Flyback Design_Problems

[treez]

@ treez, re post #56, for 1.37mH and 180Vin, the peak current required in Lpri needs to be 1.38A to get enough power thru (130W) at 100kHz, the time required (180V) to ramp to 1.38A is 10.5uS..! longer than a 100kHz period..! so cannot operate at 100kHz...!

..yes my bad, I was guilty of copy and pasting then not deleting the inductance values. OP said 100khz so I would re-calc the L's for that

Also, I forgot to add above that with the vin ,vout, pout spec, the flyback should have D<0.2 at min vin prefereably so that you decrease sec rms current.
-but I forgot to say that getting D small in this case isn't important for a 2 transistor forward, because it has the output inductor

 

[Bjtpower]

Are you trying to keep your original transformer with 50 T and 5 T and getting the correct inductance value by adjusting the air gap? That will give you that large gap of over 7 mm.

I know EPCOS only has pre-gapped cores up to 1 mm maximum. You will have to modify the turns to use one of these.

If you want to use the ETD 44/ 1mm gap part, then you will have to go with 19 T and 2 T with a higher peak current of about 6A (using 2 switch design).

- - - Updated - - -

If you still want to go with a single switch, then use 25 T and 2 T, but you will have the snubber losses to deal with again. I will suggest you use 2 switches instead.

Hi
You can check the attached zip files of my calculation, i am getting the .78cm (Airgap, I am confused will such large gap exist in trafo calculations or i am wrong).
also by keeping the same gap i can get the same Inductance what i need.

Kindly help for the No of turns calculations.
I am taking approch Np=(Ku x Wap)/(3*Bare area)
In this factor Only ku factor Can be adjustable.
Np=0.3*1.254(cm2)/(3*1.6(cm2)(gauge #26)=79T
and by calculating fringing flux it gives a 51 T

Spreadsheet will give you a exact idea.

Thanx
Marx

 

[Easy peasy]

it appears your calc's are wide of the mark....

 

[vietchiase]

Bjtpower:-
In post #11 you say NP=51, NS = 5
But in post #2, you say LP=1.37mH , LS=25uH

…this doesn’t add up.

NS/NP = SQRT(LS/LP)

So by your inductance measurements, your NP/NS = 7.4

- - - Updated - - -

also just noticed you are using a high side low side driver.....(si8234)
**broken link removed**

I think now we need to check if your duty is >50%, because you are using a half bridge driver....OK, its fine, your D=0.34 according to your pri/sec values of post#2, and considering your vin=180vdc and vout=12vdc

 

[treez]

*****************************************
VIN=180-240VDC (out of interest what is this from?)
VOUT=12V
IOUT=10A
FSW=100KHZ
DCM or CCM, see whats best
Isolation ..not full mains isolation
Prefer single switch flyback
less than 5W of loss in the RCD clamp.
********************************

BJTpower I take it the above is your spec?

If so I will have a look whilst im doing the laundry if you can confirm the above……we need to look through all core sets and find which are pre-gapped and work with those….getting cores grinded is too expensive, and polyester film gapping is too hit and miss
Please confirm your spec

(by the way, as you know, my earlier excel sheet, in post #25, was just for the parameters BJTpower gave, and wasn't me trying to do ccm or dcm, it came out ccm with the high LP , as Easy Peasy noted, but that was just from the parameters that bjtpower gave. I appreciate it wasn't DCM, but at that stage, there was no stipulation that it had to be dcm, it was just a case of wapping BJTpower's parameter's in and showing BJTpower how it came out)

Let us please ask OP what the real requirements are and get it cracked. Can you please confirm?

 

[Bjtpower]

*****************************************
VIN=180-240VDC (out of interest what is this from?)
VOUT=12V
IOUT=10A
FSW=100KHZ
DCM or CCM, see whats best
Isolation ..not full mains isolation
Prefer single switch flyback
less than 5W of loss in the RCD clamp.
********************************

BJTpower I take it the above is your spec?

If so I will have a look whilst im doing the laundry if you can confirm the above……we need to look through all core sets and find which are pre-gapped and work with those….getting cores grinded is too expensive, and polyester film gapping is too hit and miss
Please confirm your spec

(by the way, as you know, my earlier excel sheet, in post #25, was just for the parameters BJTpower gave, and wasn't me trying to do ccm or dcm, it came out ccm with the high LP , as Easy Peasy noted, but that was just from the parameters that bjtpower gave. I appreciate it wasn't DCM, but at that stage, there was no stipulation that it had to be dcm, it was just a case of wapping BJTpower's parameter's in and showing BJTpower how it came out)

Let us please ask OP what the real requirements are and get it cracked. Can you please confirm?

Hi Treez

Parameters are Here:
Input voltage range:180-250V dc
Output Voltage Range:50-55 V dc

Output current:10 amp
Frequency:100khz
I calculated it in DCM Operations.

But you can give in both the Conduction modes so i can cross check.

These are Confirming parameters and i want go for Flyback (doesn't bother Snubber Losses).

Here i am attaching the Excel sheet of zip.
Thanks
Marx.

 

[treez]

Thanks, please may I ask what is the 180-250vdc?...is it the output of USA mains boost power factor corrector?

Also, you have changed your vout from 12vdc to 50-55vdc now?
What sort of isolation do you/don't you need

 

[E-design]

Wow! 55 V @ 10 A? You are leaving the territory of FB now. You should interleave or look at another topology.

Peak current in your single switch design will be about ≥9 A and the snubber losses will be a nightmare.

 

[E-design]

This is the only way I can see for you to achieve this power level with the least amount of headaches (better chance of success) while staying with the FB topology without interleaving.

The required core is large with a 1 mm gap.