The use of switched-mode voltage regulators has increased considerably in recent years in parallel with technological developments. Several different types of switching regulators are designed. In this chapter; The type of up-regulator (step-up or boost) used in the design of switched-mode voltage regulators will be examined with their general characteristics and basic logic will be explained.
The regulated voltage taken from the output of the regulators with boost (boost) may be greater than the regulated DC voltage applied through the input. This is the main advantage of such regulators. The simplified basic circuit of the up-regulated voltage regulator is given in figure-2.5.
As shown in the example, when the S1 switch is open, V1 = V0. This voltage is the smallest voltage at the regulator output. When the S1 switch is off (TON) the L bobbin is energized. The energy in the coil L is transmitted to the output together with the Vi voltage when the switch S1 is open. For this reason, the output voltage of such regulators can be greater than the input voltage without regulation.
Let’s consider the tON time that the S1 switch is off. At this time, diode D is polarized in the reverse direction because the output voltage V0 is positive and the feedback loop is on. Thus, capacitor C discharges through RL. Enabled; When C · RL >> is selected, the drop over V0 is very small. During this interval there is a non-regulated input voltage on the L bobbin and the I L inductor current;
Now let’s consider the tOFF interval (duration) that the S1 switch is open. In this case; the IL current will flow through the diode to the capacitor C because IL (tON -) = IL (tON +) and diode conduction will pass because the current of the coil L will not change abruptly. When the voltage on capacitor C is stable, the period ends at the same time (T = tON + tOFF), which is the same as at the beginning (t = 0).
it is necessary to decrease in the current tOFF range as in the increase of VI · tON / L in the t0N interval. [(Language / dt) <0]. If the voltage on the diode is neglected, the instantaneous value of the output voltage;
Because language / dt is negative. Briefly, the following equation can be written for the output tension in such a regulator,