Power Management
Overview
Standby Mode
System Sleep Time-Out
Hard-Disk Drive Time-Out
Serial Port
Internal Modem
Low Battery Warnings
Charging Strategy
Overview
Dell notebook computers have a complex power management system. The computer has a system power management (SPM) board with a highly efficient DC-to-DC converter and battery-switching circuitry. A 2-bank main battery and a reserve battery maximize operational time. The AC power adapter is a simple DC power supply that provides operation and charging. The power management system has 4 modes of operation:
Off
Only the NVM, RTC microcontroller's SRAM, and battery removal latch operate from the reserve battery.
Off 
External Power:
The power management system operates from the external power AC or auto adapter and charges the main and reserve batteries.
On Battery Power:
The system operates from battery power. The power management system monitors and switches batteries as necessary.
On External Power:
The system operates from the external AC or auto adapter. The power management system trickle charges the main and reserve batteries.
Standby Mode
When standby mode is activated, the following components are affected:
Processor on hold
Processor speed reduced to 2 MHz
LCD panel turns backlight off
Hard-disk drive standby mode
I/O chip low-power mode
Optional internal modem off mode
The Power LED flashes on and off once per second to indicate standby mode. The computer retains data and returns to normal operation only when the standby button is pressed again.
When the display is closed over the keyboard, the standby button is pressed and the computer automatically goes into standby mode, unless an external monitor is attached.
System Sleep Time-Out
The system sleep timer can be set in the System Setup program. This timer starts counting whenever there is no disk, video, or keyboard activity. If the timer elapses, the computer enters a sleep mode similar to standby mode except the processor is not put on hold. The computer reactivates if there is video or drive activity, or if any key is pressed.
Hard-Disk Drive Time-Out
The hard-disk drive timer can be set in the System Setup program. This timer starts counting whenever there is no hard-disk drive activity. If the timer elapses, the hard-disk drive is placed in its standby mode. The hard-disk drive is reactivated, after a brief delay, when it receives a request to read or write data.
Serial Port
If the serial port is not used, it can be turned off to conserve power through the System Setup program.
Internal Modem
One of 2 power conservation modes for the modem can be selected in the System Setup program:
ON = Reduces power to a maximum of 50 mW. This mode of operation ensures compatibility with all communications software.
OFF = Reduces power to a maximum of 10 mW.
The OFF option requires a transition of the modem port's RTS control line to reactivate to normal operation and may be incompatible with some software.
Low Battery Warnings
Main battery first warning:
Battery life remaining 10 minutes
Low battery LED on
Auto alarm 2 beeps/sec for 5 sec
Main battery second warning:
Battery life remaining 2 minutes
Low battery LED flashing, 1-sec intervals
Auto alarm 2 beeps/ 5 sec
When the main battery is depleted, the system switches to the reserve battery and enters standby mode.
Reserve battery/standby mode:
Battery life remaining 2 minutes
Power LED flashing, 1-sec intervals
Keyboard off
LCD off
When the reserve battery is depleted, the computer sounds a steady tone for 3 seconds and shuts down the DC-to-DC converter. The only way to prevent shutdown is to insert a charged battery or connect an external power source.
Charging Strategy
The charge rate and charge time are based on algorithms stored in firmware. The battery characteristics that indicate full charge can be changed by updating the algorithm. This permits the system to use new battery technology with only a firmware change. During charge, the algorithm can detect batteries with shorts or opens and beep the system speaker to indicate a defective battery. The NiCad batteries shipped initially are charged until the cell voltage begins to decrease. This is known as negative dV/dt full charge detection.