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I'm trying to build a switching regulator using the TPS54383 dual output regulator, Now I've got most of the components and schematic figured out here.

Schematicpdf

Except the inductor's and diode; I'm running one output at 12V with a possible draw of 3A and the other at 5V with a maximum draw of 500mA. What value's should I be looking at when ordering a diode and inductor?

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  • \$\begingroup\$ What does it tell you in the data sheet - there is usually a formula that relates possible input voltage range with switching frequency in order to calculate L. Diito D. \$\endgroup\$ – Andy aka Nov 18 '14 at 18:19
  • \$\begingroup\$ I already know my inductance values. I need to know what they should be treated for, such as sat and rms values \$\endgroup\$ – Sam W Nov 18 '14 at 18:20
  • \$\begingroup\$ Data sheet tells you how to calcluate this sort of stuff usually. \$\endgroup\$ – Andy aka Nov 18 '14 at 18:22
  • \$\begingroup\$ And I'm asking for help, some of us don't know how or what to interpret for that data. \$\endgroup\$ – Sam W Nov 18 '14 at 18:24
  • \$\begingroup\$ For a start you could make a link that works: ti.com/lit/ds/symlink/tps54383.pdf \$\endgroup\$ – Andy aka Nov 18 '14 at 18:48
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I already know my inductance values. I need to know what they should be treated for, such as sat and rms values

If the maximum load current is 3A, then you know one thing - the inductor saturation current has to be above this value. 3A flowing in your load is also the average current flowing in the inductor and providing the regulator doesn't enter discontinuous mode, the peak inductor current won't get above 6 amps.

enter image description here
(source: tantosonline.com)

The above picture shows an inductor in "continuous mode" and also when it enters discontinuous mode.

It's probably a good idea/rule of thumb to make the ripple p-p current about the same as the full-load average current (as an approximation to best practise) and this means the peak inductor current will be 4.5 amps on full load.

For decent efficiency you should choose and inductor that is probably rated twice this value for saturation current. Another rule of thumb.

As for the flyback diode I'd probably choose a 5A device off the top of my head and without going into the details of the device because it's too much to expect!

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  • \$\begingroup\$ ok and for the 5V side, I've come across this inductor; what do you guys think? mouser.com/Search/… \$\endgroup\$ – Sam W Nov 18 '14 at 20:05
  • \$\begingroup\$ No, that one probably won't do and neither will the mouser details - it says it has 8 ohms resistance and can take 1 A - that's dissipating 8 watts and mouser can't be right about this. Redo what I did above. 500mA DC might have a peak current of 750mA and double this for an acceptable saturation current. Also with 8 ohms resistance, at 500mA you are going to lose 4 volts DC across the inductor. \$\endgroup\$ – Andy aka Nov 18 '14 at 21:14

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