Battery charging apparatus

A mode-convertible battery charging apparatus is provided. According to the invention, regardless of whether the battery being charged is a completely discharged battery, a fully charged battery or a battery which has a certain amount of electric charge, charging is automatically completed only after the battery is fully charged. Users can detect the charged state of the battery pack, and therefore life shortening of or a damage to the battery due to overcharging of the battery pack can be avoided so as to increase the reliability of the battery. When the detected voltage goes beyond the limit of automatic charging control, the charging operation is not conducted so as to prevent battery damage due to overcurrent.

CLAIM OF PRIORITY 
This application makes reference to, incorporates the same herein, and 
claims all benefits accruing under 35 U.S.C. .sctn. 119 from an 
application for A BATTERY CHARGING APATUS earlier filed in the Korean 
Industrial Property Office on the 15.sup.th of October 1996 and there duly 
assigned Serial No. 46038/1996. 
BACKGROUND OF THE INVENTION 
1. Technical Field 
The present invention relates to a battery charging apparatus for 
rechargeable batteries used for portable computers, model machinery, 
headphone stereos, and portable cordless telephones, and more particularly 
to a mode-convertible charging apparatus operational under a constant 
voltage and a constant current charging mode. 
2. Related Art 
Generally speaking, second batteries mean batteries which can be reused and 
recharged by a power supply through a reversible reaction after use. 
Recently, first battery charging apparatuses have been commercialized. 
However, this starts from the possibility that first batteries can also be 
charged rather than the characteristics of the charging apparatuses. 
Therefore, first batteries can not be recharged as many times as second 
batteries. 
Rechargeable batteries are more economical in case batteries have to be 
replaced frequently. Also, due to a desirable discharging characteristic 
they are unavoidable for the model machinery and portable machinery which 
require high current. Recently, various kinds of batteries have been 
commercialized, ranging from 500 mAh to several Ah capacity, but the 
charging apparatuses are not yet as diversified as the batteries. 
Compared to regular batteries, rechargeable batteries have very low 
internal resistance, and therefore can provide a large amount of current 
instantaneously, and also can keep a stable voltage until a discharge 
terminal voltage is reached because of a good discharge characteristic. 
Here, a discharge terminal voltage means a limit voltage of a terminating 
discharge in battery tests. To charge rechargeable batteries, a proper 
amount of current should be introduced into the batteries. Charging period 
can be reduced with a high current, but there is a risk of overcharge 
(charging beyond a full charge limit). In case of overcharge, most 
batteries produce gas internally which can be absorbed in case the amount 
of gas is small. A large amount of gas can be produced under high charging 
current however, and can rupture overcharged rechargeable batteries. 
Lead batteries which are popular in cars and in emergency power supplies 
are cheap, but they are not adequately protected from overcharge or 
overdischarge. Nickel Cadmium (Ni--Cd) batteries have superior 
characteristics in charge-discharge and maintenance. However, they are 
losing popularity because of a low volume energy density (Wh/l) and, 
especially, due to environmental contamination (heavy metal contamination 
such as Cadmium). In the design of an automatic battery charging 
apparatus, the most important task is the determination of the charge 
completion point (the point where the battery is fully charged). 
Electrical detection of the increase of terminal voltage of a battery is 
the only way to accomplish the latter task. 
Exemplar recent efforts in the art include U.S. Pat. No. 5,656,917 to 
Theobald, entitled Battery Identification Apparatus And Associated Method, 
U.S. Pat. No. 5,648,715 to Patino et al., entitled Method And Apparatus 
For Current Compensation Of A Battery In A Charger, U.S. Pat. No. 
5,644,210 to Hwang, entitled Charging Control Method And Circuit Of 
Recharging Battery, U.S. Pat. No. 5,637,981 to Nagai et al., entitled 
Method For Charging A Secondary Battery And Charger Used Therefor Using 
Constant Current And Constant Voltage, U.S. Pat. No. 5,631,537 to 
Armstrong, entitled Battery Charge Management/Protection Apparatus, U.S. 
