Battery charging apparatus and method with charging mode convertible function

A battery charging apparatus for use with batteries that require charging in a constant current mode and/or constant voltage mode. The charging apparatus includes a constant current charging control circuit converting the charging current supplied with the battery into a voltage signal and applying the voltage signal to a feedback input terminal of a switching regulator in response to a charging speed control signal F.sub.-- Q, and a constant voltage charging control circuit providing a control signal to the feedback input terminal for controlling constant voltage charging if the battery voltage level has reached a preset voltage level, whereby a constant voltage charging is possible during the charging operation in response to a charging mode selection signal CHG.sub.-- MOD. A microcomputer produces the charging mode selection signal CHG.sub.-- MOD when it is detected the charging voltage of the battery in the constant current mode and the detected voltage reached to a preset level in order to convert the charging mode into the constant voltage mode. Further, a charging speed control signal F.sub.-- Q is produced to enable the switching regulator to perform quick charging operation. With this arrangement, the constant voltage (CV) charging mode can be performed when the battery is in the preset condition, regardless of type of batteries. In addition, by provision of a protection circuit, possible damage of the CV charging control circuit due to the excessive static or surge is effectively prevented.

CLAIM FOR PRIORITY 
This application make reference to, incorporates the same herein, and 
claims all benefits accruing under 35 U.S.C. .sctn.119 through my patent 
application entitled A BATTERY CHARGING APATUS WITH CHARGING MODE 
CONVERTIBLE FUNCTION earlier filed on the 24.sup.th day of June 1996 in 
the Korean Industrial Property Office, and there regularly assigned Ser. 
No. 1996/23162. 
FIELD OF THE INVENTION 
The present invention relates to battery charging processes and apparatus, 
and, more particularly, to battery charging processes and circuits used in 
portable computers for charging batteries in constant current modes and 
constant voltage modes. 
BACKGROUND OF THE INVENTION 
Recently, rechargeable batteries, i.e., secondary batteries, have been 
widely used to provide electrical power for driving battery powered 
electronic appliances such as, by way of example, portable radio cassette 
players, portable computers, camcorders, cellular telephones and other 
devices. Alkaline batteries such as nickel cadmium (Ni--Cd) or nickel 
metal hydride (Ni--MH) batteries have been generally used as the secondary 
battery. Recently, lithium ion (Li-ion) batteries with an organic 
electrolytic cell have gained popularity in high-end portable electronic 
devices because they exhibit high energy density, low temperature 
characteristics, and stable storage capability. 
Rechargeable batteries require an electronic charger for recharging 
depleted batteries. A charger should include an internal charger circuit 
incorporated into the battery powered appliance. A charger will begin 
charging the battery whenever the device is powered by alternating current 
(i.e., AC) power. External battery chargers accepting one or more 
batteries to be charged, are equipped with an independent power supply and 
connectors. 
Although rechargeable batteries have various types of battery chemistry, 
battery pack voltage, and battery pack capacity, there have been few 
methods of charging the batteries adopted in battery chargers. Generally, 
the charging method is either a constant voltage charging process or a 
constant current charging process. Constant voltage charging applies a 
constant voltage that is higher in amplitude than the nominal voltage of 
the battery across the terminals of a battery. Constant voltage charging 
process is typically used for charging a backup battery where frequent 
charging and discharging is not occurring. The charging voltage is 
continuously applied to the battery. On the other hand, the constant 
current charging process applies a constant current to the battery 
irrespective of any increase in the voltage across the terminals occurring 
as the charging progresses. Constant current charging is useful for 
rapidly charging a battery. Constant current charging however, requires a 
time limit in order to avoid damage of the battery due to overcharging. 
Except those used in the portable radio cassette players, most battery 
chargers use a constant voltage charging process because it is simple in 
construction and is relatively inexpensive. This charging process requires 
relative long time, approximately about ten hours. Thus, constant voltage 
charging processes can be ineffective for portable use of the appliance 
powered by batteries. 
In an effort to provide a more rapid charging process with battery 
protection, a charging mode convertible type charger has been developed. 
