Current source "without" temp drift

Hi,

I'd like to make a High precision current source with excellent temp drift (10 to the power of -6 or at best better than that). Current: about 0.5 Ampere

At the moment I have an AD624 combined with a Vishay resistor in mind. How can I go further? Is there a place for me to look up stuff like this?

Thanks

Matthias

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  • This is going to be very challenging. If you use a reasonably large value resistor, e.g. 0.2 ohms (200 milliohms) then you will drop 100 mV across it. This means your sense amplifier must have a drift of less than 0.1uV. Opamps like the AD8628, TLC2652, AD8571 or LTC1050 have a typical drift of less than 0.01uV/C, so they may be suitable over a temperature range of 10 C. The trouble is that the resistor will be dissipating 50mW, and even a very good quality foil resistor has a coefficient of 5 ppm at full power. This means you will need to run the resistor at perhaps 2% of its rating.

    If you reduce the sense resistance, the resistor may be more stable but the contribution from the sense amplifier becomes more significant.

    Electrical joints also become very troublesome as thermocouple effects can swamp 0.1uV.

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  • This is going to be very challenging. If you use a reasonably large value resistor, e.g. 0.2 ohms (200 milliohms) then you will drop 100 mV across it. This means your sense amplifier must have a drift of less than 0.1uV. Opamps like the AD8628, TLC2652, AD8571 or LTC1050 have a typical drift of less than 0.01uV/C, so they may be suitable over a temperature range of 10 C. The trouble is that the resistor will be dissipating 50mW, and even a very good quality foil resistor has a coefficient of 5 ppm at full power. This means you will need to run the resistor at perhaps 2% of its rating.

    If you reduce the sense resistance, the resistor may be more stable but the contribution from the sense amplifier becomes more significant.

    Electrical joints also become very troublesome as thermocouple effects can swamp 0.1uV.

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