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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 7-7. 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.