Pat. No. 5,612,607 to Nicolai, entitled Method For The Fast Charging Of A 
Battery And Integrated Circuit For The Implementation Of This Method, U.S. 
Pat. No. 5,541,496 to Simmonds, entitled Apparatus And Method Of Rapidly 
Charging Nickel-Cadmium Batteries, U.S. Pat. No. 5,541,490 to Sengupta et 
al., entitled Computer Power Supply System, U.S. Pat. No. 5,510,690 to 
Tanaka et al., entitled Battery Pack, Battery Discrimination Control 
Apparatus And Method Therefor, U.S. Pat. No. 5,504,416 to Hooloway et al., 
entitled Battery Charger Circuit Including Battery Temperature Control, 
U.S. Pat. No. 5,500,584 to Shimomoto, entitled Battery Charging Method And 
Apparatus Using Initial Charging Step With Gradually Increasing Charging 
Current, Quick Charging Step With Large Charging Current And Final 
Charging Step With Decreasing Charging Current, U.S. Pat. No. 5,489,834 to 
Pitkanen, entitled Battery Type And Temperature Identification Circuit, 
U.S. Pat. No. 5,485,090 to Stephens, entitled Method And Apparatus For 
Differentiating Battery Types, U.S. Pat. No. 5,485,073 to Kasashima et 
al., entitled Personal Computer For Performing Charge And Switching 
Control Of Different Types Of Battery Packs, U.S. Pat. No. 5,438,248 to 
Hyuck, entitled Method And Apparatus For Recognizing Different Types Of 
Batteries, U.S. Pat. No. 5,345,392 to Mito et al., entitled Battery Charge 
Monitor For A Personal Computer, U.S. Pat. No. 5,321,627 to Reher, 
entitled Battery Monitor And Method For Providing Operating Parameters, 
U.S. Pat. No. 5,200,690 to Uchida, entitled Quick Charge Control Apparatus 
And Control Method Thereof, U.S. Pat. No. 5,193,067 to Sato et al., 
entitled Battery Condition Detection Apparatus, U.S. Pat. No. 5,027,294 to 
Fakruddin et al., entitled Method And Apparatus For Battery-Power 
Management Using Load-Compensation Monitoring Of Battery Discharge, U.S. 
Pat. No. 4,707,795 to Alber et al., entitled Battery Testing And 
Monitoring System, and U.S. Pat. No. 4,377,787 to Kikuoka et al., entitled 
System For Measuring State Of Charge Of Storage Battery. 
As evidenced by the foregoing efforts in the art, the change of terminal 
voltage in charging depends on individual battery state or aging change, 
and a perfect automatic charging apparatus is highly difficult to achieve. 
Compromise has to be made among the protection, fast and sufficient 
charging of battery (in case of high capacity rechargeable batteries using 
an electrolyte, measurement of a density of the electrolyte is the best 
way of determining the charging completion point). 
There are two ways to charge batteries. One is a constant voltage charging 
method and the other is a constant current charging method. In the 
constant voltage charging method, batteries are charged under a constant 
voltage higher than the nominal voltage in a certain ratio. This method is 
widely used in an emergency power supply charging mode where a complete 
charge or discharge are not common. This mode is also called an 
alternating-current floating charge mode because batteries are charged in 
a normal period, but they are discharged in case a load is higher than the 
charging power supply. This method is advantageous in that extra timing 
apparatuses for battery protection are not necessary, but it is 
disadvantageous because a large amount of current in the initial charging 
period can hurt battery or power supply. To overcome this problem, current 
controlled resistance could be used to control initial current. An 
increase in voltage however, during the charging period reduces charging 
current. Therefore, the charging period also increases and sufficient 
charging is difficult to achieve. This method is popular for economical 
reasons. In the telephone handset charging apparatus, current is supplied 
for about twenty hours charging, and charging voltage is kept at higher 
than the defined value for the alternating-current floating voltage so as 
to control initial current, incomplete charging and reduction of charging 
period. This method is common in inexpensive products. The popularity of 
this method in a telephone handset starts from the high tolerance of 
nickel cadmium battery against overcharge, in addition to a simple circuit 
structure composed of a power supply and a resistance. 
