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TPA3255EVM: Transformer at PWM stage

Trevor Haanstad
Prodigy 30 points
Part Number: TPA3255EVM
Other Parts Discussed in Thread: TPA3255,

I am working on a project where we are interested in using the TPA3255 to power a magneto strictive actuator.  This actuator requires higher voltage than the TPA3255 can provide (81VRMS), and we are exploring the option of placing a high frequency transformer: PL300-104L directly at the PWM output stage of the TPA3255 and then adding a LC filter at this higher voltage level.  Our goal using this method is to reduce the size of the transformer.

When connecting a set of 3x series of these transformers we are expecting a 1:4 step up of voltage in the configuration we have implemented (1:4 step up of 463kHz square wave tested as working with this transformer set and function generator).  On the TPA3255EVM I have tapped into the PWMA and PWMD test points and configured the eval board in PBTL configuration (original EVM output filter still installed).  I am able to drive the PWM output of this configuration (20V input to EVM) directly to a relatively high resistance load (91Ω), but when I connect to the same load though the transformer configuration, I see an overload fault.  I see this fault after approximately 3.7ms of PWM captured with an oscilloscope.  

Do you have any idea why the OL fault is occurring?  Is this possibly triggered by a DC offset voltage?  Do you have suggestions about how to modify the circuit to accommodate this configuration?

Thanks!

T

  • 0
    TI__Guru 51070 points

    Hi Trevor

      For PBTL using, PWMA and C need to be shorted, same with B and D, we could short them from back of the board, or remove L3 and L4 to give space. Please kindly check your settings.

      For your trouble, we could try to capture the current at OUT+ and OUT- at the same time, to see if there's any unwanted DC current, or short circuit. Usually it's no problem to use with transformer load.