Precision Programmable Current Sources Use Digital Pots

摘要

The circuit shown in Figure 1 implements a programmable O-to 20-mA precision current source. The REF192 low-headroom 2.5-V voltage reference (U1) can source up to 30 mA. An AD5280 digital potentiometer (U2) controls the voltage-divider ratio of the reference voltage. U3, an OP1177 op amp, closes the loop by forcing V_L = V_W.