The constant current charging method charges a battery with a constant 
current regardless of the increase in battery terminal voltage during the 
charge process, as explained below. This mode is employed in initial 
charging and fast charging. In this method, timed charging should be used 
unless overcharge causes a shortening of battery life. Also, a constant 
current power supply is necessary in this method because constant current 
should be supplied to a battery in spite of the increase in battery 
terminal voltage during a charging process. According to this method, 
batteries are charged by a constant current, so that the charging period 
can be reduced and sufficient charging is possible, but overcharge can 
cause a fatal damage on a battery compared to an overcharge in the 
constant voltage charging mode. For rapid charging in a constant current 
charging mode, the power supply should be disconnected at the charging 
completion point, which is not easy to determine based on the charging 
period unless a battery is charged after a complete discharge. This means 
that a 50% discharged battery requires less time than a completely 
discharged battery in fast charging. 
In some of the commercialized fast charging apparatus (e.g., those used in 
walkman stereo headphones), batteries are not charged immediately, but are 
discharged for a certain period which examining the drop of terminal 
voltage and determining the fast charging period (based on a 
pre-programmed procedure) when they are placed for charging. Again, in 
this method, the same level of charging is difficult to achieve unless a 
prediction on an aging change is included; in addition, this method cannot 
be applied to different model batteries in the same way. 
Therefore, there is a need in the prior art for development of a 
mode-convertible battery charging apparatus which can precisely determine 
a completely charged state of a rechargeable battery, and which is free 
from damage resulting from static, surge or noise on removal of the 
battery. There is also need in the prior art for development of a battery 
charging apparatus which can detect the type of rechargeable battery pack, 
and can selectively perform the best charging method (constant current or 
constant voltage charging) based on the type of battery pack. 
SUMMARY OF THE INVENTION 
It is, therefore, an object of the invention to provide a mode-convertible 
battery charging apparatus which can precisely determine a completely 
charged state of a rechargeable battery (or a battery pack). 
It is another object of the invention to provide a battery charging 
apparatus which is free from damage to a constant voltage charging 
regulator circuit thereof as a result of static, surge or noise on removal 
of the battery. 
It is another object of the invention to provide a battery charging 
apparatus which can detect the type of rechargeable battery pack based on 
cell composing material, and can selectively perform the best charging 
method based on the type of battery pack. 
According to an aspect of the invention, to accomplish the above objects, a 
battery charging apparatus includes an input terminal to which external DC 
voltage is applied; an output terminal for supplying charging current for 
the battery pack; a charging current control means, comprising a current 
path which connects the input terminal to the output terminal and a 
control terminal to which control voltage is applied, for controlling the 
amount of the charging current flowing from the input terminal through the 
current path according to the control voltage; a charging current 
detecting means for detecting the charging current flowing through the 
current path, and outputting current detecting signals whose intensity 
corresponds to the detected current to the control terminal; a voltage 
dividing means for dividing the output of the charging current detecting 
means; a constant voltage control means for detecting the charging voltage 
of the output terminal, and varying the voltage of the control terminal 
according to the detected voltage to maintain the charging voltage at a 
predetermined level; a battery temperature detecting means for detecting 
the temperature of the battery pack, and generating a battery temperature 
signal which has an intensity corresponding to the detected temperature; a 
battery type detecting means for detecting the type of a battery pack by 
receiving the cell composition information, and generating a battery type 
signal corresponding to the detected type; a battery voltage detecting 
means for detecting the terminal voltage of the battery pack, and 
outputting a battery voltage signal corresponding to the detected voltage; 
a charging control means for receiving the battery temperature signal, the 
battery type signal, the battery voltage signal and the output of the 
voltage dividing means, and outputting a charging enable signal for the 
charging current control means to conduct a charging operation, a quick 
charging control signal for controlling the charging speed of the battery 
pack, a mode control signal for making the charging current control means 
operate under any one of constant current charging mode and constant 
voltage charging mode according to the type of the battery pack, and at 
least one charging current compensating signal for equalizing the amount 
of the charging current to a predetermined reference current amount; a 
quick charging control means for controlling charging speed by varying the 
voltage of the control terminal in response to the quick charging control 
signal; a charging mode selecting means for selectively outputting the 
constant voltage control signal to the control terminal to vary the 
voltage of the control terminal in response to the mode control signal; 
and a charging current compensating means for compensating the charging 
current by varying the voltage of the control terminal in response to the 
at least one of charging current compensating signals. 