This charger performs charging operations in the both constant current 
mode and in the constant voltage mode. This type of charger starts 
charging the battery in a constant current mode when the battery is 
discharged in order to provide a fast charging operation, and 
automatically converts to a constant voltage mode at a predetermined 
charging level in order to complete a typical charging operation. Thus, 
rapid charging is provided while avoiding damage to the battery due by 
allowing the battery to remain connected to the charger for an excessively 
long time. 
Some circuit designs such as the Apparatus For Controlling Charging Of A 
Storage Battery of Yeong J. Joo, U.S. Pat. No. 5,175,485 seek to initially 
apply a constant current, and then a constant voltage when the voltage 
across the terminals of a battery reach a desired value. Recent circuit 
designs such as the Rechargeable Battery Charging Method of M. Tamai, U.S. 
Pat. No. 5,442,274, have used hysteresis charging to a set value, followed 
by constant voltage charging. Other recent efforts in the art include the 
Method For Charging Secondary Battery And Charger Used Therefor by T. 
Nagai, et alii, U.S. Pat. No. 5,576,608 and the Method For Charging A 
Secondary Battery And Charger Used Therefor Using Constant Current And 
Constant Voltage by T. Nagai, et alii, U.S. Pat. No. 5,637,981, for 
converting after detection of various characteristics from a constant 
current to a constant voltage that is equal to the fully charged voltage. 
In a constant current charging process, rapid and full charging is possible 
within a time limit during which a constant current is applied to the 
battery. In the mode convertible type charging process, initial charging 
is performed in the constant current mode for a predetermined time period, 
and then the charging operation is switched to the constant voltage mode, 
so that a full charge of the battery is achieved with the charging voltage 
being constantly maintained. 
Ni--Cd and Ni--MH batteries can require the constant current charging mode, 
while Li-ion batteries require both the constant charging mode and the 
constant voltage charging mode. In the constant current charging mode, the 
end point of time at which the battery must cease its charging is 
determined by detecting an increase in the terminal voltage of the battery 
when the battery is fully charged. There is some difficulty in detecting 
the exact charge end point, because the full charge time varies with the 
residual capacity of the battery. 
In a specific rapid charger, the charge time is determined by detecting 
voltage drop across the battery terminals because some amount of current 
is discharged from the battery when charging begins. The charge time is 
determined in accordance with an internal charging program. This method is 
difficult because the full charging of a battery can not be assured during 
the preset charging time due to the fact that the preset charging time 
does not reflect aging of the battery. Moreover, unless the battery to be 
charged is made by the manufacturer of the charger, the full charge time 
necessary for the battery can not be uniformly provided to the battery. 
Consequently, the terminal voltage of the battery being charged varies 
with the residual capacity and degree of aging of the battery. The 
conventional battery charger has endeavored to provide a compromise 
between rapid full charging and protection of the batteries. 
A conventional charger for charging a Li-ion battery by using both a 
constant voltage charging process and a constant voltage charging process 
supplies a charging current to the battery by controlling the current or 
voltages between the output of a switching regulator and the battery being 
charged. This mode convertible type of battery charger unnecessarily 
consumes power because it always performs a constant voltage charging 
operation. When a Li-ion battery is being charged, the constant voltage 
charging mode is only necessary for supplemental charging subsequent to 
the constant current charging. Moreover, the constant voltage control 
circuit of the charger is apt to be damaged by the occurrence of static, 
noise or surges when the battery pack is either mounted on or detached 
from the appliance. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide an improved 
mode convertible battery charging process and battery charger. 
It is another object to provide a mode convertible battery charging process 
and charger able is to provide constant voltage charging when necessary 
during a constant current charging mode, irrespective of the type of 
battery being charged. 
It is another object to provide a mode convertible battery charging process 
and battery charger able to protect the charging control circuits from 
being damaged by unexpected electrical shocks. 
