0
\$\begingroup\$

As the title says, I have capacitors rated 100VDC 18pF. Can I use these on a board that uses 5V Max ?

I can't really find any direct answer to that question.

What I want to do is to put a crystal to a chip and hopefully use these caps on the crystal.

\$\endgroup\$
1
  • \$\begingroup\$ Rule of thumb for electronic design: If it does more than what you need, even if it does much more than what you need, but it fits, and the price is right, then use it. \$\endgroup\$ Commented Jul 20, 2015 at 16:56

3 Answers 3

3
\$\begingroup\$

The voltage rating on a capacitor is a maximum value; you can use it in a lower voltage circuit just fine.

\$\endgroup\$
1
  • \$\begingroup\$ thanks for quick answer! was suspecting that but can't be sure if not electronics guru :) \$\endgroup\$
    – Deko
    Commented Jul 20, 2015 at 15:35
2
\$\begingroup\$

While Nick Johnson's answer is correct, there is a faint possibility that you might want to consider the following:

In the aerospace/hi-rel world, it is known that using tantalum electrolytic capacitors which are grossly overrated is not ideal. 50-volt capacitors used at 5 volts show a significantly higher failure rate than when used at 35 volts. As far as I know, the chemistry details are not accepted, and it's a pretty specialized (and easily avoided) problem, so there hasn't been much research on it.

In your case, you are talking about ceramic capacitors, and these do not have the same problem. As it happens, making lower-voltage versions just wouldn't save much, and these sorts of capacitors were developed back in vacuum tube days when voltages were much higher, so 100 V ceramics are very common. It's more a matter of inertia than anything else.

\$\endgroup\$
5
  • \$\begingroup\$ Not doubting that was true somewhere sometime, but the last manufacturer's recommendation I read was for at least 3:1 voltage overrating for tantalums used as bypass capacitors. Maybe that means you shouldn't used them at all. Fortunately, ceramics are getting good enough we don't have to use them very often anymore. \$\endgroup\$ Commented Jul 20, 2015 at 17:16
  • \$\begingroup\$ @SpehroPefhany - hi-rel is weird. You also do things like putting resistors in series with tantalums to keep the surge currents down. \$\endgroup\$ Commented Jul 20, 2015 at 17:20
  • \$\begingroup\$ That's recommended too (in their &**&* fine print).. something like several ohms IIRC. Makes it pretty useless as a low-Z bypass. \$\endgroup\$ Commented Jul 20, 2015 at 17:22
  • 1
    \$\begingroup\$ @SpehroPefhany - Yeah, but it also keeps them from occasionally bursting into flame. Long live MLCs! \$\endgroup\$ Commented Jul 20, 2015 at 17:37
  • \$\begingroup\$ One from today (out of a fancy $8K instrumentation board we bought). Just toasty, no flames. \$\endgroup\$ Commented Jul 20, 2015 at 17:52
0
\$\begingroup\$

Yes above answers are right.Rated voltage is the maximum value at which capacitor can be operated and is safe to use at voltages below that

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.