Need AC/DC converter

Hi Erfan,

The cap drop design shown in the following application note should work for your application.

Here's the link: http://www.ti.com/lit/pdf/slva491

Anthony

Hi Anthony,

My application has 100mA current requirement but this circuit has maximum current limit as 50mA. Can you please suggest some other circuit with 100mA output or the same circuit with necessary changes for generating 100mA.

Regards,

Erfan

The equations in the application note can be used to redesign for the high current. There is also a spreadsheet to aid with the calculations in the following link.

http://www.ti.com/lit/zip/slvc392

I'm also interested in this design for a slightly higher current (100-150 mA).

I have some questions, and there are some bugs in the design document and spreadsheet:

First is what to do with the pre-converter.  Bumping C1 up to 2000 nF end up
pushing PRin to 5W.  Bumping C1 to 1300 nF to get ~100 mA out gives 2W in PRin.
Is there any way to avoid all this loss by tweaking R1 (or something else),
or is this just a limitation of the design?

The Input of Converter section claims power in R2+R3 to be 306.1 mW, I think
that must be wrong.  Shouldn't it be about 40*40/1859000 = .00086W?

On page 5, the calculation for R3 contains a reference to R1 that I think
is left over from the datasheet for the TPS5401 and should actually be R2
(with respect to this design).

How is the value of C2 selected?

Why 560E for R1 in spreadsheet and just 560 in ref design?  What does the
E mean?

Lomax and Lomin appear to be mislabeled in the spreadsheet (crossed over).
I don't think this error propagates out of this section, since the min
inductance is chosen manually and that value propagates to elsewhere.

properties of R1 (wattage?), C1 (tantalum)?, C2 (organic poly?)

When is bulk capacitance referred to in "Input Capacitors" section required?

Pre-Converter Section, eq 41, putting in the numbers mentioned in that
paragraph I get pd1 and pd2 = 41.2mW, not 32.8mW that the document says.
I think maybe the spreadsheet result got put in the document, but a different
efficiency number was used or something.  Also, the equation lists "Pd1 and 2"
but then the discussion below mentions "Pd2 and 3".  Since the pre-converter
diodes are D1 and D2 for this design I'm guessing the latter reference
is incorrect.

Its kind of weird that you have to set the Max Output Current (cell B82)
manually in the Power Supply Specs section of the spreadsheet in order for
the inductor values to get computer.  The max output current is determined
by the values chosen in the Capacitor Drop Design section of the spreadsheet,
so shouldn't the value for IDCout from there be used?

Incidently I like the spreadsheet better than the shrink-wrapped web tool
generated approach, though I do wish a BOM could be provided somehow.
Then again for the switch mode supply web tool it helpfully supplies CUSTOM
for the transformer part...