How to shrink a power supply: Tweak the topology


Engineers at Texas Instruments have developed a revolutionary power supply: A new buck converter that is one-fifth the size of a conventional one. The result is a dramatic reduction in circuit board space and weight.

The smaller step-down converter rethinks a buck converter’s basic topology; clever circuit design — not just smaller transistors — accomplishes a breakthrough product.

Buck converters, which are used to step down DC voltages, are a type of switched-mode power supply. In operation, the input voltage is switched on and off very rapidly. An inductor and other components smooth the pulses into a lower continuous output voltage that is proportional to the input signal’s “on time.” It’s a design that has seen few changes for years — until now.

The problem with the conventional design is that inductors are not only lossy, but also large — as big as all the other power supply components combined. Inductor size, which is inversely proportional to the power supply switching frequency, can be reduced at higher frequencies. But, higher frequencies mean higher switching losses and, thus, lower conversion efficiencies. And, a short input-signal on time — needed for higher input–output voltage ratios — can degrade converter control.

TI engineers resolved these high-frequency issues through the brilliantly simple expedient of adding a switched capacitor to a traditional multiphase converter. The new converter design, described in detail in the paper, “Breakthrough power delivery for space-constrained applications,” achieves three design goals at one fell swoop: Smaller space, higher input-output voltage ratio and high current.

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