The charging control means outputs information indicating the charged state 
of the battery pack according to the output of the voltage dividing means. 
This apparatus may further comprise an indicating means for indicating the 
charged state of the battery pack according to the charged state 
information output from the charging control means. Since users can detect 
the charged state of the battery pack using the indicating means, life 
shortening of or damage to the battery due to overcharge of the battery 
pack can be avoided, thereby increasing the reliability of the battery. 
This apparatus may further comprise an external voltage detecting means for 
detecting the external DC voltage and outputting a signal corresponding to 
the detected voltage. The charging control means disables the charging 
current control means when the voltage detected by the external voltage 
detecting means is below a predetermined reference voltage. As described 
above, when the detected voltage goes beyond the limit of automatic 
charging control, the charging operation is not conducted to prevent 
battery damage due to overcurrent. 
According to another aspect of the invention, a battery charging apparatus 
includes 
a charging power supply, comprising a current path and a control terminal 
for supplying charging current, for supplying the battery pack with the 
amount of the charging current which corresponds to the variation of 
control terminal voltage through the current path; a charging current 
detecting means for detecting the charging current which flows through the 
current path and varying the voltage of the control terminal according to 
the detected current; a constant voltage control means for detecting 
charging voltage which is applied to the battery pack through the current 
path and outputting a constant voltage control signal for varying the 
control terminal voltage according to the detected voltage to maintain the 
charging voltage at a predetermined level; a battery temperature detecting 
means for detecting the temperature of the battery pack, and generating a 
battery temperature signal which has an intensity corresponding to the 
detected temperature; a battery type detecting means for detecting the 
type of battery pack by receiving cell composition information, and 
generating a battery type signal corresponding to the detected type; a 
battery voltage detecting means for detecting the charged voltage of the 
battery pack, and outputting a battery voltage signal corresponding to the 
detected temperature; a charging control means for receiving the battery 
temperature signal, the battery type signal and the battery voltage 
signal, and outputting a charging enable signal to conduct the charging 
operation, a quick charging control signal for controlling the charging 
speed of the battery pack, a mode control signal for making the charging 
power supply operate under any one of constant current charging mode and 
constant voltage charging mode according to the type of the battery pack, 
and at least one charging current compensating signal for equalizing the 
amount of the charging current to a predetermined reference current 
amount; a quick charging control means for controlling charging speed by 
varying the voltage of the control terminal in response to the quick 
charging control signal; a charging mode selecting means for selectively 
outputting the constant voltage control signal to the control terminal to 
vary the voltage of the control terminal in response to the mode control 
signal; a charging current compensating means for compensating the 
charging current by varying the voltage of the control terminal in 
response to the at least one of charging current compensating signals; and 
a charging current information generating means for providing information 
about the amount of the charging current flowing through the current path 
to the charging control means. 
In this apparatus, the charging control means outputs charged state 
information for indicating the charged state of the battery pack according 
to the charging current amount information. 
This apparatus may further comprise an indicating means for indicating the 
charged state of the battery pack according to the charged state 
information output from the charging control means.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
While the invention has been described in terms of an exemplary embodiment, 
it is contemplated that it may be practiced as outlined above with 
modifications within the spirit and scope of the appended claims. 
As shown in FIG. 1A, fast charging is possible under a constant current 
charging condition, but voltage drops after a certain period. However, 
FIG. 1B shows that constant voltage charging after charging under constant 
current for a specified time provides an almost completely charged 
battery. 
Lithium ion batteries with characteristics of high voltage, high energy 
density, long life and high stability are developed and currently in use. 
These batteries requires both the constant current and voltage charging. 
Therefore, a charging apparatus operational under only a constant current 
or constant voltage method cannot charge the lithium batteries. 