According to one aspect of the present invention, there is provided a 
battery charging process and a battery charger for use with batteries 
required to be charged in a constant current mode and/or constant voltage 
mode. This uses a switching regulator generating a switching voltage from 
a DC voltage source; a constant current charging controller for detecting 
the current of the DC output provided by the switching regulator to 
produce a charging control signal for enabling the switching regulator to 
operate in the constant current mode; a battery detector for detecting the 
voltage level of the battery; a second controller for producing a charging 
mode selection signal, a charging speed control signal, and a charging 
enable signal in response to the voltage level detected from the battery 
detector; a charging speed controller for enabling the switching regulator 
to perform fast charging or quick charging operations in response to the 
input level of the charging speed control signal; a constant voltage 
charging controller for generating a control signal at the feedback input 
terminal of the switching regulator in order to operate the switching 
regulator in the constant voltage charging mode whenever the battery 
voltage level has reached a preset voltage level; a protection stage for 
preventing the constant voltage charging control circuit from being 
damaged by an excessive surge voltage; and a charging mode selector for 
enabling the constant voltage charging control circuit to operate in 
response to the charging mode selection signal. 
Preferably, the constant current charging controller includes a resistor 
for detecting the output current of the switching regulator applied to the 
battery, and a comparator for amplifying the voltage drop at the resistor 
as much as the voltage gain thereof and for supplying the amplified 
voltage with the feedback input terminal of the switching regulator. 
The charging speed controller includes a switching transistor having a base 
electrode connected with the charging speed control signal input via 
resistors, and a collector electrode coupled with the feedback input of 
the switching regulator. 
Also, the constant voltage charging controller includes a voltage divider 
for detecting the charging voltage of the battery, a reference voltage 
generator, a comparator for producing the mode converting signal when the 
divided voltage is higher than the reference voltage, and a transistor for 
providing the charging voltage with the feedback input terminal of the 
switching regulator in response to the mode converting signal. 
The protection stage includes a first transistor switched on in response to 
the high level signal of the charging mode selection signal, and a second 
transistor switched on in response to the turn on state of the first 
transistor to provide the charging voltage with the constant voltage 
charging controller. 
The charging mode selection means includes a transistor for connecting, or 
disconnecting, the output of the constant voltage charging controller with 
the feedback input terminal of the switching regulator in response to the 
charging mode selection signal. Also, the charging mode selector includes 
a diode for blocking current flow from the output of the constant current 
charging controller to the output of the constant voltage charging 
controller.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
As shown in FIG. 1A, prior art constant current charging processes were 
able to provide a rapid and full charging of a battery within the time 
limit (shown by the dashed line) during which a constant current is 
applied to the battery. As shown in Fig. 1B, in the mode convertible type 
charging process, when initial charging is performed in the constant 
current (CC) mode for a predetermined time period and then the charging 
operation is changed to a constant voltage (CV) mode, a full charge of the 
battery is achieved with the charging voltage being maintained constantly. 
In this context, the Ni--Cd and Ni--MH batteries can require the constant 
current charging mode, and the Li-ion batteries require both the constant 
current charging mode and the constant voltage charging mode. In the 
constant current charging mode, the end point of time at which the battery 
must cease to be charged is determined by detecting an increase of the 
terminal voltage of the battery when the battery is fully charged. A 
problem arises in detecting the exact end point of the charging operation 
because the full charge time varies with the residual capacity of the 
battery. In a specific rapid charger, the charge time is determined such 
that at the time the charging started some amount of current is discharged 
to detect voltage drops at the battery terminals, and the charge time is 
determined in accordance with an internal charging program. This method is 
unreliable because fall charging of a battery can not be assured during 
the preset charging time, since aging of the battery is not considered. If 
the battery to be charged is not made by the manufacturer of the charger, 
the full charge time can not be uniformly obtained for other types of 
batteries. Therefore, since the terminal voltage of the battery being 
charged varies with the residual capacity and degree of aging of the 
battery, conventional battery chargers have sought a compromise between 
the rapid fall charging and the protection of the batteries. 
