JP2010011574A - Charging/discharging control circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a charging/discharging control circuit having an inexpensive safety device which prevents an overcharge caused when a signal showing the completion of the charging of a secondary battery cannot be detected due to the shortage of a charging current when charging the high-capacity secondary battery. <P>SOLUTION: The charging/discharging control circuit includes: a secondary battery block charged with power from an external power supply input terminal; a charging/discharging control circuit which controls the charging/discharging of the secondary battery block; an electronic switch means which turns on and off a charging/discharging path to the secondary battery block; a battery temperature-voltage conversion means which converts a temperature to a voltage by dividing a reference voltage by using a thermistor which has a negative temperature coefficient and varies a resistance value by a temperature of the secondary battery, and a fixed resistor which is connected to the thermistor in series thereto; and a battery abnormal temperature monitoring means which operates independently from the charging/discharging control circuit, and monitors an output voltage of the battery temperature-voltage conversion means. The charging/discharging control device is also characterized in that the electronic switch is forcibly turned off, and connects the thermistor and the resistor in parallel with each other when the output voltage of the battery temperature-voltage conversion means exceeds a predetermined range. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a charge / discharge control circuit for a secondary battery.

  In recent years, portable electronic devices such as notebook personal computers, mobile phones, and PDAs have become widespread, and secondary batteries have been widely used as power sources. Along with this, secondary batteries have been increasingly adopted as a power source for devices that have conventionally employed dry batteries. Normally, as a method for charging these secondary batteries, a temperature sensor for monitoring the temperature of the battery is attached, and charging control is performed by knowing the charging state of the secondary battery by input from this temperature sensor. It is common.

  On the other hand, the energy density stored, as typified by lithium secondary batteries for mobile phones, has been improving year by year. There is now more safety than ever. At the same time, consumer demand for prices has become stricter year by year, and even safety-related parts can no longer be indifferent to costs.

  In recent years, a number of AC adapters have been released that use the USB mounted on personal computers as a power source for battery charging and that use the USB mounted on the personal computer only as a power connector. There is a movement to standardize the output. As a consumer need, a general-purpose charger and power source are required instead of a dedicated charger and a battery pack.

  A battery pack in which a plurality of unit cells are grouped is known as a conventional secondary battery for product operation. This battery pack normally has a thermistor built in as a temperature sensor. As a safety device for these batteries, a PTC and a current fuse are further incorporated in the pack battery, and when the battery is in an abnormal state, these safety devices work to prevent ignition and smoke.

  On the other hand, these secondary batteries are packed as pack batteries with different sizes and ratings for each product, and there is no mutual compatibility between different models, and the charger is also compatible between different models. There was no. With regard to the charger, as is typified by a mobile phone, it is commonly used as a trend in the world, and as a conventional product, a charger that charges a commercially available battery using a USB power feeding function is known.

  The conventional charging / discharging circuit is a secondary battery that is a chemical battery such as a Ni-MH battery or a lithium ion battery, a PTC that is a thermal protection blocking element, an electronic switch element, and an overcharge or overdischarge protection. A temperature detection unit that detects a temperature to be performed, a discharge control switch element that is an external switch element based on the temperature detected by the temperature detection unit, a switch control circuit that controls on / off of the charge control switch element, and the like (For example, refer to Patent Document 1 and Patent Document 2).

On the other hand, many commercially available USB chargers charge a battery by simply stepping down 5V from a power input terminal in order to charge one or two AA batteries. However, in the current USB standard, only a current of up to 500 mA can be taken out, and charging cannot be performed with a current higher than that.
Japanese Patent No. 3534309 JP 2006-149177 A

  However, in the conventional configuration, only a PTC or a current fuse is used as a safety device in the event of a device malfunction, and when the control circuit runs away, the temperature protection depends only on an element having a temperature protection function such as a PTC. . Therefore, a circuit configuration using a combination of a circuit for protecting overcharge and overdischarge and a PTC, or a combination of a thermal fuse has been adopted.

  The PTC is a positive temperature characteristic thermistor that is normally mounted on the secondary battery side and has a high impedance so that charging / discharging current does not flow when the temperature of the secondary battery becomes high. Additional safety devices are required from the flow.

