PMP8740: Full Bridge Transformers

Hello Per,

most of the magnetics are custom designs by magnetic vendors:

PSFB xfmr T4 is made by KASCHKE
pulse xfmr T2/T3 by VITEC
shim ind T7 by CLICK

Please get in contact w/ vendor for further info,

Best regards, Bernd

Hello Bernd ,

Firstly thanks for your reply,

I contacted with KASCHKE . Their answer  " please note that we need a LOA from TI that we are allowed to send you samples or an offer.

The reason is, that this is a customized part" .

Actually , I have no idea about LOA.

-Can you give me information about LOA ? 

Hello Per,

The reason why Kaschke wanted to have our allowance, is because this reference design has been built for another customer.

But this design is now public, so they can accept request of samples, or purchase for this design. This includes the main transformer T4 and the inductor L3.

The shim inductor T7 has been built by hand. The construction details are visible at page 21 of the article I wrote in the recent Power Supply Design Seminars, available at the link:

If still Kaschke is reluctant to provide samples, please let me know the email address of your contact at Kaschke and I will explain them the situation.

Best regards,

Roberto

Hello Roberto,

Thanks for your reply.

Yesterday.  I contacted with Kaschke . Kascke is still reluctant to provide samples.

I contacted with Mr. Hagen Fuchs. (Key-account-Manager at Kaschke Component)

E-mail address: H.Fuchs@kaschke.de

If you can contact and explain the situation. I will be glad

Thanks for your interest.

Hello Bilgin,

I just wrote an email to Mr. Fuchs, explaining him that this design is not anymore restricted only to one customer.

Let´s wait for the answer.

Please let mw know if have still questions.

Regards,

Roberto

Hello Roberto,

I still haven't received answer from Mr.Fuchs. 

Today I will write an new email to Kaschke and I will wait for their answer.

If Kaschke  reply to my email.I will inform you.

Did you get an answer from  Mr. Fuchs  for your email ?

Thanks.

Hello Bilgin,

I also didn´t receive any answer from my email to Mr. Fuchs.

Maybe due to COVID-19 situation some offices are working with limitations.

If I get an aswer, I will inform you ASAP, no problem.

Please let me know if you get one, or even if you don´t get any.

Regards,

Roberto

Hello Roberto,

Unfortunately ,I didn't receive any answer from Kaschke. I decide to make own transformer. I read  past posts from the PMP8740 forum and I have some information about T4 transformer like  Np = 19 turns, 1.6mm diameter (LITZ wire); Ns1 = Ns2 = 2 turns 6mm diameter (LITZ wire). Also,  I found "PMP8740 UCC28950 Excel design tool " and T4 transformer technical datasheet . In the datasheet transformer core metarial is PQ50/50 / K2010 or equiv.

Here I have some questions ,

1) For  PQ50/50 / K2010 core , I didn't find K2010 core meterial , I found PQ50/50 N95 , PQ50/50 N87, PQ50/50 N97...etc.

    Which one is suitable for this design ?

    Transformer core material link:

    https://www.mouser.com.tr/Search/Refine?Keyword=PQ50%2f50

2) Also, In excelsheet there are some informations about Primary Magnetizing Inductance=3,2mH, Transformer Primary DC Resistance=40mH,Transformer Secondary DC Resistance=0,8mH, Measured Transformer Primary Leakage Inductance=10uH.

 -Are these information true for T4 transfomers ?

3)In the UCC28950 ic Design & Development website UCC28950 and UCC28951 TINA-TI Steady State Reference Design (Rev. A) simulation circuit is available , this circuit is for 12V 50A 600W  dc-dc converter.

  Now, I am trying to simulate your 2kW (PMP8740) dc-dc converter circuit in TINA-TI . I am using PMP8740 dc-dc converter schematic circuit identically except for Voltage and current loop Op-amps . I adjusted the output of dc dc converter 32V 1920W at full load because in the PMP8740 UCC28950 Excel design tool " output is 32V and 1920W. My purpose is determine  T4 transformers technical specs and understand the circuit.

 There are some differences between  Excelsheet results and PMP8740 dc-dc converter schematic circuit. For example, Redelab,Redelcd,Redlef resistors etc. 