A conventional charger for charging a Li-ion battery by using both a 
constant current charging process and a constant voltage charging process 
is exemplified by FIG. 2. A power supply 1, a switching regulator 2, a 
constant current control circuit 3, and a constant voltage control circuit 
4 are provided for charging the Li-ion battery 5. The power supply 1 
includes, although it is not shown, a transformer for converting AC outlet 
power into the required amplitudes of voltage, a rectifying and smoothing 
circuit for providing the DC power sources, and a voltage regulator for 
supplying stable DC output voltages. The power supply 1 may include 
switching regulator 2. The constant current control circuit 3 includes a 
current detection resistor 3a coupled at the power supply line to the 
positive terminal of battery 5, and operational amplifier 3b for detecting 
the voltage drop within preset voltage range produced when the maximum 
current is applied to resistor 3a during a rapid charging operation. 
Constant voltage control circuit 4 includes divider resistors 4a, 4b for 
obtaining a divided voltage from the battery power supply line, a 
reference voltage capacitor 4c, and an operational amplifier 4d comparing 
the divided voltage with the reference voltage and producing a constant 
voltage control signal to be supplied to switching regulator 2. 
Although this convertible type of battery charger supplies a charging 
current to the battery controlling the current or voltages between the 
output of switching regulator 2 and battery 5, it always performs a 
constant voltage charging operation which unnecessarily consumes 
electrical power. When a Li-ion battery is being charged, the constant 
voltage charging mode is only necessary for supplemental charging 
occurring subsequent to the constant current charging. The constant 
voltage control circuit for the charger is apt to be damaged by occurrence 
of static, noise or electrical surges when the battery pack is mounted on 
or detached from an electrical appliance. 
Turning now to FIG. 3 to FIG. 9 inclusive, a battery charging circuit 
constructed according to the principles of the present invention can have 
a constant current charging control circuit 20 converting the charging 
current supplied to the battery into a voltage signal and applying the 
voltage signal to a feedback input terminal FB of the switching regulator 
10 in response to a charging speed control signal F.sub.-- Q applied to 
fast/quick charging control circuit 50. A constant voltage charging 
control circuit 80 generates a control signal to feedback input terminal 
FB for controlling constant voltage charging when the voltage level of the 
battery has reached a preset voltage level, whereby a constant voltage 
charging is possible during the constant current charging operation in 
response to a charging mode selection signal CHG.sub.-- MOD. Charging 
speed control signal F.sub.-- Q and the charging mode selection signal 
CHG.sub.-- MOD, as well as a charging enable signal CHG.sub.-- EN are 
supplied by a microcomputer 90 incorporated into the charging circuit. 
Microcomputer 90 produces the charging mode selection signal CHG.sub.-- 
MOD when it detects that the charging voltage of the battery during the 
constant current mode has reached a preset level, in order to convert the 
charging mode into the constant voltage mode. Charging enable signal 
CHG.sub.-- EN is produced by microcomputer 90 in response to the signal 
A.sub.-- IN representing the point of time when the power is supplied from 
the adapter of the power supply circuit (not shown) is input, in order to 
permit the switching regulator 10 to start the charging operation. 
Charging speed control signal F.sub.-- Q is produced to enable the 
switching regulator 10 to initiate a quick charging operation. 
EMBODIMENT 1 
Referring to FIG. 3, there is shown a configuration of a battery charging 
circuit having a charging mode convertible function constructed as one 
embodiment of the present invention. The battery charging circuit uses a 
switching regulator 10 for producing DC output required for charging the 
battery from a DC power source, a constant current charging control 
circuit 20 detecting the current of the DC output provided by the 
switching regulator 10 to produce a charging control signal, a battery 
detection circuit 30 for detecting the charged voltage and the temperature 
of the battery 40, a fast/quick charging control circuit 50 enabling the 
charging operation to be performed in fast charging mode or quick charging 
mode in response to the charging speed control signal F.sub.-- Q. Further 
included is a constant voltage charging control circuit 80 outputting a 
control signal to the feedback input terminal for controlling constant 
voltage charging if the battery voltage level has reached a preset voltage 
level, a protection circuit 70 for preventing the constant voltage 
charging control circuit 80 from being damaged by the excessive surge 
voltage, and a charging mode selection circuit 60 for enabling the 
constant voltage charging control circuit 80 in response to the charging 
mode selection signal CHG.sub.-- MOD. 
