ZOLL Base Powercharger 4x4, Service Manual

Page: 32 / 75

FUNCTIONAL DESCRIPTION
IV-11
When no battery is present in a charging compartment, the voltage feedback amplifier
with inputs at U103.1 and U103.2 dominates control of the loop. The negative input of
the amplifier is tied to the temperature compensated reference through R103 for
isolation purposes. The positive input of the amplifier senses the power supply output
voltage via voltage divider R128 and R119 through R108. The divider is filtered by
C127 and C118. R/C network R102 and C106 compensate the amplifier ensuring
stable operation. R120 is placed in parallel with R119 via Q102 to change the
maximum charging voltage during CV or CC charging. R121 is the gate protection
resistor in Q102.
During battery charging, the current feedback amplifier U102A dominates control of
the loop. The output current of the power supply is measured through sense resistor
R127. The sense voltage developed across this resistor is then compared to a
fraction of the on board 1.2V reference determined by the voltage divider resistors
R104 and R105. The result of this compare function is to limit the output current of the
power supply to 1A during CV charging and by placing R129 across R104 to 500mA
during CC charging. Capacitor C125 provides stabilization for this control loop. C105
and C113 provide RF filtering and C104 provides power supply bypassing. R 107 is a
balance resistor for U102A.
A second current feedback amplifier with inputs at U103.13 and U103.14 limits supply
current to 2A in the event of a failure of amplifier U102A. Operation of this amplifier is
similar to that of U102A with resistor divider R118 and R101 providing a reference
voltage to compare against the voltage generated across current sense resistor R127
through R116. C126 stabilizes the amplifier ensuring proper control loop operation.
R130 is a series gate protection resistor for Q104.
A final level of component failure protection is provided by the 2A pico-fuse F101.
Each Compartment output voltage is protected by a transorb from positive to negative
terminal TV101. JP101 and a transformer, rather than an inductor, allows the
switches to be converted from a Buck regulator to a flyback style.
Battery Test Control Circuitry
The microprocessor initiates a battery test sequence when it has detected the
presence of a battery in the charging compartment and the test switch has been
pressed. A fail-safe charge enable circuit is provided which requires that the
microprocessor is functioning properly before the test load can be applied to the
battery. Refer to the
Charge Control Circuitry Section (Page IV-8) for a description
of the Charge Enable Control circuitry.
Once the Charge Enable control is established, the microprocessor may either
charge or discharge the battery to prepare a battery for use or determine its ability to
perform under load. To apply the test load, the microprocessor asserts SSEL1- high
(at U104.25) which places the load resistor (R3) across the battery via the output of
U106.12 through R122 to the transistor Q101. As the load is applied across the
battery, the power supply is caused to shut down via the current flow through diode
D104.
Diodes D105 provides static discharge protection for the gate of the load control FET
(Q101).