JP3469709B2 - Battery charge control device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a battery charge control device provided with a pulse charging circuit for pulse charging a secondary battery and an overcurrent protection circuit for protecting the secondary battery from overcurrent.

[0002]

2. Description of the Related Art FIG. 3 shows a battery charge control device having a pulse charging circuit for pulse charging a secondary battery and an overcurrent protection circuit for protecting the secondary battery from an overcurrent.

In this device, for example, a secondary battery B composed of a lithium ion secondary battery, a switching element Q1 composed of a MOSFET connected in series to the secondary battery B, and a battery voltage of the secondary battery B are set to a set voltage. When it exceeds, the switching element Q1 is turned off, and when the battery voltage becomes lower than the set voltage, the switching element Q1 is turned on. When the charging current flowing through the secondary battery B exceeds the set value, the switching element Q1 is turned on. And an overcurrent protection circuit 2 that is turned off.

The pulse charging circuit 1 outputs a low level signal from the output terminal OUT when the battery voltage of the secondary battery B exceeds a set voltage (for example, 4.20V). As a result, the switching element Q1 is turned off by turning on the transistors Q2 and Q3. On the other hand, when the battery voltage of the secondary battery B falls below the set voltage, a high level signal is output from the output terminal OUT. Therefore, the transistors Q2 and Q3 are turned off, and the switching element Q1 is turned on.

On the other hand, the overcurrent protection circuit 2 has a switching element Q based on the ON resistance component of the switching element Q1.
The voltage across 1 is measured and this is compared with the reference voltage by the comparator COMP. Then, when the voltage across both ends is higher than the reference voltage, that is, when the charging current flowing through the secondary battery B exceeds the set value, the comparator COMP outputs a high level signal to turn on the transistor Q3 and turn on the switching element Q1. Turn off.

An excessive current may be detected by connecting a current detecting resistor in series with the secondary battery B and detecting the voltage across the current detecting resistor.

[0007]

However, the above-mentioned device has the following problems. That is, when the pulse charging circuit 1 outputs the low level signal from the output terminal OUT to turn off the switching element Q1, the voltage across the switching element Q1 (that is, the comparator C
If the charging voltage is Vc and the battery voltage is Vb, Voff = (Vc−V)
b). The magnitude of this Voff is the reference voltage (that is,
If it is larger than the voltage of the negative input terminal of the comparator COMP, the comparator COMP outputs a high level signal.

Therefore, the output terminal OU of the pulse charging circuit 1
Even when the high level signal is output from T and the transistor Q2 is turned off, the transistor Q3 is kept on by the high level signal output from the comparator COMP. As a result, the switching element Q1 maintains the off state, and the secondary battery B is no longer charged.

Such an erroneous operation is highly likely to occur when the battery voltage of the secondary battery B is low (thus, the magnitude of Voff becomes large), which is not preferable.

[0010]

SUMMARY OF THE INVENTION A battery charge control device according to the present invention includes a secondary battery, a switching element connected in series with the secondary battery, and a battery voltage of the secondary battery exceeding a set voltage. Turning off the switching element,
A pulse charging circuit for the ON state of the switching element and the battery voltage becomes lower than the set voltage, the switching
A charging current flowing through the secondary battery based on the voltage across the switching element, an overcurrent protection circuit for turning off the switching element when the charging current exceeds a set value, and the pulse charging circuit. When the switching element is turned off, the operation of the overcurrent protection circuit is canceled.

Further, the battery charging control device according to the present invention includes a secondary battery, a switching element connected in series with the secondary battery, and the switching element when the battery voltage of the secondary battery is lower than a set voltage. is turned on, a pulse charging circuit for outputting an on-off signal for the switching element in the off state and the battery voltage exceeds the set voltage, the
A charging current that flows through the secondary battery based on the voltage across the switching element is detected, and an overcurrent protection circuit that outputs an off signal that turns off the switching element when the charging current exceeds a set value is provided. When the pulse charging circuit outputs an ON signal, the switching element is forcibly turned on regardless of the output signal of the overcurrent protection circuit.

[0012]

FIG. 1 shows an embodiment of the present invention. The device of this embodiment is different from the device of FIG. 3 in that a transistor Q5 which is on / off controlled by the output of the transistor Q2 is connected between the output terminal of the comparator COMP and the ground potential.

The pulse charging circuit 1 outputs a low level signal from the output terminal OUT when the battery voltage of the secondary battery B exceeds the set voltage. As a result, the switching element Q1 is turned off by turning on the transistors Q2 and Q3.