The battery pack 40 has a plurality of battery cells 41 which can be any 
type of rechargeable battery. However, the charging circuit of the 
invention is preferable to use with the Li-ion battery. Usually, the 
Li-ion battery pack 40 has a temperature sensing terminal T.sub.-- BATT 
for sensing surface temperature of the battery cells, coupled with the 
negative terminal BATT(-) of the battery pack 40 via a thermistor 42. 
Also, the battery pack 40 has a battery controller having data and clock 
terminals for sensing types of battery material, coupled with the positive 
power terminal BATT(+) via a full-up resistors R65 and R64, respectively. 
In the event that the battery pack 40 has so called smart battery as 
well-known in the art, the battery controller is composed of a 
microcomputer. 
Further, the battery detection circuit 30 includes a divider resistors R61, 
R62 coupled with the power supply line led from the output of the 
switching regulator 10 through a diode D 1. Battery voltage detection 
terminal V.sub.-- BATT is provided at the junction point of the two 
resistors R6 1, R62. The battery detection circuit 30 further includes a 
microcomputer 90 having inputs for receiving signals from the 
above-mentioned terminals T.sub.-- BATT, V.sub.-- BATT, Data, and Clock. 
The microcomputer 90 has outputs for providing control signals F.sub.-- Q, 
CHG.sub.-- MOD, and CHG.sub.-- EN with the fast/quick charging control 
circuit 50, the charging mode selection circuit 60, and the switching 
regulator 10, in response to the input signals, respectively. 
The microcomputer 90 determines the battery charging state from the voltage 
level of the V.sub.-- BATT terminal and the battery type from the Data and 
Clock terminals. If the Data terminal is corresponding to logic low level 
and the Clock terminal is logic high, the microcomputer 90 regards the 
battery pack 40 as a Ni-MH or Ni-Cd battery. Otherwise, if the Date 
terminal is high and the Clock terminal is low, a Li-ion battery is found. 
The constant current charging control circuit 20 is provided to operate 
such that the DC output is produced in a PWM (Pulse Width Modulation) form 
in response to the voltage variation detected at the resistor R21 provided 
in the DC output line of the switching regulator 10. The detected voltage 
of the resistor R21 is amplified at the operational amplifier OP21 as much 
as the voltage gain thereof. There, the DC output voltage is applied to 
the divider resistor R22, R23 and the divided voltage is applied to the 
non-inverting input of the operational amplifier OP21 and the detected 
voltage at the resistor R21 is applied to the inverting input of the 
operational amplifier OP21 through the resistor R24. 
The details of the fast/quick charging control circuit 50 of the battery 
charging apparatus is shown in FIG. 4. The fast/quick charging control 
circuit 50 includes a transistor Q5 1; the base thereof is connected with 
the charging speed control signal input FQ via resistors R52 and R54, and 
the collector with the feedback input of the switching regulator 10 via 
resistors R5 1 and R53. The emitter of the transistor Q51 is grounded. In 
response to high level input of the charging speed control signal F.sub.-- 
Q, the transistor Q51 will be turn on and switch the collector terminal to 
the ground, which disables the applying of a quick charging signal to the 
feedback input of the switching regulator 10 and enables the regulator 10 
to operate in a normal charging operation. Otherwise, at the low level 
input control signal F.sub.-- Q, the transistor Q51 will be turn off and 
the switching regulator 10 performs quick charging operation in response 
to the output voltage of the constant current charging control circuit 20. 
The feedback input terminal FB of the switching regulator 10 is set to the 
reference voltage of 1.24 Volts. Thus, the switching regulator 10 turns on 
the switching transistor (not shown) until the feedback input terminal FB 
reaches the reference voltage by the supplying voltage from the constant 
current charging control circuit 20. And if the voltage of feedback input 
terminal FB exceeds the reference voltage, the switching transistor will 
be turned off. Like this, the charging current generated by the repeat of 
turn on/off of the switching transistor of the switching regulator 10 is 
applied to the battery 40 and the quick charging can be achieved. 
