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Voltage to current converter

Discussion in 'Datasheets, Manuals and Component Identification' started by pyrohaz, Dec 12, 2012.

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  1. pyrohaz

    pyrohaz

    33
    0
    Oct 28, 2012
    Hey, I'm designing a voltage to current converter using a single 5v supply. Most bipolar op amps (that aren't open collector) don't seem to go that low. I need to ensure that the input and output are both rail to rail so that leaves me with generally just cmos op amps.

    After simulating my circuit within LTspice, the LT1006 and LT1007 fit the bill perfectly but seem a bit overspecced and pricey for the job.

    How would the CA3240 hold up? I know its a tad old but it still boasts quite good spec. Failing that, the TS272 or LMC662?

    The input will be a time varying signal but will have a maximum period of 50Hz so bandwidth is not a major biggy. The output will be a green LED with a 120ohm feedback resistor The green LED has a forward voltage of 2.8v (measured @ 20mA) therefore at 5v, maximum current flow with the 120ohm feedback resistor can be about 18mA. The input voltage will be about 1v so theoretically with 1v dropped across 120ohm, the current flow will be about 8mA which is fine.

    Would the TS272 be suited to this application? (Its the cheapest of the bunch, swiftly followed by the CA3240)

    Cheers
     

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  2. pyrohaz

    pyrohaz

    33
    0
    Oct 28, 2012
    Anyway know at all?
     
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,448
    2,809
    Jan 21, 2010
    What does "a maximum period of 50Hz" mean?

    And where is the output of your circuit? What range of resistances does it need to drive and what range of currents does it need to supply? These together will tell you the minimum supply voltage (to which you need to add a couple of volts)
     
  4. pyrohaz

    pyrohaz

    33
    0
    Oct 28, 2012
    Hey steve, sorry I meant a maximum period of 20ms (I was stating the maximum required frequency!) Output wise, its literally just driving the LED in series with a resistor.
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,448
    2,809
    Jan 21, 2010
    It doesn't sound like the requirements for the o-amp will be fairly modest, so you won't need anything special.

    One other requirement though will be that the inputs can be grounded, and that the common mode range includes the negative rail.
     
  6. pyrohaz

    pyrohaz

    33
    0
    Oct 28, 2012
    Thats good to hear! Well the only op amps I generally use are the TL0xx series or the mc1458 but neither of these will work on 5v. What such op amps would you recommend me to use?

    Cheers!
     
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