At last digital technology is coming to the power supply industry, always a stronghold for analog control. In the last few years there has been increasing activity in the development of digital-control power supplies, equipped with digital interfaces and using digital processing for output voltage feedback control. But these have never really penetrated the market. With the exception of large-scale supplies for communication systems and a few similar applications, very few digital supplies are in commercial use.
Bellnix Co Ltd of
Japan has developed the BDZ series of DC-DC converters (see Fig) to
change this situation, opening up a pathway for evolving from analog
power supplies to digital. The products are point-of-load (POL)
converters for devices such as field-programmable gate arrays (FPGA)
and application-specific integrated circuits (ASIC).
Inside, the POL converter is a digital power supply, which has a PMBus digital interface and digital technology to implement output voltage feedback control. For users who don't want to use it as a digital supply, though, it has the features needed for use as an analog supply, too.
For example, to change the output voltage in a standard digital power supply, a command must be issued by the host microcontroller and passed through the PMBus to set the new voltage. The BDZ series, however, uses an innovative circuit configuration to enable external resistors to be used to set the output voltage, as is the case with analog supplies. Even better, basic performance - including output voltage stability, conversion efficiency and load response - is about the same as it is with currently available analog power supplies. The price is also about the same as that of analog designs.
Bellnix developed the POL converter, according to Shotaro Suzuki, president of the firm, because, "Eventually, all power supplies are going to be digital. And if that's the case, it makes sense to get into the market with digital supplies before the competition, get customer feedback early, and develop our next product."
The transition path mapped out by Bellnix from analog to digital supplies begins with marketing the newly-developed POL converter as an analog supply. Many manufacturers using the analog power supply will actually be getting a disguised digital supply.
The next step is to educate users in the merits of digital power supplies, and gradually increase the number of analog supply customers switching to digital supply functionality. According to Bellnix's Suzuki, "The digital power supply function that looks most attractive to equipment manufacturers is probably fine control of output voltage, but this function is really only needed when the supply voltage drops to about 1V. It is difficult to control analog supplies to 1V+/-1%."
by Katsumi Yamashita
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