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LM5023-2NBEVM: LM5023-2NBEVM with DC voltage supply.

Phán Bùi
Prodigy 120 points
Part Number: LM5023-2NBEVM
Other Parts Discussed in Thread: LM5023

Hello everyone,
I want to use LM5023 to design a flyback with a DC voltage supply. So, I think I'll buy a LM5023-2NBEVM board for the test. 
And I have a question: Can I supply 60V-80V DC at the red point such as the below image?

That means I will bypass the diode rectifier bridge. Do the board work normally?

Thank you!

Have a nice day!

Phan

  • 0
    TI__Mastermind 30380 points

    Hello Phan, 

    Thank you for your interest in the LM5023 EVM.

    This EVM is designed for 90Vac to 264vac input voltage range.  Because it is rectified, the bulk voltage ranges between the peaks of these AC-line limits, which are from 127Vdc to 373Vdc.  There is some bulk ripple voltage that may drop the minimum operating voltage to ~80Vdc or so, but the EVM is not designed thermally to operate at that low of a voltage continuously.  Such low voltage is present for only ~1ms out of 10ms.  The peak primary current is very high at this voltage, but such low voltage is normally present for only ~1ms out of 10ms.  

    To avoid overheating the transformer windings and primary-side semiconductors, I recommend to apply no lower than 120Vdc to the EVM input. 

    Furthermore, I recommend to apply your DC voltage to the AC input connector, rather than after the diode bridge.  That way you will not have to worry about always connecting the DC input in the correct polarity at the Red Point.  A mistake in connection there may damage the board beyond repair. 
    Connecting at the AC input will always provide the correct polarity to the bulk rail, regardless of how the DC is applied.  And it will allow the EMI line filter to provide your DC source with significantly reduced switching noise.    

    Regards,
    Ulrich