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Paralleling power supplies: Benefits and drawbacks

Posted: 23 Mar 2016 ?? ?Print Version ?Bookmark and Share

Keywords:paralleling? power supplies? resistors? amplifier?

Nonetheless, having this load-line output characteristic permits multiple DCM outputs to be placed directly in parallel, while each still has its own error-amplifier control-loop still active. The distribution of the load current over the DCMs in the array is ideally equal if all DCMs have the same external (real) path resistances to the load, have the same trim setpoint, and are at the same temperature. Parallel DCMs thus behave like a single DCM but with a higher output current (figure 4).

With the DCM converter family, temperature changes in individual units are not a problem due to their negative voltage-temperature coefficient. If one supply is loaded more than the others, its temperature will rise relative to the others, which in turn will cause its output voltage to decrease. Since the output voltages of the other parallel DCMs match that of the loaded DCM, their outputs would follow their load lines, increasing their share of the load current and bringing the circuit back to equilibrium.

Figure 4: With the Vicor DCM converters, units connected in parallel perform as a single converter; also, as the load-line shows, if the array is sized as N+1 redundant relative to the maximum load, the array continues to function despite the failure of any single converter. (Reference 1)

The issues and approaches to paralleling DC-DC supplies apply to larger converters such as the DCM series from Vicor, but also to power-supply ICs which are intended for much-smaller loads. For example, the LT3083, a 3A low-dropout (LDO) linear regulator from Linear Technology Corp., supports parallel operation using a 10-m ballast resistor between each supply and their common output rail.

Using power supplies in parallel is an attractive and viable technique to realise benefits in inventory and stocking, product commonality, additional output current, and N+1 redundancy. However, it must be done with an understanding of the possible paralleling topologies, and well as how the closed-loop supply regulation will be maintained across the multiple supplies.

References
1. "Application Note AN-030: Parallel DCMs," Ugo Ghisla, Vicor Corp.
2. "Back to Basics: What is Active ORing?," Vicor Corp.
3. "Learn to connect power supplies in parallel for higher current output," Keysight Technologies.
4. "Power Tip 27: Parallel power supplies with droop method," Robert Kollman, Texas Instruments.
5. "Application Note 140: Basic Concepts of Linear Regulator and Switching Mode Power Supplies," Henry J. Zhang, Linear Technology Corp.

About the author
Arthur Russell is the Principal Applications Engineer at Vicor Corp.


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