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UCC25800-Q1: One transformer w/ 2 secondaries for SiC Gate drive bias.

certified powerpoint technician
Prodigy 145 points
Part Number: UCC25800-Q1
Other Parts Discussed in Thread: UCC25800EVM-1

Hi,

In the bias supply design guide it states that driving a transformer with 2 secondaries is possible, but stipulates that the regulation is not as good as . 

My question is this: the EVM uses primary side resonance and the output regulation is acceptable without the additional regulator; if we used a 8 pin bobbin with 2 secondaries for an isolated gate drive bias, one providing 15V and other providing -4V, would the regulation be worse in this configuration than if we had just one +15V or +19V rail with a single secondary?"

Second question: The design guide it says there may be risk of noise between the windings. Is this referring to a situation where both secondaries are functionally isolated? I don't see that this would apply to the application for isolated gate drive bias where the supplies are referenced to same pt. 

Best,

Jeejmas

  • +1
    TI__Expert 3110 points

    Hello Jeejmas,

    The UCC25800EVM-1 uses secondary side resonance. But, if a design uses a transformer with 2 secondary windings then the design will use primary side resonance. If the two secondary windings have balance loading conditions, then each output regulation will be ok.

    Case 1: Single secondary winding is split into double outputs

    Case 2: Double secondary windings for double output

    Both are good and have comparable Vout regulation as long as loading is balanced, which is the case for IGBT inverter gate driver bias. 

    If you use 2 windings on the secondary side of the transformer, then the 2 secondary windings will have mutual coupling. So, one winding noise can be coupled to the other winding, regardless of isolation. If the windings are isolated, then there will be a parasitic capacitive effect coupling between the 2 windings generating noise.

    Regards,

    Jonathan Wong