Electronic – Selecting a Cap Value for Offsetting

capacitor

How should I select an Electrolytic capacitor to get an Offset for an Input.
I have a Sinusoidal input wave (around 0, at 10V amplitude above and below 0), and want to offset it by 20V above 0.

Best Answer

For this specific scenario you need to consider:

  1. Working voltage: you will have a 20 V difference between the two sides of your capacitor. You probably want to de-rate and choose a cap with at least 40 V WV rating. You should also consider turn-on and turn-off transients and be sure not to exceed your cap's WV rating at any time.

  2. Capacitance: You want the capacitor to present a low impedance at the frequency of your ac signal. "Low" means low enough compared to the source and load impedances that it doesn't affect the circuit operation. Since \$X_C = 1 / (2 \pi f C)\$, you want a larger capacitor value the lower the frequency of your signal.

Of course, as with any other time you're selecting a capacitor, you need to look at operating temperature range, reliability, physical size, etc.