Attaining Low Power

Discussion in 'General Electronics Chat' started by Management, Nov 15, 2007.

  1. Management

    Thread Starter Active Member

    Sep 18, 2007
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    If you are looking at a circuit schematic and you would like to redesign it for the sole purpose of reducing the power, what are things you would be looking for to do so?

    I figured that reducing the draw from the power supply would be a good start. But I can only think about replacing the current ICs with ones that have less supply current draw. Besides that I can't really think of anything else. I am a
    fairly young engineer so please excuse if anything has went over my head.

    BTW, could you please assume that it is an analog design. Mostly Pre-Amp design.

    Thank you.

    - Dru
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    Is the power supply included in this power reduction effort? Or the exercise to reduce the power consumption of the analog circuitry only?

    hgmjr
     
  3. Management

    Thread Starter Active Member

    Sep 18, 2007
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    I am first thinking about the analog circuitry only. I understand the design but would like to know what one can do or look for in attempting to reduce the power. Thank you for your response.

    - Dru
     
  4. Management

    Thread Starter Active Member

    Sep 18, 2007
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    I have another question what concerns should one have if trying to good from dual supply +/- to single supply operational amplifiers? This would help with power consumption correct? But scarifying system performance correct?
     
  5. beenthere

    Retired Moderator

    Apr 20, 2004
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    As long as the voltage is sufficient to allow the full magnitude of signal swing, it should not affect performance. Just remember the coupling capacitors. TI makes a zillion op amps characterized for single-supply usage.
     
  6. techroomt

    Senior Member

    May 19, 2004
    198
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    first thing that came to mind in analog circuits is would be to substitute any class a amps with lower power amps - class b or ab.
     
  7. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
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    You really need to give us more of clue about your circuit. I assume it is a multistage something in which the signal builds up as it passes through?

    Very often all stages are run from the same power supply, for convenience, but by reducing the power rail to earlier stages, power saving can be had.

    With transistors you can increase the bias resistors, thereby reducing the current in the bias chains. This is of course eventually at the expense of stability.

    If your something includes optional stages such as tone controls or filters you could switch these off when not wanted.

    Indicator lights consume significant amounts of power so dispense with as many as possible or make the remaining ones multi function.
     
  8. Management

    Thread Starter Active Member

    Sep 18, 2007
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    I apologize for the absence. I'm currently working with two different preamp circuits.

    The first is connected to a Galvanic Sensor and can also be connected to a Polargraphic Sensor. Both these sensors output current into the preamp. The Galvanic Sensor outputs current from 0-50uA and the Polargraphic Sensor outputs current from 0-1uA. So the first stage is a current to voltage configuration with a LMC6041 opamp. The Galvanic Sensor current that goes through the current to voltage stage is not 0-50uA but is intentionally decreased to 0-350nA. All of the Polargraphic sensor current flows into the current to voltage stage.

    Output Voltage of the I to V stage for the Galv. sensor is -3mV to -500mV and -10mV to -1.5V for the Polargraphic sensor. The next stage is an amplifying stage (1 opamp LTC1050 w/ resistor network and 4051 IC) that has variable gain to set range of approx. 1.5V to -1.5V (this is only approx.).

    Like Studiot said, all ICs are ran from the +/-4.2 power supplies. What I would like to know is that can I half the power consumption by designing the opamps to use a single supply configuration?

    The other preamp circuit has voltage input but has a bunch of opamps for gain and filtering and what not. Just trying to see what type of issues I would have to look out for if I wanted to save or lessen power consumption if I had a +/-4.2 power supply. Also, opamps like the OPA244UA are used in the latter preamp. A bunch actually.

    Thank you.

    Andrew
     
  9. Management

    Thread Starter Active Member

    Sep 18, 2007
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    Actually I think I can answer my own question after doing some thinking. Power consumption is dependent on opamp supply range. So obviously making the range smaller will make the power consumption smaller. So making the supply +/-2.1 instead of +/-4.2 would yield the same effect as have a single supply of +4.2, correct?

    So I am guess that the only benefit of using single supply is when you cannot change the power supply voltage the operating opamps on single supply will yield the lower power consumption, correct?

    Thank you. Sometimes writing things out on a form makes your brain think a little. Kind of like reading an English paper out loud.

    Andrew
     
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