8 Service and Maintenance
Common Mode Current Noise
210 E364xA User’s and Service Guide
Common Mode Current Noise
The common mode current is the AC current component
which exists between the output or output lines and chassis
ground. 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 output current flow multiplied
by the impedance.
1 Turn off the power supply and connect a 100 kΩ resistor
(R
S
) and a 2200 pF capacitor in parallel between the –
terminal and chassis ground at the rear output terminals.
2 Connect a digital voltmeter (DVM) across R
S
.
3 Turn on the power supply. Select the output to be tested
and the high voltage range (20 V/1.5 A)
[1]
, enable the
output, and set the display to the limit mode. When the
display is in the limit mode, program the voltage to the
maximum programmable value and the current to the full
rated value (20.6 V
[2]
and 1.5 A
[1]
).
4 Record the voltage across R
S
and convert it to current by
dividing by the resistance (DVM reading/100 kΩ). Note
that the current is less than 1.5 μA.
5 Repeat step 1 through step 4 for the other output.
[1] For the E3646A model. For other models, refer to Tabl e 8 -5 .
[2] For the E3646A model. For other models, refer to Tabl e 7 -3 .
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