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High Voltage MLCCs Part 3: It Ain’t the Volts, It’s the Amps

Posted by Mike Randall on October 14, 2014


This is Part 3 of a Three Part Series

  • Part 1:It’s What’s Inside that Counts
  • Part 2:Judging a Book by Its Cover:Don’t Forget the Outside
  • Part 3:It Ain’t the Volts, It’s the Amps: Some Applications and Considerations

Now that we have discussed the internal design of high voltage MLCCs (HVMLCCs) as well as several factors regarding the outside of HVMLCCs and the surrounding circuity, let’s discuss some applications and considerations when using HVMLCCs.  It is important to use the right HVMLCCs for your application.  In general, HVMLCCs are used in numerous applications where high voltage (either AC or DC or both) are encountered.  HVMLCCs are carefully designed to perform correctly via careful dielectric selection, internal and external design to prevent surface arcing through a “quasi-plasma” that may be established due to electric fields encountered in the related application.  This corona discharge is to be avoided as it will degrade and possibly destroy the HVMLCC or the surrounding circuitry.

 Overview:  Actually, It’s the Volts and the Amps

The energy stored in a capacitor is related to the square of the voltage through the relationship:


  • E is energy in Joules
  • C is capacitance in Farads
  • V is voltage in Volts

Take away?  Even though HVMLCCs typically have much lower capacitance values than standard MLCCs, they still can store about the same amount of energy at rated voltage. 

Additionally, since the impedance of HVMLCCs can be quite low at high frequencies, it is important to understand the frequencies and voltages associated with your application.  For example, if the impedance of the HVMLCC selected is low at a frequency utilized in your application, a great amount of current may be passed through the device at that frequency if the voltage associated with that frequency is high.  In these situations, it is highly important to understand the current capacity (typically called ripple current capability) of the HVMLCC that you are thinking about selecting for your application; as use of a device with inadequate ripple current capability may result in overheating of the component, and damage to the component and the circuit.  In the same context, it is important to understand the voltages that the HVMLCC you select will experience.  This is especially important because HVMLCCs typically have low ESR values at relatively high frequencies.  AC applications utilizing frequencies >10 KHz, or applications that may include voltage surges, are especially important to evaluate carefully, as most voltage ratings are based on DC voltages which may not be relevant at all to these situations.  

For most relatively low frequency AC applications (i.e., less than ~10 KHz), it’s typically OK to select an HVMLCC having  a VRated value that is about 2.8X that of the VRMS of the application.  This is based upon the logic that VRated should be about the same as VP-P.  At higher frequencies, as impedance decreases, this multiplier should increase.  It is highly important for the designer to test the circuit to insure proper device selection for his or her specific application.  Testing will also inform the designer of other issues such as piezoelectric buzzing, overheating or the like.  In these cases, redesign of the circuit or selection of a more appropriate HVMLCC is in order prior to sending the design to production.


There are many applications for HVMLCCs.  Many of these require specially rated or certified devices (e.g., applications requiring safety rated capacitors and the like).  The designer should always be familiar with all applicable specifications; and should specify each HVMLCC device accordingly.   With that said, let’s discuss some applications.

 Power supplies are a major area of application.  As an example, Cuk (pronounced “chook”) convertors are DC-DC convertors, invented by Slobodon Cuk, that use a capacitor for energy storage during the voltage conversion process.  In this type of design, the voltage across the capacitor is typically:



  • VC is the voltage across the capacitor
  • VO is the output voltage
  • D is the duty cycle

From the above, it is evident that, depending upon the output voltage and the duty cycle used, the voltage on the HVMLCC in the Cuk converter can be quite high. 

HVMLCCs are also used in cold cathode fluorescent lamp (CCFL) driver circuits or lighting ballast circuits which typically require one or more HVMLCCs.  High intensity discharge (HID) lamps also require similar boost-type power supplies which also require HVMLCCs.  HVMLCCs are also used in certain high brightness light emitting diode (HBLED) driver circuits as well as in certain camera flash strobe circuits.  

