Seeking Proposals for Capacitor, Inductor or Resistor Projects

Having worked at a capacitor company, I can suggest projects like these where the caps are, relatively speaking, critical. Or at least, they are not an after-thought.

Power Banks

Sometimes these are called "hold-up" circuits. Situations that require a large bank, or reserve, of energy but batteries, are not suitable. A common one is

UPSes (uninterrupted power supplies) which may have large banks of aluminum electrolytic or supercapacitors that provide energy until the batteries can start supplying it. SSDs are another one. SSD drives generally have large capacitor banks so that their TOC can be flushed to flash memory when the rails drop.

Variable Frequency Drives

With the popularity of electric vehicles, "DC Link" capacitors have been popular as well. In a motor drive (or inverter, or VFD) you typically have an incoming voltage and frequency (aka supply) with an output voltage and frequency (aka output). In between are inverters to convert the incoming AC (if it is AC) to DC and then the output stage is DC to AC. That conversion allows for changing the output's voltage and frequency. In between the stage sits huge capacitors. For electric vehicles, windmills, and solar panels this can be 10s of thousands of microfarads. But any situation where you are driving something with variable speed, you need a capacitor for more than just "decoupling."

IoT / Harvesting

On the smaller end of the scale are IoT devices. In this case, I mean the types that harvest energy from the environment. They might include a piezo element that captures energy from vibration. Or, more commonly, solar panels. Storing that energy in a battery is sometimes costly, regarding power, because of the electrochemical process. So instead, energy is stored in a capacitor. The challenge here is designing a capacitor bank that has very low leakage. (In this situation, ceramics are good, (wet) aluminum electrolytics are not.)

Switched Capacitor Power Supply

An idea that keeps floating around power supply engineers is to eliminate inductors by using a "switched capacitor" design. It might be interesting to look at a DC-DC converter for a project like a small robot (something with high current motors and relatively high current microcontroller). You could build a traditional inductor based DC-DC converter as well as a switched capacitor design to compare efficiency, size, cost, etc.

Just a few to think about. Hopefully, someone can build something more creative on top of those.

Hi James,

You said "An idea that keeps floating around power supply engineers is to eliminate inductors by using a "switched capacitor" design" - do yuo know why that is?

Perhaps inductors, due to their series resistance, are inherently less efficient at storing/returning energy than the best electrolytics ?  Maybe they are also heavier - adding net weight to the design and also being more at risk of damage if the device is dropped. I dropped my LED totch a few weeks ago whilst under the car, the torch stopped working and upon dismantling I found an inductor as been ripped off the PCB by the force of the impact. When I repair it I will be adding a good blob of adhesive or encapsulate it completely.

On a reliability viewpoint, I would have thought that inductors are far more reliable than electrolytics (blown ends, high ESR).

Rod

... eliminate inductors by using a "switched capacitor" design" - do yuo know why that is?

It is the usual design reasons, cost, parasitic losses, and physical size. Also, if you look at a coil manufacturer, the reason there are so many variations within a catalog series is that some application required a minor tweak. As a result, they add the "new" part number to the catalog. It makes multi-sourcing the inductor difficult because they are effectively custom designed.

The sourcing concern may not be an issue in most applications. But for the ones pushing the limits of power density, it is a significant problem.

On a reliability viewpoint, I would have thought that inductors are far more reliable than electrolytics

The applications where this technique might work wouldn't use electrolytics. It'd be high-frequency wide bandgap converters using ceramics. Large banks of C0G ceramics.

... eliminate inductors by using a "switched capacitor" design" - do yuo know why that is?

It is the usual design reasons, cost, parasitic losses, and physical size. Also, if you look at a coil manufacturer, the reason there are so many variations within a catalog series is that some application required a minor tweak. As a result, they add the "new" part number to the catalog. It makes multi-sourcing the inductor difficult because they are effectively custom designed.

The sourcing concern may not be an issue in most applications. But for the ones pushing the limits of power density, it is a significant problem.

On a reliability viewpoint, I would have thought that inductors are far more reliable than electrolytics

The applications where this technique might work wouldn't use electrolytics. It'd be high-frequency wide bandgap converters using ceramics. Large banks of C0G ceramics.

James, thank you for all the useful info.