Zeta PWM DC/DC Converters

By swapping the positions of the switch tube V and the diode circuit D in the SEPIC converter and the input/output relationship, we get the Zeta converter as shown in Figure 1.

The converter can be considered to be a combination of the Buck-BccGt circuit and the Buck circuit. However, in order to make the second-stage Buck circuit work without increasing the complexity of the circuit, only the basic functional unit part of the Buck circuit is selected (see the right figure in Figure 1 (a)), and the voltage of the diode D of the first-stage Buck-BooGt circuit is taken as the first-stage output. As shown in Figure 1 (b), the output waveform of the previous stage is the same as the input waveform of the next stage. Moreover, the diode D can be shared, so it can be combined into a Zeta converter as shown in Figure 1 (e). Its output/input relationship is: the voltage on C1 is negative on the left and positive on the right, and its value is

The input voltage of the second stage is Ui+Uc. At this time, the capacitor C1 can be considered as a voltage source with an amplitude of Ui·Du/(1-Du). At the same time, the effect of L1 on the subsequent stage is ignored. The circuit shown in Figure 1 (e) is equivalent to a superposition of the input end.

As shown in Figure 1, the evolution process of the combination of Buck-Boost circuit and Buck circuit to form Zeta converter

The voltage source of -Ui·Du/(1-Du) is shown in Figure 2. Therefore, the equivalent input voltage is

The output/input relationship of the second stage is

Where U'i = Ui/(1-Du), the total output/input voltage relationship is

As shown in Figure 2, C1 in the circuit of Figure 1 (e) is equivalent to a voltage source.