JPH0475436A - Secondary battery charging circuit - Google Patents

Abstract

PURPOSE:To improve reliability and safety and to reduce cost through reduction of the number of component by judging the loading of a new secondary battery without employing mechanical contacts and resetting a holding circuit based on the judgment. CONSTITUTION:At the final stage of charging operation, temperature of a battery 6 rises and the output of a temperature detecting circuit 8 goes High and thereby a thyristor 23 is turned ON to interrupt quick charging operation. When the battery 6 is temporarily removed and a new battery 6 is loaded, voltage Va at point A drops and the output of a voltage comparator 11 in a voltage detecting circuit 10 makes a transition from Low to High level. Consequently, a transistor 27 in a pulse generating circuit 14 is turned ON for a time interval determined by the time constant of a capacitor 25 and a resistor 26 and since retaining current does not flow through a thyristor 23, the thyristor 23 is turned OFF thus starting quick charge operation.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a charging circuit for a secondary battery, and more particularly to a charging circuit that controls charging by detecting the temperature of a secondary battery during charging.

(Prior Art) There are various charging methods for secondary batteries, but one method that prevents overcharging by detecting the temperature of the secondary battery and controlling charging is, for example, disclosed in Japanese Patent Laid-Open No. 83 -2774
There is a charging circuit described in Publication No. 31.

In this known charging circuit, the temperature determination circuit is reset by a mechanism that turns on and off mechanical contacts in response to attachment and detachment of the secondary battery to the charger. Specifically, for example, when a secondary battery is inserted into a charger, the contact is turned OFF and the temperature detection circuit is reset, allowing the temperature detection circuit to determine when the newly installed battery has finished charging. .

(Problems to be Solved by the Invention) However, since the conventional charging circuit described above uses mechanical contacts, it not only has a large number of mechanical parts and is expensive, but also tends to have low reliability and unstable operation.

For example, in conventional charging circuits, when a secondary battery is inserted into a charger, the contacts are turned OFF, or even if the battery is inserted, the contacts do not work properly and remain ON, resulting in a temperature detection circuit. Since the temperature is not set, the temperature discrimination circuit will not work even if the temperature rises, and charging will not stop. In such a case, the secondary battery may become overcharged and cause an abnormal temperature rise, which may cause damage to the battery itself or equipment that uses it.

The present invention has been made to solve these conventional problems, and is designed to prevent damage to the secondary battery in a charging circuit that prevents overcharging by measuring the temperature of the secondary battery and controlling charging. The purpose of the present invention is to provide a low-cost charging circuit that is highly reliable and safe and does not cause damage to equipment or equipment.

(Means for Solving the Problems) In order to solve the above problems, the charging circuit of the present invention includes a charging control circuit comprising a switching circuit connected in series to a secondary battery and a resistor connected in parallel with the switching circuit. and a temperature sensor that detects the temperature of the secondary battery and generates a signal corresponding to the temperature, and detects that the temperature of the secondary battery has reached a set value based on the signal from this temperature sensor,
A temperature detection circuit that generates a detection output, a holding circuit that holds the detection output of the temperature detection means and turns off the switching circuit, and a voltage detection circuit that detects the terminal voltage on the secondary battery side of the charging control means. , and a pulse generation circuit that generates a pulse based on a change in the output of the voltage detection circuit to reset the holding circuit.

(Function) In secondary batteries such as nickel-metal hydride batteries, heat is generated from inside the battery at the end of charging5, and the surface temperature rises until a balance is reached between heat generation and heat radiation. Overcharging is prevented by detecting this temperature rise and controlling charging when it reaches a set value. In this case, once the -degree charging control state is entered, that state is held by a holding circuit that holds the detection output of the temperature detection circuit so that the battery will not be charged again even if the temperature drops after charging is stopped.

When charging is completed and the secondary battery is removed, the terminal voltage on the secondary battery side of the charging control circuit increases.