A mode-convertible charging apparatus has been developed for reasons 
described above. This charging apparatus automatically carries out 
constant current charging when batteries are discharged to a certain 
point, so that fast charging is possible, as shown in FIG. 1B. If 
batteries are charged above a certain level, the apparatus conducts a 
constant voltage charging. Constant voltage charging followed by constant 
current charging keeps the charging time below 10 hours and maintains a 
constant voltage condition without switching back to a constant current 
mode. This constant voltage is enough to charge batteries with the 
apparatus, and trickle charging is conducted. For example, if a telephone 
handset is charged by this charging apparatus, for a rapid charging 
purposes, constant voltage charging is conducted after the handset is used 
for a short period of time, and constant current charging is conducted 
after a long use of the handset. 
FIG. 2 shows a circuit structure of a conventional mode-convertible battery 
charging apparatus. To charge a battery 5, this charging apparatus 
includes a power supply unit 1, a switching regulator 2, a current 
detection unit 3, and a constant voltage regulation unit 4. 
The power supply unit 1 is composed of a transformer for a power supply 
commensurate with the number of batteries, a main power supply circuit for 
charging, a 5V regulator for a power supply for the constant voltage 
standard voltage and logic circuit, an auxiliary power supply for a 
V.sub.EE of operational amplifier and constant current standard voltage, 
although the above power supply unit 1 is not depicted in detail in the 
figure. This power supply provides a DC power supply where AC power supply 
is rectified and smoothed. The apparatus may also comprise a switching 
regulator 2. 
Current detection unit 3 is placed between a switching regulator 2 and a 
battery 5 where charging current is provided. This current detection unit 
3 comprises current detection resistance 3a which converts a current for 
charging battery 5 to a voltage, and operational amplifier 3b which 
amplifies a reduced voltage by the current detection resistance 3a and 
provides the voltage to the feedback terminal of the regulator 2 mentioned 
above. 
Constant voltage control unit 4 comprises dividing resistors 4a and 4b 
which divide the charging voltage for a battery by a predetermined ratio, 
standard voltage generator 4c for generating a standard voltage, and 
operational amplifier 4d which compares the above mentioned divided 
voltage with the standard voltage and generates a constant voltage 
charging control signal. 
Users can charge battery 5 either in constant current charging or constant 
voltage charging utilizing this mode-convertible charging apparatus. 
However, this apparatus cannot distinguish one model of battery from 
another, and fails to perform constant voltage charging when necessary. 
Also, this apparatus cannot prevent damage to current detection unit 4 
from static, noise or surge when the battery pack is removed, and lowers 
the reliability. 
In the mode-convertible charging apparatus where charging is switched from 
constant current mode to constant voltage mode, the charging completion 
point of discharged battery is generally calculated by the execution time 
of either the constant current charging mode or the constant voltage 
charging mode. This mode forces charging to be terminated regardless of 
real charging capacity. In the previous apparatuses, precise determination 
of charge completion point was not possible because the charging current 
amount was not detected in a constant voltage charging mode. Especially, 
for lithium ion batteries, no change of the terminal voltage prevents its 
level of charging from being determined during the constant voltage 
charging mode, even though the level of charging can be discovered during 
the constant current mode as a result of the gradual increase in the 
terminal voltage. Therefore, users can not tell the level of charging 
precisely, and incompletely discharged batteries used to be overcharged 
due to charging beyond full charge. In the case of the constant current 
charging, only current control in each step, such as fast charging or 
quick charging, was possible. Detection of charging current beyond the 
predetermined level in each step was impossible. Failure in detection used 
to cause damage to a battery pack due to overcharge, or reduced the 
operation time of the apparatus due to incomplete charging of batteries. 
Referring to FIG. 3, battery pack 100 uses two switches SW1 and SW2 for 
indicating information as to cell composition. When the battery pack 100 
is composed of Nickel Cadmium or Nickel Metal Hydride cells, the switch 
SW1 is switched on and the switch SW2 is switched off. On the contrary, 
when the battery pack 100 is composed of Lithium ion cells, the switch SW1 
is switched off and the switch SW2 is switched on. The battery pack 100 
uses the battery cells 101, the anode terminal 102, the cathode terminal 
103, the thermistor 104 for detecting the temperature of cells 101, the 
temperature terminal 105 and the output terminals 106 and 107 for 
outputting the battery type information. When the battery pack 100 is 
mounted on the charging apparatus, its respective terminals are connected 
to their corresponding terminals 102a, 105a, 106a and 107a of the charging 
apparatus. 
