JPH0440927B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a charger with an overcharge prevention function for charging a battery such as a NiCd battery or a lead-acid battery.

BACKGROUND TECHNOLOGY Chargers often have a built-in function to prevent overcharging of batteries, but this overcharging has been prevented using the -ΔV method.

A battery has the property that as charging progresses, its terminal voltage increases, and when charging is completed and the battery begins to progress into an overcharged region, the terminal voltage drops slightly. The -ΔV method takes advantage of this property of batteries to stop charging before overcharging progresses. In other words, a conventional charger with an overcharge prevention function recognizes the completion of charging by detecting a drop in the terminal voltage of the battery.

Problems to be Solved by the Invention However, in a charger with an overcharge prevention function that adopts this method, the battery is slightly overcharged each time it is charged, which has a negative effect on the charge/discharge cycle life of the battery. It was hot.

The present invention was devised to solve the above-mentioned problems, and includes an overcharging prevention function that detects the completion of charging by utilizing the fact that the internal resistance of the battery changes as charging progresses. The purpose is to provide chargers.

Means for Solving the Problems The charger with an overcharge prevention function according to the present invention is provided in the middle of a power line connecting a power source and a battery, and turns on/off the charging current flowing through the power line. a voltage detector that determines that the battery is connected by detecting a voltage drop in the power supply line; and a voltage detector that repeatedly outputs a trigger and starts outputting the trigger based on the determination result. a trigger generator; a current controller that performs constant current control of the charging current so that H-level and L-level charging currents flow respectively in response to changes in the trigger signal; A ΔV detector detects the voltage change ΔV of the power supply line due to the change in voltage and compares this ΔV with a preset threshold value to detect the completion of charging the battery, and a ΔV detector detects the completion of charging of the battery and starts counting. Based on the determination result, the switch is turned off when the count ends, and when the detection result indicates that charging of the battery is completed,
It is characterized by being equipped with a total timer that accelerates counting in order to finish counting faster than a preset time.

Function When the battery is connected to the power line and preparation for charging is completed, a load is connected to the power source, and the voltage of the power line decreases. By detecting this voltage drop, the voltage detector determines that the battery is ready to be charged, and operates the trigger generator and total timer.

The charging current flowing through the power line is controlled by a current controller, so ΔV on the power line indicates a change in the internal resistance of the battery. The ΔV detector detects this ΔV and
Completion of battery charging is determined by comparing this ΔV with a predetermined threshold value indicating the internal resistance at the time of battery charging completion.

On the other hand, the total timer has already started counting, but when the ΔV generator determines that battery charging is complete, it accelerates the remaining charge count and operates the switch faster than the preset time. The charging current is cut off.

Embodiment FIG. 1 is a circuit configuration diagram of an embodiment of a charger with an overcharge prevention function of the present invention, and FIG. 2 is a timing chart showing its main signals.

A power source 10 that supplies charging energy and a battery 30 are connected by a power line 50,
A diode 40 is provided along the way to prevent reverse flow of charging current.

The power supply 10 is a DC output power supply, and although a series type power supply is used in this embodiment, a switching type power supply may also be used. However, power supply 10
The output impedance of is negligibly low.

Charger 20 with overcharge prevention function according to the present invention
This is to monitor the progress of charging the battery 30 and prevent overcharging, but it uses changes in the internal resistance of the battery 30 as charging progresses to prevent overcharging. It is designed to cut off the current.

The charger 20 with an overcharge prevention function is provided in the middle of the power supply line 50, and includes a switch 21 that cuts off the charging current based on a control signal 53 to be described later.
A current controller 22 is provided in the power supply line 50 after this switch 21 and controls the charging current at a constant current based on a current control signal 52 to be described later.
and a voltage detector 23 that determines that the battery 30 is ready for charging and outputs this determination result as a ready signal 51; and a voltage detector 23 that outputs a repeat trigger as a current control signal 52 and prepares to start this output. The trigger generator 24, which is performed based on the completion signal 51, detects the voltage change ΔV of the power supply line due to the change in the trigger signal, and compares this ΔV with a preset threshold value. It consists of a ΔV detector 26 that outputs the result as a determination signal 54, and a total timer 25 that starts counting based on the ready signal 51 and outputs a control signal 53 when the counting is finished.

The switch 21 is a switch such as a relay, and operates to cut off the charging current when the control signal is at L level.

The current controller 22 performs constant current control of the charging current, and depending on the signal level of the current control signal 52,
Control is performed so that an L-level charging current I ₁ and an H-level charging current I ₂ flow. This current controller 22
Although not shown, is a constant current circuit consisting of a combination of a transistor, a Zener diode, etc.

The voltage detector 23 determines that preparation for charging the battery 30 is complete by detecting a drop in the voltage of the power line 50 due to the battery 30 being attached to a battery holder (not shown). It is a comparator. This voltage detector 23 outputs an active ready signal 51 when the voltage of the power supply line 50 falls below the open circuit voltage V ₁ of the power supply 10 .