Meanwhile, when the charging speed control signal F.sub.-- Q becomes high 
level and the transistor Q51 is turned on, the output level of the 
constant current charging control circuit 20 will be lowered due to the 
resistors R5 1, R53. This will continue the turn on state of the switching 
transistor of the switching regulator 10 until the feedback input terminal 
FB reaches the reference voltage (1.24 Volts) and permits flow of much 
charging current to the battery 40. 
Specifically, when the transistor Q51 of the fast/quick charging control 
circuit 50 is turned on, the voltage Vfbf applied to the feedback input 
terminal FB of the switching regulator 10 can be obtained by the following 
equation: 
##EQU1## 
where, Va means an output voltage of the operational amplifier OP21 of the 
constant current charging control circuit 20. 
Further, when the transistor Q51 is turned off, the voltage Vfbq applied to 
the feedback input FB of the switching regulator 10 can be obtained by the 
following equation: 
##EQU2## 
Where, Va means an output voltage of the operational amplifier OP21 of the 
constant current charging control circuit 20. 
In this circuit, the voltage Vfbf is normally larger than the voltage Vfbq, 
however, since the reference voltage of the feedback input terminal FB 
should be 1.24 Volts, the constant current outputted in the fast charging 
mode is larger than that of in the quick charging mode. 
The detailed configuration of the constant voltage charging control circuit 
80 of the apparatus is shown in FIG. 5. There, the constant voltage 
charging control circuit 80 includes an operational amplifier OP81 that 
functions as a comparator, and a switching transistor Q81. The 
non-inverting input of the operational amplifier OP81 is connected with a 
divider resistors R81, R82 for supplying with the divided charging voltage 
fed from the output of the protection circuit 70, and the inverting input 
is connected with another divider resistors R83, R84. Both ends of the 
serial divider resistors R8 1, R82 are connected parallel with a Zener 
diode D81. This diode D81 will prevent the constant voltage charging 
control circuit 80 from being damaged by inputting of an excessive static 
or surge voltage. Also, at both ends of the resistor R84, i.e., between 
the inverting input of the comparator OP81 and the ground terminal, there 
is provided another Zener diode D82 to supply a reference voltage. 
In this circuit 80, if the charging voltage divided by the resistors R81, 
R82 is lower than the reference voltage provided by the Zener diode D82, 
the comparator OP81 produces a low level output and thus the transistor 
Q81 will be turned off. This represents that the charged voltage at the 
battery 40 has not reached a desired level, for example in case of a 
Li-ion battery, 4.1 or 4.2 Volts/cell. On the other hand, if the charged 
voltage at the battery 40 reached above the desired level, the comparator 
OP81 produces a high level output that allows the transistor Q81 to be 
turned on. Thus, charging voltage is supplied through the transistor Q81 
with an input A of the charging mode selection circuit 60, and then 
applied to the feedback input terminal of the switching regulator 10 to 
increase voltage level applied to the feedback input terminal FB. 
Therefore, the constant current charging operation is converted into the 
constant voltage charging mode. 
The protection circuit 70 of the battery charging apparatus includes a 
signal input CHG.sub.-- MOD connected to an output of the microcomputer 90 
and two voltage inputs connected to the output of the constant current 
(CC) charging control circuit 20 and the output of the diode D 1 of the 
power supply line led to the battery pack 40, as shown in FIG. 6. Further, 
the protection circuit 70 consists of a transistor Q71 and Q72, and 
related biasing resistors R71 to R74. The signal input terminal CHG.sub.-- 
MOD is connected to the base of the transistor Q71 via the resistor R73 
and the two power supply inputs are connected with the collector of the 
transistor Q71 via the resistor R72 and with the collector of the 
transistor Q72. There, the collector output of the transistor Q71 is 
connected to the base input of the transistor Q72. And the emitter of the 
transistor Q71 is grounded and the emitter of the transistor Q72 is 
connected with an input of the constant voltage (CV) charging control 
circuit 80. Also, a resistor R7 1 is connected between the signal input 
terminal CHG.sub.-- MOD and the output of the CC charging control circuit 
20. The resistor 74 is connected between the base and emitter of the 
transistor Q72. 
