RESISTANCE TRIMMING CIRCUIT AND TRIMMING THEREOF

摘要

PROBLEM TO BE SOLVED: To enable the readjustment by constituting a tripping circuit part with a fuse-diode parallel circuit and applying a breakdown voltage to short- circuit diodes. SOLUTION: To readjust an R1-R1a parallel circuit, a first trimming flows e.g. a current of about 100 mA between adjusting terminals T1, T2 to blow a fuse and open the circuit, resulting in that the resistance of this part is R1. A second trimming for readjusting the circuit part to return to the original R1-R1a parallel circuit applies e.g. a backward (pulse) voltage of about 5 V between the terminals T1, T2 i.e., Zener diode D1 to cause the junction breakdown and flows a pulse current of about 500 mA to short-circuit the Zener diode, resulting in the recovery to a parallel circuit equivalent to that when the fuse exists. Thus the re-trimming is possible.