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MOVing Out Noise

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b2ap3_thumbnail_Soundwaves-lo-res.jpgTransients have many sources, but the most common are:

  • Electrostatic discharge (ESD)
  • Lightning (LEMP)
  • Nuclear (NEMP/HEMP)

There are a few options available to the circuit designer to mitigate the effects of over-voltage transients. Historically, either transient absorption zener diodes (TAZ) or metal oxide varistors (MOV) have been used as shunt devices to handle the transient current environment during such events. Each option has its own set of advantages and disadvantages, but we will focus on the MOVs. In the past, MOV architecture has been single-layer, but technological advancements with MOV construction have expanded the capability and stability of these devices with the introduction of multi-layer varistor (MLV) designs. This technology has allowed MOV/MLV components to be efficiently packaged inside electrical connectors in the form of a disc, similar to what is used for capacitive (filter) components. MLV architecture has an innate ability to be able to handle high transient current.  For example, transient testing per the FAA’s Environmental Conditions and Test Procedures for Airborne Equipment (RTCA-DO-160G, Sec 22, waveform 4, level 5 (1600V/320A, 500 pulses) has been performed on Amphenol’s MLV planar devices with no degradation of leakage or breakdown characteristics. The question may be asked, “When should an MLV device be specified?” It should be used when:

  • Capacitance is not an issue
  • High-transient currents are encountered
  • Increasing either the length or diameter of the connector is not reasonable
  • There is some flexibility with an increase of voltage clamp (VCLP) characteristics combined with increase of the maximum pulse current


An MLV’s transient capability is then specified by two parameters:

  • The maximum current with an 8 x 20 µS exponential transient (range from 250 to 350A), which is commonly associated with lightning events
  • The maximum energy with a 10 x 1000 µS exponential transient (range from 1.2 to 3.0 joules), which is commonly associated with a man-made event.

The maximum current and energy for other waveforms are then interpolated from these two parameters. MOV/MLV devices can be supplied with a range of working voltages between 8 and 45 volts. Planar MLV devices can also be easily coupled with an RFI low-pass filter network internal to the connector. This arrangement would provide both RFI filtering and transient protection in a very space-efficient package. Amphenol Aerospace has a long history of packaging discrete MLV planar arrays within connectors. Contact our experienced engineering team today to discuss designing an MOV/MLV device for your system.

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Gary Toombs is a Senior Design Engineer for Amphenol Aerospace’s Filter Products Group. He has been with Amphenol for 36 years.

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Guest Wednesday, 24 October 2018

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