Portable Device Power Supply Design Strategy-EEWORLD

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From the perspective of product definition planners, the two most important power design indicators for portable devices are continuous working time and standby time. So, for a system design engineer responsible for product development, what aspects should be taken to optimize the performance of these two indicators?

Obviously, we should first consider how to increase the amount of power supply. If we can solve this problem at the source, that is, find a battery with higher power density than the existing lithium-ion battery , then the continuous operation time and standby time performance of all popular portable devices can be greatly improved.

In this regard, the industry has both good news and bad news. The good news is that fuel cells with a power density 1.5 or 2 times higher than existing lithium-ion batteries are close to commercialization. For example, MTI Micro, a US fuel cell supplier, has overcome the three major obstacles on the road to commercialization, namely the water discharge problem of fuel cells, the use of cheap methanol as a raw material, and miniaturization. Samsung has developed prototypes of digital cameras and mobile phones based on fuel cells, and Toshiba also launched the Gigabeat MP3 player using micro fuel cells in 2002.

However, the bad news is that many people in the industry still think that the price of fuel cells is still a bit expensive, which is difficult for consumer electronics manufacturers with increasingly slim profits to accept immediately. For example, Andy Khayat, director of marketing for Micrel power products, said: "Although high-performance fuel cells for consumer electronics have been launched for several years, their prices are still too high, and people are worried about the potential reliability problems of flammable liquid fuels. Therefore, the representative consumer electronics market has not accepted fuel cells, and it will take longer for them to be accepted by the mass consumer electronics market, and it may take until after 2015."

Tony Armstrong, product marketing director of Linear Technology's Power Products Division, also believes: "Although fuel cells have proven their effectiveness in the laboratory, and some have even achieved commercialization. However, due to the difficulties in managing their thermal and update issues, their success is limited. In fact, from a commercial point of view, fuel cells are still some distance away from becoming an ideal power source for mobile computers."

It is precisely because of such practical problems that the industry is currently focusing on reducing power consumption, improving power conversion efficiency and reducing static current/ leakage current .

In order to reduce power consumption as much as possible, system development engineers generally adopt two methods at the same time: one is to optimize the circuit design as much as possible; the other is to find alternatives with the lowest power consumption among similar devices as much as possible.

In order to maximize the power conversion efficiency, system engineers generally use two methods at the same time. One is to use devices with high power conversion efficiency as much as possible, such as replacing Class AB amplifiers with Class D amplifiers and replacing LDOs with switching DC-DC converters. The other is to use various measures (PWM/PFM modulation mode conversion, changing the supply voltage and operating frequency, etc.) to improve the power conversion efficiency under various load conditions.

The main purpose of reducing quiescent current/leakage current is to maximize standby time. In this regard, the only method available to system engineers is to use similar devices with lower quiescent current/leakage current as much as possible during design.

In addition, another power supply issue that should be paid special attention to is electrostatic discharge ( ESD ) protection. If ESD protection is not up to standard, many products cannot be exported to the important European, American and Japanese markets. Therefore, ESD control is a necessity, not an option, for portable products. ESD is a common problem faced by the entire electronics industry. Electronic products will be affected or even damaged by ESD in every link of design, production, packaging, testing, and transportation.

However, despite the importance of ESD, it does not mean that resources must be evenly allocated to prevent the impact of ESD in the manufacturing and design processes. In fact, it is not wise to spend too much resources on ESD protection at the component level. We should focus more on ESD protection at the system level.

Of course, for system design engineers, system-level ESD protection mechanisms should not only make electronic components and systems more resistant to ESD impacts, but also take into account cost, technology and customer needs.