The take away here is that HVMLCCs are used in numerous switching power supply circuits for numerous applications.  Other examples of this include snubber circuits in switch mode power supplies (SMPS) that reduce or eliminate voltage transients from MOSFET (metal oxide field effect transistor) switching events or the like, as well as resonator circuits, high voltage blocking circuits, high voltage coupling circuits, and input and output filter capacitors in power supply circuitry.  These are all common power supply applications for HVMLCCs.

HVMLCCs are also used in general high voltage circuit applications, such as voltage multipliers, RF power circuits, and general applications requiring high voltage DC blocking or AC coupling.  Additionally, HVMLCCs are used in general applications where voltage surge suppression is required such as LAN products, including but not limited to, LAN/WAN interfaces, Ethernet switches, and analog and digital modems.  They may also be used for DC blocking in modems for tip and ring applications.  HVMLCCs are becoming more popular in automotive applications as well, and are used in numerous telecommunications, medical and military/aerospace/space applications.  This is especially true for the latter with the increasing popularity of “fly by wire” technology. 

As HVMLCCs typically have very high insulation resistance (IR), they are also popular for use with high temperature semiconductors (e.g., silicon on insulator (SOI) or the like) and in elevated temperature applications, as well as in specialized test and diagnostic equipment.  Finally, remember that HVMLCCs with floating electrode (FE) design are also an excellent choice when the device is to be used across a battery line or application that should not fail short.


As mentioned in my previous post, it is very important that the HV circuit be properly designed in order to prevent surface arcing or corona discharge.  This is even more important in space or low vacuum applications as the “quasi-plasma” becomes “real plasma” in vacuum, and corona discharge is more likely at lower voltages at the relatively low gas pressures encountered in space.  There are numerous excellent HV design guides for HV circuit boards that cover the above, as well as many additional important topics related to HV circuit design and component selection.  One particular favorite is the “HIGH VOLTAGE PRINTED CIRCUIT DESIGN & MANUFACTURING NOTEBOOK.”[1]  It describes numerous “rules of thumb” and is an excellent resource for the HV circuit designer.

In summary, always be sure to choose the right HVMLCC for your application, considering all of the voltages, transients, and frequencies as well as ripple voltages/currents involved.  It is also important to consider and comply with all applicable certification requirements and specification requirements.  Be sure to design and to test your circuit carefully, and know that floating electrode (FE) HVMLCCs rarely fail short, and thus are good for battery line applications in addition to all of the HV applications noted above.

Tags: voltage, volts, HVMLCC, High Voltage MLCCs

High Voltage MLCCs Part 2: Judging a Book by Its Cover

Posted by Mike Randall on October 08, 2014


This is Part 2 of a Three Part Series

  • Part 1:It’s What’s Inside that Counts
  • Part 2:Judging a Book by Its Cover:Don’t Forget the Outside
  • Part 3:It Ain’t the Volts, It’s the Amps:Some Applications and Considerations

Shhhhh!  Don’t tell my Momma, but she wasn’t always right, and it isn’t only what’s inside that counts.  Sometimes the outside is important too.  If you are a car fan, you know what I’m talking about.  For example, few auto enthusiasts salivate at the site of an AMC Pacer or Matador, but how many “jaws drop” at the site of a black-on-red ’67 Tri-Power ‘Vette or a ’69 Mach 1 big block with a shaker hood, or a shocking orange Hemi Superbird, or an original Lamborghini Countach or an Auburn Boattail Speedster, or…?  I wouldn’t know personally, but I’ve been told that this also works with people too! J  I’m not saying whether it’s wrong or right, but “it is what it is” (forgive me Momma!).

It’s What’s Outside that Counts Too

High voltage MLCCs can fail internally and we spent our last post discussing how to avoid that, but we didn’t talk about external arcing or any external-related failures.  But it should be pretty simple, right?  After all, the “MLCC thing” just looks like a brick with a metal cap on each end.  How complicated can this be?   Well, as it turns out, it’s not quite that simple.  External failure usually results from at least one external arcing event, and that’s simple enough, but how does that arc get started and how might that arc repeat itself until device failure?  There are several potential reasons and we will go through each. 