At this time, the transistor Q5 is turned on and the potential of the output terminal of the comparator COMP becomes the ground potential, so that the potential of the + side input terminal of the comparator COMP becomes higher than the potential of the − side input terminal. However, the potential of the output terminal of the comparator COMP never becomes high level. Therefore, when the transistor Q2 is turned off, the transistor Q3 is also turned off and the switching element Q1 is turned on.

On the other hand, when the battery voltage of the secondary battery B falls below the set voltage, a high level signal is output from the output terminal OUT. Therefore, the transistors Q2 and Q3 are turned off, and the switching element Q1 is turned on.

At this time, since the transistor Q5 is in the off state, when the charging current flowing through the secondary battery B exceeds the set value, the comparator COMP outputs a high level signal to turn on the transistor Q3. , The switching element Q1 is turned off.

FIG. 2 shows another embodiment of the present invention.
The device of this embodiment differs from the device of FIG. 3 in that the transistor Q2 is on / off controlled by the output of the transistor Q2.
4 and a transistor Q6 connected between the base and the emitter of the transistor Q3 and controlled to be turned on and off by the transistor Q4, and C between the transistors Q4 and Q6.
The R time constant circuits C1 and R1 are connected.

In such a configuration, when the pulse charging circuit 1 outputs a low level signal from the output terminal OUT to turn off the switching element Q1, the voltage Voff across the switching element Q1 is the reference voltage (as described above). That is, the voltage of the negative side input terminal of the comparator COMP)
If it is larger, the comparator COMP outputs a high level signal. Therefore, the output terminal O of the pulse charging circuit 1
A high level signal is output from the UT, and the transistor Q3
Is in the on state, and the switching element Q1 maintains the off state.

From this state, the battery voltage of the secondary battery B falls below the set voltage, and the pulse charging circuit 1 outputs the output terminal OUT.
When a higher level signal is output, the transistor Q2 is turned off and the transistor Q4 is turned on. Therefore, the transistor Q6 is turned on for the time determined by the CR time constant circuits C1 and R1, so that the transistor Q3 turns off the transistor Q3 even if the comparator COMP outputs a high level signal. As a result, the switching element Q1 is turned on, and the secondary battery B can be charged.

When the time constant time determined by the CR time constant circuits C1 and R1 elapses, the transistor Q6 is turned off, so that the overcurrent protection circuit 2 causes the charging current flowing in the secondary battery B to reach a set value. When a high level signal is output from the comparator COMP when it is detected that
The transistor Q3 is turned on and the switching element Q1 is turned off.

[0021]

According to the present invention, a secondary battery, a switching element connected in series to the secondary battery, and when the battery voltage of the secondary battery exceeds a set voltage, the switching element is turned off, A pulse charging circuit that turns on the switching element when the battery voltage becomes lower than a set voltage, and an overcurrent protection circuit that turns off the switching element when the charging current flowing through the secondary battery exceeds a set value. When the pulse charging circuit turns off the switching element, the operation of the overcurrent protection circuit is canceled, so that malfunctions due to the overcurrent protection circuit are prevented and pulse charging of the secondary battery by the pulse charging circuit is prevented. And the protection operation by the overcurrent protection circuit can be performed accurately.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is a circuit diagram showing another embodiment of the present invention.

FIG. 3 is a circuit diagram showing a conventional example.

[Explanation of symbols]

B secondary battery Q1 switching element 1 pulse charging circuit 2 Overcurrent protection circuit

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Claims (2)

(57) [Claims] 1. A secondary battery, a switching element connected in series to the secondary battery, and when the battery voltage of the secondary battery exceeds a set voltage, the switching element is turned off so that the battery voltage is lower than the set voltage. When it becomes low, the pulse charging circuit that turns on the switching element and the switch
A charging current flowing through the secondary battery is detected based on the voltage across the charging element, and an overcurrent protection circuit that turns off the switching element when the charging current exceeds a set value is provided, and the pulse charging circuit is A battery charge controller, wherein the operation of the overcurrent protection circuit is canceled when the switching element is turned off. 2. A secondary battery, a switching element connected in series to the secondary battery, and when the battery voltage of the secondary battery is lower than a set voltage, the switching element is turned on, and the battery voltage changes to the set voltage. When it exceeds, a pulse charging circuit that outputs an on / off signal that turns off the switching element, and a charging current that flows through the secondary battery is detected based on the voltage across the switching element. An overcurrent protection circuit that outputs an off signal that turns off the switching element when it exceeds a set value, and when the pulse charging circuit outputs an on signal, it is forced regardless of the output signal of the overcurrent protection circuit. A charging control device for a battery, wherein the switching element is turned on.