I am looking for snubber caps to put on my chip amp PSU.
People say that MKP caps are the best among all, but I also found some others that look very good on paper too.
- ceramic caps
- multicoated ceramic ( KDPU )
- tantalum
Ceramic are commonly used in HF applications, so why wouldn't they suit PSU filtering up to MHz ?
Tantalum, for larger values have a good reputation too.
What characteristics should be analyzed to compare snubber caps ?
People say that MKP caps are the best among all, but I also found some others that look very good on paper too.
- ceramic caps
- multicoated ceramic ( KDPU )
- tantalum
Ceramic are commonly used in HF applications, so why wouldn't they suit PSU filtering up to MHz ?
Tantalum, for larger values have a good reputation too.
What characteristics should be analyzed to compare snubber caps ?
pooge said:
My problem is not especially reliability but rather quality.
I have seen some datasheets that show the impedance vs. frequency graph.
I assume that the cap must have the highest possible resonnance frequency to damp correctly the MHz + rubbish.
Is there something else in favour of one of those caps ?
PS : I'm not willing to spend much on small caps, that's why I'm asking the question
Something to look at when comparing caps in general is thier dielectric constant (k). A lower K dielectric will absorb less RF than a higher one. This is important in some applications, as among other things this absorbed RF becomes heat.
Polypropylene has the second lowest K (~2.2) of commonly used solid dielectrics. Teflon is lower, but suffers from high wallet leakage. If your going to abuse a cap, poly is probably your choice. Snubber capacitors for SCRs and IGBTs are almost invariably polypropylene.
Ceramic has a much higher K, allowing a higher capacitance for a given amount of plate area, so less inductance and ESR is possible. Ceramics tend to be used for local HF coupling and decoupling as the inductance is critical here. Having the worlds lowest ESR isnt necessarily desirable in a snubber, they can lead to high Q circuits that may resonate and ring.
Tantalums have thier place with some much desired properties, but are not famous for reliability and really dont like being reversed(pop!).
Heres some gratuitous pictures of cap abuse.
Polypropylene has the second lowest K (~2.2) of commonly used solid dielectrics. Teflon is lower, but suffers from high wallet leakage. If your going to abuse a cap, poly is probably your choice. Snubber capacitors for SCRs and IGBTs are almost invariably polypropylene.
Ceramic has a much higher K, allowing a higher capacitance for a given amount of plate area, so less inductance and ESR is possible. Ceramics tend to be used for local HF coupling and decoupling as the inductance is critical here. Having the worlds lowest ESR isnt necessarily desirable in a snubber, they can lead to high Q circuits that may resonate and ring.
Tantalums have thier place with some much desired properties, but are not famous for reliability and really dont like being reversed(pop!).
Heres some gratuitous pictures of cap abuse.
the X and Y cap comment was not about reliability but about safety. More specificly about caps catching fire or shorting in a way that injures the user.
With rasgasrd to snubbers, however, the following article is often cited:
http://www.hagtech.com/pdf/snubber.pdf
even if you find the calculations a bit difficult to apply exactly, note that without the inclusion of a series resistor the benefits of snubber caps (regardless of type) is rather limited.
Nice article ! Good stuff to read this afternoon
I will use the snubbers on the DC side of the PSU, so maybe 600V is overkill there.
But yes, caps are quite dangerous when abused, a friend of mine did have some little problems with Xover caps he used in a speaker filter and that where underated. He told it did "bang" inside the cabinet
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