ADDC02828SA

REV. 0

–13–

at any frequency. When this is done, the worst case output

ripple at the frequency of the input ripple occurs at 5 kHz, at

which point there is typically a 25 mV peak-to-peak output

ripple.

It should be noted that MIL-STD-704 has a more relaxed require-

ment for rejection of low frequency differential signals injected on

the dc inputs than MIL-STD-461D. MIL-STD-704 calls for a

lower amplitude ripple to be injected on the input in a narrower

frequency band, 10 Hz to 20 kHz.

CS114: This test measures the ability of the converter to oper-

ate correctly during and after being subjected to currents in-

jected into bulk cables in the 10 kHz to 400 MHz range. Its

purpose is to simulate currents that would be developed in these

cables due to electromagnetic fields generated by antenna trans-

missions. The converter is designed to meet the requirements

of this test when the current is injected on the input power leads

cable. Consult factory for more information.

CS115: This test measures the ability of the converter to oper-

ate correctly during and after being subjected to 30 ns long

pulses of current injected into bulk cables. Its purpose is to

simulate transients caused by lightning or electromagnetic

pulses. The converter is designed to meet this requirement

when applied to its input power leads cable. Consult factory for

more information.

CS116: This test measures the ability of the converter to oper-

ate correctly during and after being subjected to damped sinu-

soid transients in the 10 kHz to 100 MHz range. Its purpose is

to simulate current and voltage waveforms that would occur

when natural resonances in the system are excited. The con-

verter is designed to meet this requirement when applied to its

input power leads cable. Consult factory for more information.

RE101: This requirement limits the strength of the magnetic

field created by the converter in order to avoid interference with

sensitive equipment located nearby. The measurement is made

from 30 Hz to 100 kHz. The most stringent requirement is for

the Navy. Figure 13 shows the test results when the pickup coil

is held 7 cm above the converter. As can be seen, the converter

easily meets this requirement.

RE102: This requirements limits the strength of the electric

field emissions from the power converter to protect sensitive

receivers from interference. The measurement is made from

10 kHz to 18 GHz with the antenna oriented in the vertical

plane. For the 30 MHz and above range, the standard calls for

the measurement to be made with the antenna oriented in the

horizontal plane as well.

In a typical power converter system setup, the radiated emis-

sions can come from two sources: 1) the input power leads as

they extend over the two meter distance between the LISNs and

the converter, as required for this test, and 2) the converter

output leads and load. The latter is likely to create significant

emissions if left uncovered since minimal EMI filtering is

provided at the converter’s output. It is typical, however,

that the power supply and its load would be contained in a

conductive enclosure in applications where this test is applicable.

A metal screen enclosure was therefore used to cover the con-

verter and its load for this test.

Figure 14 shows test results for the vertical measurement and

compares them against the most stringent RE102 requirement;

the horizontal measurement (30 MHz and above) was similar.

As can be seen, the emissions just meet the standard in the

18 MHz–28 MHz range. This component of the emissions is

due to common-mode currents flowing through the input power

leads. As mentioned in the section on CE102 above, the level

of common-mode current that flows is dependent on how the

load is connected. This measurement is therefore a good indi-

cation of how well the converter will perform in the final con-

figuration, but the user should confirm RE102 testing in the

final system. (Reference the last section of EMI Considerations

for how to adjust the external components in the test setup

circuit to increase the margin between the specification limit

and the measured results.)

RS101: This requirement is specialized and is intended to check

for sensitivity to low frequency magnetic fields in the 30 Hz to

50 kHz range. The converter is designed to meet this require-

ment. Consult factory for more information.

RS103: This test calls for correct operation during and after the

unit under test is subjected to radiated electric fields in the 10 kHz

to 40 GHz range. The intent is to simulate electromagnetic

fields generated by antenna transmissions. The converter is

designed to meet this requirement. Consult factory for more

information.

Circuit Setup for EMI Test

Figure 15 shows a schematic of the test setup used for the EMI

measurements discussed above. The output of the converter is

connected to a resistive load designed to draw full power. There

is a 0.1

µF capacitor placed across this resistor that typifies by-

pass capacitance normally used in this application. At the input

of the converter there are two differential capacitors (the larger

one having a series resistance) and two small common-mode

capacitors connected to case ground. The case itself was con-

nected to the metal ground plane in the test chamber. For the

RE102 test, a metal screen box was used to cover both the con-

verter and its load (but not the two meters of input power lead

cables). This box was also electrically connected to the metal

ground plane.

With regard to the components added to the input power lines,

the 100

µF capacitor with its 1 Ω series resistance is required to

achieve system stability when the unit is powered through the

LISNs, as the MIL-STD-461D standard requires. These

LISNs have a series inductance of 50

µH at low frequencies,

giving a total differential inductance of 100

µH. As explained

earlier in the System Instability section, such a large series

source inductance will cause an instability as it interacts with the

converter’s negative incremental input resistance unless some

corrective action is taken. The 100

µF capacitor and 1 Ω resis-

tor provide the stabilization required.

It should be noted that the values of these stabilization components

are appropriate for a single converter load. If the system makes

use of several converters, the values of the components will need

to be changed slightly, but not such that they are repeated for

every converter. It should also be noted that most system appli-

cations will not have a source inductance as large as the 100

µH

built into the LISNs. For those systems, a much smaller input

capacitor could be used.

Increasing Margin Between Specification Limit and Measured

Results

With regard to the 2

µF differential-mode capacitor and the two

82 nF common-mode capacitors, these components were in-

cluded in the test setup to augment the performance of the