First, since HVMLCCs can be as small as 0603 (EIA) case size, it is important to control the minimum separation of the terminations.  In the case of an 0603 (EIA), that is about 0.047” (~1.2 mm), so maximum voltage rating (~250 VDC) is limited compared to larger case MLCCs with larger termination separations (e.g., 1206 (EIA) with maximum VRated of ~3 KV having minimum termination separation of about 0.073” (~1.85 mm), and 1808 (EIA) with maximum VRated of ~5 KV, having a minimum termination separation of about 0.128” (~3.25 mm)).

Next, it is important to note that all surfaces (e.g., 4 sides) between the two external terminals must be clean in order to maximize surface resistance between the terminals, as contamination tends to be more conductive than ceramic dielectrics.  Additionally, it is important that the external surfaces separating the two terminals are also dense and smooth, as porosity and surface roughness can trap contamination and have lower surface resistance. 

It is also important to carefully design your circuit board so that the termination lands have maximized separation distance, and one must take care to avoid the use of solder fluxes that contain ionic species that could facilitate arcing beneath the chip, or on one or more of the sides of the chip during operation.  Of course, any residues resulting from surface mount (SMT) activities should be removed as well.  “OK, “Commander Obvious”[1]!  Nothing too esoteric yet, where’s the complicated stuff” you say?

Touché!  Well, did you know that surface arcing also depends upon ionization of the air immediately covering the surface of the area of the region that arcs,[2] and that the “quasi-plasma” that is formed in the air in that region that enables the arcing is affected by the electric field that is associated with the internal structure of the MLCC (i.e., electrode design)?  And did you know that said “quasi-plasma” and associated electric field is affected by the dielectric constant (K) of material from which the arcing surface is made (i.e., Class 2 ceramic dielectrics, such as Y5V, X5R or X7R or the like have a higher propensity toward surface arcing at a given voltage than do Class 1 ceramic dielectrics such as C0G)?  And did you know that any impurities in the “quasi-plasma” formed in the air near the surface of the component or on the surface of the component can be deposited on the surface during arcing, or converted in a manner that results in a lower resistance path between the two external terminals, thereby almost guaranteeing that the old adage that “lightening never strikes the same place twice” does not at all apply to HVMLCCs?  In fact, continued multiple external arcing is not an uncommon failure mode for HVMLCCs.  OK then, have some respect for “Commander Obvious.” 

So, Repeat After “Commander Obvious”

What is outside also counts!  It is important to properly design your circuit and terminal solder pads properly for high voltage.  It is important to understand that external arcing is affected by several factors (some obvious, some not).  Use of wider terminal separations and lower K dielectrics should be considered.  Understand that sometimes it is necessary to use Class 2 dielectrics, and in that case X7R should be favored over X5R or Y5V dielectrics as they typically have higher K than X7R dielectrics (which would result in a higher surface field on the HVMLCC that may cause surface arcing at lower voltage than the lower K X7R).  The surfaces of the HVMLCCs used should be dense, smooth and clean as well for HV applications.  Sourcing your HVMLCCs from aquality vendor is recommended as they have knowledge of, and experience with, the above factors.  Use of fluxes containing any residue during SMT operations should also be avoided and proper cleaning of the board after SMT may be required as well. 

Finally, it may be beneficial to add a conformal coating over the surface of the HVMLCCs and/or other HV components to prevent surface arcing.  The coating should have a high breakdown strength, combined with a high resistivity (surface and bulk), as well as high breakdown strength.  Silicones tend to be ideal for this application.  If something more mechanically rugged is needed, then an epoxy (typically difficult to rework) or a urethane (typically easier to rework) should be good.  And, most important of all, if you tell my Momma about any of this, I swear, I will deny it!…TTFN!


Tags: High Voltage, High Voltage MLCCs, MLCCs

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