Power Supply Signals - Fluke 867B Service Manual

Power Supply Signals

Signal Name
BACKLIGHT_ON* Control signal generated by U25. In Model 867B, this signal toggles the backlight
power levels.
BATT_LVL Monitors an attenuated (0 to 5V) version of the raw battery voltage. This signal is
monitored by the U25 microprocessor A/D Converter. The attenuation factor is
0.0909:1 with an output impedance of approximately 91 kΩ.
BATT_TYPE Monitors an attenuation level of the battery charging voltage. The attenuation ratio is
0.0901:1 with an output impedance of approximately 91 kΩ.=If the measured voltage
is greater than 11 volts, the battery is assumed to be an alkaline cell. Voltages 10.5
volts and below indicate that a Fluke BP7217 battery pack has been installed.
BATT_ELIM This is a contact on the battery eliminator input receptacle. It is pulled to LINE with 5
kΩ and tied to GND4 through=475Ω,=forming a 10.51:1 divider. If open (voltage
>1.0V), a line-powered battery eliminator has been installed. If closed (shorted to
ground), the battery eliminator is not plugged-in or is not powered.
CONTRAST PWM signal from U25. The frequency is set at U25_SYSCLK/(CLOCK_DIVIDER x
COUNTER_LIMIT), yielding 4.8 MHz/(4 x 4096), equaling 293 Hz. The PWM signal
has 12-bit resolution, which can vary the duty cycle from 0 to 100%.
IBL+ Current source generated by power supply used to run the LCD backlight. Current
source is controlled by the BACKLIGHT_ON* control signal. Typical current level is
80 mA. This is the sourcing node derived from unregulated DC, typically +6.0V
(5.8V minimum.)
IBL- Current return for IBL+, with approximately 1V burden.
POWER_DOWN Powers down the GMM. Signal is generated by U25. This signal shuts the GMM off
completely. Pulled-down to GND with 20 kΩ.
PWR_RESET* Signal generated by the power supply when the VCC power supply drops below 3.0
volts. The reset lasts 100 milliseconds minimum. If the selector is left in the OFF
position or the GMM is powered down, the PWR-RESET* signal restarts the 100 ms
time-out period. This signal is pulled up to VCC by 10 kΩ .
VEE_ON Control signal generated by U25. Turns the VEE power supply on and off. Pulled
down to ground by 100 kΩ .
WAKEUP* This signal is generated by both the rotary selector switch and the WAKEUP button.
Upon going LOW, followed by a return to HIGH, the GMM powers up. In the OFF
position, this feature is overridden by the OFF switch.
Table 2-3. Power Supply Signals
Description
Theory of Operation
Power Supply
2-7.
2
2-7