TITLE

Current source enables op amp's output to go to ground

AUTHOR(S)
Chan, Frank
PUB. DATE
August 2004
SOURCE
EDN;8/5/2004, Vol. 49 Issue 16, p84
SOURCE TYPE
Trade Publication
DOC. TYPE
Article
ABSTRACT
This article discusses the LM324 as a cost-effective choice for an optical amplifier, specially when one needs to apply ground-level inputs. Although its output purportedly includes ground, its poor current-sinking capability limits the applications. One can add an external current-sinking circuit to bring the usable output voltage down to the millivolt level. A design uses a 2N2222 transistor for its low saturation voltage. The output characteristic of the added transistors, Q1 and Q2. Using this current source, the output voltage is linear down to 22 mV above ground. One can configure a leftover optical amplifier as a voltage comparator to cut off the current source when the output voltage is higher than 1 volt.
ACCESSION #
14078967

 

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