  In addition, the conventional charger cannot obtain a charging current of 500 mA or more, and a secondary battery with a higher capacity recently has a charging current shortage, so a secondary battery charging completion signal (temperature change or battery terminal voltage change) As a result, overcharge was easily performed, and as a result, secondary battery deterioration was promoted. Further, when a plurality of secondary batteries having different capacities are attached, there is a problem that proper charging cannot be performed for each battery.

  In order to solve the conventional problems, the charge / discharge control circuit of the present invention performs charge / discharge control of an external power supply input terminal, a secondary battery block charged with electric power from the external power supply input terminal, and the secondary battery block. A charge / discharge control circuit, an electronic switch means for turning on / off a charge / discharge path to the secondary battery block, a thermistor having a negative temperature coefficient and a resistance value varying with the temperature of the secondary battery, and the thermistor connected in series A battery temperature / voltage conversion means for converting a temperature into a voltage by dividing a reference voltage with a fixed resistor, and a battery that operates independently of the charge / discharge control circuit and monitors the output voltage of the battery temperature / voltage conversion means Having an abnormal temperature monitoring means, when the output voltage of the battery temperature voltage conversion means is out of a certain range, the electronic switch means is forcibly turned off and the thermistor and resistor are connected in parallel. And wherein the Rukoto.

  By using the present invention, it is possible to add a secondary battery protection circuit at low cost using a temperature sensor that is normally used for control by the charge control circuit, and to charge a plurality of batteries. In addition, since the battery block connection switching circuit performs circuit switching so that the secondary battery can be individually charged during charging, a sufficient charging current can be obtained. Further, at the time of discharging, the secondary battery can be switched to the serial connection by the battery block connection switching circuit, and a high voltage output can be obtained. As described above, according to the present invention, the additional safety device can be configured at low cost by using the voltage monitoring IC that is distributed at low cost.

  Furthermore, it is possible to obtain a sufficient charging current for performing accurate charging control using an inexpensive charger on the market, and it is possible to minimize deterioration of the secondary battery.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

(Embodiment 1)
FIG. 1 is an explanatory view showing Embodiment 1 with a charge / discharge control circuit according to the present invention. In FIG. 1, secondary batteries 1a and 1b are chemical cells such as nickel-cadmium batteries, nickel-metal hydride batteries, lithium ion batteries, and lithium polymer batteries, and charge control switch element 5 is a switch element for performing charge control. The control switch element 6 is a switch element for performing control during discharge.

  At the time of charging, the charge / discharge control circuit 4 controls the gate of the charge control switch element 6 to charge the secondary batteries 1a and 1b with a predetermined voltage and current. At that time, when a sufficient current for charging cannot be obtained, the charge / discharge control circuit 4 switches the switch control circuit 3 to alternately charge the secondary batteries 1a and 1b. During discharging, the charge / discharge control circuit 4 switches the discharge control control switch element 6 in series and supplies power to the external power output terminal 101.

  During charging or discharging, the charge / discharge control circuit 4 monitors the temperature of the secondary batteries 1a and 1b by monitoring the voltage divided by the thermistor 7 thermally coupled to the secondary batteries 1a and 1b and the reference voltage. When an abnormal state is detected, a low level voltage is applied to the gates of the charge control switch element 5 and the discharge control switch element 6 to turn off the charge control switch element 5 and the discharge control switch element 6, and the unsafe state is established. Control to prevent it.

  Further, even when the charge / discharge control circuit 4 fails, the voltage detection unit 2 operating independently of the charge / discharge control circuit 4 includes a thermistor 7 thermally coupled to the secondary battery and a reference voltage. The divided voltage is monitored, and when it falls below a predetermined voltage level, a Low level is output.

  The diode element 8 is an element for cutting off the signals of the respective control units and enabling the signals to the respective units only when the voltage detection unit 2 outputs a low level, and further control in the event of an abnormality is required. In this case, by connecting the diodes in parallel, control can be performed without affecting other block operations during normal operation.

  The feedback resistor 9 is electrically connected in parallel with the thermistor 7 when the voltage detection unit 2 outputs a low level in the event of an abnormality, thereby forcibly reducing the divided input voltage of the voltage detection unit 2 and the secondary battery 1a. And 1b are for maintaining the state until the temperature is sufficiently lowered.

