Method for controlling a power supply in an external terminal connection of a personal data assistant

A power management method for a PDA (personal digital assistant) which can be connected with an external communication terminal is described. Upon detecting power-on of the external communication terminal, the PDA detects a battery voltage of the PDA and compares the battery voltage with a reference voltage which is slightly higher than an inoperable voltage of the PDA. If the battery voltage is lower than the reference voltage, the PDA generates a low-voltage alarm message. Otherwise, if the battery voltage is higher than the reference voltage, the PDA supplies electric power to the external communication terminal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a personal digital assistant, and in particular, to a power management method for a personal digital assistant which can be connected to an external communication terminal.

2. Description of the Related Art

A personal digital assistant (hereinafter referred to as PDA) is a multimedia device which allows one to access desired information in a desired form anytime and anywhere. The PDA has various utilities according to the user. For instance, the PDA has a personal information management (PIM) function for managing an address book, a telephone directory, a personal scheduler and memorandum. The PDA also has an additional function for gathering and exchanging information by way of facsimile or personal computer (PC) communications. Recently, the PDA may also be connected with an external communication terminal, such as a portable radio telephone. If necessary, the PDA and portable radio telephone may be unified into one body.

When the external communication terminal and the PDA are unified, the PDA may become overloaded due to lack of power supply voltage. Therefore, there has been a demand for a PDA capable of preventing the overload, even in the case where the external communication terminal is connected to the PDA.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a power management method for preventing overload of a personal digital assistant which is connectable with an external communication terminal.

To achieve the above object, there is provided a power management method for a PDA (personal digital assistant) which can be connected to an external communication terminal. Upon detecting power-on of the external communication terminal, the PDA detects a battery voltage of the PDA and compares the battery voltage with a reference voltage which is slightly higher than an inoperable voltage threshold of the PDA. If the battery voltage is lower than the reference voltage, the PDA generates a low-voltage alarm message. Otherwise, if the battery voltage is higher than the reference voltage, the PDA makes a second voltage comparison between a) the difference between the battery voltage and the power required for the external communication terminal and b) the inoperable voltage threshold of the PDA. If the difference indicated in a) is larger than the voltage of b), the PDA supplies electric power to the external communication terminal.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will be described in detail hereinbelow with reference to the accompanying drawings. To provide a comprehensive description of the present invention, the present invention will be illustratively described, confined to the specific embodiment, but the invention is not limited thereto. Furthermore, it should be noted that the present invention can be implemented by anyone skilled in the art with the following general description. In the description, well-known functions or constructions are not described in detail to avoid obscuring the invention.

Referring toFIG. 1, a PDA114includes a central processing unit (CPU)100for controlling an overall operation of the PDA114according to a control program stored in a ROM (Read Only Memory)104. The ROM104stores the control program of the CPU100, data representative of a voltage drop according to the power consumption of an external communication terminal connected to the PDA114, and various reference data (e.g., data indicative of an inoperable voltage Vi of the PDA). A RAM (Random Access Memory)106temporarily stores data generated in the process of executing the control program by the CPU100. A keypad108includes a plurality of numeric and function keys for generating key data to the CPU according to a key operation supplied by the user. A display110displays the operational status of the PDA114under the control of the CPU100. A connector112consists of a serial port to connect the PDA114to the external communication terminal, and interfaces various data and control signals with the external communication terminal under the control of the CPU100. A battery level detector102detects a voltage level of a battery (not shown) of the PDA114under the control of the CPU100.

FIG. 2shows a flowchart for managing the power of the PDA114. Generally, the CPU100detects a voltage difference between a battery voltage Vc and a voltage drop Ve according to the power consumption of the external communication terminal. The CPU cuts off the electric power to the external communication terminal if the voltage difference is lower than the inoperable voltage threshold Vi of the PDA114. The control flow ofFIG. 2is programmed into the ROM104and executed by the CPU100.

Now, referring toFIGS. 1 and 2, if the user turns on the external communication terminal connected to the PDA114at step200, the CPU100of the PDA114proceeds to step202to detect the battery voltage Vc by virtue of the battery level detector102. The CPU100checks, at step204, whether the battery voltage Vc is higher than a first reference voltage Vo indicative of an alarm generation voltage. The alarm generation voltage Vo is a voltage slightly higher than a threshold voltage at which the PDA114cannot operate normally. The alarm generation voltage Vo can be properly set according to various operating conditions of the PDA114. If the battery voltage Vc is lower than the alarm generation voltage Vo, the CPU100proceeds to step218to generate a low-voltage alarm message through the display110or a speaker (not shown) and to cut off electric power to the external terminal. Thereafter, the CPU100checks, at step220, whether the battery voltage Vc is lower than the inoperable voltage Vi at which the PDA114cannot operate normally. If the battery voltage Vc of the PDA114is higher than the inoperable voltage Vi, the CPU100ends this process. However, if the battery voltage Vc of the PDA114is lower than the inoperable voltage Vi, the CPU100sets the PDA114to a sleep mode in step222. In the sleep mode, every part of the PDA114is inactive other than particular functions of the CPU100, such as a power-on/off function.

However, if the battery voltage Vc is higher than the alarm generation voltage Vo at step204, the CPU100proceeds to step206to read, from the ROM104, a voltage drop Ve corresponding to the power consumption, or voltage drop, of the external communication terminal. The ROM104previously stores data corresponding to the voltage drops Ve of respective external communication terminals to be connected to the PDA114. The CPU100checks, at step208, whether a voltage difference (Vc−Ve) between the battery voltage Vc and the voltage drop Ve is higher than the inoperable voltage threshold Vi of the PDA. If the voltage difference is lower than the inoperable voltage Vi, the CPU100proceeds to step212to generate an alarm message informing the user that it is impossible to power on the external communication terminal connected to the PDA114. Subsequently, the CPU100checks, at step214, whether the external communication terminal is powered off. If it is not powered off, the CPU100returns to step212to repeat the steps212and214until the user powers off the external communication terminal. If the external communication terminal is powered off at the step214, the CPU100cuts off the electric power to the external communication terminal at step216. However, if the voltage difference (Vc−Ve) is higher than the inoperable voltage Vi, the CPU100proceeds to step210to supply electric power to the external communication terminal and then, returns to step202. In this way, the PDA according to the present invention can prevent the overload of the battery.

Although an illustrative embodiment of the present invention has been described herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to the precise embodiment so disclosed. Various other changes and modifications may be effected by one skilled in the art without departing from the scope or spirit of the invention.