HK1024345B - Charging and discharging control circuit and charging type power supply device - Google Patents

Description

Charging and discharging control circuit and charging type power supply device

Technical Field

The present invention relates to a charge and discharge control circuit for a secondary battery including a delay circuit using one capacitor, and also relates to a charging type power supply device using the charge and discharge control circuit.

Background

In fig. 2, there is shown a conventional charge and discharge control circuit for a secondary battery, which includes a delay circuit using a capacitor, and a charging type power supply device using the charge and discharge control circuit. In general, a rechargeable power supply device has been put on the market as a battery pack used in notebook PCs, camera integrated VTRs, and the like.

A charger is externally connected to the external terminals 106 and 107 to charge a secondary battery 103. When the battery 103 is in an overcharged state after charging has been performed, a comparator is switched so that the delay circuit 102 starts charging a capacitor 104. When the capacitor reaches a prescribed voltage, the delay circuit 102 outputs a signal that turns off a switching element 101 to stop charging the secondary battery 103.

The delay circuit using the charging and discharging of the capacitor shown in fig. 2 encounters the following problems.

In the above-described delay circuit, when the capacitor 104 is damaged and becomes a short-circuited state, a terminal 108 connected to the capacitor 104 is always fixed to a ground potential.

In this case, when the secondary battery 103 starts to be charged and the secondary battery is overcharged, the capacitor 104 must start to be charged. However, since capacitor 104 is in a fault state, the voltage on terminal 108 is at ground potential and does not rise. Therefore, the delay circuit 102 does not output a signal to turn off the switching element 101. As a result, the charging operation is continued, and the battery 103 will catch fire, for example, in the case of a lithium-ion battery.

In general, in a circuit provided for protection or safety improvement, some protection is necessary even if a failure occurs. That is, so-called "fail-safe" must be performed.

Disclosure of Invention

In order to solve the above-mentioned problems, according to the present invention, in a delay circuit which utilizes a charging and discharging operation of a capacitor to set a delay time, means for monitoring a voltage across the capacitor based on an external signal is provided to recognize whether a terminal voltage on the capacitor is a normal voltage.

According to an aspect of the present invention, there is provided a charge and discharge control circuit for controlling a charge and discharge operation of a secondary battery, the charge and discharge control circuit comprising: detecting means for detecting whether the secondary battery is in one of an overcharge state, an overdischarge state and an overcurrent state and generating a corresponding output signal; delay means for delaying said output signal from said condition sensing means, generating a delayed output signal, providing said delayed output signal to a switching element for opening a circuit containing said battery to prevent current flow through said battery; and a checking means for checking whether the delaying means operates normally.

According to another aspect of the present invention, there is provided a charging type power supply apparatus including: a storage battery; an external terminal connected to the battery; a switching element located between the battery and the external terminal; a charge and discharge control circuit including a delay device connected in parallel with the battery; and a checking means for checking whether the delaying means operates normally.

Drawings

Fig. 1 is a circuit diagram showing a charging type power supply apparatus using a charging and discharging control circuit according to the present invention.

Fig. 2 is a circuit diagram showing a conventional charging type power supply apparatus using a charging and discharging control circuit.

Detailed Description

In fig. 1 showing an embodiment of the present invention, the external terminals 106 and 107 are terminals for externally connecting a charger. The external terminal 106 is connected to a battery 103 via a charge stop switching element 101, and then to an external terminal 107. The positive voltage of the battery 103 is input to a charge and discharge control circuit 105. The charge and discharge control circuit 105 can be formed into one integrated circuit. The positive voltage of the battery 103 is input to a comparator 109, and the comparator 109 compares the positive voltage of the battery 103 with a reference voltage Vref of a reference voltage circuit. The output of the comparator 109 is supplied to the gate of the transistor 110 to turn on/off the transistor 110. One terminal of the transistor 110 is connected to a constant current source 111. Their node a is connected via a switch 112 to a capacitor 104 and also to a microcomputer or similar device, the capacitor 104 being connected to the terminal 108. Further, the node a is connected to a comparator 113, and the comparator 113 compares the voltage of the node a with a reference voltage Vref of a reference voltage circuit to control the on/off operation of the switching element 101. On the other hand, a signal from a microcomputer or the like is supplied to a terminal 114 and connected to the terminal 108 through an inverter, a resistor, and a switch 115. Also, another signal from a microcomputer or the like is supplied to a terminal 116 to control the opening and closing operations of the switches 112 and 115.

The operation of this embodiment will be described below. The secondary battery 103 is charged by a charger connected to the external terminals 106 and 107. In this case, the switching element 101 is conductive. As charging proceeds, when the voltage across the secondary battery 103 rises to a voltage at which a charge stop voltage is reached, that is, an overcharged state, the comparator 109 is switched to a low voltage. As a result, the transistor 110 is turned off. In this state, the switch 112 is closed, and the current from the constant current source 111 starts to charge the capacitor 104. This charging allows the voltage at node a to rise and when the voltage exceeds the reference voltage Vref on the reference voltage circuit provided to the comparator 113, the comparator 113 is switched to a high voltage to turn off the switching element 101. The time period during which the comparator 109 is switched to the low voltage and the time period during which the comparator 113 is switched to the high voltage correspond to one delay time. As a result, the operation of charging the battery 103 is stopped. The above description is applicable to a case where a system normally operates.

