Power switching unit of a portable telephone capable of monitoring and controlling a battery supply voltage thereof

A portable telephone comprising:

• a radio unit for providing a radio communication function;
• a control unit, being operable with a lower power than said radio unit, for controlling operation of said radio unit and providing storage function which stores a list of names and telephone numbers;
• and
• a power switching unit, operably coupled to said radio unit and said control unit, for supplying power to the control unit and the radio unit, wherein said power switching unit comprises:
• a battery for generating power for the control unit and the radio unit,
• a first voltage monitor means for monitoring a supply voltage of said battery to output a first voltage drop signal when said supply voltage falls below a first lower limit of voltage at which said radio unit can work, and
• communication disconnection means for receiving said first voltage drop signal and for stopping power supply to said radio unit upon reception of said first voltage drop signal, wherein upon reception of said first voltage drop signal by said communication disconnection means and upon stopping by said communication disconnection means of said power supply to said radio unit, said communication disconnection means for said control unit continues to at least provide said storage function which stores said list of names and said telephone numbers,
• voltage adjustment means for adjusting voltage supplied to the control unit from said battery to a predetermined operating voltage of said control unit for supplying said predetermined operating voltage to only said control unit and for operating said control unit even if said radio unit becomes inoperable,
• second voltage monitor means for monitoring voltage supplied to said voltage adjustment means to output a power shutoff signal when said voltage falls below a second lower limit of voltage at which said voltage adjustment means can work, and
• power shutoff means for stopping power supply to said control unit and said radio unit upon reception of said power shutoff signal,
• said power switching unit further including third voltage monitor means for monitoring output voltage from said voltage adjustment means for outputting a reset signal when said output voltage falls below a third predetermined value, wherein said control unit receives said reset signal and is reset upon reception of said reset signal to thereby prevent said control unit from being upset.