The charging apparatus according to the embodiment has microcomputer (or a 
microprocessor) 300 as a means for controlling the overall charging 
operation of the battery pack 100. This microcomputer is supplied with 
power (V.sub.DD) by the regulator circuit (composed of 290, C10, C11 and 
R23). The microcomputer 300 is connected to an oscillation circuit formed 
with crystal oscillator X1, the resistor R20 and the capacitors C6 and C7. 
A charging current control unit 210 as a charging source is connected to 
the input terminal 11, to which DC voltage (Vin) from an AC adaptor is 
applied, and the output terminal 102a for supplying the battery pack 100 
with charging current (Iout). The charging current control unit 210 is a 
switching regulator with switching unit 211 located on current path 12 for 
supplying charging current, and the pulse width modulation integrated 
circuit (PWMIC) 212. The switching unit 211 is composed of the resistors 
R3 and R4, the diode D1 and the transistors Q1 and Q2. The PWMIC 212 
controls the on/off time of the transistor Q2 within the switching unit 
211 by outputting a pulse signal which has a duty cycle corresponding to 
the voltage level of the control terminal 213. Thereby, the charging 
current (Iout) flowing from the input terminal 11 through the current path 
12 is controlled according to the control voltage which is input to the 
control terminal 213 of the PWMIC 212. 
The energy storing unit 220 composed of the inductor L1, the diode D2 and 
the capacitor C3 is provided to store the electric energy coming from the 
charging current control unit 210. 
The charging current detecting unit 230 is connected to the energy storing 
unit 220. The charging current detecting unit 230 is composed of the 
resistors R5.about.R9' and the operational amplifier 231. 
The detecting unit 230 detects the charging current flowing through the 
current path 12 using the voltage dropped by the resistor R5 for detecting 
the charging current, and outputs to the control terminal 213 of the PWMIC 
212 a current detecting signal having an intensity corresponding to the 
detected current. 
The voltage dividing unit 240 for dividing the output of the charging 
current detecting unit 230 by a predetermined ratio is composed of the 
resistors R10 and R11, the diode D4, and the capacitor C4. The output 
voltage of the charging current detecting unit 230 is divided by the 
dividing resistors R10 and R11, and the divided voltage is converted to a 
DC level stable voltage for input to the diode D4 and the capacitor C4, 
and is provided to the microcomputer 300. The microcomputer 300 can 
discern the amount of the charging current through the voltage dividing 
unit 240 when operating in the constant voltage charging mode. For 
example, if the resistance of the charging current detecting resistor R5 
is 0.1 ohm, the amplification factor of the operational amplifier 231 is 
25, the ratio between R10 and R11 satisfies R10:R11=1:4, and 2 A of 
charging current flows through the current path 12. The voltage difference 
between both ends of the resistor R5 will be 0.2V, the output voltage of 
the operational amplifier 231 will be 5.0V, and a voltage of 4.0V will be 
applied to the terminal (CC) of the microcomputer 300. Under the same 
condition as above, if 0.5 A of charging current flows through the current 
path 12, a voltage of 1.0V is applied to the terminal (CC) of the 
microcomputer 300. FIG. 4 illustrates the output voltage waveform of the 
voltage dividing unit 240 when charging is consecutively conducted under 
the constant current charging mode and the constant voltage charging mode. 
The output of the voltage dividing unit 240 maintains a constant level 
under the constant current charging mode, but the output of the voltage 
dividing unit 240 decreases with the lapse of time under the constant 
voltage charging mode. As described above, the voltage dividing unit 240 
fulfills its function as a charging current information generating circuit 
in that it provides the microcomputer 300 with information about the 
amount of charging current flowing through the current path. 
