KR0151494B1 - Charging mode conversion circuit of battery - Google Patents

Abstract

The present invention is to more accurately detect the ΔV during rapid charge of the rechargeable battery and to prevent shortening of the battery life, the operational amplifier 10, the diode (D1), capacitors (C1, C2), output voltage It is composed of a voltage supply unit 10, a comparator 30 that can be adjusted, and when the fast charging of the battery, the voltage that is reduced due to the natural discharge that occurs after the battery is fully charged or the predetermined voltage (ΔV) or more When a predetermined time elapses from the time when the battery is fully charged to the time when the internal temperature of the battery starts to rise rapidly, the rapid charging mode of the battery is automatically converted into the trickle charging mode.

Description

Charge mode conversion circuit of the rechargeable battery

1 shows a characteristic curve of a rechargeable battery.

2 is a circuit diagram of a preferred embodiment of a charge mode conversion circuit according to the present invention.

3 is a waveform diagram of an output voltage of a charging mode conversion circuit according to a battery voltage.

* Explanation of symbols for main parts of the drawings

10: operational amplifier 20: offset voltage supply

30: comparator 40: trickle charging mode conversion stage

C1, C2: Capacitor D1: Diode

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging IC for a rechargeable battery, and more particularly, to a mode conversion circuit for automatically converting a charging mode according to its state of charge during rapid charging of a rechargeable battery.

In recent years, the demand for portable electronic devices using rechargeable batteries (hereinafter, abbreviated as 'batteries') is rapidly increasing. In addition to this trend, batteries in portable electronic devices are required to be capable of fast charging, to be used longer, and to have a longer life.

When fast charging the battery, due to the characteristics of the battery, as shown in FIG. 1, after the battery is fully charged, in general, the voltage of the battery is reduced to a predetermined voltage (ie, at full charge) according to a natural discharge. ΔV). At this time, the charging mode of the battery must be changed from a quick charge mode to a trickle charge mode that supplies a current equal to a natural discharge amount. However, if the charging mode is not supplied even after the battery is fully charged and the charging current is continuously supplied to the battery, the battery is overcharged and its internal temperature is rapidly increased, which shortens the battery life. If is repeated, the battery eventually becomes unusable. Therefore, during fast charging, it is very important not to shorten the life of the battery, and after full charging of the battery, charging must be cut off before its internal temperature rises.

To this end, conventionally, a microprocessor (mircoprocessor) is used, and the voltage change amount ΔV due to the natural discharge of the battery is detected by a sample and hold method. According to this technique, in order to detect DELTA V more accurately, the number of sampling must be increased. This requires additional control circuits, which makes the mode conversion circuit complex and expensive.

The main object of the present invention is to provide a mode conversion circuit having a simple configuration and capable of detecting DELTA V more accurately.

Another object of the present invention is to prevent shortening of the life of the battery that may occur during rapid charging of the battery.

In the mode conversion circuit of the present invention for achieving the above objects, when the fast charging of the battery, the voltage that is reduced due to the natural discharge that occurs after the battery is fully charged, the battery over the predetermined voltage (ΔV) or After a predetermined time elapses from the time when the battery is fully charged to the time when the internal temperature of the battery starts to rise rapidly, the rapid charge mode of the battery is automatically switched to the trickle charging mode. As a result, rapid charging may be performed without affecting the life of the battery.

The battery charge mode conversion circuit according to the present invention has a noninverting input terminal to which a battery voltage V _batt is applied and is relatively higher than the rate of decrease of the battery voltage when the battery voltage begins to decrease. An operational amplifier providing an output signal Vout having a reduction rate, a cathode electrode is connected to an inverting input terminal of the operational amplifier, and an output terminal of the operational amplifier a diode having an anode electrode connected to the terminal, a first capacitor having a first electrode connected to the cathode electrode of the diode, and a second electrode connected to the ground and a positive and negative electrode; A voltage supply unit having negative electrodes, the negative electrode being connected to the anode electrode of the diode and capable of varying an output voltage; A second capacitor connected in parallel with an electrode, a first capacitor of the two electrodes connected to the cathode electrode of the diode, and a second electrode connected to the anode electrode of the diode; A trickle charge mode converting stage for supplying a non-inverting input terminal connected to the inverting input terminal connected to the first electrode of the first capacitor and a current equal to a natural discharge amount to the battery. It is characterized by including a comparator having an output terminal connected thereto.

2 shows a preferred embodiment of the charging mode conversion circuit according to the present invention. Referring to FIG. 2, the battery charge mode conversion circuit of the present embodiment includes an operational amplifier 10, a diode D1, first and second capacitors C1 and C2, a voltage supply unit 20, and a comparator 30. It is composed of The battery voltage V _batt is applied to the non-inverting terminal of the operational amplifier 10. Its inverting and output terminals are connected to the cathode and anode terminals of diode D1, respectively. One terminal of the first capacitor C1 is connected to the cathode terminal of the diode D1 and the other terminal thereof is grounded. Both terminals of the second capacitor C2 are connected to its anode terminal and the cathode terminal in parallel to the diode D1, respectively. The anode electrode of the diode D1 and the non-inverting terminal of the comparator 30 are respectively connected to the negative electrode and the positive electrode of the voltage supply unit 20 which can vary the output voltage. The inverting terminal and the output terminal of the comparator 30 are connected to the first capacitor C1 and the trickle charge mode conversion terminal 4, respectively.

