MIL Grade EMC Filter for DC/DC Converters
Jun 16, 2023
DC/DC-converters are electronic devices that can change a direct current (DC) voltage into another DC voltage. They can act like an isolating transformer or a step-up or step-down transformer but with direct current instead of alternating current (AC) supplies.
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About DC/DC Converters
DC/DC converters are electronic devices that convert one direct current (DC) voltage into another. In essence, they can function like an isolating transformer or a step-up/step-down transformer, but operate with direct current instead of alternating current (AC). Since conventional transformers only work with AC, all DC/DC converters internally operate as DC-to-AC-to-DC systems.
Because DC/DC converters use switching elements (such as transistors) to generate the internal AC waveform, their input and output currents are inherently pulsating. This switching action produces electromagnetic interference (EMI). Electromagnetic compatibility (EMC) filters are specialized circuits designed to manage this EMI effectively, helping the converter meet EMC compliance standards with adequate margin below the permitted limits. Their primary role is to suppress unwanted electromagnetic signals, preventing interference that could affect or degrade the performance of nearby sensitive electronic equipment.
Because DC/DC converters use switching elements (such as transistors) to generate the internal AC waveform, their input and output currents are inherently pulsating. This switching action produces electromagnetic interference (EMI). Electromagnetic compatibility (EMC) filters are specialized circuits designed to manage this EMI effectively, helping the converter meet EMC compliance standards with adequate margin below the permitted limits. Their primary role is to suppress unwanted electromagnetic signals, preventing interference that could affect or degrade the performance of nearby sensitive electronic equipment.
About MIL-STD-461G
Military-grade compliant EMC filters are engineered to meet stringent Army, Air Force, and Navy standards, using high-quality components and undergoing rigorous testing to ensure reliability under extremely harsh environmental and operating conditions. With their exceptional EMI suppression capabilities, these filters play a crucial role in safeguarding critical military systems and enhancing their overall electromagnetic compatibility.
The United States Military Standard (MIL-STD) applicable to EMC is MIL-STD-461 (Requirements for the Control of Electromagnetic Interference Characteristics of Subsystems and Equipment). The most current version of this standard is MIL-STD-461G, although many legacy projects still follow the earlier version, MIL-STD-461E.
The United States Military Standard (MIL-STD) applicable to EMC is MIL-STD-461 (Requirements for the Control of Electromagnetic Interference Characteristics of Subsystems and Equipment). The most current version of this standard is MIL-STD-461G, although many legacy projects still follow the earlier version, MIL-STD-461E.
Classes and Lebels of MIL-STD-461G
MIL-STD-461G establishes classes and test levels to define the limits for EMC across various military platforms. These classes and their corresponding limits apply to a wide range of military vehicles and systems, including:
Ground Vehicles
Class A: Non-critical systems with moderate emission and immunity requirements.
Class B: Combat vehicles with intermediate emission and immunity requirements.
Class C: Mission-critical systems, such as command and control units, with the strictest emission and immunity requirements.
Class B: Combat vehicles with intermediate emission and immunity requirements.
Class C: Mission-critical systems, such as command and control units, with the strictest emission and immunity requirements.
Aircraft
Class A: Non-critical avionics and systems meeting moderate limits.
Class B: Critical avionics with intermediate emission control and immunity requirements.
Class C: Vital systems, including flight control and communication equipment, meeting the strictest limits for emission and immunity.
Class B: Critical avionics with intermediate emission control and immunity requirements.
Class C: Vital systems, including flight control and communication equipment, meeting the strictest limits for emission and immunity.
Submarines
Class A: Non-critical systems with moderate emission and immunity requirements.
Class B: Critical subsystems with intermediate emission control and immunity requirements.
Class C: Vital systems such as navigation and communication equipment, subject to the strictest emission and immunity requirements.
Class B: Critical subsystems with intermediate emission control and immunity requirements.
Class C: Vital systems such as navigation and communication equipment, subject to the strictest emission and immunity requirements.
Requirements Matrix
MIL-STD-461G specifies a comprehensive set of test procedures designed to meet the U.S. Department of Defense (DoD) specifications and requirements, depending on the intended operational environment. These test procedures are divided into four groups: radiated emissions (RE), conducted emissions (CE), radiated susceptibility (RS), and conducted susceptibility (CS). Each procedure is identified by a two-letter group abbreviation followed by a numeric code—for example, CS101 refers to the test “Conducted Susceptibility, Power Leads.”
A = Applicable
S = Specified in procurement
L = Limited applicability
Blank = Not applicable
| Equipment | CE101 | CE102 | CE106 | CS101 | CS103 | CS104 | CS105 | CS114 | CS115 | CS116 | CS117 | CS118 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Surface Ships | A | A | L | A | S | L | S | L | S | A | L | S |
| Submarines | A | A | L | A | S | L | S | L | S | L | S | S |
| Aircraft, Army | A | A | L | A | S | S | S | A | A | L | A | |
| Aircraft, Navy | L | A | L | A | S | S | S | A | A | L | A | |
| Aircraft, Airforce | A | L | A | S | S | S | A | A | L | A | ||
| Space Systems | A | L | A | S | S | S | A | A | L | |||
| Ground, Army | A | L | A | S | S | S | A | A | S | |||
| Ground, Navy | A | L | A | S | S | S | A | A | S | |||
| Ground, Airforce | A | L | A | S | S | S | A | A |
Table 1: MIL-STD Conducted Emissions and Susceptibility Matrix
A = Applicable
S = Specified in procurement
L = Limited applicability
Blank = Not applicable
| Equipment | RE101 | RE102 | RE103 | RS101 | RS103 | RS105 |
|---|---|---|---|---|---|---|
| Surface Ships | A | A | L | L | A | L |
| Submarines | A | A | L | L | A | L |
| Aircraft, Army | A | A | L | A | A | L |
| Aircraft, Navy | L | A | L | L | A | L |
| Aircraft, Airforce | A | L | A | |||
| Space Systems | A | L | A | |||
| Ground, Army | A | L | L | A | ||
| Ground, Navy | A | L | L | A | L | |
| ... | ... | ... | ... | ... | ... | ... |
Table 2: MIL-STD Radiated Emissions and Susceptibility Matrix
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