# Capacitor voltage in a 555 timer circuit

If I change a 10V capacitor in a timer circuit with a 16V capacitor, will the circuit turn on longer?

• This seems like an acceptable question from someone learning. It would be improved by posting your schematic, but I don't really see a reason for the down-votes. We've all asked naive questions at some point. Mar 5, 2014 at 17:34

No, unless the leakage of the capacitor was affecting the timing, and in that case it would tend to make the time shorter. Or in the case of a high capacitance (Class 2 or Class 3) MLCC (multilayer ceramic) capacitor (see below).

Assuming you're using an electrolytic (for example, aluminum, polymer or tantalum) capacitor, capacitance does not change significantly with operating voltage. Film caps too, but they are seldom rated as low as 10V. Also NP0 ceramic capacitors. All have quite stable capacitance regardless of applied voltage relative to rated voltage.

The voltage number is a maximum rating, ideally a 10V capacitor at 9V acts the same as a 100V rated capacitor at 9V.

Here is an overview of capacitor technologies (see page 2). Note that none of them, with the exception of some MLCC ceramic capacitors, have a significant voltage coefficient.

There is an exception in that high capacitance MLCC ceramic capacitors CAN have a significant voltage coefficient. One should never use a Y5V or Z5U capacitor for timing, but even relatively stable X7R and X5R capacitors can have significant voltage coefficients. The less stable types also change significantly with temperature and with aging.

In the case of a ceramic capacitor of Class 2 or Class 3 (X7R, Y5V, etc.), using a higher voltage rated capacitor would tend to make the time longer, because the average capacitance would be higher at the operating voltage.

(from the reference above)

• Can I have a reference of what you said for better learning? Mar 5, 2014 at 11:44
• I've added some references and also expanded on the MLCC capacitor voltage coefficient. Mar 5, 2014 at 12:43
• I just used a simple 555 timer circuit and I think the timing does'nt should not affect based on what I read. Mar 5, 2014 at 12:43
• If you use a 10uF ceramic capacitor (and they are now available at reasonable prices) it will be affected. Otherwise, not so much. Mar 5, 2014 at 12:52

The voltage on the capacitor is the breakdown voltage, or the voltage at wich the insulation will break and therefor break the capacitor (http://en.wikipedia.org/wiki/Breakdown_voltage)

The time of the 555 you can change the time by using a bigger/smaller capacitance, or by changing the resistor through which the capacitor loads (T = R* C) where T is Time R is resistance and C is capacitance

• That isn't the correct equation for the 555. It's either T = 1.1RC (monostable mode) or T = 0.693RC (half period for astable mode). Mar 5, 2014 at 12:29