STEP_GENERATOR

Published:2009/7/10 5:55:00 Author:May | From:SeekIC

Base-step generator produces series of voltage or current steps synchronized with beginning of each collector voltage sweep, for application to base or gate of three-terminal semiconductor, device while sweep voltage is applied to collector of curve tracer that displays current-voltage characteristics on CRO. Circuit is bulk around Motorola MC1406L 6-bit D/A converter U5. U1 (7400), U2, and U3 (both 7473) form synchronous divide-by-8 counter whose outputs are applied to A1-A3 inputs of US. U6 (MC1741P1) and Q2 form current amplifier. al is general-purpose NPN transistor having DC current gain of about 30. Point A goes to output of full-wave rectifier using two 50-PIV 1-A diodes connected across 26.4-V secondary of transformer. Table gives values for R3 through R8 as ratio of R2 for various gains and steps. Thus, for 500-mV steps (gain of 100), R7 is about 101 ohms. Accuracy depends on values of R2-R9 used. Never apply voltage steps to base of bipolar transistor.-H. Wurzburg, Integrated Circuit Base-Step Generator, Ham Radio, July 1976, p 44-46.



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