As shown in FIG. 7, the charging mode selection circuit 60 includes a 
transistor Q61, a base biasing resistor R61, and a diode D61. The base of 
the transistor Q61 is connected with the charging mode selection signal 
line CHG.sub.-- MOD, and the collector of the transistor Q61 is connected 
with the output terminal A of the CV charging control circuit 80 as well 
as the feedback input of the switching regulator 10 via the diode D61. 
In operation, when the battery 40 is coupled with the charging circuit of 
this invention, the charging operation proceeds at the constant current 
mode with the charging mode selection signal CHG.sub.-- MOD being 
maintained at logic high level. The microcomputer 90 detects the charging 
state of the battery from the voltage level at the terminal V.sub.-- BATT 
of the battery detection circuit 30. If the charged voltage exceeds the 
preset voltage level, or the detected voltage and temperature level, etc. 
are corresponding to the preset transition condition in case of the Li-ion 
battery, the microcomputer 90 produces a low level charging mode selection 
signal CHG.sub.-- MOD to convert the charging mode into the constant 
voltage mode. At this time, the low level signal CHG.sub.-- MOD is applied 
to the base of the transistor Q71 of the protection circuit 70, which 
permit the transistor Q71 to be turned off and the transistor Q72 on. The 
low level charging mode selection signal CHG.sub.-- MOD is also applied to 
the base of the transistor Q61 of the charging mode selection circuit 60, 
which turns off the transistor Q6 1. This result in supplying of the 
charging voltage at the power supply line with the CV charging control 
circuit 80. 
As previously mentioned, the CV charging control circuit 80 receives the 
charging voltage supplied with the battery 40 when the charged voltage 
reached above the desired level, and the charging voltage is supplied 
through the resistor R85 with an input A of the charging mode selection 
circuit 60, and then applied to the feedback input terminal of the 
switching regulator 10, in order to increase voltage level at the feedback 
input terminal PB. Therefore, the constant current charging operation that 
proceeded in the switching regulator 10 is changed to the constant voltage 
charging mode. 
More specifically, in the charging mode selection circuit 60, when the 
charging mode selection signal CHG.sub.-- MOD is in the high level, the 
transistor Q61 will be turned on and the anode of the diode D61, i.e., 
collector of the transistor Q61 is grounded. Thus, the diode D61 
interrupts the output of the CV charging control circuit 80, and the 
output voltage of the CV charging control circuit 80 does not affect the 
output of the CC charging control circuit 20. 
In the above arrangement, the CV charging mode can be carried out when the 
battery is found to be in the preset condition, regardless of type of the 
batteries. In addition, by provision of the protection circuit 70, the 
possible damage of the CV charging control circuit 80 due to the excessive 
static or surge is effectively prevented. 
FIG. 8 and 9 show another embodiments of the battery charging apparatus in 
accordance with the present invention. Also, in FIG. 8 and FIG. 9, all of 
the constituents having the same configuration and performing the same 
functions as those illustrated in FIG. 3 shall have the same reference 
numbers. 
EMBODIMENT 2 
Briefly, the circuit configuration of the battery charging apparatus shown 
in FIG. 8 is the same as those in FIG. 3 except omission of the protection 
circuit block 70. Therefore, the output of the CC charging control circuit 
20 providing a charging voltage for the battery 40 is directly connected 
with the input of the CV charging control circuit 80. 