- Which one can I reference circuit for first step 32V 1920W simulation ?

-Why there are some differences between  Excelsheet results and PMP8740 dc-dc converter schematic circuit ?

I attached excelsheet and transformer technical datasheet below.

Thanks.

4113.PMP8740 UCC28950 Excel Design Tool_SLUC222C.xls145400-a_eng.pdf

Hi Roberto 

Thanks for your valuable informations.

Hi Roberto

I have questions about T7  Resonant (shim) inductor and T4 transformer design. I need your help.

1) In the shim inductor 10 turns (160 X 0.1mm) litz wire was used. This means ,

From πr²  ,  1 pcs 0,1mm litz wire has "3.1416 X 0.05mm X 0.05mm = 0.007854 mm² " cross sectional area.

160 pcs litz wires have " 160 X 0.007854=1.256  mm² "   cross sectional area in total.

Instead of  1.256  mm²  litz wires. Can I use copper sheet winding with same cross sectional area ?

For example, " 0,1mm X 12,56mm = 1.256  mm² " copper sheet winding. Is it OK ?

2) In the T4 transformer, primary side 19 turns 1,6mm diameter and secondary side 2 turns 6mm diameter  litz wires was used .

Is it 1 pcs litz wire with 1.6mm diamater ? or Many  litz wires were used to create 1.6 mm diamater ?

For example , Like shim inductor Could it made by  16 pcs and  0.1mm (16X0.1mm) litz wire in total  ?

If more than one litzs wire was used to create 1.6mm diameter, How many litz wires are used and What is the diameter of these wires?

Same  questions for secondary side.

3) Can I use copper sheet winding in the T4 transformer instead of litz wire ? Is it suitible for T4 transformer?

 Thanks.

Hi Roberto 

Thanks for your help .

I want to make L1 pfc inductor (in pfc circuit) and L3 inductor (in dc-dc converter circuit) by hand and I have some questions about these inductors. 

For Pfc Inductor:

Which core can I use for L1 pfc inductor? 

Which wire can I use for L1 inductor and what is your suggestion for wire diameter ? 

For L3 Inductor:

From the datasheet ,  L3 has  HS-400 /26  core material but I haven't  HS-400 /26 core. 

Which core can I use to be alternative for HS-400 core ?

Thanks.

Can you also share the technical details of T4?
I would like to build a 240Vdc to 24Vdc battery charger, using a planar transformer. So a different ratio but I really would like to know what you have used for your 400Vdc to 24V converter

Thanks in advance,
Mark

Hi Roberto 

Thanks a lot for your help .

For Pfc inductor, The total inductance is 210uH and number of turns=35 and the total Al value is 171.43 nH /N^2 . One core has 85.714 nH / N^2 Al value.      I didn't find same NKL  CM400125 D0522-00 part number core. I find micrometals powder core  Al= 80nH /N^2 and u=60. When I used 2 core from micrometals, the total Al is 160nH/N^2  and to get 210uH inductance , I should wound 36 turns (207.3uH total inductance approx). I attached datasheet of the micrometals core. Is this core suitable for my PFC inductor ?   

Also I have question about T2 and T3 full bridge gate drive transformers . Can you suggest any transformer with part number for T2 and T3 transformers?

Thanks.

PFC Core.pdf

Hi Roberto 

Thanks a lot  for your help.

I have a question about gate drive transformers .In the  datasheet there is  also P0584ANL part number transformer. Do you suggest this transformer instead of P0584NL ?  and Are there important differences between  P0584NL and P0584ANL transformers? 

My another question about PFC Heat sinks. In PFC schematic HS1 for bridge rectifier and part number SK 481-50 and length of this heat sink  50mm. It is Ok.    HS2 and HS3 has SK 481-100 part number and length of this heat sinks are  100mm . If HS2 and HS3 are used together , total  heat sink length  should be 200mm. But in the PFC layout total length is 100mm.  Are HS2 and HS3 part number  correct ?  and Why do you use two seperate heat sink to obtain 100mm lengt.? Could one heat sink to be enough? 

My last question about AC voltage sensing transformer T2 PA3000NL in PFC schematic. I didn't find  this transformer with same part number. Can  you suggest a transformer instead of PA3000NL ?

Thanks.

