JPS63277430A - Battery charging circuit - Google Patents

Abstract

PURPOSE:To charge in a short time and prevent overcharging from, by charging with comparatively great current on starting the charching, and with slight current after the great current comes to saturation voltage. CONSTITUTION:A first charging circuit is composed of a diode D1 and the current limiting resistor R1 of a great resistance value, and a second charging circuit is composed of a diode D4, a Zener diode ZD, and the current limiting resistor R2 of a small resistance value. Diodes D1, D2, D3, D4 are used for counter-current-proofing. When the charged voltage of a battery B is lower than saturation voltage, then the Zener diode ZD is to be turned ON, and charging is quickly performed by the first and second charging circuits. When the charged voltage of the battery B attains saturation voltage, then the Zener diode ZD is turned OFF, and the charging is slowly performed only by the first charging circuit.

Description

[Detailed Description of the Invention] [Summary] In a charging circuit for a rechargeable battery, when the battery terminal voltage is below a certain value, the charging current is increased to shorten the charging time, and when the voltage exceeds the certain value, the charging time is shortened. The battery is charged using current to prevent overcharging.

(Industrial Application Field) The present invention relates to a charging circuit for a rechargeable battery, and particularly to a battery charging circuit used as a backup power source for information equipment such as a personal computer.

[Problems to be solved by conventional technology and inventions] Recent information devices have functions to count or display date and time, and non-volatile memory using CMOS memory has a backup function that keeps the power on at all times. Power source is used. There are examples in which a non-rechargeable but long-life lithium battery is used as a backup power source, and examples in which a rechargeable nickel cadmium (NiCd) battery is combined with a charging circuit. Generally, the former increases the cost, so the latter backup power source is used.

FIG. 5 shows a conventionally commonly used NiCd battery and its charging circuit. While the device side DC power supply Vcc is operating, power is supplied to the load circuit via the diode D2, and at the same time, the battery B is charged via the diode DI and the resistor R1. When the power to the device is cut off at night, etc., power is supplied from battery B to the load circuit via diode D3.

In such a configuration, rechargeable batteries such as NiCd have the characteristic that they will not be overcharged if they are charged with a minute current below a certain value. , prevents overcharging after charging is complete.

However, the charging current in this case is 2 times the battery capacity.
Since the current is 1/0 or less, there is a problem in that it takes more than 20 hours to complete charging after discharging.

[Means and effects for solving the problems] The object of the present invention is to provide a battery charging circuit that solves the above-mentioned problems. Basically, when the battery terminal voltage is below a certain value, a large current and a small current are generated. The battery is charged with both currents, and when charging progresses and the battery terminal voltage exceeds a certain value, charging is continued with a minute current until it reaches the saturation voltage.

In other words, as shown in the basic configuration diagram in Figure 1, after battery B is discharged, it is charged by both C1 and C2 charging circuits until a certain voltage value is reached, and when the voltage exceeds a certain value, charging is continued only by CI. This is what I did. Therefore, the current limiting resistor of circuit CI is made large so that a minute current flows, and the current limiting resistor of circuit C2 is made relatively small so that a large current flows. With this configuration, charging time can be shortened and overcharging can be prevented.

〔Example〕

FIG. 2 is a circuit diagram of an embodiment of the battery charging circuit according to the present invention. In FIG. 2, the first charging circuit CI is composed of a diode DI and a current limiting resistor R1 with a large resistance value, and the second charging circuit C2 is composed of a diode D4, a Zener diode ZD, and a current limiting resistor R1 with a small resistance value. It is composed of a resistor R2. Note that the diode D2 is used to prevent backflow when the battery is used, and the diode D3 is used to connect the device power supply V.
To protect the battery when using CC, diodes D1 and D4 are used to prevent backflow when using the battery.

In such a configuration, when the device is in operation, power is supplied to the load circuit via the diode D2, and at the same time, the battery B is charged via the circuits C1 and C2. The charging characteristics of battery B are shown in FIG. In Figure 3, the vertical axis ■ is the charging current, and the horizontal axis V is the battery terminal voltage, V
ZO is the breakdown voltage of the Zener diode ZD, and VCC is the power supply voltage of the device. Then, the straight line [1 is the charging current by the circuit C1, the straight line 2 is the charging current by the circuit C2, and the straight line 2 is the sum of 2 and 3.

Here, increase the power supply Vcc by +5. When V-Vza is 2.2V and the battery saturation voltage is 2.4V, the device operates and V
When cc is being supplied, since VCC>V2, the Zener diode ZD is on, and the charging current flows to the battery via the circuits CI and C2, and is supplied as shown by the straight line (2). Charging progresses and the battery terminal voltage is 2.8V
When the voltage between the terminals of the Zener diode ZD exceeds 2.2
Since the voltage is less than v, the Zener diode ZD is turned off. Therefore, the circuit C2 stops operating, and charging is performed only by the small current (linear!) of the circuit C1.

FIG. 4 shows another embodiment of the second charging circuit C2. In this case, a field effect transistor FET is used instead of the resistor R2.
is used. That is, it utilizes the constant current function of PET, which eliminates the influence of current dependence of Zener voltage and enables more stable charging.

〔Effect of the invention〕

As explained above, according to the present invention, since charging can be performed with a relatively large charging current at the start of charging, charging time can be shortened, and after reaching the saturation voltage, charging can be performed with a small current. , overcharging can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a basic configuration diagram of a charging circuit according to the present invention, FIG. 2 is a circuit diagram of an embodiment of the charging circuit according to the present invention, and FIG. 3 is a diagram showing the relationship between charging current and battery terminal voltage according to the present invention. FIG. 4 is a circuit diagram of another embodiment of the second charging circuit, and FIG. 5 is a circuit diagram of a conventional charging circuit. (Explanation of symbols) C1...First charging circuit, C2...Second charging circuit, B...Battery, Di~D4...Diode, ZD...Zener diode, R1, R2... ...Resistance, L...Load circuit.

Claims (1)

[Claims] 1. In a charging circuit for a rechargeable battery, when the battery terminal voltage is below a certain value, a first charging circuit supplies a minute charging current, and a first charging circuit supplies a relatively large charging current. A battery charging circuit that charges the battery by a second charging circuit, and charges the battery by the first charging circuit when the battery terminal voltage exceeds the certain value. 2. Claim 1, wherein the second charging circuit comprises a resistor with a relatively small value, a Zener diode that turns on when the value is below the certain value and turns off when the value exceeds the certain value, and a diode for preventing backflow. Battery charging circuit as described. 3. Claim 1 in which the second charging circuit comprises a field effect transistor having a constant current function, a Zener diode that is turned on when the current is below the certain value and turned off when it is above the certain value, and a diode for preventing backflow. Battery charging circuit described in section.