Introduction

An article on “Examination of Losses” is being added to “Characteristics and Evaluation Method of Switching Regulators” in the DC-DC Converter Evaluation edition.

Here “losses” means, of course, power losses relating to a power supply. In any event, power losses are directly converted into heat, and therefore are an extremely important subject for study. Heat generation is one major factor that detracts from the reliability of components and devices, and in the worst case, can even culminate in the occurrence of accidents involving smoke and flames. Hence the importance of understanding such losses should be obvious.

When erroneous design, defective components, and defective device assembly are excluded, nearly all problems with components and devices arising from heat generation are basically due to the failure to perform adequate thermal calculations and thermal design. Common examples are changes made to components, modifications of board layouts for greater device compactness, and other model-change scenarios, which are regarded as only slight changes, so that proper verification prior to executing the changes is neglected.

Regardless of the reason, if a heat generation problem is discovered, a countermeasure must be devised. Measures basically take the form of reducing the heat generation, or possibly increasing heat dissipation. In order to reduce heat generation, losses in the components of the power supply circuit are reduced. To increase heat dissipation, heat sinks may be added, or the heat dissipation effect may be enhanced, that is, thermal resistance reduced, by increasing the PCB copper area or the number of layers.

Reducing power losses of power supply circuit components

• ・DC-DC converter IC losses (including package thermal resistance)
• ・Losses of external FETs
• ・Losses of external rectifying diodes (asynchronous rectification)
• ・Coil losses

Increasing heat dissipation

• ・Addition of heat sinks
• ・Increasing PCB copper area
• ・Increasing the number of layers of the PCB

Example of increasing allowable losses by increasing the PCB copper area and number of layers

In this new chapter on “Examination of Losses”, we will explain what kinds of losses occur in which parts of a circuit, and the causes of such losses, in order to be able to implement countermeasures. The chapter is planned as follows.