100%. If the charging current supply operation of the rechargeable battery 6 is continued for a predetermined time t from the time T when the detection transistor 10 detects the predetermined value I of the charging current, the charging capacity of the rechargeable battery 6 is approximately 100%.
Can be

[0035]

According to the present invention, since the diode is connected in parallel to the detection resistor inserted in the charging current supply path to detect the charging current, the voltage loss in the state where the charging current is large can be reduced. it can.

Since the potential difference across the detection resistor is determined by the forward voltage of the diode, the resistance value of the detection resistor can be increased. Therefore, the present invention has an advantage that the value of the detected charging current can be set small and the detecting operation can be performed immediately before the charging operation of the rechargeable battery is completed.

Further, according to the present invention, since the operation of supplying the charging current to the rechargeable battery is continued for a predetermined time from the time when the charging current detection operation is performed, the charging capacity of the rechargeable battery becomes approximately 100%. Can be charged until

[Brief description of drawings]

FIG. 1 is an example of a charging circuit of the present invention.

FIG. 2 is a charging characteristic diagram of a rechargeable battery.

FIG. 3 is an example of a charging circuit of the present invention.

[Explanation of symbols]

 6 Rechargeable Battery 7 Charging Current Supply Circuit 8 Charging Control Circuit 9 Detection Resistor 10 Detection Transistor 12 Diode 13 First Detection Resistor 14 Second Detection Resistor 15 Schottky Diode

Claims (4)

[Claims] 1. A charging current supply circuit for supplying a charging current to a rechargeable battery, a detection resistor inserted and connected in a charging current supply path between the charging current supply circuit and the rechargeable battery, A detection transistor that detects a potential difference across the detection resistor that changes according to the charging current flowing through the detection resistor, conducts when the potential difference is large, and controls the charging current supply operation of the charging current supply circuit. And a diode connected in parallel with the detection resistor. 2. A charging current supply circuit for supplying a charging current to a rechargeable battery, and first detection resistors connected in series in a charging current supply path between the charging current supply circuit and the rechargeable battery. And a second detection resistor having a resistance value larger than the first detection resistor, and a potential difference between both ends of the detection resistor that changes according to a charging current flowing through the first detection resistor and the second detection resistor. A charging circuit including a detection transistor that detects and conducts when the potential difference is large, and controls the charging current supply operation of the charging current supply circuit, and a Schottky diode connected in parallel to the second detection resistor. . 3. The method according to claim 1, wherein when the detection transistor is turned off, the operation of supplying the charging current from the charging current supply circuit to the rechargeable battery is stopped. The charging circuit described in. 4. A timer operation is performed when the detection transistor is reversed to a non-conducting state, and the operation of supplying the charging current from the charging current supply circuit to the rechargeable battery is stopped when the time set by the timer operation has elapsed. The charging circuit according to claim 1 or 2, wherein