The Electronic Load

The Electronic Load
Application Notes ZS PL H&H
ZSLC
Water-cooled
ZSLV
Low Voltage
PMLI
Multi-channel
ZSAC
AC
NL
Source-Sink
Acessories
H&H Application Note #7
Avoiding inrush current peaks and minimizing the dead time at voltage connection
Function
The electronic loads are all fitted
with a controller to set the
preset reference value.
If no input voltage is connected
and a setting value has been
specified for a load, the
controller will attempt to set the
required load current and turns
the output stage on because
since there is no input voltage no
actual value is received.
If a voltage is now applied, a
Elimination of Dead Time
A small trick can almost
eliminate these times.
It is also possible to maintain
the load within the chosen state
if a small voltage, sufficient to
supply the current, is supplied
from another voltage source.
This auxiliary voltage is coupled
via a diode. If the test unit is
not yet connected the auxiliary
voltage is applied to the load
input via the diode and the load
can control the set current.
If the test unit is then
connected, only the input
voltage changes. The load
however, needs not to readjust.
This considerably reduces the
dead time and the settling time.
short circuit occurs on the load
input at the moment of
connecting.
The controller recognizes the
much too high current and
reduces it according to its
preset control time.
Current peaks when switching on the voltage
Note
For EMC reasons the electronic
loads have an input filter.
A specific capacity is therefore
present in the load input. The
output stage itself also has an
inherent capacity which depends
on the number of semiconductors
used and therefore
on the size and power of the
device.
When voltages are connected
this capacity is evident due to
load currents at the moment of
connecting the input voltage.
The capacity values are defined
in the devices´ technical data.
Remedy
To avoid these inrush current
peaks a minimum voltage
detector is installed in the H&H
devices which prevents the
controller from switching on
the output stage fully in the
absence of input voltage.
Depending on the device series
the minimum voltage is fixed
or variable. If the input voltage
is lower than the minimum
voltage, the output stage is
disabled and the controller is
enabled only when the input
voltage is sufficient to set the
required load current.
The load current is then
increased from 0A to the
preset current. In addition to
the control time a dead time
also exists, caused by the
minimum voltage detection.
Delay due to setting of the minimum
voltage detection
Wiring of an auxiliary power supply
Software
GTC
H&H offers no guarantee for the function of
the suggested applications.
H&H offers no guarantee for damage resulting
from such applications.
Delay-free switching of the input voltage
by using an auxiliary voltage source
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