Learning How To Power Circuits

: Description : Notes on different approaches and techniques for powering electronic circuits (with a focus on battery power)--drawing on the knowledge of those who actually understand this arcane art.

: Status : Research—don't take my word for it.

Types of Power Supply IC

This outline of available Power Supply IC options is from "Selecting the correct IC for power-supply applications" from Texas Instruments' Application Notes for Single Channel LDO page:

 Inductive switchers are usually the best choice for
highest efficiency. The inductive
switcher circuits require a switching element,
rectifier, inductor, and input and output capacitors.
For many applications, the solution size
can be reduced by choosing a device where
the IC switching element and rectifier are
internal. These circuits have typical efficiencies
ranging from 80 to 96%, depending on
the load. Switching converters usually
require more space due to the size of the inductor and are
generally more expensive. The switching converter also
causes electromagnetic interference (EMI) radiation from
the inductor and noise on the output due to the switching."

 Low-dropout linear regulators (LDOs) step down dc
voltages by dropping the input voltage across a pass element.
The benefit of this topology is that it requires only three
parts (pass element and input/output capacitors). LDOs
are usually a cheaper solution and are much less noisy
than inductive switchers. The device input current is
equal to the load current, so the efficiency of the solution
is equal to the output-to-input voltage ratio. The drawback
of this solution is the low efficiency for high input-to-output
voltage ratios. All of the power is dissipated by the pass
element, which means that an LDO is not an ideal solution
for high-current applications where the input-to-output
difference is large. These high-power applications require
heat sinking, which increases the solution size."

 Charge pumps step up/down or invert dc voltages using
“flying” capacitors as storage elements and use internal
switches to connect the capacitors in such a way as to
perform the desired dc/dc conversion. Charge pumps are
generally cheaper than inductive switchers and do not
emit EMI, but the output ripple is usually greater than
that of inductive switchers. Charge pumps are limited in
their output power, and the transient response is limited
to the rate at which the flying capacitors can charge.
Additionally, efficiency is usually very low in applications
where the input voltage is near the output voltage."

This document also has a helpful case study working through how to choose one or more power supply ICs for a particular project.

Another issue to consider is the amount of heat the regulator needs to dissipate—this is related to the difference between the input and output voltages:

Where thermal considerations are challenging, another approach is to look at a switching
regulator. Often, the additional efficiency that can be possible with a switching design can
alleviate thermal issues faced when using a linear regulator approach. There are many
considerations in migrating from a linear to a switching design that are beyond the scope of this
application report.

Low-Dropout Regulators (LDOs)

A really good explanation of some of the terms used in discussing LDOs can be found in Understanding the Terms and Definitions of LDO Voltage Regulators--it includes helpful diagrams of how changes in one parameter affects the other parameters. (An almost identical document is Technical Review Of Low Dropout Voltage Regulator Operation And Performance but it does seem a little more technical—although one improvment is it includes larger diagrams.)

While not totally clear, this image (from another application note) visually shows how the voltage dropout affects the regulator's operation:

(Source: Digital Designer's Guide to Linear Voltage Regulators & Thermal Mgmt (LDO) (ti.com))

LDO Links

How to use specific solutions

Here are links to further pages detailing my research into implementing specific power supply solutions:

General links