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Split power supply

Curt Gibson
Prodigy 90 points

Other Parts Discussed in Thread: LM675, TINA-TI, OPA541, OPA549, LM1875, LM3886

Many amplifiers need split power supplies to produce AC wave forms. When all you have available is a single DC source there are a few ways to fabricate an inverted source and virtual ground. I have tried a few of these schematics by building them in Tina-TI, and remarkably most do not work. Even the one on the LM675 datasheet (figure 3) does not work in Tina-TI when built exactly verbatim.

The chip based versions are usually limited to 500mA but I need 5A. Can someone suggest a schematic that will absolutely work to provide +/-20V from a 48V source?

 

 

  • 0
    TI__Guru 65186 points

    Hi Curt,

    I know the LM675 Vs/2 circuit works...I have used it in the past. DO NOT forget the output "snubber" network!

    The LM675 does not have a model. What model did you use? Did you run a transient sim or just a DC analysis? Run the transient analysis for at least 100ms. Also, some models fall apart when the supply voltage is beyond what the device was rated for. Try using the OPA541E model. Using he OPA541 model, the circuit works fine.

    The OPA541 and OPA549 should be able to handle the job.

    You can also use audio power amplifiers - since they are basically just power op-amps. The LM3886 should handle this with no problem. The LM675 is just a re-spec'd LM1875 audio amplifier (same die). Note that these audio devices are a minimum gain of 10 - which is why they have feedback networks that provide noise gain.

    Regards,

  • 0 in reply to Curt Gibson
    Prodigy 90 points

    Paul,

     

    Thanks for your reply. Due to your confirmation, I went back and found that I had grounded everything, and should have just connected to the negative terminal instead. Now it works. I will probably add a couple capacitors and be done.

    I have attached the working Tina file just in case anyone wants it. I am planning on production of a commercial product with this and if there is any input to guide me to a correct solution, that would be appreciated.