If you have a signal that passes through a capacitor or transformer, you will lose the DC portion of the signal. What do you do? If you need it, you can restore the DC bias using various techniques, as [Sam Ben-Yaakov] shows in a recent video.

These types of circuits were common in analog TVs, and, in fact, [Sam] shows the schematic of a TV to explain the need for the DC level. In that case, a vacuum tube diode does the work, but a solid state one will do the same job.

Of course, using a diode means dealing with a diode drop, and there are a few ways to handle that. [Ben] shows the circuits and Spice simulations, explaining how they work.

It is common to see level restoration after DC blocking capacitors. However, transformers are another common case where you lose DC signal information. His examples are also good illustrations of how to model transformers in Spice, a topic we’ve discussed before. Want more basics on transformers? We can help there, too.