124
PLZ-4WL
Operating Area
How constant voltage (CV) mode works
In CV mode, the PLZ-4WL sinks current so that the voltage at the load input end of the PLZ-
4WL is constant.
Constant voltage mode operation
When the PLZ-4WL is used in constant voltage (CV) mode, it operates as a constant-voltage
load (shunt regulator) as shown in the figure below. When V1 is greater than V, the input
voltage V is kept constant even when the input current I varies. Current does not flow when
V1 is less than or equal to V. In the figure below, R
1
is the internal resistance of the constant-
voltage power supply. The PLZ-4WL may operate unstably if R
1
is low.
Transition of the operating point: overpower protection (OPP)
In this example, we will assume that the PLZ-4WL is being used in constant voltage (CV)
mode to test the load characteristic of a constant-voltage power supply.
When the overcurrent protection (OCP) setting I
OCP
is greater than current I
N
at point N, the
voltage of the constant voltage power supply is V
M
. Current will not flow if the PLZ-4WL
voltage V
M0
is greater than V
M
. If the voltage of the PLZ-4WL is decreased so that V
M0
is
less than V
M
, current starts flowing. If the voltage is decreased further (V
M1
V
M2
V
N
) so
that the input current (load current) increases, the operating point moves along segment MN
(M
1
M
2
N).
When point N is reached, overpower protection (OPP) is activated. At this point, one of two
types of operations occurs, depending on the protection action setting for OPP.
If the protection action is set to LOAD OFF, the load turns off.
If the protection action is set to LIMIT, the PLZ-4WL sinks current as a constant-power load at
point N. Even if you attempt to decrease the voltage, the current will not increase beyond
point N. If you increase the voltage, overpower protection (OPP) is cleared. The PLZ-4WL
returns to constant voltage (CV) mode, and the operating point moves along segment MN.
PLZ-4WL Series
Constant-voltage
power supply
I
V
R
1
The voltage is constant even
when the current varies.
V
1
Current I
Voltage
V
0
Input current [A]
Input voltage [V]
Logarithmic scale
V
M
V
M0
V
N
V
M2
V
M1
Constant power line
(constant voltage setting)
Constant voltage line
Operating area
OPP activation point
(OPP setting)
M
N
I
N
I
OCP
M
1
M
2