Soft-start and input inrush current surge – Rockwell Automation 1606-XLDC92D Power Supply Reference Manual User Manual
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All parameters are specified at 24V, 3.8A, 24Vdc input voltage, 25°C ambient and after a 5 minutes run-in time, unless noted otherwise.
Rockwell Automation Publication 1606-RM023A-EN-P — January 2014
5
Bulletin 1606 Switched Mode Power Supplies
4. Soft-start and Input Inrush Current Surge
Inrush current limitation
An active inrush limitation circuit (inrush limiting resistor which is bypassed by a relay contact) limits the input inrush
current after turn-on of the input voltage.
The charging current into EMI suppression capacitors is disregarded in the first microseconds after switch-on.
Inrush current
max.
1.6A
peak
-25°C
to
+70°C,
input:
24Vdc
typ.
1.2A
peak
-25°C
to
+70°C,
input:
24Vdc
Inrush energy
typ.
negligible
-25°C to +70°C, input: 24Vdc
Fig. 4-1 Input inrush current, typical behavior
Input Current
Input Voltage
Output Voltage
Input:
24Vdc
Output:
24V, 3.8A, constant current load
Ambient: 25°C
Upper curve:
Input current 2A / DIV
Middle curve: Input voltage 20V / DIV
Lower curve:
Output voltage 20V / DIV
Time basis:
100ms / DIV
Soft-start function:
After the DC/DC converter is turned on, the internal output current rises slowly to its nominal value. This method
charges the output capacitors (internal and external capacitors) slowly and avoids high input currents during turn-on.
High input currents can produce a high voltage drop on the input wiring (especially with long and thin cables) which
reduces the terminal voltage on the DC/DC converter. If the terminal voltage is below the shut-down voltage, the
DC/DC converter will turn-off and will make a new start-up attempt. This effect is avoided with the integrated soft-
start function. Please note, that this function increases the rise time of the output voltage by a small amount.
Fig. 4-2 Soft-start behavior
Input Current
Input:
24Vdc
Output:
24V, 3.8A, constant current load
Ambient: 25°C
No additional external output capacitors
Upper curve:
Input current 2A / DIV
Lower curve:
Output voltage 10V / DIV
Time basis:
20ms / DIV
Output Voltage