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Hbridge transformer driving series cap

Hi,

I am driving a transformer with an Hbridge, like this circuit:

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I am wondering about using a series cap on the transformers primary, if it is necessary or not. I am using an FPGA to control the fets gates, so should be able to keep the on times of one Hbridge leg very close to the on time of the opposite Hbridge leg to minimize the DC current in the transformers primary, but can the flux build up and saturate the transformer without a series cap?

cheers, Jamie

Reply to
Jamie Morken
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Jamie Morken wrote in news:Tsn4k.1226$L03.850 @edtnps92:

  1. Best to start out with a series cap until you can prove that your controller guarantees no DC under all operating conditions, including power-up, power-down, brown-out, etc, etc.
  2. Don't count on analog current feedback to drive the system back to AC symmetry. Under many conditions, the feedback can become non-linear. One example: error amplifier outputs saturate, especially when bias voltages are low, as happens during power-up and power-down.
  3. Flux walking is the Achilles heel of many full bridge designs. According to TI/Unitrode engineers, problems relating to DC in primary account for a high proportion of design and field problems and are probably the main reason why their UCC3895 chip never became very popular.
  4. You can also consider adding an air gap to the transformer, but this has other drawbacks. Paul Mathews
Reply to
Paul Mathews

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