Transfer Function

Transfer function of each converter


Points of this article

・The concepts of the state-space averaging method are used to derive transfer functions for various control modes.

・It was reconfirmed that what is derived, for converters, is Δvout/ΔD、ΔiL/ΔD

・The ultimate goal is derivation of a "monotonous unified approach" for the purpose of sharing transfer functions.

From here, we embark on a new chapter, “Transfer Functions for Converters”. Using the concepts introduced in the previous chapter on “The State-Space Averaging Method“, we derive transfer functions for various control modes.

As we stated previously, the “part to be derived” is the 161110_img01 in Figure 1 below.


In fact, from here we have repetition of a fairly monotonous task. Do you remember the applicable theme here, explained in the initial section?

To summarize the initial section, “the theme here is determining the transfer functions of DC-DC converters, but it was thought that the great variety of transfer functions could be summarized in a single unified approach, and so we decided, when addressing the derivation of transfer functions for DC-DC converters, to make a ‘common approach’ our goal.”

The path we have taken up to this point is a “monotonous unified approach” for the purpose of commonization or sharing of transfer functions, culminating in the transfer function sharing shown in Figure 2. In other words, the monotony of the tasks from here on out was, in a sense, the original goal.


From the next section, we shall derive transfer functions for step-down converters, step-up converters, and step-up/down converters, with a view to sharing of transfer functions.

Information on Downloading Technical Documents

Downloadable materials, including lecture materials from ROHM-sponsored seminars and a selection guide for DC-DC converters, are now available.