Precision Current Source

The 2N5457 and PN2222 bipolar serve as voltage isolation devices between the output and the current sensing resistor, R1. The LM101 provides a large amount of loop gain to assure that the circuit acts as a current source. For small values of current (<1 mA), the PN2222 and 10K resistor may be eliminated with the output appearing at the source of the 2N5457.

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Precision Current Sink

The 2N5457 JFET and PN2222 bipolar have inherently high output impedance. Using R1 as a current sensing resistor to provide feedback to the LM101 op amp provides a large amount of loop gain for negative feedback to enhance the true current sink nature of this circuit. For small current values, the 10 K resistor and PN2222 may be eliminated if the source of the JFET is connected to R1.

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Precision 1uA to 1mA Current Sources

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Current Source for Low Resistance Measurements

Useful for low-resistance measurements, this 1-A current source will produce 1 A in unknown resistance Rx. For best results, Rx should be less than 1 to 2 ohms, because only 3 V are available. U1 is a flyback converter to generate 9 V for U2.

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Current Source

This precision current source has 10 uA to 10 mA ranges with output compliance of 30V to -5V. Output current is fully adjustable on each range with a calibrated, ten-turn potentiometer. Error light indicates saturation.

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