Chapter 7 Tutorial
Connecting the Load
150
Load Consideration
Capacitive Loading
In most cases, the power supply will be stable for almost any size load capacitance.
Large load capacitors may cause ringing in the power supply's transient response. It
is possible that certain combinations of load capacitance, equivalent series resistance,
and load lead inductance will result in instability. If this occurs, the problem may often
be solved by either increasing or decreasing the total load capacitance.
A large load capacitor may cause the power supply to cross into CC or unregulated
mode momentarily when the output voltage is reprogrammed. The slew rate of the
output voltage will be limited to the current setting divided by the total load
capacitance (internal and external).
Table 7-2. Slew Rate
Inductive loading
Inductive loads present no loop stability problems in constant voltage mode. In
constant current mode, inductive loads form a parallel resonance with the power
supply’s output capacitor. Generally this will not affect the stability of the power
supply, but it may cause ringing of the current in the load.
Pulse Loading
In some applications the load current varies periodically from a minimum to a
maximum value. The constant current circuit limits the output current. Some peak
loading exceeding the current limit can be obtained due to the output capacitor. To
stay within the specifications for the output, the current limit should be set greater
than the peak current expected or the supply may go into CC mode or unregulated
mode for brief periods.
AWG Internal
Capacitance
Internal Bleed
Resistor
Slew Rate at No Load and
Full Scale Current Setting
+6V Output 1000 μF 390 Ω 8 V/msec
+25V Output 470 μF5 kΩ 1.5 V/msec
-25V Output 470 μF5 KΩ 1.5 V/msec
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