I did a simulation on TI Power Bench for a isolated power supply,

There I got transformer spec in BOM,

Core=Wurth Elektronik , CoilFormer=Wurth Elektronik

Core=150-2340 , CoilFormer=070-4477

Core Type = ER14.5 Core Material = TP4A Turns Ratio(Nps) = 5:2

Is this available purchase/ready to buy or Wurth Elektronik would custom made for this spec with ?


Ti does not provide no inductance of the coil

ti web bench parameters

  • Vin min 7.9V
  • Vin max 8V
  • Vout 5V
  • Isolated yes
  • Iout 1A
  • temperature 30 Celsius
  • \$\begingroup\$ Wurth Elektronik online catalog we-online.com/catalog/en/SMT_ER_BOBBIN shows part number 070-4477 is the bobbin itself, you have to separately buy the EI core 150-2340 and the wire, and wind the bobbin and terminate the wires to the pins as per your custom spec. Besides turns ratio, you'd also need to spec the primary and secondary inductance and the series resistance. Best contact Wurth applications support directly and request a quote and samples. \$\endgroup\$
    – MarkU
    Sep 9, 2020 at 8:32

2 Answers 2


A look at using the Wurth WE-Flex TFR 749196540 at 1:2 , this enable two or 3 windings in parallel on the primary

WE-Flex 1:1.5

only gets to 0.8A though. WE flex 1:1.5 performance


Try same transformer at 2:3 , but DCR will be quite high we-flex 2:3 we-flex 2:3 perf.


Finally try same transformer at 1:1 , this also allows a whole lot of choice from other manufacturers , plus easy to wind, and very low leakage inductance.

we-flex 1:1 we-flex 1:1 perf


Use 1:1 with a coupled inductor from Coilcraft the MSD1260 in 4.7uH 5.6uH, 4.7uH, 6.8uH should work (highest efficiency first), https://www.coilcraft.com/en-us/products/power/coupled-inductors/1-1-shielded-coupled/msd/msd1260/msd1260-562/

MSD1260-562 MSD1260-562 perf

or a bit bigger core 15mm slightly more efficient. MSD1583-103 https://www.coilcraft.com/en-us/products/power/coupled-inductors/1-1-shielded-coupled/msd/msd1583/

MSD1583-103 msd1583-103 perf

A wind-your-own core would still outperform these, but for a <3% gain in efficiency, probably not worth the bother.

  • \$\begingroup\$ i am new to transformer designing, can we depend on these calculators provided by texas instruments? ti power bench also cannot simulate fly back smps designs \$\endgroup\$
    – kobi89
    Sep 11, 2020 at 4:07
  • 1
    \$\begingroup\$ The web-bench designs will work, There was a time about 10yrs back when I wanted to make an evaluation for boosting a PV panel, I did the web-bench design on the device that looked promising, and ordered a sample kit from the web-bench,They posted out to me the eval board and the same components as on the webbench BoM, I put it together, and it tested the same as the webbench, I wasn't even using the chip in the normal fashion (I was using it as sync boost rather than sync buck) I don't think they do the direct order thing any more.:( \$\endgroup\$
    – BobT
    Sep 11, 2020 at 12:29
  • 1
    \$\begingroup\$ It is recommended to use their eval PCB on your first attempt, You can then solder that to a bigger board, or cut tracks on , and move things around. Then make your own PCB, and compare it's performance to the eval PCB.. Stray inductances will rob flyback convertors of their efficiency. So you need to be sure to maximaise track width, and minimize area enclosed by the transformer tracks. \$\endgroup\$
    – BobT
    Sep 11, 2020 at 12:35

You have got part numbers for a bobbin and a core , you need to add your own wire, Does web bench provide an inductance value? you have a turns ratio of 5:2 listed. This the bobbin data sheet https://www.we-online.com/catalog/datasheet/070-4477.pdf

Wurth do have some pre-manufactured transformers , e.g. from here https://www.we-online.com/catalog/en/cm/pcd/mid_power_magnetics/

drill down to here https://www.we-online.com/catalog/en/MID-IBTI/#750312547.

Mouser or Digikey probably have a transformer that might work, here are 515 in-stock parts to pick from. https://au.mouser.com/Wurth-Elektronik/Power/Transformers/Power-Transformers/_/N-8u9n5?P=1z0jmj8&Keyword=power+transformer&FS=True

OK , I've messed about with the design tool. You can get it to work with a 1:1 transformer, but a 1:1.5 gets more sensible capacitor values and slightly higher efficiency. I've entered 4.7uH and 20mohm per winding and get ~ 85% efficiency, which is pretty good for 5v , without synchronous rectification. eval spreadsheet

Finding a transformer gets more difficult , possibly something like this https://au.mouser.com/datasheet/2/445/749196547-1723684.pdf (it's 3.4uH/segment) so about 12uH with two segments.. ( Hmm I'm thinking for one-off's it's so much easier to wind your own !!!) OK, I'll look again at the core you mentioned earlier.

  • \$\begingroup\$ in/ out parameters are updated in question, chip LM25184, fly back, no inductance is provided in the ti simulation \$\endgroup\$
    – kobi89
    Sep 9, 2020 at 8:57
  • 1
    \$\begingroup\$ OK , you can't design a flyback convertor without knowing the inductance.... There is a design tool, I'm just downloading now ...ti.com/tool/LM25183-LM25184DESIGN-CALC .. So input ~8v (two Li-ion batteries I guess) Vo=5v ,1A \$\endgroup\$
    – BobT
    Sep 10, 2020 at 8:59
  • \$\begingroup\$ OK I've finished editing the other answer now, looks like there are some cost effective simple options out there. \$\endgroup\$
    – BobT
    Sep 10, 2020 at 11:28

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