VARIABLE_CURRENT_SOURCE0_TO_5A

Published:2009/7/17 3:23:00 Author:Jessie | From:SeekIC

The variable-current source generates 0 to 5 A with a compliance range of 4 to 30 V. The 12-bit digital-to-analog converter (DAC), IC2, makes it digitally programmable. The switch-mode step-down regulator, IC1, is more efficient than the alternative current source with linear pass transistor.IC3 is a high-side current-sense amplifier. In this circuit, it senses output current as a voltage drop across R5, and produces a proportional signal current at pin 8. The regulator's feedback voltage (IC1 at pin 1) is set by the DAC and modified by IC3's current feedback, which flows across a parallel combination of R2 and R3. This current feedback opposes any change in load current because of a change in load resistance. The DAC generates 0 to 10 V, producing a source current that varies inversely with code: FFFHEX (10 V from IC2) produces 0mA, and 000HEX (0V from IC2) produces 5 A. The circuit can be reconfigured for other ranges of output current (Isource) by resizing R2 and R3: Isource=2217[VFB(R2+R3)-(R3VDAC)]/R2R3 where VFB 2.21 V and VDAC can range from 0 to 10 V. The desired range for Isource defines values for R2 and R3:VDAC=10V for the low value of Isource and VDAC=0V for the high value of Isource. Substituting these two sets of values in the equation yields two equations to be solved simultaneously for the values of R2 and R3.



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