Power control circuit in wireless mobile communication system

A power control circuit for a wireless mobile communication system includes an over-voltage detection circuit that detects whether a battery is connected to or disconnected from the system, and generates a switching control signal in dependence upon the detection. A switching circuit responds to the switching control signal provided from the over-voltage detection circuit by connecting a voltage supplied through charging terminals to the battery when the switching control signal indicates that the battery is connected to the system, and disconnecting the voltage supplied through the charging terminals when the switching control signal indicates that the battery is disconnected from the system.

CROSS-REFERENCE TO RELATED APPLICATIONS 
This application makes reference to, incorporates the same herein, and 
claims all benefits accruing under 35 U.S.C. .sctn.119 arising from an 
application for Power Control Circuit In Wireless Mobile Communication 
System earlier filed in the Korean Industrial Property Office on 6 Oct. 
1995 and there duly assigned Ser. No. 34355/1995. 
BACKGROUND OF THE INVENTION 
The present invention relates to a power control circuit for a wireless 
mobile communication system, and more particularly, to a power control 
circuit for protecting a wireless mobile communication system by 
interrupting the supply of a charging voltage when a battery is not 
connected to the system. 
The concept of power control within wireless mobile communication systems 
has been the subject of several earlier circuit designs. Among these 
references include U.S. Pat. Nos. 5,101,507 and 5,239,695 assigned to the 
same assignee as the present invention. Both of these exemplary 
references, however, only discuss power control in regards to controlling 
radiating power during signal transmission. They fail to disclose how to 
control power that is provided to a battery of the communication system 
from a charging device. 
In a conventional wireless mobile communication system, charging terminals 
for supplying a charging voltage are integrally combined with a battery 
pack that provides operating power to the system. Since the charging 
terminals and battery pack are combined, charging power from a charging 
device can not be input to the system when the battery pack is detached 
from the system. 
Recently manufactured wireless mobile communication systems, however, 
employ a battery pack having a semi-pack form in which the battery and the 
charging terminals are separately provided for the purpose of reducing 
material costs. In these cases, the semi-pack battery can be easily 
separated from the system while a charging device is connected to a 
printed circuit board (PCB) of the wireless mobile communication system. 
Since the voltage provided from the charging device is substantially 
greater than the desired operating voltage, the voltage supplied to the 
system when the battery is detached can cause great damage to the 
circuitry of the wireless mobile communication system. The present 
invention is directed towards solving this problem. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide an 
improved wireless mobile communication system. 
It is another object to provide a power control circuit for a wireless 
mobile communication system. 
It is yet another object to provide a power control circuit for a wireless 
mobile communication system that prevents transmission of a charging 
voltage when a battery is not connected to the system. 
It is still another object to provide a power control circuit for a 
wireless mobile communication system that prevents damage to the system 
caused by excessive voltage. 
To achieve these and other objects, the present invention provides a power 
control circuit for a wireless mobile communication system. The power 
control circuit may be constructed with an over-voltage detection circuit 
that detects whether a battery is connected to or disconnected from the 
system, and generates a switching control signal in dependence upon the 
detection. A switching circuit responds to the switching control signal 
provided from the over-voltage detection circuit by connecting a voltage 
supplied through charging terminals to the battery when the switching 
control signal indicates that the battery is connected to the system, and 
disconnecting the voltage supplied through the charging terminals when the 
switching control signal indicates that the battery is disconnected from 
the system.