However, the system cannot operate normally in the event that the capacitor 104 is damaged and an internal short circuit is generated for some reason. In other words, since the terminal 108 is grounded, even if the current from the constant current source 111 flows through the node a, the voltage on the node a cannot rise. This disables the switching element 101 from being turned off, thereby continuing to charge the secondary battery 103, which results in a very dangerous situation. However, in the present invention, the signal from the microcomputer or the like and input to the terminals 114 and 116 can prevent such a dangerous situation. In particular, a signal input by terminal 116 turns switch 112 off and switch 115 on. Next, the signal input from the terminal 114, that is, the first signal is set to a low level signal, and a high level signal is supplied to the terminal 108. In this case, if the capacitor 104 is damaged due to an internal short circuit, the terminal 108 maintains a low voltage. This low voltage is supplied to an a/D converter such as a microcomputer, and the voltage is read by the a/D converter. Since the microcomputer outputs this low level signal to terminal 114, the voltage on terminal 108 is expected to be a high voltage. However, the microcomputer determines that the capacitor 104 is broken because the voltage at the terminal 108 is a low voltage due to the short circuit. In this case, the microcomputer can take an alarm by some means, so that the charging operation is immediately stopped or the use of the battery is stopped. On the other hand, the present invention is effective even in the case where the terminal 108 is abnormally shorted to a high voltage, such as VDD. That is, when the microcomputer inputs a high level signal to the terminal 114, although the terminal 108 should become a low voltage, a high voltage is supplied to the microcomputer due to some abnormality. The microcomputer judges that this is an abnormality, and can perform the same processing as described above.

In this embodiment, the judgment of the stop of the charging operation is made by the comparator 113. In addition, the stop of the charging operation can also be determined by a signal supplied to the microcomputer through the terminal 108. Specifically, it is detected whether or not the terminal voltage of the capacitor 104 is supplied to an a/D converter such as a microcomputer and whether or not it becomes a prescribed voltage. If the terminal voltage reaches the prescribed voltage, the microcomputer causes the charger to stop the charging operation, or issues a control signal, i.e., a second signal, so that the switching element 101 is turned off, although its connection is not shown in fig. 1.

Preferably, the means for checking whether the function of the delaying means is operating normally receives a first signal from a control means, such as a microcomputer, for outputting a second signal to said control means, such as a microcomputer, in response to the first signal.

Preferably, the means for checking whether the function of the delaying means is operating normally receives a first signal from a control means such as a microcomputer, so as to output a second signal to the control means such as a microcomputer in response to the first signal.

This embodiment is described using an example in which the charging and discharging control circuit 105 has only a charging control function. However, generally, the charge and discharge control circuit 105 additionally provides a function of suppressing an overcurrent or provides an overdischarge suppressing function by providing a switching element for suppressing overdischarge. In this example, the embodiment is suitable for use in the case where one delay circuit is required, as in the case of the overcharge suppressing function.

Although the present invention is described above, the present invention can be implemented regardless of variations or changes in the input and output logic of the comparator.

The above-described embodiments can be constituted by one semiconductor integrated circuit. In this case, it is difficult to provide a capacitor in the integrated circuit and to connect the capacitor to the outside. Thus, the effect of the present invention is shown.

As described above, since an abnormal state in which the inside of the capacitor is short-circuited or the terminal is short-circuited to the potential of the electric field voltage or the ground potential can be detected with the addition of only a simple circuit, the present invention increases the reliability of the entire device and improves the safety.

Claims (4)

1. A charge and discharge control circuit for controlling charge and discharge operations of a secondary battery, the charge and discharge control circuit comprising:

detecting means for detecting whether the secondary battery is in one of an overcharge state, an overdischarge state and an overcurrent state and generating a corresponding output signal;

delay means for delaying said output signal from said condition sensing means, generating a delayed output signal, providing said delayed output signal to a switching element for opening a circuit containing said battery to prevent current flow through said battery; and

checking means for checking whether the delaying means operates normally.

2. A charging type power supply device comprising:

a storage battery;

an external terminal connected to the battery;

a switching element located between the battery and the external terminal;

a charge and discharge control circuit including a delay device connected in parallel with the battery; and

checking means for checking whether the delaying means operates normally.

3. The charge and discharge control circuit of claim 1, wherein: said means for checking whether the function of said delaying means is operating normally receives a first signal from a control means, such as a microcomputer, to output a second signal to said control means, such as a microcomputer, in response to the first signal.

4. The charging type power supply device according to claim 2, wherein: said means for checking whether the function of said delaying means is operating normally receives a first signal from a control means, such as a microcomputer, for outputting a second signal to said control means, such as a microcomputer, in response to the first signal.