4: Technical Description
PRC-BC4-MS 4-3
4.2.3 Float State
The float state maintains the battery voltage at 13.3 VDC. Charger IC U1
changes the cutoff voltage by changing pin 10 from ground (in the bulk charge
state) that places R1 in parallel with R3, to a high impedance that places R1 in
series with R3, shifting Vcutoff to 13.3V. The PRC-BC4 uses whatever
current (up to 1.1A) necessary to maintain this voltage. The BB-LA6 is now
fully charged and can be left on the charger in this state for many years.
If for some reason the BB-LA6 voltage drops below 12 VDC, the PRC-BC4
returns to the bulk charge state and repeats the charge cycle.
4.3 Status LEDs
The front panel LEDs provide charge level status. Charger IC U1 provides
two signals to control the status LEDs: the enable comparator output at pin 11
and the state level output at pin 10.
4.3.1 Fault LED
The enable comparator output (pin 11) goes directly to the Display board
where it drives the FAULT LED through current limiting resistor R2. It also
drives the base of Q1 that shunts voltage away from diodes D1 and D2 when it
is conducting, preventing the CHARGING and READY LEDs from lighting.
4.3.2 Charge LED
The state level output (pin 10) drives the inverting input to operational
amplifier U5B. The non-inverting input is fixed at 1.3 VDC. Pin 10 is at
ground potential during the bulk charge and overcharge states keeping the
output of U5B high. When U5B is high (near B+ voltage but always greater
than 12 VDC), the CHARGING LED conducts through R8; it also
reverse-biases the READY LED so that it cannot light up.
4.3.3 Ready LED
During the float charge state, pin 10 goes to a high impedance condition with
the voltage level equal to pin 13 (normally about 2.5 VDC). This causes U5B
to go low. When the U5B output is low (near ground potential), the READY
LED conducts through D3 and R5. The 12V supply provides the voltage for
the
CHARGE and READY LEDs.
4.4 Component Locations, Schematic, and Parts List
This section includes the component locations diagrams, schematic, and parts
lists for the Charger board.
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