Source: Ali Bazzi, Department of Electrical Engineering, University of Connecticut, Storrs, CT.

While it is simple to step up or down AC voltages and currents using transformers, stepping up or down DC voltages and currents in an efficient and regulated manner requires switching power converters. The DC/DC buck converter chops the input DC voltage using a series input switch, and the chopped voltage is filtered through the L-C low-pass filter to extract the average output voltage. The diode provides a path for the inductor current when the switch is off for part of the switching period. The output voltage is this less than or equal to the input voltage.

The objective of this experiment is to study different characteristics of a buck converter. The step-down capability of the converter will be observed under continuous conduction mode (CCM) where the inductor current is non-zero. Open-loop operation with a manually-set duty ratio will be used. An approximation of the input-output relationship will be observed.

This experiment will utilize the DC-DC converter board provided by HiRel Systems. http://www.hirelsystems.com/shop/Power-Pole-Board.html

Information about the board operation can be found in this collections video “Introduction to the HiRel Board.”

The procedure shown here applies to any simple buck converter circuit that can be built on proto boards, bread boards, or printed circuit boards.

1. Board setup

1. Connect

It is expected the output-input voltage relationship of an ideal buck converter to be related to the duty cycle or duty ratio D. If the input voltage is V_in and the output voltage is V_out, V_out/V_in = D, where 0≤D≤ 100%. Therefore, for an input voltage of 24 V, V_out≈ 12 V for D = 50%, V_out≈ 7.2 V for D = 30%,

Buck converters are very common in electronic device chargers where they provide excellent voltage regulation required for battery charging. They are commonly used in power supplies that power computers, integrated circuits and electronic boards, as well as in renewable energy applications and battery fed systems.