Specifications

Superimposing Noise On the Output
Question: How can I superimpose noise on the output of a dc power supply?
Answer: Agilent power supplies are designed to have the lowest noise that is practically possible. For some
application it is desirable to simulate the effect of noise on the output, for example to test system immunity to power
line disturbances. Many Agilent power supplies have an analog programming input which can be used to modulate
the output with a signal typically 0.0 to 5.0 volts. This can provide a satisfactory solution for some cases, however,
the bandwidth is limited with this approach, generally to less than 10KHz.
For applications where it is necessary to simulate higher frequency noise, the solution involves using a current
coupling transformer in series with the output. The desired signal, presumably from a suitable signal generator, is
connected to primary of the transformer (refer to the figure below). Information on the specifications of a suitable
transformer are included. Note that for some applications a wideband power amplifier may be necessary to avoid
excessive loading on the noise source.
Low noise, Linear Power Supply
DUT
Operated in CONSTANT VOLTAGE
+
-
+
-
1 turn
500 - 1000 turns
Noise
Source
NOTES:
Core on transformer is critical to
performance of system.
E/I steel or tape wound: 5Hz - 20Kz noise
Tape wound toroid: 20Kz - 120Khz noise
Powered Iron/Ferrite: 120Khz - 300Khz noise
Ferrite: 300Khz - 1Mhz noise
Air core: >1Mhz noise
Under some conditions a wideband power amplifier
may be required between the noise source and
the current coupling transformer.