Boost Converter - Circuit Analysis - Operating Principle - Discontinuous Mode

Discontinuous Mode

If the ripple amplitude of the current is too high, the inductor may be completely discharged before the end of a whole commutation cycle. This commonly occurs under light loads. In this case, the current through the inductor falls to zero during part of the period (see waveforms in figure 4). Although slight, the difference has a strong effect on the output voltage equation. It can be calculated as follows:

As the inductor current at the beginning of the cycle is zero, its maximum value (at ) is

During the off-period, IL falls to zero after :

Using the two previous equations, δ is:

The load current Io is equal to the average diode current (ID). As can be seen on figure 4, the diode current is equal to the inductor current during the off-state. Therefore the output current can be written as:

Replacing ILmax and δ by their respective expressions yields:

Therefore, the output voltage gain can be written as follows:

Compared to the expression of the output voltage for the continuous mode, this expression is much more complicated. Furthermore, in discontinuous operation, the output voltage gain not only depends on the duty cycle, but also on the inductor value, the input voltage, the switching frequency, and the output current.

Read more about this topic:  Boost Converter, Circuit Analysis, Operating Principle

Other articles related to "discontinuous mode, discontinuous, modes, mode":

Buck Converter - Theory of Operation - From Discontinuous To Continuous Mode (and Vice Versa)
... As mentioned at the beginning of this section, the converter operates in discontinuous mode when low current is drawn by the load, and in continuous ... The limit between discontinuous and continuous modes is reached when the inductor current falls to zero exactly at the end of the commutation cycle ... output current (equal to the average inductor current) at the limit between discontinuous and continuous modes is (see above) Substituting ILmax by its value On the limit between the two modes, the output voltage ...
Buck–boost Converter - Principle of Operation - Discontinuous Mode
... of the output voltage gain for the continuous mode, this expression is much more complicated ... Furthermore, in discontinuous operation, the output voltage not only depends on the duty cycle, but also on the inductor value, the input voltage and the output current ...

Famous quotes containing the word mode:

    I have no scheme about it,—no designs on men at all; and, if I had, my mode would be to tempt them with the fruit, and not with the manure. To what end do I lead a simple life at all, pray? That I may teach others to simplify their lives?—and so all our lives be simplified merely, like an algebraic formula? Or not, rather, that I may make use of the ground I have cleared, to live more worthily and profitably?
    Henry David Thoreau (1817–1862)