Author Topic: isolated dc/dc converter input capacitors and output ferrite beads  (Read 963 times)

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Offline V_KingTopic starter

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  • Country: gb
Hello,
I want to incorporate 3x isolated dc/dc converters to give me galvanic isolation and all required voltages for a small control board.
I have two questions as follows:
1. For power inputs, the manufacturers recommends certain capacitor values, but if I have three DC/DC converters in parallel, do I put same value capacitor in front of each dc/dc converter, or do I put one same value or bigger cap? All manufacturers give max input/output capacitances, so I want to avoid instability issues.
2. Same for the power input fuse as above. Do I triple the current requirement, or put three fuses for each of the DC/DC converters
3. Finally, I've read application note from analog devices, recommending to use ferrite beads after dc/dc converter and LDO to reduce the ripple and noise. Application note says the ferrite bead impedance @ freq. must be matched to the dc/dc converter switching frequency. But all dc/dc converters I find are around 100kHz and ferrite beads rated at 25MHz and above. have I misread something, or am I looking at the wrong ferrite beads? Or in real life, a few paralleled caps should do the trick?

The power supplies are going into powering op-ams and ADC analogue side.

Thanks
 


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