Hi Roberto ,

Thanks a lot .

Ok. For gate drive transformer .I will use  P0584NL  transformer and for heat sink I will use one heat sink 100mm lenght .

For AC voltage sensing transformer : In audio transformer you suggested me , turns ratio Np/Ns 1:1 and 2:1. Which one can I use for same voltage sensing circuit in the schematic. 1:1 or 2:1.  In PA3000NL datasheet turns ratio 1:1.

Hi Roberto,

Thanks a lot.

Ok for voltage sensing transformer. 

I have another questions

In Pfc schematic one pin of bridge rectifier heat sink (HS1) connected to the GND-P and one pin of HS3 (for boost diodes and mosfets ) connected to 1000pF capacitor.  Are these connections  important ?  

Also , in pfc schematic there is a BAS21 (D100) diode connected to the pin 3 of ucc28180 ic in rev. E schematic but in PFC pcb layout I didn't find D100 diode. Why did you add this diode in revision E schematic.? and  Where can I place this diode in pcb layout ?

My last question : In Pfc schematic ,   "PCB Rule " was written above the some connections. What does it mean?  Are there  important points here for layout?

I attached related file.

 Hi Roberto ,

Thanks a lot for your valuable informations .

I have another questions  about resonant( shim ) inductor and its calculation.

-From the resonant inductor pdf  PQ20/20 N97, gap=0.77mm Ue= 57 Epcos core are recommended for shim inductor  but  the datasheet say that the Epcos N97 core has not  gap , this core is ungapped core. My question is here, the total winding lenght of N97 core for wire or copper foil is 7.15mm X2=14.3mm. When I add 0.77mm air gap the total lenght will be 15.07mm without tolerances. Is it true? So I  add gap later  for N97 core or Can I select core with gap ?

-My another question about calculation of shim inductor .From the formula of shim inductor calculation  :

Coss(Qa,Avg)=336pF, Vin(Fb,nom)=400V, Load(min)=0.15, IPP=7.526A,ILout=12A, Nps(fb)=9.5 , Llk=3.5uH the shim inductor(Ls) value  is  118uH  approx. (If we want %15 ZVS and we use IPP65R190CFD mosfet). For example If I want to adjust the minimum load current for ZVS operation to 30%  Ls is 26.9 uH. approx. Is it true ?

-If I adjust ZVS operation to  30% , Should I make any changes in the  the full bridge circuit ?

-Also, there is a leakage inductance Llk=3.5uH from the shim inductor formula. What is this leakge inductance? . Does it come from full bridge main transformer primary leakage inductance?

I attached N97 core datasheet and Shim inductor calculation pdf.

Thanks.

pq_20_20.pdfResonant Inductor.pdf

Hi Roberto

Thanks. 

Sorry for my poor explanation. Ok I understood  your explanations. I wanted to say the height of one core for winding is 7.15mm  when I use two core, the total height will be 14.3 mm without gap. With 0.77mm gap , the total height will be 15.07 mm . I attached  my  related png file below. I drew my explanation  in the photo . I hope it will be more understable. 

For shim inductor,

Here , I studied  whole calculations for a UCC28950 PSFB topology pdf which you added. My purpose is to use same full bridge circuit in the PMP8740 design. In the calculation   COSS _ QA _ SPEC   and  COSS _ QA _ AVG values available. Using the COSS _ QA _ SPEC value from the datasheet , COSS _ QA _ AVG value is calculated and this value was used for shim inductor calculation but you was suggested "effective output capacitance, time related  for the calculation of the ZVS times."  I didn't use this calculation and I used effective output capacitance, time related value from the datasheet.       Are there imporatant differences between COSS _ QA _ AVG  and effective output capacitance, time related value? 

As I understood from the calculations for 30% ZVS I don't need change the full bridge circuit . What do you think ? Is it true?

If I think wrong  , Can you suggest proper mosfet for %15 ZVS circuit  because I dont want to change full bridge circuit for my desing. I want to use  same circuit. Also , I found IPP50R199CP mosfet with Coss=160pF time related from the PMP8740 UCC28950 excel file. Maybe you used this mosfet for first prototype.  Using this mosfet Ls=54uH approx.  

