5_mA_WITH_VARIABLE_SLOPE_START

Published:2009/7/13 4:52:00 Author:May | From:SeekIC

UP-Low-cost NSL5022 LED typically has 1.6-V drop at 2 mA, to produce constant 0.9 V across 390-ohm emitter resistors in circuit shown. Use of two current sources, each feeding other's LED reference, eliminates all voltage defects except for small voltage-dependent changes in transistor parameters. Adding 240K slope resistor can eels these changes, holding current constant within 0.1% over supply voltage range of 5-20 V. Applications include use as voltage divider with gain, Q multiplier for tuned circuits, and bias compensation. -P. Lefferts, Variable Slope Current Source Starts at 2.5 v, EDN Magazine, Nov. 5, 1975, p 100.



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