On the other hand, as illustrated in FIG. 5, a circuit composed of a Zener 
diode ZD1 whose cathode and anode are connected to the output terminal of 
the operational amplifier 231 and ground voltage, respectively, the 
resistor R24, the diode D6 and the capacitor C12 may be used. In this 
circuit, damage or malfunction of the microcomputer 300 due to surge 
current or overcurrent is avoided because voltage exceeding the operation 
voltage of the microcomputer 300 due to surge current or overcurrent is 
not applied to the microcomputer 300 as a result of the presence of the 
Zener diode ZD1. 
Referring to FIG. 3 again, well-known constant voltage control unit 250 
detects the charging voltage (Vout) across output terminal 102a and local 
reference terminal (e.g., a ground lead) 103a, and outputs a constant 
voltage control signal for varying the control terminal voltage of the 
PWMIC 212 according to the detected voltage so as to maintain the charging 
voltage at a predetermined level. 
The battery type detecting unit 260 detects the type of the battery by 
receiving the cell composition information from the battery pack 100, and 
provides the microcomputer 300 with the battery type signal corresponding 
to the detected type. In detail, if the switch SW1 of the battery pack 100 
is switched on, the microcomputer 300 perceives that Nickel Cadmium or 
Nickel Metal hydride battery is connected since the terminal (106a) 
voltage of the battery type detecting unit 260 is changed to a ground 
voltage level. In this case, the microcomputer 300 causes the battery pack 
100 to be quick and fast charged only under the constant current charging 
mode. On the contrary, if the switch SW2 of the battery pack 100 is 
switched from the position shown to an electrical on state, the 
microcomputer 300 perceives that a Lithium ion battery is connected for 
charging since the terminal (107a) voltage of the battery type detecting 
unit 260 is changed to a ground level. In this case, the microcomputer 300 
causes the battery pack 100 to be quick and fast charged under the 
constant current and the constant voltage charging modes. 
The battery temperature detecting unit 270, composed of the resistor R21 
and the capacitor C8, detects the temperature of the battery pack 100 by 
means of the thermistor 104 which has a resistance which varies according 
to the temperature, and provides the microcomputer 300 with a battery 
temperature signal whose intensity corresponds to the detected 
temperature. 
The battery voltage detecting unit 280, also composed of the resistor R22 
and the capacitor C9, detects the terminal (102 or 102a) voltage of the 
battery pack 100, and provides the microcomputer 300 with a battery 
voltage signal BV according to the detected voltage. 
The microcomputer 300 outputs, based on the input signals, the charging 
enable signal CE for the charging current control unit 210 to conduct the 
charging operation, the quick charging control signal FQ for controlling 
whether the battery pack 100 is quick charged or fast charged, the mode 
control signal CM for making the charging current control unit 210 operate 
under any one of the constant current charging mode and constant voltage 
charging mode according to the type of the battery pack 100, and at least 
one of charging current compensating signals LC and HC for equalizing the 
amount of the charging current in accordance with a predetermined 
reference current amount. 
Well-known quick charging control unit 310 controls the charging speed by 
varying the control terminal (213) voltage of the PWMIC 212 in response to 
the quick charging control signal FQ from the microcomputer 300. If the 
level of the quick charging control signal FQ is high, the quick charging 
control unit 310 increases the charging current amount flowing through the 
switching unit 211 as illustrated in FIG. 6 by lowering the voltage of the 
control terminal 213. On the other hand, if the level of the quick 
charging control signal FQ is low, the quick charging control unit 310 
decreases the charging current amount flowing through the switching unit 
211 as illustrated in FIG. 7 by heightening the voltage of the control 
terminal 213. Thereby, the battery is quick charged. 
The charging mode selecting unit 320 is composed of the diode D5, the 
capacitor C5, the resistors R16 and R17, and the transistor Q5. The 
charging mode selecting unit 320 selectively provides the output signal of 
the constant voltage control unit 250 to the terminal 213 according to the 
mode control signal CM from the microcomputer 300. If the level of the 
mode control signal CM is high, the transistor Q5 is switched on. Thereby, 
the charging apparatus of the embodiment operates under the constant 
current charging mode since the output of the constant voltage control 
unit 250 is not supplied to the terminal 213. On the contrary, if the 
level of the mode control signal CM is high, the transistor Q5 is switched 
off. Thereby, the charging apparatus operates under the constant voltage 
charging mode since the output of the constant voltage control unit 250 is 
supplied to the terminal 213. 