Then, when a new secondary battery to be charged next is installed, this terminal voltage decreases. In the present invention, a change in terminal voltage at the time of attaching and detaching the secondary battery is detected, and the holding circuit is reset based on the change, so that charging of a new secondary battery is started.

In this way, it is determined whether a new secondary battery has been installed without using mechanical contacts, and the holding circuit is set based on this determination, thereby making it possible to charge the battery. Therefore, there are no problems due to contact failures that occur when mechanical contacts are used, and reliability and safety are improved, and at the same time, costs are reduced by reducing the number of mechanical parts.

(Example) Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of a charging circuit according to an embodiment of the present invention. In the figure, a charging power source 1 is connected via a charging control circuit 2 and a diode 5 to a nickel-metal hydride battery (hereinafter simply referred to as a battery) 6 which is a secondary battery. As the charging power source 1, a power source that obtains direct current by rectifying the output of an alternating current power source or another relatively large capacity battery is used.

The charging control circuit 2 includes a switching circuit 3 connected in series to the battery 6 and a resistor 4 connected in parallel with the switching circuit 3. As described later, the switching circuit 3 is turned on during charging, and the charging At the end of the process, the switching circuit 3 is turned off and the charging control state is entered.

Note that the diode 5 is for preventing backflow from the battery 6 to the charging power source 1 side, and is not necessarily necessary depending on the application.

The temperature sensor 7 is built into the battery 6 or connected to the battery 6.
is located close to. This temperature sensor 7 is connected to the battery 6
detects the temperature of the sensor and generates an electrical signal with a voltage corresponding to that temperature. The signal from the temperature sensor 7 is sent to the temperature detection circuit 8
is input. The temperature detection circuit 8 is a circuit that detects that the temperature of the battery 6 has reached a set value based on a signal from the temperature sensor 7, and specifically, for example, a standard corresponding to the output voltage of the temperature sensor 7 and the temperature set value. It consists of a voltage comparator that compares the voltage. In this case, the voltage comparator of the temperature detection circuit 8 inverts its output when the output voltage of the temperature sensor 7 exceeds the reference voltage, and generates a detection output indicating that the temperature of the battery 6 has reached the set value.

The output terminal of the temperature detection circuit 8 is connected to the set input terminal S of the holding circuit 9. This holding circuit 9 is a circuit that holds the detection output of the temperature detection circuit 8, and its output terminal Q
is connected to the control terminal of the switching circuit 3 in the charging control circuit 2.

On the other hand, a voltage detection circuit 10 is connected to a terminal A of the charging control circuit 2 on the battery 6 side (diode 5 side). This voltage detection circuit 10 includes a voltage comparator 11 and resistors 12 and 13 for dividing the terminal voltage at point A. That is, the reference voltage V ref is applied to the non-inverting input terminal of the voltage comparator 11, and the inverting input terminal is connected to the resistor 1.
2. Connected to the midpoint of 13.

The pressure from the voltage detection circuit 10 is input to the pulse generation circuit 14 . The pulse generation circuit 14 is a circuit that generates a pulse by detecting an inversion of the output change of the voltage detection circuit 10 when the battery 6 is attached or detached, and its output is input to the reset input terminal R of the holding circuit 9.

Next, the operation of this charging circuit will be explained.

When rapid charging is started, a rapid charging current is supplied from the charging power source 1 to the battery 6 via the switching circuit 3 and diode 5 in the charging control circuit 2. As charging progresses and reaches the end of charging, the temperature of the battery 6 begins to rise. battery 6
The temperature is converted by the temperature sensor 7 into an electrical signal with a voltage value corresponding to the temperature, and the output signal of the temperature sensor 7 is input to the temperature detection circuit 8. The temperature detection circuit 8 detects that the output voltage of the temperature sensor 7 is at a preset temperature (for example, 50°C to 60°C).
When the voltage (reference voltage) corresponding to 0° C. is reached, a detection output is generated.

