Technical Information Site of Power Supply Design

2015.09.03 AC/DC

# DC/DC Conversion (Regulated) System after Smoothing

DC/DC Conversion (Regulated) System after Smoothing

We explained that the AC/DC conversion based on the transformer system involves AC – low AC – rectifying/smoothing (DC) – [optional: DC regulation], and the AC/DC conversion based on the switching system involves AC – rectifying/smoothing (DC) –regulated DC (AC–rectifying/smoothing –DC regulation). In this section, we describe in each system a method for converting the DC voltage generated by the rectifying/smoothing indicated in blue in the above text to a desired regulated DC voltage.

With regard to the AC/DC conversion based on the switching system, we used the expression, “chopping DC to convert to AC and rectifying/smoothing it again to produce DC.” However, because this process itself is a switching DC/DC conversion, in what following we will simply refer to it as “switching DC/DC conversion,” as opposed to linear DC/DC conversion. Although some readers might think that DC/DC is equal to switching, strictly speaking DC/DC only means conversion of DC to DC. In the following descriptions we will assume that a DC/DC conversion involves both switching and linear conversion methods.

Figure 12. DC/DC conversion part based on a transformer system

Figure 13. DC/DC conversion part based on a switching system

In Figures 12 and 13, which illustrate circuits based on AC/DC conversion systems, the parts enclosed in circles represent blocks that convert a given DC voltage into a desired DC voltage. In practice, in many cases a converter cannot be used as a power supply unit for electronic circuits unless a conversion is made into a regulated and accurate DC voltage.

#### Key Points:

・The transformer system requires the addition of a regulated DC/DC converter as necessary. In the switching method, the provision of a control circuit delivers the regulation of the DC output.