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amplifier output is a 0-volt to 5-volt level that is compared to a
voltage representing actual power supply output current
(or voltage).
4-75
The programming voltage is also applied to a com¬
parator in the constant current reference circuit block (not
shown on the simplified schematic) and compared to the
l-MONITOR AMPLIFIER OUTPUT, a voltage that is propor¬
tional to actual power supply output current. This comparator
is used for reading back the output current when the power
supply is operating in CV mode, as follows.
4-76
When the microprocessor is asked to transmit to the
controller the actual output current (the controller knows the
programmed limit), the microprocessor starts to program pro¬
gressively lower output current values, one bit at a time. Even¬
tually the CC PROGRAMMING VOLTAGE becomes equal to
or slightly lower than the I MONITOR AMPLIFIER OUTPUT
voltage, and the readback comparator changes state. The
comparator's output goes low to indicate that the CC DAC
output is proportional to the power supply output current. The
microprocessor then knows that the most recently programm¬
ed output current equals the actual output current from the
power supply. The microprocessor encodes that value for
transmission to the controller, and the microprocessor
restores the current limit previously programmed.
4-78
This circuit is similar to the constant current reference
circuit. The CV DAC OUTPUT produces the CV PROGRAM¬
MING VOLTAGE, and the CV DAC OUPTUT is compared to
the ± Sense lines to read back the actual power supply output
voltage when the unit is operating in CC mode.
4-79
Voltmeter Range Circuit
4-80
The voltmeter is designed to blank the display if it
goes overrange. This circuit monitors two segments of the
most significant whole digit to note if the display goes blank,
and switches in greater attenuation to the voltmeter input.
This circuit also enables the proper decimal point for high or
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