Column: DC/DC converters


The differences between non-isolated buck, boost and buck-boost converters


TDK-Lambda’s i7C Series 300W buck-boost DC-DC converter


By Lars Foerster, DC/DC Business Development Manager EMEA, TDK-Lambda N


on-isolated buck, boost and buck-boost topologies are found in many AC-DC power supplies and non-isolated DC-DC converters.


Although many of the patents of DC-


DC converters were filed in the 1970s, their simplicity, low cost and very high efficiencies make these devices widely used even now. Standard, off-the-shelf products are still being introduced, taking advantage of new techniques like digital control, improved components and more efficient magnetic materials.


Main differences The main difference between an isolated and a non-isolated DC-DC converter is the transformer, or lack of it. In an isolated converter, the transformer provides a safety barrier between the DC input (primary) and the DC output (secondary). Non-isolated converters are powered by low-voltage batteries or by an AC-DC power supply which already contains the safety barrier. Non-isolated converters fall into


three main categories – buck, boost and buck-boost; see Figures 1-3. To make the schematics more understandable,


08 December/January 2021 www.electronicsworld.co.uk


they are drawn using switches rather than transistors, and diodes instead of synchronous rectifier circuits.


Buck converters A buck converter reduces voltage, and the output voltage is lower than the input voltage; see Figure 1. When transistor (S) is turned on,


energy is stored in an inductor (L) as the current flows through it to the load, and also charges capacitor (C). When S is turned off, the energy stored in L is released and current flows into the load and circulates via a diode (D).


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