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Offline flyback with solid polymer output capacitors

cupoftea

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Hi,
The LS15-13B12 is a 15W, 12Vout offline flyback. (datasheet below)

Page 3 of its datasheet specifies a 470uF/16V "solid polymer" Al capacitor at the output. However, for the LC post filter capacitor it merely specs “220uF/16V”.

We can appreciate that this 220uF capacitor can be either Solid polymer or Wet electrolytic, but solid polymer would give the product advantageous longer lifetime. Why has the datasheet missed the opportunity to offer the 220uF capacitor as a solid polymer Al capacitor?

LS15-13B12
 

c_mitra

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While it is good to consider longer life for individual components, we must not forget the overall expected lifetime for the unit (the power supply in the present case). There may be other components that may have considerably lower expected life within the same power supply. In turn, the power supply may be used in some units that may be have a quite short life cycle.

The designer of the power supply may not have much control on the life of the final product in which the power supply may be used. Therefore it may be prudent to use quality components in all sub assemblies. Usually using an over-rated component, if available, can extend the life considerably. On the other hand, if you have control on the specific end use, you should focus on the various possible failure modes of the assembly.
 

FvM

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C2 is exposed to switcher ripple current, also extra low ESR of solid polymer may be required to achieve the voltage ripple specification. C3 is isolated from output riple by L1, C3 ESR may be even advantageous to reduce filter ringing with load transients.
 

cupoftea

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Hi,
This again concerns the Mornsun power module....

The Mornsun 15W, 12Vout offline Flyback datasheet recommends a 330uH diff mode inductor. Surely, this is far too high value? There is already a 33uF, 450V electrolytic bus capacitor, plus the leakage inductance of the 10mH common mode inductor. Surely 330uH is just going to have too much interwinding capacitance, and worsen common mode emissions? (even though it’s a diff mode inductor)

Also, why no 10nF ceramic radial cap in parallel to the 33uF,450V capacitor. Such a small, cheap capacitor massively reduces diff mode emissions

Mornsun 15w
 

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