Tutorial 6
Output Characteristics
E364xA User’s and Service Guide 161
Normal mode voltage noise is in the form of ripple related
to the line frequency plus some random noise. Both of these
are of very low value in the power supply. Careful lead
layout and keeping the power supply circuitry away from
power devices and other noise sources will keep these values
low.
Common mode noise can be a problem for very sensitive
circuitry that is referenced to earth ground. When a circuit
is referenced to earth ground, a low level line- related AC
current will flow from the output terminals to earth ground.
Any impedance to earth ground will create a voltage drop
equal to the current flow multiplied by the impedance. To
minimize this effect, the output terminal can be grounded at
the output terminal. Alternatively, any impedances to earth
ground should have a complementary impedance to earth
ground to cancel any generated voltages. If the circuit is not
referenced to earth ground, common mode power line noise
is typically not a problem.
The output will also change due to changes in the load. As
the load increases, the output current will cause a small
drop in the output voltage of the power supply due to the
output impedance R. Any resistance in the connecting wire
will add to this resistance and increase the voltage drop.
Using the largest possible hook up wire will minimize the
voltage drop. Using the remote sense leads at the load will
compensate for lead resistance in the load leads.
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