asymmetric timer

Posted on Feb 6, 2014

A simple astable timer made with the 555, the mark (on) and space (off) values may be setindependently. The timing chain consists of resistors Ra, Rb and capacitor Ct. The capacitor, Ct charges via Ra which is in series with the 1N4148 diode. The discharge path is via Rb intointo pin 7 of the IC. Both halves of the timing period can now be set inde

asymmetric timer
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pendently. Please note that the formula for T(on) ignores the series resistance and forward voltageof the 1N4148 and is therefore approximate, but T(off) is not affected by D1 and is thereforeprecise.

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