JPH0365102B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a charging circuit for a secondary battery as a backup power source used in communication terminal devices and the like.

(Conventional technology) Traditionally, disaster prevention equipment such as communication terminals and fire alarms that use commercial power supplies have been powered by secondary batteries as a backup power source in order to prevent loss of functionality even in the event of a commercial power outage. It was adopted in

As a method for monitoring performance deterioration of secondary batteries in such a backup power source, for example,
As shown in Publication No. 106336, when it is detected that the terminal voltage of a secondary battery during trickle charging has decreased below the reference value, a predetermined rapid charging current is applied to the secondary battery, and then a predetermined forced charging current is applied to the secondary battery. A method has been proposed in which the performance of the secondary battery is determined by performing a discharge and comparing the terminal voltage during the discharge or at the end of the discharge with a reference voltage again.

In order to enable such a backup power source monitoring system, a charging circuit for a secondary battery is required to have a rapid charging function and a trickle charging function over a wide temperature range.

(Problems to be Solved by the Invention) Up to now, a secondary battery charging circuit that satisfies the various functions described above and has a simple configuration has not been provided. According to the present invention, the magnitude of the trickle charging current supplied by applying a trickle charging signal is automatically controlled according to the ambient temperature, and the trickle charging signal is stopped to change from trickle charging to quick charging. The present invention provides a switchable secondary battery charging circuit.

(Means for Solving the Problems) In order to achieve this object, a charging circuit for a secondary battery according to the present invention includes a DC power supply and a constant current circuit that performs constant current control on the charging current supplied from the DC power supply. , a reference voltage source for generating a reference voltage to be supplied to the constant current circuit, and a voltage dividing resistor group consisting of a first resistor, a second resistor, and a third resistor for dividing the voltage of the reference voltage source. and a transistor switch circuit that shorts both ends of the first resistor according to a separately supplied trickle charge signal, and a transistor switch circuit that is connected in parallel to the second resistor and that shorts the second resistor depending on the ambient temperature. and a bypass circuit that bypasses a part of the flowing current, so that the reference voltage for operating the constant current circuit is given as the sum of the voltages across the first resistor and the second resistor. This is what I did.

(Function) According to this configuration, when the trickle charge signal is applied, the first resistor is short-circuited by the transistor switch circuit, so that the reference voltage supplied to the constant current circuit is set to the voltage of the reference voltage source. 2nd and 3rd
The voltage is divided by the resistors, and has a smaller value than when the first resistor is not short-circuited. The constant current circuit operates so that this reference voltage and the voltage drop across the fourth resistor caused by the charging current flowing through the fourth resistor are always equal, so the charging current in this case is small; It becomes a trickle charging current. Further, part of the current flowing through the second resistor flows into a bypass circuit connected across this resistor,
Moreover, the magnitude of the bypass current changes depending on the ambient temperature. As the bypassing current increases, the current flowing through the second resistor decreases, the reference voltage decreases by that amount, and as a result, the trickle current decreases.

Next, when the application of the trickle charge signal is stopped, a voltage is generated across the first resistor, and this voltage automatically turns the bypass circuit into a cut-off state. Therefore, the reference voltage is the sum of the voltages across the first resistor and the second resistor, and has a large value. As a result, the charging current increases and becomes a rapid charging current.

(Example) An example of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a secondary battery charging circuit in one embodiment of the present invention. In FIG. 1, 1 is a DC power supply, 2 is a constant current circuit that controls the charging current supplied from the DC power supply 1,
It mainly consists of an error amplifier A and a first transistor Tr _-1 for current control, and the output of the first transistor Tr _-1 is connected to the secondary battery 7 via a fourth resistor _R4 and a backflow prevention diode D. Supplied.
A reference voltage source 3 is mainly composed of a Zener diode Z, and one end of the reference voltage source 3 is connected to the collector of the first transistor Tr _-1 .
4 is a voltage dividing resistor group, which is composed of a series circuit of a first resistor R ₁ , a second resistor R ₂ and a third resistor R ₃ , divides the voltage of the reference voltage source 3, and divides the voltage of the reference voltage source 3.
Generates Vref. Reference numeral 5 denotes a transistor switch circuit, which is mainly composed of two transistors, second and third, Tr _-2 and Tr _-3 . Third
The emitter and collector of the transistor Tr _-3 are respectively connected to both ends of the first resistor R ₁ . Reference numeral 6 denotes a bypass circuit, which is mainly composed of a fourth transistor Tr _-4 , a heat-sensitive element R _t , and the like. The emitter of the fourth transistor Tr _-4 is connected to the connection point between the first resistor _R1 and the second resistor _R2 , and the collector is connected to the second resistor R2 and the _third resistor through the fifth resistor _R5 . The resistor R is connected to the connection point of ₃ .
Further, the base is supplied with a voltage obtained by dividing the voltage of the reference voltage source 3 by the sixth resistor R ₆ and the parallel resistances of the heat-sensitive element R _t and the seventh resistor R ₇ .