The operation is similar with that of the first embodiment. That is, when 
the battery 40 is coupled with the charging circuit shown in FIG. 8, the 
charging operation is proceeded at the constant current mode with the 
charging mode selection signal CHG.sub.-- MOD being maintained at logic 
high level. The microcomputer 90 detects the charging state of the battery 
from the voltage level at the terminal V.sub.-- BATT of the battery 
detection circuit 30. If the charged voltage exceeds the preset voltage 
level, or the detected voltage and temperature level, etc. are 
corresponding to the preset transition condition especially provided for 
the Li-ion battery, the microcomputer 90 produces a low level charging 
mode selection signal CHG.sub.-- MOD to convert the charging mode into the 
constant voltage mode. 
At this time, the low level charging mode selection signal CHG.sub.-- MOD 
is applied to the base of the transistor Q61 of the charging mode 
selection circuit 60, which turns off the transistor Q61. This result in 
supplying of the charging voltage at the power supply line with the CV 
charging control circuit 80. 
The CV charging control circuit 80 receives the charging voltage supplied 
with the battery 40 when the charged voltage reached above the desired 
level, and the charging voltage is supplied through the resistor R85 with 
an input A of the charging mode selection circuit 60, and then applied to 
the feedback input terminal of the switching regulator 10, in order to 
increase voltage level at the feedback input terminal FB. Thus, the 
constant current charging operation that proceeded in the switching 
regulator 10 is changed to the constant voltage charging mode. 
With this arrangement, the CV charging mode can be carried out at the 
preset condition, regardless of type of batteries, that is the charging 
voltage of the battery and the surface temperature of the battery, etc. 
reached a preset level. 
EMBODIMENT 3 
FIG. 9 illustrates the third embodiment of the battery charging apparatus 
according to the present invention. Briefly, the circuit configuration of 
the battery charging apparatus shown in Fig. 9 is the same as those in 
FIG. 3 except omission of the charging mode selection circuit 60 which 
enables the switching regulator to operate in the constant voltage mode 
other than the constant current mode. Therefore, it is configured so that 
the charging mode selection signal CHG.sub.-- MOD supplied from the 
microcomputer 90 can safely be applied to the input of the protection 
circuit 70, and the output of the CV charging control circuit 80 is 
directly connected with the feedback input terminal of the switching 
regulator 10 together with the output of the CC charging control circuit 
20. 
In operation, similar with that of the first embodiment, when the battery 
40 is coupled with the charging circuit shown in FIG. 9, the charging 
operation is proceeding at the constant current mode with the charging 
mode selection signal CHG.sub.-- MOD being maintained at logic high level. 
The microcomputer 90 detects the charging state of the battery from the 
voltage level at the terminal V.sub.-- BATT of the battery detection 
circuit 30. If the charged voltages exceed the preset voltage level, or 
the detected voltage and temperature level, etc. are corresponding to the 
preset transition condition especially provided for the Li-ion battery, 
the microcomputer 90 produces a low level charging mode selection signal 
CHG.sub.-- MOD to convert the charging mode into the constant voltage 
mode. 
At this time, the low level signal CHG.sub.-- MOD is applied to the base of 
the transistor Q71 of the protection circuit 70, which permits the 
transistor Q71 to be turned off and the transistor Q72 on. This result in 
supplying of the charging voltage at the power supply line with the CV 
charging control circuit 80. The CV charging control circuit 80 receives 
the charging voltage when the charged voltage at the battery 40 reached 
above the desired level, and then the charging voltage is supplied through 
the resistor R85 with the feedback input terminal of the switching 
regulator 10, in order to increase voltage level at the feedback input 
terminal FB. Therefore, the constant current charging operation that 
proceeded in the switching regulator 10 is changed to the constant voltage 
charging mode. In the meantime, when the charging mode selection signal 
CHG.sub.-- MOD maintains the high level, the CV charging control circuit 
80 will not operate when the battery pack 40 is mounted in the charging 
circuit. 
With the above arrangement, the CV charging operation can be carried out 
when the battery is found to be charged in the CV charging mode, 
especially the Li-ion battery is used in the charging circuit of this 
invention. In addition, by provision of the protection circuit 70, the 
possible damage of the CV charging control circuit 80 due to the excessive 
static or surge is effectively prevented. 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.