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DRV8874: DRV8874 as bus converter driver

Antenna_Head
Genius 11375 points
Part Number: DRV8874
Other Parts Discussed in Thread: DRV8873,

Need to construct a bus converter that takes Vin = 15V and outputs 60V or 75V depending on the turns ratio of the transformer.

Would operate the DRV8874 in EN/PH mode, driving PH with 50% duty cycle.  OUT1/OUT2 would be connected to the primary of the transformer, as a full bridge driver.   The output would use full-wave rectification (diode ring).

I understand we're limited to 100 kHz operation here, but do you see any issues using the DRV8874 to drive a transformer in this fashion?

Thanks!

-Steve

  • 0
    TI__Mastermind 37683 points

    Hi Steve,

    From my own experience, I have not seen a motor driver used to drive a transformer. Let me do some research if this is possible. I will get back to you within 48 hours.

  • 0 in reply to Pablo Armet
    TI__Mastermind 37683 points

    Hi Steve,

    One of the main concerns, as you mention, is the switching frequency requirement. Switching at frequencies higher than 100Hz will drastically increase switching power losses in the driver and may cause problems in the driver since it is above the abs max.

    Another concern is current. How much current does this transformer require? If above 6-A, there will be thermal issues and will trip the overcurrent protection on the device. Both of these safety features cannot be disabled. If you require more current, the DRV8873 may be a better option.

  • 0 in reply to Pablo Armet
    TI__Genius 11375 points

    When using EN/PH control, what is the break-before-make (or non-overlap) time when commutating the bridge from forward to reverse direction? 

    Is this the "Output Dead time" spec of 100ns on page 6?

    The inductance of the transformer primary is about 200 uH and the current is only about an Amp, so I think there is no danger of tripping over current limit.

  • 0 in reply to Antenna_Head
    TI__Mastermind 37683 points

    Hi Antenna,

    The dead-time is the time inserted when one half-bridge is switching from High-side to Low-side or vice-versa. During this period, current flows through the body diode of the FETs. The purpose of adding this dead time is to prevent a cross-conduction event (both FETs of one half-bridge turning on at the same time) from happening.

    Antenna_Head said:
    The inductance of the transformer primary is about 200 uH and the current is only about an Amp, so I think there is no danger of tripping over current limit.

    In that case, I would say the DRV8874 can be used as long as the switching frequency is below 100kHz. You can run your own evaluation using a DRV8874EVM.