I met Tom Lawson founder and president of CogniPower at APEC 2013. CogniPower had a small, inconspicuous booth surrounded by giants with huge booths like Vishay. But this company, although small, has a clever concept called “Predictive energy balancing”, a novel technique that Bill Morong and Lawson had developed. The big guys are looking closely at it at APEC.
CogniPower booth left to right: EDN Power editor, Steve Taranovich and founder and president of CogniPower, Tom Lawson
CogniPower introduced their Predictive Energy Balancing audio amplifier here at APEC 2013.. Operating on a completely different principle from other switched-mode amplifiers, this new topology offers the efficiency of the most efficient switched-mode amplifiers with the fidelity of a linear amplifier. They enable better sound for cell phones, tablets and portable media players while extending battery life. These amplifiers can be significantly smaller and less expensive than the amplifiers used now. In addition, the technology is scalable from piezo speakers for cell phones to theater speakers.
Block Diagram of a PEB amplifier. This version resembles the H-bridge configuration of a class D amplifier, but with a different arrangement of components and different controls.
Earlier this year, CogniPower announced it had completed the first prototype of this new type of audio amplifier based on its Predictive Energy Balancing (PEB) technology. Applying its patented PEB technology to switched-mode amplifiers enables more agile and efficient operation. These power amplifiers can drive piezo or dynamic speakers, or can be optimized for any power amplifier application.
According to Founder Tom Lawson, "The PEB amplifier is essentially a bidirectional power converter. Once its capabilities as an audio amp are appreciated, it can be operated as a DC/AC or DC/DC converter. Its bidirectionality even allows it to operate as an energy harvesting device."
CogniPower’s offerings and evolution at the last four APEC conferences
A screen shot from a Yokogawa DLM2000 oscilloscope probing the evaluation board.
A simulation identifying what we see on the oscilloscope
The PEB amplifier demo board was designed with handheld audio devices in mind.
The distortion and noise levels, as tested, came out far better than existing amplifiers for portable audio. That extra fidelity can enable the same PEB amplifier that drives a built-in speaker to drive a high-fidelity headphone output.
Even before attempting to optimize for a high-fidelity application, we measure less than 0.1% distortion at 1 kHz. The noise floor is near -90 dB and the harmonic content is minimal.
Audiophile-quality test equipment would be necessary to fully explore the capabilities of the demo board.
Because the demo system is constrained by the need to operate at the low battery voltage of a cell phone, its performance does not represent the limits of the predictive approach to switched-mode amplifiers. There is every reason to expect that a version of the amplifier running on 5 V instead of 3.5 V could reach 0.01% total harmonic distortion. When the controls are optimized for fidelity, even better performance will be achievable.
The balance point is when supply and demand meet
PEB Control Loops Show Intrinsic Stability
With the balance properly scaled, the voltage on the filter capacitor will equal the regulation voltage after the inductive energy transfer completes. In this way the predictive calculation removes the output filter pole delay from the feedback loop. Each control cycle becomes a self-contained operation, not reliant on previous conditions. Excellent transient response, without sub-harmonic behavior, is the direct result. PEB allows use of theoretic minimum value filter capacitor.
There are many other applications for this architecture such as MRI machines, switched-mode power supplies, Point of Load Converters, LED Lighting, Electric Vehicles, Smart Grid, Computers and File Servers, Solar Inverters, AC-AC Converters---stay tuned for further applications to come
Other related articles on EDN:
New approaches to switched-mode audio power amplifiers (Part 1)