dc-dc fundamentals1-1 an introduction

7/28/2019 DC-DC Fundamentals1-1 an Introduction

1/9


2/9

Wherever theres a need of energy, theres a power supply.

We are in the age of electricity: the majority of energy we use is generated, stored,

transferred and applied in the form of electricity. From cell phones, computers, TV sets and

home appliances we use everyday to and to the telecom base stations, server data centers ,video broadcasting equipment and various industrial and infrastructural applications,

electronic systems are everywhere. A power converter is an electronic circuit that

processes and provides power to such a system, or a load, from a power source.

So, DC-DC converters is the kind of converters that delivers power in direct current (DC) and

controlled voltage level from a direct current (DC) source. Almost all electronic products

today use components that are designed to operate under DC supply, and they have varied

requirements for voltage/current level, supply tolerance and dynamic performance. Also,

the DC source could have a varied voltage range. The DC-DC converter should be able to

regulate the output voltage and meet the requirements. Based on the applications, thereare various types of DC-DC converters.


3/9

In general, there are two basic types of converters: the linear type and the switcher type.

The power delivery in linear regulators is continuous: the pass elements that regulate the

current flow from source to load operates in linear region, which is similar to a variable

resistor and control the output voltage by adjusting its resistance.

For switcher type converters, the power delivery is in bursts: the pass elements are

switchers that turn on and off by cycles. A switching regulator must have energy storing

components like capacitors or inductors that can temporally store and release energy

between on and off cycle.

The linear regulators offer small physical size and low noise operation, but usually have low

efficiency. In the case of a switching regulator, the switcher is more efficient, but at the

expense of adding switching noise to the system and requiring additional components.

The linear type can be further divided into voltage references and LDO (low dropout

regulators).

There are two main types of the switching regulators inductor based (inductive) and

charge pump (capacitive or inductor-less).

Usually, the IC chips with integrated switching FETs are called regulators, whereas those

using external FETs are called controllers.


4/9

A DC-DC converter is designed for certain output voltage and maximum load for a certain

input voltage range. It is important to know the essentials of a converters characteristics

before the power supply design or selection.

Efficiency is the ratio of output power to input power. It is a good criteria to evaluate a

converters performance. Losses occur in the current-flowing resistors, in the magnetic-

field-changing inductor cores, when the switch switches. Therere numerous ways to

improve the converter efficiency, but theres no 100% efficiency.

Steady state indicates that the input voltage and output load condition are stable. The

converter should be able to provide a stable output voltage. However, some regulators will

have ripples in the output voltage caused by switching or coupling from other sources.

The transient response is the change of the output voltage and current over time asresponse to a change in the input voltage or load. Specifically, the response to input voltage

is called the line regulation and the response to load change is called the load regulation.

Usually, the design specification has restriction on the voltage variation and settling time

under transient.

In converter design, therere always tradeoffs between performance and other practical

considerations like size, cost. The design with best performance is not always the best

design.


5/9


6/9

In the inductive switcher the energy is pulsed from Vin to Vout through the inductor. The

inductor acts as a reservoir of energy during every pulse. As the voltage reaches the desired

level, only the energy needed by the load needs to be drawn from Vin and transferred to

Vout. The output capacitor acts like a filter to smooth out the power transition between

input and output. This energy transfer procedure is closely controlled by the switchers.Thanks to the advancement in integrated circuit (IC) technology, fast and precise control of

the switching is made possible that we can even make a power supply small enough to fit

into the portable device yet powerful enough to supply tens of ampere current feeding the

need of the microprocessor.


7/9

The charge pump switcher is also known as switched capacitor regulator.


8/9

The table shows the comparing between the 3 converter types in typical case. It can be

seen that theres no absolute winner.

The lowest cost solution will, most often, be the Linear regulators. However, this is not the

most power efficient and could create local heating in case of high load applications. Thehigher the difference between Vin and Vout, worse the linear regulator efficiency.

The inductor in the inductive (also known as Magnetic) switcher could consume a lot of

board space but this is the most power efficient configuration. For high current and large

Vin-to-Vout variation, switching regulators are preferred to achieve high efficiency.

The charge pump (also known as switched capacitor) configuration provides smaller and

fewer external components than the inductive switcher and better efficiency than the

linear regulator.


9/9

dc-dc fundamentals1-1 an introduction

Documents