Chapter 7 Tutorial
Remote Programming
146
Remote Programming
During remote program ming a constant-voltage regulated power supply is
called upon to change its output voltage rapidly. The most important factor
limiting the speed of output voltage change is the output capacitor and load
resistor.
Figure 7-8. Speed of Response - Programming Up (Full Load)
The equivalent circuit and the nature of the output voltage waveform when the
supply is being programmed upward are shown in Figure 7-8. When the new
output is programm ed, the pow er supply regulator circuit senses that the
output is less than desired and turns on the series regulator to its maximum
value I
L
, the current limit or constant current setting.
This constant current I
L
charges the ou tput capacitor C
O
and load resistor R
L
parallel. The output therefore rises exponentially with a time constant R
L
C
L
towards voltage level I
L
R
L
, a value higher than the new outpu t voltage being
programmed.
W hen this exponential rise reaches the newly programmed voltage level, the
constant voltage amplifier resumes its normal regulating ac tion and holds the
output constant. Thus, the rise tim e can be determined approxim ately usi ng
the formula shown in Figure 7-8.
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