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EPS Stromversorgung GmbH
Alter Postweg 101 • 86159 Augsburg
Germany
Fon: +49 821 / 570451-0
Fax: +49 821 / 570451-25
www.eps-germany.de
PSI 10000 4U Serie
3.2.2
Current regulation / constant current / current limiting
Current regulation is also known as current limiting or constant current mode (CC).
The DC output current is held constant by the power supply, once the output current to the load reaches the ad
-
justed limit. Then the power supply automatically switches to CC. The current flowing from the power supply is
determined by the output voltage and the load’s true resistance. As long as the output current is lower than the
adjusted current limit, the device will be either 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 sets the
output current according to I
MAX
= P
SET
/ U
IN
, even if the maximum current value is higher. The current set value,
as determined by the user, is always an upper limit.
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 with abbreviation
CC
and this message will be passed as a signal to the analog
interface, as well stored as status which can also be read as a status message via digital interface.
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 true 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.
In remote sensing operation, i. e. when the Sense input is connected to the load, the increased
voltage output and thus also increased power output isn’t included in the actual power value,
because the device then measures and regulates the voltage on the Sense input.
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.