Chapter 7 Tutorial
Remote Programming
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7
If no load resistor is attached to the power suppl y output termi nal, then the
output voltage will rise li nearly at a rate of C
O
/I
L
when programmed upward,
and TR = C
O
(E
2
-E
1
)/I
L
, the shortest possibl e up-pro gram m in g time.
Figure 7-9. Speed of Response - Programming Down
Figure 7-9 shows that when the power supply is programmed down, the
regulator senses that the output vo ltage is higher than desired and turns off
the series transistors entirely . Since the control circuit can in no way cause the
series regulator transistors to conduct backwards, the output capacitor can
only be discharged through the load resistor and internal current source (I
S
).
The output voltage decays linearly with slope of I
S
/C
O
with no load and stops
falling when it reaches the new output voltage which has been demanded. If
full load is connected, the output voltage will fall exponenti all y faster.
Since up-programming speed is aided by the conduction of the series regulating
transistor, while down programming normally has no active element aiding in
the discharge of the output cap acitor, laboratory power suppli es norm all y
program upward mor e rapidly than downward.
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