Connecting dropping resistors in series with resistive loads often leads to significant energy dissipation. In AC circuits, using dropping capacitors can greatly minimize this energy loss. For low-power supplies, these capacitors can even serve as a viable alternative to transformers.

In electronic design, the problem of voltage drop occurs frequently. A common-sense practice is to avoid high dropout values on resistors or linear regulators, just due to the large amount of energy (and heat) that would be dissipated — and wasted.

drop cap fig1
Figure 1: Starting from relatively low input voltages, in some cases the use of dropping resistors is still
simple and cost-effective, even from an energy point of view.

A First Practical Example

In AC circuits, the component most commonly employed to induce a large voltage drop is the transformer, but it is bulky, heavy and relatively expensive. To look for a possible solution, let’s start from the practical example shown in Figure 1. It’s a vacuum...