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UCC28950: Primary side vs Secondary side gate drive signal issue

Suttichai Chindaprayoonwong
Prodigy 50 points
Part Number: UCC28950

Hi ti team,

Regarding to this EVM http://www.ti.com/tool/UCC28950EVM-442

 And the schematic here http://www.ti.com/lit/ug/sluu421a/sluu421a.pdf.

Where UCC28950 Output A,B and C,D are for Primary side and Output D,E for Secondary side.

From the above signal, @10A load, when Primary gate drive signal Output "D" turn OFF but SW-D (MOSFET) not completely OFF (Purple color).

And Secondary side output "E" try to turn ON while primary side output "D" still ON

This caused over shoot current (I_TR primary) and LOST at Primary transformer (Yellow color)

 


But no issue @20A load and >>20A.

 

Please advise how to solve this issue, or how to configure or add some delay for secondary side output (Output E and F).

 

Thanks,

Suttichai

  • 0
    TI__Mastermind 25570 points

    Hello Suttichai

    Please check that the probe for the Vgs_D signal is correctly placed - it looks like it is picking up the Vgs_E signal. If this is so then the voltage waveforms make more sense to me.

    Please provide a sketch / schematic showing exactly where you have placed the current probe - ITR_pri. For example, the current in the shim inductor is not the same as that in the transformer primary because some of the current flows in the clamp diodes.

    Regards
    Colin

  • 0 in reply to Colin Gillmor
    TI__Mastermind 25570 points

    Hello Suttichai

    SInce you haven't posted a reply I'll assume that you have solved the issue and so I'll close the thread. Please feel free to re-open it or to post a new thread if you have any problems

    Regards
    Colin