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Chapter 7 Tutorial
Remote Programming
158
Remote Programming
During remote programming 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 programmed, the power 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 output 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 output voltage being
programmed.
When this exponential rise reaches the newly programmed voltage level, the
constant voltage amplifier resumes its normal regulating action and holds the
output constant. Thus, the rise time can be determined approximately using
the formula shown in Figure 7-8.