RDR-239 putting out 19V

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I built up the RDR-239 and it is putting out 19V as opposed to 24V. Instead of using the inductor shown in the reference design, I am using two inductors with the second inductor taking on the parasitic. Would it be helpful for me to include schematics? How would you recommend to get to the 24V? Thank you

Hi rffx,
You basically build RDR-239 yourself using the same values but you used different transformer design with external Lres instead of integrated right? What is your Lpri, Lmag and Cres used? Providing your schematic will help. Thank you.


We are using an "ideal" transformer 287uH and a "parasitic" inductor that is 53uH.

What do you recommend we do to get to the 24V? Thank you

Hi rffx,

I observed that your transformer and leakage inductance is measured/trimmed @ 10kHz. If we measure your inductance near the intended operating frequency 200kHz-300kHz, I wonder how off it is from our target inductance which is changing your gain curve. I'm pretty sure you'll get a lower number. Can you check that and adjust as needed. Check rdr-239 document and you'll see that inductance measurement is @ 300kHz.

The measurements for the inductance at frequency

LLC @ 295kHz = 2.81E-04 H

Shim @ 295kHz = 4.88E-05 H

It looks pretty close.

what are your suggestions?

Unfortunately, there is not enough data on the transformer and inductor to feed it back into a spreadsheet to determine design feasibility. Leakage inductance is not specified for the transformer, and it looks possible that the primary is wound in a single section. This will add considerably to the leakage inductance, which in turn adds to the resonating inductor value and will shift the operating frequency. The balance of the two phases will depend on the closeness of coupling of the two secondary sections. They may need to be twisted together to balance the phases properly. What is the operating frequency of the supply at nominal B+ voltage? If it is operating at a frequency considerably below resonance, the turns ratio may be insufficient to deliver the required output voltage. If you can get the actual core and number of turns from the vendor, it would help in analysis, as these values can be fed back into a PIXLS spreadsheet to check the design parameters.

Here is the leakage for the transformer from the mfg

LLC_LEAK.txt12.51 KB

Here are the measured inductances over frequency for both transformer and additional inductor

LLC_-_Copy.txt12.51 KB
SHIM_L_-_Copy.txt12.51 KB

PI Please give some input on this.

I don't know what criteria Renco used to design the magnetics shown, but the inductor looks very small for the power level. If it is saturating, it could be the reason for your inability to reach your specified output voltage. The inductor should also be wound using Litz wire to lower losses, meaning a larger core would be necessary to fit the wire.
I really can't proceed in giving you any more advice without more details on the magnetics construction. Core type and turns are necessary. Attached is a design I ran using an EF25 core for the main transformer and an EE19 core for the separate inductor as an example of a design that would probably work well. An EER28 core would be an even better choice for the transformer than the EF25, requiring fewer turns.


Line 92 says EEL25. Is the correct PDF for the EF25_EE19 Design?


Yes - in the PIXLS spreadsheet for Hiper-LCS, there is no provision for custom core parameters, so you need to enter the parameter from your core of choice to override.the selected core parameters. So, that means the core selection in line 92 say EEL25, but the actual parameters entered are those for the EF25.

Hi, what is the bobbin that you use?


I would think that you would want to work with Renco to get the design straightened out. It would be useful to know how they actually came up with the design for the inductor and transformer.

The bobbin I used for a first sample of the EF25 transformer design I showed was Taiwan Shulin part # TF-2554.. The EE19 Inductor was wound on Ying Chin part # YC-1902

YingChin_EI-19.pdf477.12 KB
TF-2554.pdf749.21 KB