Primary inductance difference between full bridge and Phase Shift Full Bridge

Mirco Gonnelli

Other Parts Discussed in Thread: UCC28950

Hello All

Two years ago I developed a 3kW DC/DC phase shift Full Bridge, starting from Power Stage Designer 2.1 tool.
In Power Stage Designer 2.1 was present only FB simulator and not the Phase Shift.
Now in Power Stage Designer 3 there is Phase Shift Full Bridge. So I have tried to simulate the same and I have noticed a BIG difference in CALCULATED TRANSFORMER INDUCTANCE.

Can somebody explain me please?
Why there is this big difference? There are different formulas?

To reference I used tis formula to calculate Lprimary --> Lm=(N2*Vout2) / (32*Coss*Vout2*Fsw2)

Below the Power Stage example

over 8 years ago

0 Ulrich Goerke over 8 years ago

TI__Mastermind 40120 points

Hello Mirco,

I'll route your question to the appropriate engineer(s) to address it.

Regards,
Ulrich

0 Brian Johnson96 over 8 years ago in reply to Ulrich Goerke

TI__Expert 3200 points

Hi Micro,

I am working on you getting in contact with a member of the Power Stage Designer Tool Team. By the way, the tool is now at version 3.0.

0 Mirco Gonnelli over 8 years ago in reply to Brian Johnson96

Prodigy 30 points

Thank Brian, thank Ulrich for you help

Brian Johnson96 said:

By the way, the tool is now at version 3.0.

My doubt come from tool version 3.0, in primary inductance difference between full bridge and PSFB with the same data project.

0 Markus Zehendner over 8 years ago in reply to Brian Johnson96

TI__Intellectual 1695 points

Hi Mirco,

the calculation for the PSFB's primary inductance is based on the UCC28950 data sheet (page 39, equation 30):

The same equation can be found in the respective application report for this controller (page 3, equation 9):

Please pay attention that in one case the transformer switching frequency is used and in the other case the FET switching frequency.

However the primary inductance for the hard switched full bridge is calculated as follows:

This should hopefully explain the difference in results.

Best regards

Markus

0 evs over 8 years ago in reply to Mirco Gonnelli

Genius 5910 points

The first is a transformer and the second a coupled inductor.
For an transformer the higher the inductance the lower is the inductor switching current (don't know the english word for that) but the higher the leakage inductions.

I really doubted that using a tool you can make a good working design. real work problems aren't solved by the tool.

0 Mirco Gonnelli over 8 years ago in reply to Markus Zehendner

Prodigy 30 points

Thank you very much.
With your explanations I have understood my trouble.

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Primary inductance difference between full bridge and Phase Shift Full Bridge