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EA Elektro-Automatik GmbH
Helmholtzstr. 31-37 • 41747 Viersen
Germany
Fon: +49 2162 / 3785-0
Fax: +49 2162 / 16230
www.elektroautomatik.de
PSI 9000 DT Series
3.2.2
Current regulation / constant current / current limiting
Current regulation is also known as current limiting or constant current mode (short: CC).
The DC output current is held constant by the power supply as soon as the output current to the load reaches
the adjusted limit. The power supply will then automatically switch to CC. The actual output current of the power
supply is determined by the actual output voltage and the load’s resistance. As long as the output current is lower
than the adjusted current limit, the device will either be in constant voltage or constant power mode. If, however,
the power consumption reaches the adjusted power value, the device will switch automatically to power limiting
and set the output current according to I
MAX
= P
SET
/ U
IN
, unless the adjusted current set value value is lower. This
set value is determined by the user and is always an upper limit only.
While the DC output is switched on and constant current mode is active, the condition “CC mode active” will be
indicated on the graphic display by the abbreviation CC and also passed as signal “no CV” to the analog interface,
as well stored as status which can be read via digital interface.
3.2.3
Power regulation / constant power / power limiting
Power regulation, also known as power limiting or constant power (short: CP), keeps
the DC output power of a power supply constant if the current flowing to the load
in relation to the output voltage 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 can flow 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, the condi-
tion “CP mode active” will be shown on the graphic display by the abbreviation CP,
as well stored as status which can be read via digital interface.
3.2.3.1
Power derating
Due to fusing and cross sections of conductors and the extended input voltage range, power supply models with
1500 W rated output power have a fixed derating, which becomes active below a certain AC supply voltage (for
value see
„1.8.3. Specific technical data“
). The device would then derate the maximum available output power down
to approx. 1000 W. The derating only affects the power stage, so the full range for power set value adjustment
remains, though the device won’t provide full output power anymore. In this situation, constant power operation
can not be indicated by status “CP”. Once derating is active it can only be detected by comparing the actual power
to the set values of voltage, current and power.
There is no status “CP” available if the power set value is bigger than the derated actual output
power of the device. It means, power derating isn’t indicated.
3.2.4
Internal resistance regulation
Internal resistance control (short: CR) of power supplies is the simulation of a virtual internal resistor which is in
series to the load. According to Ohm’s law, this resistance causes a voltage drop, which will result in a difference
between the adjusted output voltage and the actual output voltage. This will also work in CC or CP mode whereas
the actual output voltage will differ even more from the adjusted voltage, because both modes limit the output
voltage additionally. CR mode is actually running in CV, but will be indicated as CR on display once the adjusted
resistance value is reached.
The adjustable resistance range of a particular model is given in the technical specifications. The voltage regulation
in dependency of the resistance set value and the output current is done by calculation in a fast ARM controller,
being only a little slower than other controllers inside the control circuit. Clarification:
U
Act
= U
Set
- I
Act
* R
Set
P
Set
, I
Set
P
Ri
= (U
Set
- U
Act
) * I
Act
With resistance mode being activated the function generator will be unavailable and the actual
power value provided by the device does not include the simulated power dissipation of Ri.
Summary of Contents for PSI 9000 DT Series
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