555 Capacitor Tolerance Adjustment circuit


Posted on Feb 7, 2014

The 555 Timer shown below is configured as an 555 Astable Multivibrator previously discussed. However additional components have been added to enhance the operation of the circuit. As soon as the circuit is powered up the 555 will begin producing a square wave determined by the value of Capacitor C1 and Resistors R1 and R2, as determined by the ti


555 Capacitor Tolerance Adjustment circuit
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ming equation below. This particular circuit uses a few additional [optional] components to allow for adjustment or compensation for variations in the tolerance of the timing capacitor [C1]. The 555 Integrated Circuit is an extremely accurate device. However it`s output is only as accurate or stable as the external components used. Standard value resistors normally come with a tolerance of either 1% or 5%, of course other resistor tolerances are available. For more information refer to Resistor Values, Tolerance and Package Sizes. Capacitors on the other hand came in a large variety of tolerances which could change by the quality of the part or by the dielectric used. There are three common capacitor types used with a 555 times, Ceramic, Tantalum, and Electrolytic dielectric. However regardless of the style used, the best tolerance value will be in the range of 10 to 20%. Also see Capacitor Dielectric Materials and their characteristics. A potentiometer [R3] can be placed on the Threshold pin to adjust the 2/3 Vcc line [recall that the potentiometer will be in parallel with the bottom two 5k resistors]. This effectively changes the trip point of the internal resistor ladder. The additional potentiometer can be used to change the trigger point and be used to compensate for variations in the Trigger Capacitor [C1]. As each new circuit is fabricated and a different capacitor used the potentiometer can be changed to adjust the...




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