Designing For Circuit Protection

[#1]

In many applications, system designers and engineers have to worry about long lasting high voltage/high current transients that their systems might see.  You may think, hey that’s and ESD shock.  You’d be right, but ESD shocks only last a few microseconds.  We are talking about events that last hundreds of milliseconds. 

An example of this might be a load dump in an automotive battery application.  These occur when a discharged car battery is removed from VBAT while the alternator takes over powering the rest of the vehicle electronics at start up.  These surges may be as high at 85V.  One way to combat this is to use overvoltage protection devices like Tyco Electronics Raychem MOVs to dissipate the energy of the surge.  TE Raychem has developed a good guide on how to choose the right part for your specific application.

[#2]

 i think filter is a better choice for you to protect circuit from EMI of high voltage. if you need any help about this matter,please contact with me.

xks@filtemc.com

[#3]

I would say that there is no right or wrong way to solve the problem.  We actually had supported a customer who needed transient suppression.  In his case, the MOVs worked great.  In other applications, a filter may work.  Either way, I really appreciate the feedback.

[#4]

In some cases, a simple bypass capacitor(s) may also be required. MOVs can be too slow for some transients. If the voltage transient reaches a high level before the MOV turns on, then the protected device might still be damaged. The main idea of protection is to divert all the excessive energy away from the device being protected.