JPH04261338A - Charging circuit - Google Patents

Abstract

PURPOSE:To shorten a refresh time by maintaining a discharge current flowing to a load circuit for discharging constant irrespective of a battery voltage at the time of refreshing of the battery. CONSTITUTION:In a charging circuit having load circuits (R1, R2, 51) for discharging, and a discharge controller 4 for starting charging after a battery voltage is detected and the battery is discharged until the voltage is lowered to a predetermined voltage, the load circuits are so composed as to detect discharge currents and to vary a circuit load so that the discharge current becomes constant in response to the detected discharge current (51-53).

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for charging storage batteries used, for example, in video cameras, telephones, etc., and more particularly to a charging device that temporarily discharges the remaining capacity during charging.

0002

[Prior Art] For example, storage batteries used for videos, etc.
If the storage battery is completely discharged, it becomes impossible to remove the tape or the like, so the battery is often charged before it is completely used up. By the way, when NiCd batteries, which are known as rechargeable storage batteries, are repeatedly charged and discharged with a certain amount of remaining capacity remaining, they become inactive, causing a temporary drop in battery capacity and battery voltage, and furthermore, the capacity decreases. This may lead to a decrease in

[0003] Conventionally, when charging a battery, a charging circuit is known which has a discharge (refresh) function that first discharges the battery until the battery voltage drops to a predetermined voltage. This discharge circuit connects a load resistor in parallel to the battery and refreshes the battery by constant resistance discharge.

0004

[Problems to be Solved by the Invention] In the conventional constant resistance discharge method described above, if the battery voltage is high or if another power source with a higher voltage than the normal load is connected to the output due to misuse, the load circuit The flowing discharge current increases in force, increasing the burden and causing safety problems due to heating, etc.

On the other hand, when the battery voltage decreases, the discharge current also decreases, resulting in a longer refresh time, which delays the start of charging. It becomes difficult to fully respond to the requests of

The present invention has been made in view of the above, and
It is an object of the present invention to provide a charging circuit that makes the discharge current flowing through a discharge load circuit constant.

[0007]

[Means for Solving the Problems] The present invention provides a charging circuit equipped with a load circuit for discharging and a discharge control circuit that detects a battery voltage and starts charging after discharging the battery voltage until it drops to a predetermined voltage. The discharge load circuit is configured to detect a discharge current and vary the circuit load in accordance with the detected discharge current so that the discharge current becomes constant.

[0008]

According to the present invention, if the battery voltage is equal to or higher than a predetermined voltage before charging is started, the remaining capacity of the battery is discharged via the load circuit prior to charging. Discharging is performed until the battery voltage drops to a predetermined voltage. At this time,
The load circuit detects the discharge current, and the circuit load of the load circuit changes according to the detected discharge current so that the discharge current becomes constant, thereby keeping the discharge current at a predetermined constant value. It will be done.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram showing an example of a charging circuit according to the present invention. In the figure, 1 is a power source such as a commercial power source or a battery. 2 is battery B that is connected during charging
The power supply circuit 2 is a power supply circuit having a converter and the like for generating a charging current to be supplied to the power supply circuit 2, and charging control of the power supply circuit 2 is performed by a control signal from a charging control circuit 3. The charging control circuit 3 controls the power supply circuit 2 in order to fully charge the battery B, and after a predetermined period of time has elapsed from the start of charging, or after a battery voltage detection means,
Full charge control is performed by sending a control signal based on the detection result from a battery temperature sensor or the like (not shown).

4 is a refresh circuit that discharges the remaining capacity of battery B, and when battery B is connected to be charged,
The battery voltage is detected, and if the battery voltage is equal to or higher than a preset reference voltage, a constant level discharge instruction signal is output to the constant current load circuit 5 in order to temporarily discharge the battery prior to charging. . This discharge instruction signal is continuously outputted until the battery voltage drops to a predetermined voltage.

