1
\$\begingroup\$

schematic

simulate this circuit – Schematic created using CircuitLab

I want to use this circuit for charging, discharging and creating negative voltages off capacitors for a special application. enter image description here

I will then charge this capacitor series by its negative terminal.

This circuit looks very vell for ceramic capacitors but my question is if it would perform the same for electrolytic polarized capacitors? Since I will be charging the negative voltage capacitors again by the capacitor's negative terminal, I don't know if I should charge those polarized capacitors by the negative terminal.

\$\endgroup\$
3
  • \$\begingroup\$ Sounds like an XY problem. What's the issue with just using a standard DC-DC inverter? \$\endgroup\$
    – uint128_t
    Jan 16, 2017 at 18:33
  • \$\begingroup\$ @uint128_t I can not reveal the whole design but believe me this is necessary. I need a simple answer, is there any harm in using polarized capacitors for this purpose? \$\endgroup\$
    – Alper91
    Jan 16, 2017 at 18:35
  • \$\begingroup\$ You are never reversing the polarity across any cap, so polarized is fine. And... I second uint128_t, you could probably use an off the shelf solution. Even the max232 generates a negative voltage w/ polarized caps :) You can do it too! \$\endgroup\$ Jan 16, 2017 at 19:03

2 Answers 2

4
\$\begingroup\$

The only rule for polarized capacitors, such as electrolytic, tantalum etc., is that a potential on a positive (\$+\$) terminal is higher than the potential on a negative (\$-\$) terminal. If you reverse polarity, the polarized capacitor will most probably blow. That said, the capacitor doesn't know what is "negative voltage". As long as \$V_+\$ is higher than \$V_-\$, you're okay.

As for non-polarized capacitors, such as ceramic, film etc., it doesn't matter how you connect them, as they're not polarized.

\$\endgroup\$
1
  • 2
    \$\begingroup\$ There is one more rule: don't exceed the maximum rated voltage. You should stay well below it. \$\endgroup\$
    – Uwe
    Jan 18, 2017 at 14:40
3
\$\begingroup\$

Since I will be charging the negative voltage capacitors again by the capacitor's negative terminal, I don't know if I should charge those polarized capacitors by the negative terminal.

I'm not sure what this means. Charging a capacitor by a single terminal is nonsensical, it's a two terminal device and current flows through it according to I = C dV/dt, which applies to both terminals.

You can use polarized capacitors if the voltage across the capacitors stays equal or greater than 0V. It's difficult to tell from the plots (and unfortunately CircuitLab doesn't seem to know how to plot the voltage across a component, which is silly), but after playing around with the simulation, it looks like this criteria is met and you could indeed use polarized capacitors.

It's worth pointing out that using polarized electrolytics for this: ceramics will likely outperform electrolytics in numerous specs at this capacitance/voltage, so you might as well use ceramics. Almost certainly smaller, for one.

Edit: after a quick look at Digikey, if you're using SMT components, you're almost forced to use ceramic. There are loads of 1206 1uF ceramics, very few SMT aluminum 1uF caps with a voltage rating above 100V.

\$\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.