Next will be described in detail the operation of this embodiment having the above configuration, in order to make it easier to understand the operation of the present embodiment, the output voltage of the charge mode conversion circuit of the present embodiment according to the battery voltage is shown Referring to FIG. 3, the operation of the circuit is described in detail by section.

With reference to FIGS. 2 and 3, first, in a period t0 ≦ tt1, the diode D1 is turned on. Accordingly, the bias current I1 of the operational amplifier 10, the current I2 flowing through the diode D1, the bias current I4 of the comparator 30, and the current I5 charged in the first capacitor C1 flow, where I5 is It can be expressed as

(Where dV _batt = V _batt (t1) -V _batt (t0), dt = t1-t0)

Next, at the time point t = t1, the first capacitor C1 is fully charged. At this time, the diode D1 is turned off because Vb = Vc = V _batt .

In the period t <tt2, the discharge of the first capacitor C1 starts, the discharge current I5 'of the first capacitor C1 flows, and the current I3 flows to the second capacitor C2. The currents I3 and I5 'at this time can be represented by the following equations (1) and (2).

Where dV _batt = V _batt (t1) -V _batt (t2) = _ΔV , dt = t2-t1 = Δt)

In addition, Vc is as following Formula (3).

Where V _C2 is the voltage of the second capacitor C2.

After the time point t1, Vb is the battery voltage V _batt , and the drop voltage V _C2 by the second capacitor _C2 is equal to the following equation (4),

As a result, after time t1 when the battery is fully charged, Vc becomes smaller than Vb.

On the other hand, the comparator 30 compares whether or not Vb = Vd, and provides an electric signal (Vout) corresponding to the result to the trickle charge mode conversion stage 40, where Vd is the following equation (5) It may be displayed as follows.

(Wherein, V _offset is the offset voltage provided to the comparator 40 from the voltage supply 20, which can vary the output voltage.)

Substituting equation (3) into the previous equation (5), Vd is represented by the following equation (6).

In Eq. (5) above, if Vd = Vb (i.e., the two inputs of comparator 20 are set equally), then V _offset becomes Eq. (7).

In the above formula (2), if dV _batt (ie, _ΔV ) and dt (ie, Δt) are determined, the discharge current I5 'from the first capacitor C1 can be obtained. When I5 'is obtained, I3 is determined from equation (1). Thus, when I3 is obtained, V _C2 can be obtained from Formula (4). Therefore, the output voltage V _offset of the voltage supply unit 20 can be adjusted to V _C2 . When the V _offset is adjusted to V _C2 as described above, the comparator 30 operates the trickle charge mode conversion stage 40 when the battery voltage decreases by V from V _batt due to the natural discharge of the fully charged battery during fast charging. The control is such that the charging mode of the battery is switched from the fast charging mode to the trickle charging mode.

Meanwhile, since the discharge current I5 ′ of the first capacitor C1 is the same as the charge current I3 of the second capacitor C2, Equation (4) may be represented by Equation (8) below. .

Substituting equation (2) into equation (8) above,

Becomes

therefore, Since this holds true, by varying V _offset ,? V can be determined.

This means that it is possible to change the charging mode of the battery by changing the V _offset .

Referring to FIG. 3, in the period t0 ≦ tt1, the battery voltage V _batt increases, and when the t = t1 time point is reached, the battery is fully charged and Vb = Vc = V _batt . Vc at the time point t1 becomes V _batt . In the period tt1, Vb maintains V _batt , while Vc is reduced by the voltage V _C2 of the second capacitor C2.

Therefore, if the offset voltage Voffset of the voltage supply unit 20 is set in advance by the decrease amount, Vd (= Vc + V _offset ) becomes larger than Vb (= V _batt ) in the period t0 ≦ tt2. Therefore, at this time (VdVb), the comparator 30 provides the output signal Vout of the 'high level' to the trickle charge mode conversion stage 40 to maintain the fast charge mode of the battery. However, in the state where the V _offset is set to V _C2 as described above, when the time t = t2 is reached, the voltage V _batt of the battery during rapid charging drops by _ΔV , in which case the output characteristic of the operational amplifier 10 Therefore, since Vb becomes higher than Vd, the comparator 30 provides an output signal Vout having a 'low level' to the trickle charging mode conversion stage 40, whereby the charging mode of the battery is trickling from the fast charging mode. The charging mode is converted.

Claims (2)

An operational amplifier having a non-inverting input terminal to which a battery voltage (V _batt ) is applied and providing an output signal (Vout) having a relatively higher reduction rate compared to the reduction rate of the battery voltage when the reduction of the battery voltage starts; A switch connected to a first terminal of an inverting input terminal of the operational amplifier and a second terminal of an output terminal of the operational amplifier, and switched on / off according to a voltage level of the output terminal and the inverting input terminal of the operational amplifier Means; A first capacitor having a first electrode of two electrodes connected to the first terminal of the switch means and a second electrode being grounded; A voltage supply having positive and negative electrodes, the negative electrode being connected to the anode electrode of the diode and having a variable output voltage; A second capacitor connected in parallel with the switch means, wherein a first electrode of the two electrodes is connected with the first terminal of the switch means and a second electrode is connected with the second terminal of the switch means; And a comparator having a non-inverting input terminal connected to the positive electrode of the voltage supply, an inverting input terminal connected to the first electrode of the first capacitor, and an output terminal connected to a trickle charge mode conversion terminal. Charge mode conversion circuit of the battery. The charging mode conversion circuit of claim 1, wherein the switch means comprises a diode.