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UCC28950: OUTA, OUTB dead time

kwangwoon Lee
Prodigy 230 points
Part Number: UCC28950

Hi, 

The waveform below is OUTA(Green) and OUTB(Blue) waveform measured after applying only VCC power to UCC28950.

DELAB, DELCD, DELEF all applied 15kohm.

After OUTA and OUTB come out, there is a delay of about 500ns.

Is this phenomenon correct?

In the above waveform condition, input power is applied and load current is applied about 10% of the target value, and the voltage across the transformer is measured as follows.

In the waveform, the amplitudes of A and B are slightly different.

Due to this, the difference in heat generation in heat generation of the MOSFET of the secondary current doubler appears.

Can the waveform of OUTA and OUTB at the top waveform cause the secondary side to be unbalanced?

Regards,

Kwangwoon.

  • 0
    TI__Guru* 85616 points

    Hello,

    Did these waveforms come from the evaluation module or your design?

    Could you share a schematic with us to evaluate?

    Regards,

  • 0 in reply to Mike O'
    Prodigy 230 points

    Hi, 

    The answer was late because of a business trip.

    The above waveform was measured on the board I designed.

    Below is the circuit diagram I designed.

    Regards.

    Kwangwoon

  • 0 in reply to kwangwoon Lee
    TI__Guru* 85616 points

    Hello,

    You are using a current doubler with two output inductors.   You might want to check the inductors currents to make sure they are equal in ripple current and magnitude.  

    I think the input voltage of the transformer might be effected by the output inductance values.  If the output inductors and currents are not equal it could lead to an asymmetrical waveform on the primary of the transformer.

    The typical design using the UCC28950 is a voltage double with a single output inductor.   In these designs the voltage across the primary is symmetrical for  both +/- voltages applied.  I do think the behavior you are seeing might be because the output inductor values are slightly different.  

    Regards,