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There's Gold in Power Supplies!

It is no secret that power supply related patent disputes can be highly lucrative. And it is not hard to see why - power supplies are ubiquitous. If you are thinking of filing a patent infringement suit, I invite you to consider the intellectual property related to power supplies.

Almost every consumer electronic device manufactured has at least one power supply (PSU). The PSU takes 110 VAC (or whatever voltage is used in the applicable country) from the wall receptacle, and converts it to the low voltage DC needed by the electronics of the device itself. Even battery-operated devices often use PSUs to regulate the battery voltage to the precise tolerances required by modern electronics.

Inventors have been concerned with power supplies for decades, and many dozens of patents have been granted for their different variants. These patents are often a cause of dispute, and power supply patent cases frequently have the potential for multimillion-dollar settlements. If some mass produced consumer product such as a computer monitor screen uses a power supply circuit that infringes on your client’s patent, the dollar volume of the product is often in the hundreds of millions of dollars, giving a very high recovery potential for an infringement suit. Many different products use the same PSU circuitry, meaning that a single lawsuit can accuse many different products sharing a common PSU. Also, the demarcation lines between different types of PSU are not very clear, making it feasible to group accused products even if the exact PSU circuitry is slightly different in each one. No wonder the power supply infringement suit can be so lucrative.

Types Of Supply


Power supplies fall into two broad types, linear and switched mode. The linear supply has been around the longest, and it consists of a transformer running at 60Hz (the usual line frequency found in residences), a rectifier, and a regulator. This type is rarely used because of its relatively high cost and weight.

Switched Mode

Most modern devices use switched mode supplies. The operating principle is that much higher frequencies are used, typically around 50,000Hz. A much lighter transformer can be used, and electronic switching both drives and regulates the transformer.


A great deal of human ingenuity (and associated patents) has been expended over the years in devising different configurations of ferrite, copper, and semiconductors. These configurations are known as power supply topologies, and the following ones are in common usage today:

Polarity Inverting Boost
Forward Converter
Half Bridge converter
Full Bridge Converter
Flyback Converter
Resonant SCR
Cuk Converter

Each of these types has a specific niche in the PSU market. For example, the buck mode supply is generally used on computer boards, where a crude 12 Volt supply must be converted to a precisely regulated 3.3 Volt source.

Offline Converters

An offline converter takes AC supply from a wall receptacle, and converts it to precisely regulated DC. The word offline is not the opposite of online; it simply means that the electricity is taken off the line (also known as the mains) supplying the residence. Most products that plug into a wall receptacle, such as TV sets, monitors, DVDs, VCRs, personal computers and so forth use offline converters. Switching electronics drives a transformer, which both changes the voltage to the desired value and provides isolation from the line voltage.

Integrated Circuits v. Discrete

An obvious way to reduce the parts count of a power supply is the use of an integrated circuit (IC). Patents owned by the semiconductor company that designed the IC generally cover these. Patent litigation possibilities open up if counterfeit chips are made that violate the patent. There are also some patents that apply to improvements in power supplies even though they include patented integrated circuits.

Clocked v. Free Running

Early switched mode power supplies were free running. That is, the frequency was not precisely controlled but rather allowed to run at its own natural value so as fully to saturate the ferrite. This guaranteed full utilization of the ferrite, but it meant that the frequency varied with load which sometimes caused interference and regulation problems. Today the clocked supply is more popular, where a clock circuit provides a fixed conversion frequency.

Short Circuit Protection

If the output of a power supply is accidentally short circuited, then a large current flows through the switching device, destroying it. It is possible to protect against this eventuality by sensing and controlling the current, although this adds to the cost. It is typically done in products such as chargers, where the output might inadvertently be short-circuited.

By Emmanuel Avionics, Inc.
Electronic Design, Intellectual Property, and Litigation Support.
ABOUT THE AUTHOR: Duncan G. Cumming, Ph.D. (Camb.)
Duncan G. Cumming, Ph.D. (Camb.) is an electrical engineering expert who specializes in Power Supplies and Prototype Design.

Copyright Emmanuel Avionics, Inc.

Disclaimer: While every effort has been made to ensure the accuracy of this publication, it is not intended to provide legal advice as individual situations will differ and should be discussed with an expert and/or lawyer.For specific technical or legal advice on the information provided and related topics, please contact the author.

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