Electronic Design

New Approach To Backup Power Raises Levels Of Redundancy

Enterprise systems require varying levels of backup power protection. In systems where the cost of a UPS can't be justified, designers may rely on a second phase of the ac mains for backup power. Such instances will need ac switching equipment. Other systems require a portable backup source, which leads to use of dc sources like batteries and associated charging and power-conversion devices.

In developing its Power Guardian technology, Transistor Devices has created an unusual backup power system that accommodates both ac and dc power sources. Yet the system takes redundancy to another level by incorporating an internal bank of nickel-metal-hydride (NiMH) batteries. Power Guardian includes circuitry for switching among the various power sources, a power-factor-corrected (PFC) boost circuit and rectification for the ac sources, dc-dc conversion, and charging for the internal batteries.

The company is developing this technology into a 1U rack-mountable unit that will provide 1000 W of dc output. That power can be supplied as a single output at -48 V or distributed among multiple outputs ranging from 1.8 up to 12 V. A formal product introduction is slated for the first quarter of next year.

The Power Guardian design accepts inputs from two ac sources as well as an external dc source (see the figure). The "preferred ac" source will typically be one phase of the ac mains. The "backup ac" may be another phase of the ac mains, an external UPS, or other source. The external dc source could be a battery, a fuel cell, or a local dc bus.

In operation, the ac-input line selector monitors the preferred and backup ac sources. If the preferred source fails, it switches over to the backup ac. Should that source fail, Power Guardian will take power from the external dc source (likely a 48-V battery). If the charge on the external battery drops to 38 V, or if no battery has been connected, the low-voltage disconnect circuit switches out the battery, and power is derived from the internal battery bank. The internal batteries provide eight minutes of runtime under full load.

For more information, contact Garry Engesser at (631) 471-7492, ext. 122, or [email protected].

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