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Understanding SWIFT Step-Down DC-DC Converters Slide 6

During the discharge state, the top FET Q1 is off and the bottom FET Q2 is on. Power is not coming from the power source any more; it is coming from energy stored in the inductor and capacitor. The graphs below show the phase voltage at zero and the output voltage dropping. The cycle will repeat itself as Q1 and Q2 turn off at a set frequency. In the case of a non-synchronous converter where a power diode replaces Q2, the current would be allowed to flow through the diode in a similar fashion, but the power loss would be higher due to the higher voltage drop as previously explained. Note that by not drawing power from the source, the efficiency is higher than a linear regulator, which always draws power from the source. A switching DC/DC converter uses stored energy to supply power to the load to save energy.

PTM Published on: 2011-11-10