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2.1. Buck

It is one of the simplest converter circuits. It has a common input and output ground and can be used in applications similar to those of a linear regulator. As shown in figure 5, it is equipped with a Q switch element which can be a bipolar transistor or mostly a MOSFET.

This element always operates in switching mode, which provides the converter with a high performance in contrast to what happens in linear regulators. The Q control signal is delivered by a pulse-width modulation (PWM) circuit that provides a rectangular waveform. Thus, the voltage waveform at the Q emitter and, therefore, at D’s cathode will be the one identified as VD in figure 4. In steady operation, current flowing through the transistor will have the waveform identified as IQ. It can be seen, that for the time Q is not on, the current at L, which cannot be interrupted immediately, now flows through diode D, which up to that moment was reversely biased. The addition of IQ + ID current will be the IL current which will be provided by the charge of C output capacitor.

This topology provides simplicity, but its main restrictions are that its output is not isolated from its input and the output voltage must always be lower than and have the same polarity as the input.

Figure-4

Figure-4

Figure-5

Figure-5