My last question about full birdge transformer , If I adjust the full bridge main transformer leakage inductance to  high enough  for example 54uH  . My calculation is also 54uH required  for shim inductor . Result will be zero and I don't need shim inductor . Is it right ? Are there any problem here?

Hi Roberto ,

Thanks a lot for your detailed informations.

Ok. I will use 30% minimum load for ZVS and  I will use IPP65R190CFD mosfet as you used the lastest version of PMP8740. As a result , my shim inductor value will be Ls= 26.9 uH approx. and I will use full bridge circuit schematic without any modification. 

I understood the differences between higher and lower shim inductance .Also, the full bridge transformer should have low leakage inductance and Shim inductor should be used to reduce the spikes. It is ok for me.

Dear Roberto , You was attached a file , but I didn't open it.and I didn't download it. Can you attached this file again? 

Hi Roberto ,

Thanks.

Now, I am trying to make my full bridge transformer. I have some questions. 

I have shim inductor technical spefications for winding . For example , 10 turns litz wire (160X0.1mm) . For full bridge transformer .  I had asked you before and You said primary side of transformer 19 turns 1.6mm single litz wire (one litz wire). Secondary 1 ,and Secondary2 =  2 turns 6mm litz wires (pack of several litz wires together for secondary side).

If I use single 1.6mm litz wire for primary side, I think it will be not good for skin effects. Because of this reason , I want to use copper foil instead of litz wire and  You was suggested this method for full bridge transformer .Also, using the copper foil the leakage of transformer will be more less.  

Normally , the amount of current flows  from the full bridge transformer primary side should be equal to the the amonut of current flows the shim inductor. So , same magnitude of current flows the shim inductor and transformer primary  side . From this point , Can I use (160X0.1mm ) litz wire instead of 1.6mm single litz wire for full bridge transformer primary side ? Am I correct?

Also , I had calculated 160X0.1mm  litz wires area is equal to the 1.256mm2  cross sectional area in total. (For shim inductor). If my idea is correct , I will use 1.256mm2  copper foil instead of single 1.6mm litz wire for full bridge transformer primary side .  

Thanks .

Hi Roberto ,

Thanks  a lot for your clear explanation. I have no doubt about full bridge transformer .

Now, I want to change auxliary power supply circuit . In this design , aux power supply output is 10W but I  want to change this output to the 24W (12V ,2A).     My first question is about some calculations in the white paper .For example , Vrefleceted voltage  is important for transformer turns ratio. According to white paper    Vin(min)=120V , Vin(max)=400V + overshoot ~ 420V approx.  Vreflected < Vin(pfc,peak)(reduced by 20% percent) was used to choose Vreflected value.  Here I have a doubt because If Vin(pfc,peak) is equal to 420V . 20% of Vin(pfc,peak) is equal to 84V or  20% reduced by 420V is equal to 336V approx. Vreflected <336 V is a large margin because Vreflected =100V was chose . How did you choose the Vreflected value ? 

-Also , what is the maximum duty cycle for this flyback converter? and  What do you suggest?

My another question is about LC output filter of flyback converter. As I understood , Lf value is equal to 2.2uH and Cf=1000uF. When  I change output is to 12V 2A , Can  Lf and Cf values change or not ? and How did you calculate these values ? 

My last question is about Snubber circuit , In this converter RCD clamper circuit is available but RCD snubber circuit for resonance(in parallel to Q6 mosfet ) is not available . Do you prefer this circuit  adding to schematic?   

Hi Roberto , 

Thanks .

As first calculation  for LM5023 ,I used power stage designer tool in TI website. There are some input parameters for calculation. For example Vin(min) RMS, Vin(max) RMS , Vout, Iout . Here my Vin(min)=120V DC and Vin(max)=420V DC (with PFC). So  Which input parameter can I select for first calculation?. For example , Vin(min)=85V RMS , Vin(max)=265 Vrms . If I select this one maximum input DC voltage will be 265 X sqrt(2)= 374V DC approx. but this one is not enough I think because our circuit has PFC stage.  If Vin(max)=300 Vrms  maximum input dc voltage will be 420 volt . Which one is suitable for this desing ?  Because when maximum input voltage changes . Some components change in circuit.

Also, Can  you share documantation about close loop and selection of this components . It will be good for me .

Thanks.