DETAILED DESCRIPTION OF THE INVENTION 
Turning now to the drawings and referring to FIG. 1, a voltage 
characteristic graph illustrating when a battery is mounted, and when a 
battery is not mounted in a general wireless mobile communication system 
is shown. As indicated in FIG. 1, when the system is connected to a 
charging device, a voltage 110 initially supplied from the charging device 
is greater than a battery voltage 112. Accordingly, when a battery pack is 
combined with the system, the voltage supplied from the charging device 
does not rise above the battery voltage 112. On the other hand, when the 
battery pack is separated from the system, the voltage 110 initially 
supplied from the charging device is greater than the battery voltage 112. 
Referring to FIG. 2, a power control circuit for a wireless mobile 
communication system constructed in accordance with the principles of the 
present invention is shown. In FIG. 2, an over-voltage detection circuit 
210 is connected between a switching device 212 and charging terminals 
through which voltage is supplied from a charging device. Over-voltage 
detection circuit 210 detects whether a battery 214 is separated or 
mounted, and then transmits a corresponding switching control signal to 
switching circuit 212. When the battery 214 is separated, the switching 
control signal is transmitted to switching circuit 212 in a logic "low" 
state, and when the battery 214 is mounted, the switching control signal 
is transmitted to switching circuit 212 in a logic "high" state. When the 
switching control signal exhibiting a logic "low" state is provided from 
over-voltage detection circuit 210, switching circuit 212 is turned off, 
and the charging voltage is not supplied to battery 214. Alternatively, 
when the switching control signal exhibiting a logic "high" state is 
provided from over-voltage detection circuit 210, switching circuit 212 is 
turned on, and the charging voltage is supplied to battery 214. 
Over-voltage detection circuit 210 includes: resistors R4 and R5 for 
dividing the voltage supplied from the charging terminals, a transistor Q3 
which generates the switching control signal and is turned on or off in 
dependence upon the voltage divided by resistors R4 and R5, and a 
capacitor C1 for momentarily turning off transistor Q3 while the charging 
voltage is initially supplied from the charging terminals. Resistor R4 and 
capacitor C1 determine the amount of time that transistor Q3 is turned 
off. If the amount of time that transistor Q3 is turned off is too long, 
damage to a system circuit 216 of the wireless mobile communication system 
may be caused. On the contrary, if the amount of time that transistor Q3 
is turned off is too short, the power control circuit can not properly 
provide a power control function. Accordingly, a proper time has to be set 
by manipulating the values of resistor R4 and capacitor C1. According to a 
preferred embodiment, transistor Q3 is turned off for a period of time 
ranging from several tens to hundreds of microseconds. 
Switching circuit 212 includes: a transistor Q2 which is turned on or off 
according to input of the switching control signal, a transistor Q1 which 
is turned on or off as the transistor Q2 is turned on or off and then 
connects or disconnects the charging terminals from the battery 214, and 
resistors R1, R2 and R3. Resistor R3 is set to a value that is sufficient 
to fully turn on transistor Q2, and resistor R2 is set to a value that is 
sufficient to fully turn on transistor Q1. 
Hereinafter, the preferred embodiment of the present invention will be 
explained in detail with reference to FIGS. 1 and 2. 
First, the operations when the wireless mobile communication system is 
connected to the charging device and the battery 214 is mounted within the 
system and is provided with voltage from the charging terminals will be 
described. In this situation, the voltage supplied through the charging 
terminals electrically charges the capacitor C1 during the time set 
according to the values of resistor R4 and capacitor C1. While the 
capacitor C1 is being charged, the voltage is not divided, and transistor 
Q3 is turned off. As a result, the voltage input through resistor R3 is 
used as a driving voltage V.sub.BE of transistor Q2. Transistor Q2 is 
turned on in response to the driving voltage V.sub.BE. Due to this fact, 
the voltage at the base terminal of transistor Q1 becomes lower than the 
voltage at the emitter terminal of transistor Q1 connected through 
resistor R1, and transistor Q1 is turned on. Accordingly, electrical power 
supplied from the charging terminals is provided to battery 214 through a 
diode D1 that inhibits a reverse flow of electrical current. The voltage 
at the charging terminals can be derived through Kirchhoff's voltage law 
as follows: 
EQU V.sub.in =V.sub.Batt +V.sub.DI +V.sub.thl, 
where V.sub.Batt represents the voltage between two terminals of battery 
214, V.sub.DI represents the voltage required when diode D1 is turned on, 
and V.sub.thl represents a threshold voltage of transistor Q1. 
Accordingly, the voltage supplied through the charging terminals is 
uniform by the constant voltage of battery 214. Transistor Q3 maintains 
the off state, and transistors Q1 and Q2 maintain the on state, thereby 
charging the battery 214. 
Next, the operations when the wireless mobile communication system is 
connected to the charging device and the battery 214 is not mounted within 
the system will be described. In this situation, transistor Q3 is turned 
on while capacitor C1 is charged, just as in the previously described 
situation when battery 214 is mounted. However, when the battery 214 is 
not mounted, the input resistance of the power control circuit is much 
greater than an output resistance of the charging device. As a result, the 
voltage V.sub.in supplied through the charging terminals rises to a point 
110, as shown in FIG. 1, and transistor Q3 of over-voltage detection 
circuit 210 is turned on by the voltage applied to its base terminal. The 
voltage provided to the base terminal of transistor Q2, which is connected 
to the collector terminal of transistor Q3, is cut off and transistor Q2 
is accordingly turned off. As a result, the voltage at the base terminal 
of transistor Q1 is equal to the voltage at the emitter terminal of 
transistor Q1, and transistor Q1 is turned off. Therefore, the voltage 
provided from the charging device is interrupted. 
As is apparent from the foregoing, when the battery is not mounted, the 
present invention senses this condition and cuts off the charging voltage, 
thereby preventing excess voltage to the wireless mobile communication 
system. Accordingly, damage to the system due to a user error can be 
prevented. Moreover, the reliability of the system is increased, and cost 
reductions can be achieved. Also, when using a battery pack having a 
semi-pack form, there is an advantage in that a reduction in material 
costs and an interchangeability between models of the parts can be 
achieved. 
While there have been illustrated and described what are considered to be 
preferred embodiments of the present invention, it will be understood by 
those skilled in the art that various changes and modifications may be 
made, and equivalents may be substituted for elements thereof without 
departing from the true scope of the present invention. In addition, many 
modifications may be made to adapt a particular situation to the teaching 
of the present invention without departing from the central scope thereof. 
Therefore, it is intended that the present invention not be limited to the 
particular embodiments disclosed as the best mode contemplated for 
carrying out the present invention, but that the present invention 
includes all embodiments falling within the scope of the appended claims.