The operation of the charging circuit for the secondary battery 7 configured as described above will be described below.

First, a state in which a trickle charge signal is applied to the input terminal L of the transistor switch circuit 5 will be described. Application of this trickle charge signal turns on the second transistor Tr _-2 and the third transistor Tr _-3 . As a result, the first resistance R ₁
Since both ends of Tr -3 are short-circuited by the third transistor Tr _-3 , the reference voltage supplied to the constant current circuit 2
Vref becomes a small value. The constant current circuit 2 operates so that the voltage drop occurring across the fourth resistor _R4 due to the charging current is equal to the value of the reference voltage Vref, so the value of the charging current is small and trickle charging is performed.

Next, the temperature characteristics of trickle charging current will be explained. Assuming that a thermistor is used as the heat-sensitive element R _t , when the ambient temperature is high, the resistance value of the thermistor R _t is small, and therefore the base voltage of the fourth transistor Tr _-4 becomes small _. becomes non-conducting. In this case, the reference voltage Vref is the voltage of the reference voltage source 3
This is a value obtained by dividing the voltage between R ₂ and the third resistor R ₃ , and is a constant value that is independent of temperature.

FIG. 2 is a diagram showing the relationship between ambient temperature and trickle current. The above-mentioned case where the ambient temperature is high corresponds to the part A in FIG. As the ambient temperature decreases, the base voltage of the fourth transistor Tr _-4 gradually increases, and eventually the collector current begins to flow. This point corresponds to the part B in FIG. When the ambient temperature further decreases, the collector current of the fourth transistor Tr _-4 increases,
Since the current flowing through the second resistor R ₂ is bypassed by the fourth transistor Tr _-4 by that amount, the reference voltage Vref becomes smaller and the trickle current decreases. This corresponds to part C in FIG.
When the ambient temperature further decreases, the collector current of the fourth transistor Tr _-4 saturates, and the increase in the collector current stops. This corresponds to part 2 in FIG.

Next, the operation when the application of the trickle charge signal is stopped will be described. When application of the trickle charge signal is stopped, the second transistor
Tr _-2 and third transistor Tr _-3 become non-conductive. As a result, the first resistance R ₁ and the second resistance R ₂
A voltage is generated at the connection point of , and the emitter of the fourth transistor Tr _-4 is connected to this point, so
The voltage between the base and emitter of the fourth transistor Tr _-4 decreases, and the fourth transistor Tr _-4
becomes non-conducting. As a result, the reference voltage Vref is the voltage of the reference voltage source 3 which is connected to the first resistor _R1 and the second resistor R1.
The value is obtained by dividing the voltage between the series resistance _R2 and the third resistor _R3 , which can be made larger than that during trickle charging, and is a constant value that is independent of temperature. By setting the charging current at this time equal to the rapid charging current, rapid charging can be performed.

In this embodiment, the reference voltage source 3 is mainly composed of a Zener diode, but the reference voltage source 3 is not limited to this.

(Effects of the Invention) As described above in detail, the present invention includes a DC power supply, a constant current circuit, a reference voltage source, a voltage dividing resistor group that divides the voltage of the reference voltage source, and a voltage dividing resistor group that divides the voltage of the reference voltage source. The structure consists of a transistor switch circuit that short-circuits one of the resistors in the voltage-dividing resistor group, and a bypass circuit that bypasses the current flowing through the other resistor in the voltage-dividing resistor group depending on the ambient temperature, so rapid charging and trickle charging are possible. It is easy to switch, and has the effect of supplying an appropriate charging current, such as reducing the trickle charging current at low temperatures depending on the temperature.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention, and FIG. 2 is a diagram showing the relationship between the magnitude of the trickle charging current of the charging circuit according to the present invention and the ambient temperature. DESCRIPTION OF SYMBOLS 1... DC power supply, 2... Constant current circuit, 3... Reference voltage source, 4... Voltage dividing resistor group, 5... Transistor switch circuit, 6... Bypass circuit, D... Backflow blocking diode, 7... ...Secondary battery, A...Error amplifier, Tr _-1 to Tr _-4 ...Transistor, Z...
Zener diode, L... input terminal, R _t ...
heat sensitive element.

Claims (1)

[Claims] 1. A DC power supply, a constant current circuit that performs constant current control of the charging current supplied from the DC power supply, a reference voltage source for generating a reference voltage to be supplied to the constant current circuit, and a voltage of the reference voltage source. First distribution
a voltage dividing resistor group consisting of a resistor, a second resistor, and a third resistor, a transistor switch circuit that shorts both ends of the first resistor by a separately supplied trickle charge signal, and a transistor switch circuit that shorts both ends of the first resistor; a bypass circuit that is connected in parallel and bypasses a portion of the current flowing through the second resistor depending on the ambient temperature, and the reference voltage is a voltage across the first resistor and the second resistor. A charging circuit for a secondary battery, characterized in that the charging circuit is supplied as the sum of the following.