For values of D tending to unity, the output becomes very sensitive to changes in (Fig.3).

Figure 3: Output voltage vs. Duty ration for Boost Converter	Figure 4: Boost converter with resistive load and emf source

 

Boost Converter with Resistive Load and EMF Source

A boost converter with resistive load is shown in Figure 4 . The two modes of operation are:

Mode 1 : This mode is valid for the time duration

                                                                                                        (4)

where D is the duty ratio T is the switching period .

The mode 1 ends at t = DT.

In this mode the switch S₁ is closed and the equivalent circuit is shown in Figure 5 . The current rises throught the inductor L and switch S₁. The current in this mode is given by

                                                                                                        (5)

Since the time instants involved are very small, the term . Hence, the solution of Equation 5 is

                                                                                                   (6)

where I₁ is the initial value of the current. Assuming the current at the end of mode 1( ) to be I₂ ( ), the Equation 6 can be written as

                                                                                                 (7)

Figure 5: Configuration of a Boost Converter in mode 1	Figure 6: Configuration of a Boost Converter in mode 2