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Linear regulator with a switching regulator input

Jon Bean1
Expert 1130 points

I need to use a linear regulator to get an output with low noise <1mV, but the output needs to vary between 0-5V@2A So I was thinking that I could use a dcdc on the input of the linear to reduce power by only having the minimum amount of head room. Are there any parts or circuits that would allow me to do this. Vary the linear from 0-5V and then vary the dcdc to maintain the mimimum head room of the linear.

Thanks

  • 0
    TI__Expert 4435 points
    Hi Jon,

    I need to ask a few questions to understand your requirements:

    What is the range of your input voltage?
    Does your output need to change between 0 V and 5 V while the linear regulator is running?
    Is the output voltage going to be tuned once or is it going to be changing?

    Note that PSRR and transient performance is degraded when the linear regulator Vin - Vout is close to or in dropout. Usually PSRR performance is specified with Vin - Vout = 1 V.
  • 0 in reply to Eric.Preiss
    Expert 1130 points
    Hi Eric

    The input voltage can really be anything I want, so whatever is best for the circuit design.
    Yes the output must be variable when its running. I need to be able to set the output between 0 and 5V under normal operation.
    What I am trying to do is create a variable supply to control a thermoelectric cooler. I know there are chips to do this, but they use PWM and I have found that there is too much noise. The TEC is in an image sensor that is extremely noise sensitive. So I need a design that has very low noise but that I can vary the output. So my idea was to use a linear regulator but power the input from a dcdc. You may know a better solution as I am more of a digital than analog person.
    Thanks
  • 0 in reply to Jon Bean1
    Guru 140200 points
    Hi Jon,

    thought about using a DC/DC-switcher with a post filter?

    Kai