Page 43
EA Elektro-Automatik GmbH
Helmholtzstr. 31-37 • 41747 Viersen
Germany
Fon: +49 2162 / 3785-0
Fax: +49 2162 / 16230
www.elektroautomatik.de
PSB 9000 3U Series
3.3.4
Internal resistance regulation (source mode)
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 voltage setting in dependency of the resistance set value and the output current is done by calculation of the
microcontroller and thus will be slower the 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.
3.3.5
Resistance regulation / constant resistance (sink mode)
In sink mode when the device is working as electronic load, which operating principle is based on a variable internal
resistance. Constant resistance mode (CR) is almost a natural characteristic. The load attempts to set the internal
resistance to the user defined value by determining the input current depending on the input voltage according to
Ohm’s law I
IN
= U
IN
/ R
SET
.
With series
PSB 9000
, the difference between external voltage supplied and internal set value determines the true
current. There are two situations:
a) The voltage on the DC input is higher than the voltage set value
In this situation, the above formula extends to
I
IN
= (U
IN
- U
SET
) / R
SET
.
An example: the supplied voltage on the DC input is 200 V, the resistance R
SET
is adjusted to 10 Ω and the voltage
set value U
SET
is set to 0 V. When switching the DC input on the current should go to 20 A and the actual resistance
R
MON
should show approx. as 10 Ω. When adjusting the voltage set value
U
SET
to 100 V now, the current would
lower to 10 A while the actual resistance R
MON
should remain at 10 Ω.
b) The voltage on the DC input is equal to or lower than the voltage set value
The PSB 9000 would not draw any current and enter CV mode. In a situation where the supplied input voltage is
approx. equal to or oscillating around the voltage set value, the sink mode would permanently toggle between CV
and CR. It is thus not advised to adjust the voltage set value to the same level as the external source.
The internal resistance is naturally limited between almost zero and maximum (resolution of current regulation too
inaccurate). Because the internal resistance cannot have a value of zero, the lower limit is defined to an achiev
-
able minimum. This ensures that the internal electronic load, at very low input voltages, can consume a high input
current from the source, up to the adjusted current set value.
While the DC input is switched on and constant resistance mode is active, the condition “CR mode active” will be
indicated on the graphics display by the abbreviation CR, as well it will be stored as internal status that can be
read via digital interface.