  When the USB is connected to the external power input terminal 100, only 2.5V power of 5V500mA is normally supplied. Usually, a secondary battery such as a nickel metal hydride battery cannot detect a voltage change or a temperature change after completion of charging unless it is charged with a current of a certain level or more in order to perform charging control. When the battery capacities of the secondary batteries 1a and 1b are large, the power is insufficient to charge the two secondary batteries at the same time. At that time, the switch control circuit 3 can be switched to charge the secondary batteries 1a and 1b individually to ensure necessary power. Further, at the time of discharging, the switch control circuit 3 can be switched in series to perform a high voltage output.

  In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible. For example, in the above embodiment, two secondary batteries have been described. However, the number of contacts of the switch control circuit 3 can be increased to increase the number of secondary batteries to be charged. Moreover, at the time of discharge, each secondary battery can also be output in parallel.

  The charge / discharge control circuit according to the present invention can add a secondary battery protection circuit at a low cost by using a temperature sensor normally used for control by the charge control circuit, and also charges a plurality of batteries. However, since the battery block connection switching circuit performs circuit switching so that each secondary battery can be charged individually during charging, a sufficient charging current can be obtained, and charging of a charger that can be charged at a low cost is appropriate. It is useful as a discharge control circuit.

Explanatory drawing which shows Embodiment 1 of this invention

Explanation of symbols

1 Secondary battery block 1a Secondary battery A
1b Secondary battery B
2 Voltage detector 3 Switch control circuit 4 Charge / discharge control circuit 5 Charge control switch element 6 Discharge control switch element 7 Thermistor 8 Diode element 100 External power input terminal 101 External power output terminal

Claims (7)

An external power input terminal,
A secondary battery block charged with power from the external power input terminal;
A charge / discharge control circuit for charge / discharge control of the secondary battery block;
Electronic switch means for turning on / off the charge / discharge path to the secondary battery block;
A thermistor having a negative temperature coefficient and a resistance value that varies with the temperature of the secondary battery;
Battery temperature / voltage converting means for converting temperature to voltage by dividing a reference voltage with a fixed resistor connected in series with the thermistor;
The electronic switch has battery abnormal temperature monitoring means that operates independently of the charge / discharge control circuit and monitors the output voltage of the battery temperature voltage conversion means, and the electronic switch when the output voltage of the battery temperature voltage conversion means falls outside a certain range A charge / discharge control circuit characterized in that the means is forcibly turned off and the thermistor and a resistor are connected in parallel.   2. The charge / discharge control circuit according to claim 1, wherein the external power input terminal is a USB terminal, has a USB communication block for performing USB communication, and starts charging after performing USB communication.   The secondary battery block is composed of a plurality of unit cells that can be replaced for each unit cell, and has a battery block connection switching circuit for switching the series / parallel connection of the secondary battery blocks. The charge / discharge control circuit according to claim 1, wherein charging is performed for each battery, and the cells are connected in series at the time of discharging.   The charge / discharge control circuit according to claim 2, wherein the secondary battery can be detached for each secondary battery block.   The charge control circuit has a charge state storage means for storing the charge state of each secondary battery block, and the charge / discharge control circuit supplies power to the external power supply output terminal unless all the secondary battery blocks are fully charged. 3. The charge / discharge control circuit according to claim 2, further comprising discharge prohibiting means for prohibiting.   The charge control circuit has a charge state storage means for storing the charge state of each secondary battery block and a battery capacity detection means for the secondary battery block, and all the secondary battery blocks are fully charged and all the secondary battery blocks are in a fully charged state. 3. The charge / discharge control circuit according to claim 2, further comprising a discharge prohibiting unit that prohibits power supply from the secondary battery to the voltage converting unit unless the battery capacity of the secondary battery block is within a certain range.   The charge control circuit has means for monitoring the voltage of each secondary battery block, and when there is no external power input, when the voltage of each secondary battery block falls below a predetermined value, voltage conversion is performed from the secondary battery. 3. The charge / discharge control circuit according to claim 2, further comprising discharge prohibiting means for prohibiting power supply to the means.

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