Why is it so Difficult to Pass MIL-STD-461, Especially with COTS Products?

The major difference between MIL-STD-461 and commercial EMI specs such as FCC and DO-160 is the measurement of conducted emissions all the way down to
10kHz. Most EMI specifications do not measure conducted emissions below 150kHz. The result of these commercial specifications is that the vast majority of COTS power supplies and equipment is designed such that the nasty emissions are kept below 150kHz and thus off the radar for commercial EMI testing.

For instance, almost all COTS power supplies switch below 150kHz, many even switch as low as 70-75kHz, so that the 2nd harmonic of the switching frequency is
also below the 150kHz limit for commercial testing purposes. These low switching frequencies require less filtering to pass commercial specs, thus reducing the cost to build and reducing the chances of failing costly EMI testing.

As you can see in the “Before” test, the fundamental switching frequency of the power supply is smack dab in the middle of the worst possible place for MIL-STD 461 testing. It is high enough in frequency (75 kHz) that it doesn’t benefit much from the increased amplitude limits at low frequencies (only 77dB at 75kHz) and it’s a low enough frequency that it is very difficult to filter (nearly impossible) with any COTS EMI filters.

COTS EMI filtering is focused on passing tests above 150kHz and offers little attenuation below that level. Additionally, filtering at 75kHz requires substantial physical size for magnetics and capacitance. In order to filter at 75kHz, the corner frequency of the filter must be much lower in frequency, preferable a decade or more below fundamental noise frequency. For many COTS power supplies, that places the necessary corner frequency below 10kHz to achieve effective filtering at 75kHz. Such a low corner frequency is generally only achievable with very large and heavy inductive elements.

Why is Passing MIL-STD-461 the First time Important?

Since MIL-STD-461 does in fact test all the way down to 10kHz, COTS power supplies cause serious problems for passing the CE102 conducted emissions portion of the MIL-STD-461 test. In fact, the use of COTS power supplies in a military system, will almost guarantee a failure when testing to MIL-STD-461 unless proper precautions are taken. Failed MIL-STD-461 testing will result in dozens of hours of re-design and re-testing time and weeks of lost schedule time on a system development effort. The cost of failing MIL-STD-461 testing is measured in the thousands of dollars, and can easily exceed $10k on a single project.

How Does BlackStone Power Solve this Problem?

Leveraging over 40 years of combined EMI/Power design and testing experience, BlackStone Power has devised the secret recipe for passing MIL-STD-461 the first
time. A combination of the right capacitance, the right type of capacitance, and the smallest magnetic size possible results in massive attenuation at low frequencies. The reduced magnetics size ensures that the filter is as compact as possible allowing for use in a multitude of space-constrained designs. The massive attenuation of the filter provides so much margin for the system designer, that passing MIL-STD-461 conducted emissions (CE102) is almost guaranteed.

What is The BlackStone Power Guarantee?

BlackStone Power is so confident in this filter design, that we provide a 100% money-back guarantee that you will pass MIL-STD-461 CE102 testing the first time!
This is the first time that any company in the industry has stood behind their product with this kind of rock-solid guarantee.

In fact, we have so much confidence that this product will overcome any deficiencies in the internal system or power supply designs, that we provide this guarantee
without having any specific details of your system design.