I have to study this circuit. I understand that Graetz's bridge is there to convert the current to positive, but why is there a LC filter at the entrance of the converter?

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    \$\begingroup\$ I've tidied up your post but you need to crop your image to remove the > 75% white space. \$\endgroup\$ – Transistor Oct 18 at 11:36
  • \$\begingroup\$ If this is automotive, say so. Cars are very electrically noisy places so a filter to keep noise out would make sense. \$\endgroup\$ – Brian Drummond Oct 18 at 14:32
  • \$\begingroup\$ no,is for a tiltmeter \$\endgroup\$ – velectron Oct 18 at 19:49

why is there a LC filter at the entrance of the converter?

That looks like a noise removal filter. The noise is generated by the 12 volt switching converter (due to high speed switching) on the left and therefore, the LC immediately to its right (its input port) will act as a 2nd order low pass filter and noise/switching artefacts travelling from left to right (left being the input to the inductor) will be significantly attenuated. So, if the whole design needs to comply with some conducted emission testing (as measured at the far right on the 24 volt port), the LC provides assistance in meeting those requirements.

Note - it's quite common to see this circuit addition on many power converters such as "Traco" and "Exar" converter products. And, if you dig down into application notes for the TM 3-2412 (your device) you'll find this general recommendation: -

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  • \$\begingroup\$ yup. Traco's are noisy as hell, on the input and output \$\endgroup\$ – JonRB Oct 18 at 12:27
  • \$\begingroup\$ I'd agree with the input but a lot of them are not bad on the output (trying to be fair) @JonRB \$\endgroup\$ – Andy aka Oct 18 at 12:41
  • \$\begingroup\$ maybe ;) don't get me wrong, Traco's are great. I have had nasty experiences with underestimating their noise (either in my designs to feed directly the analogue) or debugging other designs. \$\endgroup\$ – JonRB Oct 18 at 13:02
  • \$\begingroup\$ And how can we calculate the Output Voltage?Especiall in this circuit? \$\endgroup\$ – velectron Oct 18 at 21:42
  • \$\begingroup\$ The output voltage as in the DC voltage coming out of the Traco? \$\endgroup\$ – Andy aka Oct 18 at 22:20

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