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Chapter 7 Tutorial
Connecting the Load
146
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 F 390 8 V/msec
+25V Output 470 F 5 k 1.5 V/msec
-25V Output 470 F 5 K 1.5 V/msec