5 is a discharge resistor R1, a discharge current detection resistor R2
A constant current load circuit is formed by connecting a transistor 51 as a driving element in series, and is connected in parallel with battery B when battery B is connected. Discharge resistor R1 is a load resistor for discharging the remaining capacity of battery B. The base of the transistor 51 is connected to an output terminal of a comparison circuit 52, which will be described later, and an output terminal of the discharge instruction signal of the refresh circuit 4. This constant current load circuit 5
is adapted to start discharging when the above-mentioned constant level discharge instruction signal is input.

Reference numeral 52 denotes a comparator circuit, and one input terminal thereof is connected to a constant voltage source 53 composed of, for example, a Zener diode.
The voltage across the discharge current detection resistor R2, that is, the detection voltage corresponding to the discharge current is input to the other input terminal, and the output terminal is connected to the base of the transistor 51. This comparison circuit 52 compares the detected voltage and the reference voltage Vref and outputs the difference voltage.

Then, this differential voltage and the discharge instruction signal of the constant level are superimposed and input to the base of the transistor 51, and the base potential of the transistor 51 is controlled so that the discharge current is constant. That is, the comparison circuit 5
2 is the difference voltage between the reference voltage Vref and the detection voltage as it is,
Alternatively, it is amplified with a predetermined amplification factor and outputted, and when the detected voltage attempts to exceed the reference voltage Vref, the output becomes a low level and acts in the direction of suppressing the discharge current, while the battery voltage decreases. That is, the detected voltage is the reference voltage Vr
When the voltage drops below ef, the base-emitter voltage of the transistor 51 is controlled so that the output goes to a high level and acts in the direction of increasing the discharge current.

FIG. 2 is a partial circuit diagram for explaining the start and stop of the refresh operation by the refresh circuit 4. As shown in FIG.

The refresh circuit 4 is composed of a refresh start circuit 41, a comparison circuit 42, and a constant voltage source 43. The comparator circuit 42 receives the battery voltage of the battery B connected to be charged at one input terminal, and receives a reference voltage Eref from a constant voltage source 43 composed of a Zener diode or the like at the other input terminal. is input, and the output terminal is connected to the refresh start circuit 41.

When battery B is connected, the comparator circuit 42 compares the battery voltage with the reference voltage Eref, and if the battery voltage is equal to or higher than the reference voltage Eref, the comparator circuit 42 outputs a high-level output signal. As a result, the refresh start circuit 41 sends out the constant level discharge instruction signal that instructs the constant current load circuit 5 to discharge. When the remaining capacity of battery B decreases due to discharge to some extent and the battery voltage of battery B drops to the reference voltage Eref, the comparator circuit 42 changes its output from high level to low level, and refresh is started by this low level output. The circuit 41 changes its output to low level to stop the discharge. In this way, the remaining capacity of battery B is discharged to a required level, and at the same time as an instruction to stop discharging is given, refresh start circuit 41 outputs a charging permission signal to charging control circuit 3. The charging control circuit 3 receives this charging permission signal and causes the power supply circuit 2 to start charging operation.

[0017]

[Effects of the Invention] As explained above, according to the present invention,
Since the discharge current is detected and the circuit load of the discharge load circuit is varied so that the discharge current becomes constant according to the detected discharge current, the discharge time when the battery voltage drops can be shortened. This makes it possible to shorten the discharge time as a whole.

Furthermore, since the discharge current flowing through the discharge load circuit does not increase in force, problems such as heating are eliminated.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of a charging circuit according to the present invention.

FIG. 2 is a partial circuit diagram for explaining the start and stop of a refresh operation by the refresh circuit 4. FIG.

[Explanation of symbols]

1 Power supply 2 Power supply circuit 3 Charging control circuit 4 Refresh circuit 41 Refresh start circuit 42 Comparison circuit 43 Constant voltage source 5 Constant current load circuit 51 Transistor 52 Comparison circuit 53 Constant voltage source R1 Discharge resistance R2 Discharge current detection resistor B Battery

Claims (1)

[Claims] Claim 1. A charging circuit comprising a discharging load circuit and a discharging control circuit that detects a battery voltage and starts charging after discharging the battery voltage until it drops to a predetermined voltage, the discharging load circuit comprising: a discharging load circuit; 1. A charging circuit configured to detect a current and vary a circuit load in accordance with the detected discharge current so that the discharge current becomes constant.