TMS320F28379D: tms320f28379

The 62.1 uH is calculated based on the information above in the user guide. Can you post it the UCD link to me? I didn't find the 2.62 uH in the UCD LLC.

Chen

apologize: I somehow missed this note from you all these days.

Pl see attached pdf file I made highlighting the 2.6 uH.

Was it a typo?

In any event, which paper/method is most suited to calculate N, Cr assumed Q & Ln from where we get Lr. Given Vo , vin & Po

I have other questions in other posts...as you so desired to post each separately.

thnx

r

HB_LLC_UCD3138_DESIGN_Q.pdf

Hi,

T2 in PMP20289 design is a current sense transformer, it is not an LLC transformer.

For high frequency/ high efficiency required LLC converter, we generally need to use smaller series inductance for better efficiency.

PMP20289 has its series resonant frequency at ~400kHz with 500W maximum output power with narrow input voltage range: 380V~400V.

Regards,

Sheng-Yang Yu

Sheng-Yang

I think you might have commneted regarding a different post.

Pl take a look at the attched pdf file: my questions were about the value of the resonant inductor. We can see it is printed as 2.6uH , elsewhere resonant inductor is shown as  approx 62uH. yet, power output or input voltage & other parameters are not dramatically different. Is this a typo?

Another thing is about the turns ratio of the current transformer. For primary current of values <3 Amp max, why use 1:250?

Elsewhere, it is 1:25 a much more realistic ratio for same power & other parameters of similar range.

Thnx for your time.

robin

Robin,

My reply was focus on how I select Lr in PMP20289 - the UCD3138 based LLC reference design.

The Lr is much smaller than what's in TIDM-1001 has the following reasons:

1. The resonant frequency is higher in PMP20289 (almost doubled). 

2. The power per phase is higher in PMP20289 (also doubled).

The reason we want to switch at higher frequency is to reduce the magnetic component dimension including Lr and Lm. So you can expect Lr and Lm to be smaller in a high frequency LLC than a low frequency LLC. In PMP20289, Lm is only ~66uH while in TIDM-1001 it is ~900uH. It is already a huge difference.

Second, the ratio of Lm/Lr determines the operational range of the LLC converter. Smaller Lm/Lr gives you a wider operational range.

Like I replied in my previous message, the PMP20289 design is only designed to keep 12V output in regulation inside 380V to 400V input range. While in TIDM-1001, the actual operational range should be wider than what is stated in its specification (370V ~ 410V). In other words, the TIDM-1001 should be able "hold up" 12V output with an input voltage low than 370V (my guess is ~300V). So the true operational range for TIDM-1001 should be 300V - 410V if only consider the Vout/Vin gain curve.

Current sensing transformer used in PMP20289 is just for protection purpose. So the turns ratio and error requirements are pretty loose. I just choose what's handy.

Hope this answered your questions.

Regards,

Sheng-Yang Yu