The detection output of this temperature detection circuit 8 is held by a holding circuit 9, and the output of the holding circuit 9 is inverted.

Due to the output of this holding circuit 9, the charging control circuit 2 turns the switching circuit 3 into the OFF state and enters the charging control state.
Make the charging current smaller than usual. In this state, battery 6
is almost fully charged.

Thereafter, when the battery 6 is removed, the terminal voltage Va at point A increases, and when a new battery is installed next, Va decreases. Here, the resistance values R2 and R3 of the voltage dividing resistors 12 and 13 in the voltage detection circuit 10 are selected so that when the battery 6 is removed, the following is true, and when the battery 6 is attached, the following is true.

Therefore, when a new battery is installed, the output of the voltage comparator 11 in the voltage detection circuit 10 is inverted from the previous low level to the high level.

According to this change in the output of the voltage detection circuit 10, a pulse is generated from the pulse generation circuit 14, and the holding circuit 9 is reset. As a result, the level of the output terminal Q of the holding circuit 9 is reversed, and the switching circuit 3 of the charging control circuit 2 is turned ON again.
When the battery enters the N state, rapid charging is resumed.

Note that (1) the charging power source 1 and each circuit are powered on after the battery 6 is installed in the charging circuit, and (2) the battery is turned on after the charging power source 1 and each circuit are powered on. 6 is attached, quick charging is started and the above-described operation is performed. That is, in the case of (1), the output of the voltage detection circuit 10 becomes high level when the power is turned on, and the pulse generation circuit 14 immediately generates a pulse to reset the holding circuit 9, so that it is synchronized with the power-on. Quick charging will start. In the case of (2), rapid charging is started in the same manner as when a new battery is installed as described above.

FIG. 2 is a diagram more specifically showing the holding circuit 9 and pulse generation circuit 14 in FIG. 1.

The holding circuit 9 uses a thyristor 23 as a holding element, and the output of the temperature detection circuit 8 is input to the gate of the thyristor 23, which is a set input terminal S, through a voltage dividing circuit made up of resistors 21 and 22. The anode of the thyristor 23 is connected to the positive power supply V' and the output terminal Q via a resistor 24, and the cathode is grounded. In the second example, the reset input terminal R and output terminal Q of the holding circuit 9 are connected internally.

On the other hand, pulse generation circuit] 4 has a capacitor 25 and a resistor 26
The base of the transistor 27 is connected to the output terminal of the voltage comparator 11 in the voltage detection circuit 10 via the time constant circuit. Further, the emitter of the transistor 27 is grounded, and the collector is connected to the output terminal Q of the holding circuit 9.
It is also connected to the reset input terminal R (anode of the thyristor 23).

According to the configuration shown in FIG. 2, during rapid charging, the output of the temperature detection circuit 8, that is, the output of the holding circuit 9.

Since the input terminal S is at a low level, the thyristor 23 is in an OFF state. Therefore, the output terminal Q of the holding circuit 9 maintains a high level (approximately V' potential), and the charging control circuit 2
The switching circuit 3 is in the ON state.

At the end of charging, the temperature of the battery 6 rises and the output of the temperature detection circuit 8 (set input terminal S of the holding circuit 9) becomes a high level, so the Cyrisk 23 is turned on. Therefore, the output terminal Q of the holding circuit 9 becomes a low level, the switching circuit 3 is turned off, and rapid charging is stopped.

Next, when the battery 6 is once removed and a new battery 6 is installed, the voltage Va at point A decreases, and the pressure of the voltage comparator 11 of the voltage detection circuit 10 changes from a low level to a high level.

As a result, in the pulse generation circuit 14, the capacitor 2
The transistor 27 is turned ON for a time determined by the time constant of the thyristor 23 and the resistor 26, and a negative pulse from the positive potential to the ground potential is generated. 23 is in an OFF state because the holding current no longer flows therethrough. That is, the holding circuit 9 is reset and its output terminal Q becomes high level, so the switching circuit 3 is turned on and rapid charging is started.

