What's in a 555?

[carbonzit]

Posting this for general edification, as well as entertainment.

Now, the "old regulars" here all know this, but did you know what's actually inside that most venerable of all ICs, the 555 "timer" chip?

It must be, what, an oscillator? and some fancy divide-down circuits? after all, it's a timer, right?

I found this block diagram in an old book (Integrated Circuits for Electronics Technicians, by Edward Pasahow, published 1979 (!):

**broken link removed**

As you can see, there's not a "timer" to be seen here. But it is a damned clever arrangement of other components (two comparators, a resistor ladder, a flip-flop, an inverter and a driver transistor) that can be arranged in myriad ways by the user to perform all sorts of tasks. And that 1/3-2/3 voltage divider: pure genius!

I even saw a complete radio receiver (AM) on the web, made using a single 555. I'll have to find it again.

 

[jpanhalt]

This application note explains it quite well, see page one.

John

View attachment 555AN.pdf

 

[atferrari]

One day you will discover why the "555".

 

[carbonzit]

Hmm; according to this (The 555 Timer IC: An interview with Hans Camezind - the designer of the most successful integrated circuit ever developed), the "555" name as chosen totally at random:

How did the 555 name come about?
Signetics had “500” numbers, and the earlier product I worked on was the 565, 566 and 567. It was just arbitrarily chosen. It was Art Fury (Marketing Manager) who thought the circuit was gonna sell big who picked the name “555”.

So do you know differently?

 

[atferrari]

The three resistors have the same value. 5K IIRC.

 

[davenn]

The three resistors have the same value. 5K IIRC.

yeah thats been quoted before, but dismissed by the designer

 

[Brevor]

All this talk about 555's got me thinking. I have been involved in electronics professionally for 35 years, and have worked for several companys. In all the jobs I have had we have never used a 555 in any of our designs. I was just curious how often other professionals here have used them in real product designs ?

 

[tom_pay]

I know what is in a 555......

Smoke!!!

and I have a nasty habit of letting it out!!!

 

[upand_at_them]

There was an article in Nuts & Volts recently about reviving the 555 with new versions. Oooo, racing stripes.

 

[carbonzit]

I know what is in a 555......

Smoke!!!

and I have a nasty habit of letting it out!!!

Well, of course that's the real, technical explanation. (Actually, we tech types usually refer to it as the "magic smoke".) I was just trying to give the layperson's version.

 

[KeepItSimpleStupid]

The 555 is too finicky for me. For an oscillator its OK. As a timer it SUCKS.

OK guys. Can anyone build a FF out of a single supply OP amp(s)?