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Author Topic: Overvoltage due to LC ringing at input filter of power factor corrected SMPS  (Read 110 times)

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Offline treez

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Offline, single stage, Power factor corrected LED drivers do not have much capacitance at their input (for obvious reasons).
In order to get good filtration with such small filter capacitance, they have to use inductors [ :scared:] with the capacitors to make LC filtration.

Of course, when you have an LC circuit and little capacitance, the voltage at the filter output can ring up to very high voltages and cause damage (specially when the product is switched ON at the peak of the mains  :scared: )……hence protection circuitry must be added in to mitigate this. 8)
The best way to mitigate this,  would  you  agree, is to use a current clamp just upstream of the LC filter….. do you agree? :-//
Why is the following “current clamp” method  (as attached)  so rarely seen in designs and App Notes? :-//
In order to protect the LED driver from mains transients, we wish to use a SMCJ400A TVS. Which side of the LC filter should we best place the TVS? :-//
LTspice sim and  a schem attached. :clap:


Offline T3sl4co1l

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There can be no filter that is not terminated with resistance.  If you think you've made one without resistance, nah, it's found that resistance, somewhere.  It may not be the resistance you had hoped for.

What do you expect? :)

Not having a LISN model for the mains seems a pretty big omission.

Damping can always be added with an R+C or R||L pair, or a lossy component that is equivalent to these.

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Offline treez

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Thanks, do you think i need to add an RC damper at the output of the filter? (=input to the led driver).
All  we are  worried about is avoiding overvoltage at switch on.............or during mains transient.

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