The trigger generator 24 is a circuit that repeatedly outputs a trigger at a time interval _T1 , and receives a ready signal 5.
The rising edge of 1 is used as a start signal.

The ΔV detector 26 is a circuit that detects a change in internal resistance as the battery 30 is charged, and determines whether the charging is complete. By the way, since the charging current is always kept constant by the current controller 22,
The voltage change ΔV on the voltage line is a value proportional to the change in internal resistance of the battery 30. Furthermore, when a battery approaches the end of overcharging, gas is generated internally, which increases its internal resistance. Therefore, it is possible to determine whether the battery 30 has been fully charged by determining in advance the internal resistance at the time of completion of charging related to the type of battery, etc., and comparing this with the threshold value obtained by converting this into voltage and the detected ΔV. can. When it is determined that charging is completed, an active (H level) determination signal 54 is output.

The total timer 25 is a timer circuit that can change the count value during operation, and receives the ready signal 5.
A counting operation is performed using the rising signal of 1 as a start signal. The preset setting time is T ₂
However, in synchronization with the rise of the determination signal 54, the remaining amount count value is reduced and the set time T ₂
The count is made to finish faster. When the count ends, the active (L)
level) control signal 53 is output. Furthermore, in this embodiment, the method of accelerating the count is to reduce the count value, but the clock frequency may also be increased.

The operation of the charger 20 with an overcharge prevention function configured as described above will be briefly explained with reference to FIG. 2.

In the figure, the voltage of the power supply line 50 is shown as the voltage at point A. First, at time t1 when the power supply 10 is connected, the open circuit voltage _V1 of the power supply 10 is applied to point A. In the initial state, the total timer 25 outputs the control signal 53 at H level, and the charging current is zero. Then, at time _t2 , when the battery 30 is set, the voltage at point A drops to _V2 . Voltage detector 2
3 detects this voltage drop and disconnects the battery 30.
It is determined that preparation for charging is completed, and the trigger generator 24 and total timer 25 are operated. During charging, when the current control signal 52 is at the L level, the charging current is the current I ₁ , similarly, the H level.
At level, the current is _I2 , and each is controlled by constant current.

Further, as shown in the figure, ΔV increases as charging progresses, but the ΔV detector 26 detects this ΔV and, at time t3 when the threshold value is exceeded, determines that charging has been completed and outputs a determination signal 54. I'm standing up. However, with this signal, switch 2
Instead of operating 1 and cutting off the charging current,
This determination signal 54 is performed at the rising edge of the control signal 53 delayed by time _T3 .

This control signal 53 controls the remaining amount count of the total timer 25 when the determination signal 54 rises (at time t
3) to accelerate the count and reach the set time.
This signal is generated by ending the counting operation faster than _T2 , and operates the switch 21 at time t4 when this control signal 53 falls (at this time, the voltage and charging current at point A are zero). ).

If the completion of charging cannot be detected for some reason, there will be no change in the determination signal 54, but the total timer 25 will stop counting at the set time _T2 that has been set from the beginning (time t
5) Accordingly, the switch 21 is operated to safely cut off the charging current even in this case.

In addition, in this embodiment, the trigger generation section, ΔV
Although the detector and the total timer have been described as hardware configurations, the present invention is not limited to this, and can be similarly implemented using software.

Effects of the Invention The charger with an overcharging prevention function according to the present invention is configured to determine the completion of charging by monitoring changes in the internal resistance of the battery, so that overcharging of the battery can be reliably prevented. Since this can be prevented, the charge/discharge cycle life of the battery can be extended compared to conventional methods.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an embodiment of a charger with an overcharge prevention function according to the present invention, and FIG. 2 is a timing chart showing its main signals. 10...Power source, 20...Charger with overcharge prevention function, 21...Switch, 22...Current controller,
23... Voltage detector, 24... Trigger generator, 2
5...Total timer, 26...ΔV detector, 3
0...Battery.

Claims (1)

[Claims] 1. A switch that is provided in the middle of a power line connecting a power source and a battery, and that turns on and off the charging current flowing through the power line, and the battery is connected by detecting a voltage drop in the power line. a trigger generator that repeatedly outputs a trigger and starts outputting the trigger based on the determination result; and a voltage detector that performs constant current control of the charging current and changes the signal of the trigger. a current controller that controls the current so that H-level and L-level charging currents flow respectively in response to the change in the trigger signal; a ΔV detector that detects the completion of charging of the battery by comparing it with a certain threshold; and a ΔV detector that starts counting based on the determination result and turns off the switch when the counting is finished. , a total timer for accelerating counting so as to finish counting faster than a preset time when the detection result indicates completion of charging of the battery; and a total timer for accelerating counting. Charger with functions.