555 timer confusion

When a parts list says 555 timer and I go to find one online to order there are so many to choose from and being still new to electronics I have no idea what all the different 555 timers are. What should I be looking for in a 555 timer?

If you just need a 555 in a DIP package, this is all you need:


Excellent block diagram here too

There are a few variations, like CMOS or low-voltage types, and also dual and quad versions, but if the parts list doesn't elaborate, then most likely the standard garden-variety LM555 in a DIP package will do the job:

Thanks for the replies. Do the letters on each side of the 555 have some important bearing on what kind it is?

Initial letters usually signify manufacturer, end letters specify package, maybe technology type.
Do you have an example?

TLC555IP, TLC555CP, SE555P, NE555P, SA555P from Texas Instruments.


this has a data sheet for NE SA LM

only difference I could find with a quick scan of the doc is temperature ratings sa is the best.

might involve maximum frequencies usable as well, but seem to be pretty much the same thing.


The TLC555 is a monolithic timing circuit fabricated using the TI LinCMOS™ process. The timer is fully compatible with CMOS, TTL, and MOS logic and operates at frequencies up to 2MHz. Because of its high input impedance, this device uses smaller timing capacitors than those used by the NE555. As a result, more accurate time delays and oscillations are possible. Power consumption is low across the full range of power supply voltage.

Like the NE555, the TLC555 has a trigger level equal to approximately one-third of the supply voltage and a threshold level equal to approximately two-thirds of the supply voltage. These levels can be altered by use of the control voltage terminal (CONT). When the trigger input (TRIG) falls below the trigger level, the flip-flop is set and the output goes high.

These devices are precision timing circuits capable of producing accurate time delays or oscillation. In the time-delay or monostable mode of operation, the timed interval is controlled by a single external resistor and capacitor network. In the astable mode of operation, the frequency and duty cycle can be controlled independently with two external resistors and a single external capacitor.

The threshold and trigger levels normally are two-thirds and one-third, respectively, of VCC. These levels can be altered by use of the control-voltage terminal. When the trigger input falls below the trigger level, the flip-flop is set, and the output goes high. If the trigger input is above the trigger level and the threshold input is above the threshold level, the flip-flop is reset and the output is low.

Component calculator tool too:

Component calculator tool too:
TLC555CALC Calculation tool | TI.com

Well, that's pretty cool, except that I don't see any link to use to download it.

You're right, doesn't seem to be any way to get there, all the links just seem to go in circles.

Thanks everyone for helping out. There is some info here that is rather over my head right now but at least I now have something to work on. Every little bit helps.

I found this book really helpful:


As with Forrest Mims’ other books, it’s presented in a hand-drawn “engineering notebook” style. I happen to enjoy this approach, but it rubs some people the wrong way . There’s a lot of good information here, and IMHO it’s a steal at $13USD.