There’s
Gold In Power Supplies!
Why 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.
Almost every consumer electronic device manufactured has at least one power supply (PSU). The same is true for commercial electrical devices. 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. High power consumer devices such as electric ovens and dryers require power supplies for the electronic control circuitry.
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.
This article classifies the various power supplies in use today, and makes suggestions about where to obtain and how to enforce patents.
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. The transformer and rectifier convert the AC to crude DC, and the (optional) regulator controls this voltage to a precise tolerance if needed. Although the linear supply has been around since electricity was first used commercially, it has the disadvantages of high cost and high weight. The high weight comes from the fact that the lower the frequency, the more iron and copper are needed in the transformer. The high cost is largely that of the iron and copper metals used. However, linear supplies still have their uses in a laboratory setting.
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 then be used, although the iron has to be replaced with ferrite, a material made from sintered metal oxide powder. While ferrite has a higher cost per pound than iron, it is still cost effective for use in switched mode power supplies. The difficulty comes in generating the 50,000Hz frequencies. This is generally done using high power field effect transistors (FETS), although bipolar transistors are also used. These transistors are turned on and off at 50,000 times per second by the drive circuitry. Sensing the output voltage, then using this to modulate the drive transistors regulates the output voltage. As the load increases, the “on” time of the transistors is increased to keep the output voltage constant.
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:
Buck
Boost
Polarity Inverting Boost
Push-Pull
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, although many different topologies could be used for any one particular application. For example the Buck mode supply is often used on computer boards. Here a poorly regulated 12-volt supply must be reduced to a precise 3.3 volts, without losing too much power as heat. The Buck mode technology does this very well. It has the advantages of very simple magnetics (a single inductor and no transformer), and high efficiency (80% or more). The efficiency is important not only for conserving power, but also for avoiding excessive heat dissipation on the board. The Buck mode is also popular because inductors are available off the shelf at low cost, whereas transformers used in other topologies have to be custom wound for each application. The need for a custom wound transformer puts the cost up considerably for all but the largest production runs.
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. The steps in an offline converter are as follows:
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.
Many manufacturers eschew the use of ICs because of the high cost when compared to discrete components. Also, each type of IC tends to be unique so that second sourcing of parts can be difficult. No manufacturer wants to be held hostage to a single sourced part.
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, free running supplies are popular for electronic flash units, where the goal is to recharge the flash in the shortest time possible.
The more popular alternative is to use a clock generator to produce an accurately controlled frequency, and design the ferrite with a safety margin to prevent saturation and overload. This gives a higher efficiency, but with a higher parts count and a heavier and more expensive transformer. It is used where steady power is needed for long periods, such as in a DVD player. The clock itself is often contained on an IC, and can even be crystal controlled if extreme accuracy is needed.
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 the current through the switching device, and switching off if it gets too high. This is known as short circuit protection. There are, of course, several different types of short circuit protection. Foldback protection will shut down the supply if the maximum current is exceeded. Current limiting will keep the maximum allowed current flowing, reducing the output voltage to whatever value is necessary.
Short circuit protection is fairly expensive, because a current sensing resistor and several other parts are necessary. It also reduces the efficiency of the PSU, which may be an issue for some applications. For a device such as a VCR, where everything is internal, short circuit protection is often not used. When a fault occurs, it simply takes out the power supply along with everything else. A simple fuse will provide fire protection, but will not protect the electronics. This is because most switching devices will fail in a few microseconds, while fuses take tens of milliseconds to operate. For devices such as chargers, the user might accidentally short the output. In this case it is wise to incorporate short circuit protection, although this is not always done for reasons of cost.
A search of the USPTO database reveals that there are about 500 power supply patents as of September 2010. Some of these patents become available when business assets are liquidated, or when a business is taken over. But if you are considering acquiring a patent in this way, there are a few caveats: -
Another example that I ran across was a power supply with a special paint job. The inventor did not call it a paint job, but rather an ultra violet reactive industrial coating. But there was no doubt that he just meant fluorescent paint on one of the fan blades. And since this was filed as a utility patent rather than a design patent, that might well raise validity issues in an infringement suit.
3. How good are the claims? The claims are at the very heart of an infringement suit, yet often the inventor added them as an afterthought. The inventor is often motivated by advancement of his career rather than hopes of a lawsuit, and neither knows nor cares how to write claims. As attorneys know all too well, a carefully crafted set of claims can play a pivotal role in a lawsuit.
A Suggestion For
Acquiring Patents
There are a lot of power supply patents out there. Which one is best for you? Unfortunately, the bottom line is that you may not have a choice. Licensing organizations tend to acquire their patent portfolios in bulk, with little control over the specifics of each patent. The hope is, of course, that some of the patents in the portfolio may be valuable.
But there is another approach, the so-called “lone gunman” strategy. An inventor is simply hired to invent a suitable device, and the patent and particularly the claims are carefully crafted by the licensing organization itself in order to optimize the financial value of the patent. Also, it is generally cheaper to hire an inventor than it is to purchase a company that holds the relevant patent. The power supply has so many subtle variants, and yet is so ubiquitous, that it could have been tailor made for the lone gunman strategy. Emmanuel Avionics, Inc. is in the business of building electronic prototypes, and we have decades of experience with power supplies of all types. By all means contact us at www.emmanuelavionics.org if you would like to discuss a custom patent.
Duncan G. Cumming,
Ph.D. (Camb.)
is an electrical engineering expert who specializes in Power Supplies and
Prototype Design.
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