FIG. 3 shows another specific example of the holding circuit 9 and the pulse generating circuit 14. In this example, the holding circuit 9 has two N
It is composed of flip-flops consisting of OR (NOR) circuits 31 and 32. Further, the pulse generating circuit 14 is constituted by a differentiating circuit including a capacitor 33 and a resistor 34.

During quick charging, the temperature of battery 6 rises and reaches the set temperature.
When the output of the temperature detection circuit 8, that is, the set input terminal S of the holding circuit 9 becomes high level, the flip-flop of the holding circuit 9 is inverted, the output terminal Q becomes low level, and rapid charging is stopped.

Next, when you remove the battery 6 and install a new battery 6,
The voltage Va at point A decreases, the output of the voltage comparator 11 of the voltage detection circuit 10 changes from a low level to a high level, and the pulse generation circuit 14 generates a positive voltage for a time determined by the time constant of the capacitor 33 and the resistor 34. By generating a pulse and inputting it to the reset input terminal R of the holding circuit 9, the flip-flop of the holding circuit 9 is reset and the output terminal Q becomes high level. This turns on the switching circuit 3 and starts rapid charging.

The present invention is not limited to the above-mentioned embodiments. For example, although a nickel-metal hydride battery is used as the secondary battery in FIG. 1, other secondary batteries such as a nickel-cadmium battery or a lead-acid battery may also be used. Even in such a case, it is possible to apply the charging circuit of the present invention.

Further, the present invention can be applied not only to charging a secondary battery, but also to a floating charging circuit that connects a load to the secondary battery in parallel and supplies power to the load while charging.

Furthermore, the charging circuit of the present invention can also be implemented in combination with other known charging control methods, such as voltage charging control, timer charging control, -Δ charging control, etc.

In addition, the present invention can be implemented with various modifications without departing from the scope of the invention.

(Effects of the Invention) As explained above, according to the present invention, in a charging circuit that detects the temperature of a secondary battery to prevent overcharging, changes in the terminal voltage on the secondary battery side of the charging control circuit The holding circuit that determines whether the secondary battery is attached or removed, holds the detection output of the temperature detection circuit, and turns off the switching circuit of the charging control circuit is reset without using mechanical contacts to start rapid charging. By doing so, overcharging and the resulting abnormal temperature rise can be prevented, and reliability and safety can be improved.

There is also the advantage that costs are also reduced by reducing the number of mechanical parts such as mechanical contacts.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a charging circuit for a secondary battery according to an embodiment of the present invention, FIG. 2 is a diagram showing a specific example of the holding circuit and pulse generation circuit in FIG. 1, and FIG. 2 is a diagram showing another specific example of the holding circuit and the pulse generating circuit. 1...Charging power supply 2...Charging control circuit 3...Switching circuit 4...Resistor 6...Nickel metal hydride battery (secondary battery) 7...Temperature sensor 8...Temperature detection circuit 9...Holding circuit 10...Voltage detection circuit 14...Pulse generation circuit Patent attorney Takehiko Suzue

Claims (1)

[Claims] A charging control circuit comprising a switching circuit connected in series to a secondary battery and a resistor connected in parallel with the switching circuit; a temperature sensor that generates a signal; a temperature detection circuit that detects that the temperature of the secondary battery reaches a set value based on the signal from the temperature sensor and generates a detection output; and the detection output of the temperature detection means. a holding circuit that holds the voltage and turns off the switching circuit; a voltage detection circuit that detects a terminal voltage on the secondary battery side of the charging control means; and a voltage detection circuit that generates a pulse due to a change in the output of the voltage detection circuit; A charging circuit for a secondary battery, comprising: a pulse generating circuit that resets the holding circuit.