555 timing capacitors

[ee851]

In his tutorial, Ian Purdie says to avoid using either electrolytic
or ceramic capacitors for timing,
http://www.electronics-tutorials.com/devices/555.htm
but rather a low-leakage capacitor.

What kind of capacitor, then, would you suggest ?    Tantalum?   Or something else?

I only ask because I don't recall hearing David address this issue in his 555 PWM project video.

[w2aew]

The reason for the general statement is because electrolytics are leakier than other types, not as stable with temperature and time, etc. So, if you need precise, repeatable timing in a circuit, you would try to use a more low leakage, stable capacitor type - like a teflon, polystyrene, polypropylene, etc.  The problem is that these caps are generally not available in large capacitance values.  However, a 555 is not a precision chip, so it is not used in precise timing applications, so the use of non-ideal capacitors (from a leakage standpoint) is usually not a problem.

[c4757p]

When I use a 555, I generally use a cheap film capacitor for timing. They're not that expensive, and the timing is more predictable (yes, I have verified this), especially with high resistance values. They do cost more than a ceramic or electrolytic, but it's not exactly like my circuit is littered with 555s and I'm pissing money away by using a better capacitor here or there.

That said, a ceramic or electrolytic will usually work just fine, especially if you don't mind determining timing experimentally by trying different values instead of mathematically and expecting it to work right the first time.

[SeanB]

If you are really stuck with using an electrolytic use a high voltage one, 50, 100V or so, even though you are only running on 5V. The thicker oxide layer means lower leakage at low voltage, even though the unit physically will be larger.

[ee851]

Thank you, gentlemen, for your advice and recommendations.