The 555 integrated circuit (IC) is one of, if not the, most popular chips ever manufactured. Over the years, it has been independently manufactured by more than 10 manufacturers and is still in current production. After over 50 years, this amazing little circuit has withstood the test of time.
Originally conceived in 1970 and created by Hans R. Camenzind in 1971, it has been estimated that over 1 billion of these ICs were made in 2003 with no apparent reduction in demand. It has been redesigned, improved, and reconfigured in many ways, yet the original design can be bought from many vendors. The design of this chip was right the first time.
It has been used in everything from toys to spacecrafts. Due to its versatility, availability, and low cost, it also remains a hobbyist favorite. One of the secrets to its success is it is a true black box. Its symbolized schematic, shown in Figure 1, is simple and accurate enough that designs using this simplification as a reference tend to work the first time.
You don’t need to understand every transistor in the base schematic to make it work.
The 556 IC is a 14-pin packaged IC with two independent 555 timers and is a quad 555 timer in a 16-pin package.
What few weak points the original bipolar design has have been addressed by redesigns into complementary metal-oxide semiconductor (CMOS) technology, with its dramatically reduced current and expanded voltage operation. Yet, the original version remains.
Originally conceived as a simple timer, the 555 has been used for Schmitt triggers, oscillators, one-shots, waveform generators, VCOs, FM discrimination, and a lot more. It really is an all-purpose circuit.
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