| 摘要 |
Power supply to parts of the a portable electronic device, particularly a portable radio telephone, is cut off when the battery voltage falls below a software threshold level. The battery voltage is supplied to a boost regulator 407 which provides an internal reference signal to various circuits, including an analog to digital converter (ADC) 403. ADC 403 uses the reference signal to sample the battery voltage to provide the digitized battery voltage 427 to a processor 405 for comparison therein with the software threshold. Use of boost regulator 407 to provide the internal reference signal allows shutoff at a lower undervoltage value. When the device is in a powered-up state, a hardware shutoff circuit 417 shuts off circuitry if a comparator 413 detects that the battery voltage is below a first hardware undervoltage threshold level which is lower than the software threshold; this provides a backup or failsafe if the software power control circuitry fails. A second hardware undervoltage threshold level, higher than the first, applies when the device is in a powered-off state. When the user operates a power key to power-on the device, the shutoff circuit 417 will prevent power-up if the battery voltage is below this higher second threshold; this prevents the radio communication device from powering-up in an illegal state. The power supply control is of particular use with batteries having a linear fall in voltage during discharge, especially lithium ion batteries, since it allows a larger portion of the energy in the battery to be used before powering-off. |
