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PSI 9000 3U Series
3.2.3 Power regulation / constant power / power limiting
Power regulation, also known as power limiting or constant power (CP), keeps the
DC output power of a power supply constant if the current flowing to the load in
relation to the output voltage and the resistance of load reaches the adjusted value
according to P = U * I resp. P = U² / R. The power limiting then regulates the output
current according to I = sqr(P / R), where R is the load’s resistance.
Power limiting operates according to the auto-range principle such that at lower
output voltages higher current flows and vice versa in order to maintain constant
power within the range P
N
(see diagram to the right).
While the DC output is switched on and constant power mode is active, then the
condition “CP mode active” will be shown on the graphic display by the abbrevia
-
tion CP, as well stored as status which can also be read as a status message via
digital interface.
3.2.4 Internal resistance regulation
Internal resistance control (abbr. CR) of power supplies is the simulation of a virtual internal resistor which is in
series to the voltage source and thus also in series to the load. According to Ohm’s law, this causes a voltage
drop, which will result in a difference between adjusted output voltage and actual output voltage. This will work in
constant current mode as well as in constant power mode, but here the output voltage will differ even more from
the adjusted voltage, because then constant voltage is not active.
The adjustable resistance range is generally defined between 0 and 30 * U
NOM
/ I
NOM
of the particular model. The
voltage setting in dependency of the resistance set value and the output current is done by calculation of the mi
-
crocontroller and thus will be significantly slower the other controllers inside the control circuit. Clarification:
U
Set
= U
0
- I
Act
* R
Set
P
Set
, I
Set
With resistance mode being active, i.e. mode R/I, the function generator will be offline.