The charging current compensating unit 330 is composed of the resistors 
R12.about.R15 and the transistors Q3 and Q4. This charging current 
compensating unit 330 compensates the charging current flowing through the 
current path 12 in response to the charging current compensating signals 
LC and HC. 
The microcomputer 300 outputs the charging current compensation signal as 
follows by analyzing the current detecting signal CC from the voltage 
dividing unit 240: 
If the analysis shows that the battery is in the process of normal 
charging, the microcomputer 300 outputs the low level charging current 
compensating signal LC and the high level charging current compensating 
signal HC, respectively. 
If the analysis shows that less amount of charging current than a 
predetermined amount flows, the microcomputer 300 outputs the high level 
charging current compensating signal LC and the high level charging 
current compensating signal HC, respectively. 
If the analysis shows that a greater amount of charging current than a 
predetermined amount flows, the microcomputer 300 outputs the low level 
charging current compensating signal LC and the low level charging current 
compensating signal HC, respectively. 
As described above, the charging current flowing through the current path 
12 is compensated by the variation of the control terminal (213) voltage 
according to the amount of charging current. The charging current 
compensating unit 330 may be composed of at least three resistors which 
are connected in parallel to the control terminal 213 to vary the control 
terminal voltage, and at least three switching devices which are connected 
to the resistors and to ground so as to be switched on/off in response to 
the three types of charging current compensating signals provided from the 
microcomputer 300. In this case, the current is compensated more 
accurately. 
The microcomputer 300 outputs the information for indicating the charged 
state of the battery pack 100 according to the output of the voltage 
dividing unit 240. 
Users can know the charged state of the battery pack 100 by this charged 
state information under the constant voltage charging mode. The charged 
state of the battery, for example, a Lithium ion battery which should be 
charged under the constant voltage mode, is discriminated as illustrated 
in FIG. 8. Under the constant current charging mode in which the charging 
current provided to the battery pack 100 is constant and the charging 
voltage of the battery pack 100 rapidly increases, the microcomputer 300 
outputs the charged state information discriminated by A to D% according 
to the voltage variation of the battery pack 100. Under the constant 
voltage charging mode, in which the charging current of the battery pack 
100 is constant and the charging current decreases, the microcomputer 300 
outputs the charged state information discriminated by E to K% according 
to the charging current decreasing rate, that is, the output decreasing 
rate of the voltage dividing unit 240. 
The external voltage detecting unit 340, composed of resistors R1 and R2 
and capacitor C1, detects the external DC voltage (Vin) and outputs the 
signal VENT corresponding to the detected voltage. If the voltage detected 
by this detecting unit 340 is indicated by signal VENT to be below a 
predetermined reference voltage, microcomputer 300 responds to VENT by 
disabling the charging current control unit 210 so as to discontinue the 
charging operation. 
The diode D3 connected to the output terminal 102a is a discharge 
preventing means for preventing the charged voltage of the battery pack 
100 from discharging through the current path. In case the apparatus 
according to the embodiment is applied to portable computers, the 
component parts for indicating the charged state of the battery pack 100 
according to the charged state information output from the microcomputer 
300 is not necessary. Otherwise, it is necessary, but those skilled in the 
art would apply the charged state indicating parts to this invention 
without difficulty. 
According to the invention as described above, even though any of the 
completely discharged battery, the fully charged battery and the battery 
which has a certain amount of electric energy is charged, the charging is 
automatically completed only after the battery is fully charged. Since 
users can detect the charged state of the battery pack, a life shortening 
or a damage of battery due to the overcharge of the battery pack can be 
avoided to increase the reliability of the battery. When the detected 
voltage goes beyond the limit of automatic charging control, charging 
operation is not conducted to prevent battery damage due to overcurrent.