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DC-DC Fundamentals 1.1 An Introduction

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Presentation on theme: "DC-DC Fundamentals 1.1 An Introduction"— Presentation transcript:

1 DC-DC Fundamentals 1.1 An Introduction
XIANG FANG: Hello everyone, and welcome to the DC-DC fundamentals. In this section, we'll give you an introduction to the DC-DC converter.

2 What is DC-DC converters?
Power supply is needed everywhere Almost all electronic systems need constant voltage supply A DC-DC converter is the circuit to provide the DC power So what is the DC-DC converter? As you know, the power supply is needed everywhere. Almost all electronic systems need a constant voltage supply. And a DC-DC converter is a circuit devised to provide the DC power from a source to a load. battery Sources Loads DC-DC power converters solar cell industrial supply microprocessor amplifier data converter another converter resistor

3 Types of Converters Linear Type Switcher Type
The power delivery is continuous from source to load The pass elements (which regulate the current flow from source to load) operate in the linear region Switcher Type The power delivery is in bursts from source to load The pass elements switch on and off by cycles So there's different types of converters. In general, there's two basic types. One is called a linear type. In linear-type converter, the power delivery is continuous from the source to the load. And the past elements, which regulate the current flow from the source to the load, operate in the linear region. And the other type we call it switcher type. The power delivery in the switcher type converter is in bursts from the source to the load. And the past element of the switch is switching on and off, cycle by cycle.

4 Converters Characteristics
System requirements: output voltage, current rating, input voltage range Efficiency Steady state operation Transient response Size, Cost, … And there's a different basic converters characteristics to be reminded of. And in this system, when you're doing converter design or power IC selections, this characteristic is better to keep in mind. For example, the system requirement, we want to know the output voltage level, the current rating, and the input voltage range. And one key specification is the efficiency of the DC-DC converter and the steady state operation. It measures the performance of the DC-DC converter and also, sometimes, the transient response is very important. And always, the size and cost matters.

5 Linear Regulator Applications Advantages Disadvantages 5V 3.3V
Vref + - Error amplifier Gate drive Pass element Load 5V 3.3V Radio frequency or precise analog (measuring very small voltages) circuits that require extremely low ripple & noise Applications where VIN – VOUT is very small. Applications that require a precisely regulated. FPGA or Multi-Core processors that require fast transient response due to fast changes in the load. Advantages Disadvantages Low O/P ripple & noise Fast transient response at VOUT on large changes of the Load Low cost (for low power, at least) Few external components make the linear regulator easy to design Since linear regulators don’t switch current into an inductor there is no EMI to worry about Easy to implement short circuit protection Low efficiency at VIN>>VOUT which requires a larger supply power source Power generated from the regulator (VIN – VOUT) * IOUT is dissipated through the Regulator typically requiring a heat-sink VOUT will always be less than VIN So in this slide, I will talk about the linear regulator. The linear regulator is usually used in the radio frequency and precise analog applications. It's usually using those applications where you have a narrow V in to V out difference. And that requires a lot of precision and low noise. The advantage off using a linear regulator is, it has low output ripples and noise. And it has a fast transient response, and, usually, it has low cost and few external components is needed to make a linear regulation work. Also, there's some disadvantage of linear regulator is, the low efficiency, especially when your V in is much larger than V out. And when using linear regulator, you can only generate a V out lower than your V in. Converters characteristics-- so when you're doing DC-DC converter design or selection, there's some key specs you need to keep in mind. For example, the system requirements-- what's the output voltage? What's the current rating and input voltage range of your DC-DC power converter design? And performance-wise, the efficiency of your power converter, the steady-state operation, and the transient response is also very important. And last but not least, the size and the cost is very important for your power design, also. Linear regulator-- linear regulator is usually used in the application that requires high precisions and low noise as you can see in the slides, with these couple of typical applications for this type of regulator. An advantage of using a linear regulator is, it has low output ripples and noise. And you can achieve fast transients, and it's relatively low cost and fewer external components needed. So it's a simple-to-use kind of regulator. But the disadvantage of this type of topology is that you need to keep in mind that if your Vin is much higher than your V out, you have a very low efficiency. And the power generated from the regulator is dissipated through the whole regulator. So that will be a heat dissipation problems. And you can only generate a V out lower than your V in. That means you cannot boost your voltage.

6 Inductive Switcher Buck-Boost Applications Advantages Disadvantages
VIN VOUT Applications where high efficiency (PowerIN – PowerOUT is very small) Applications with extremely high ambient temperatures such as Industrial or Automotive Applications where VIN is much larger than VOUT Applications where the power supply has space constraints (small area) Applications requiring High output power Advantages Disadvantages Since regulation is done by dumping energy into and out of an inductor versus burning power through the regulator Higher efficiencies can be obtained Lower power dissipates through the regulator requiring a smaller heat sink. Topologies of the switching power supply allow VOUT>=<VIN High Power Density (Watt/cm2) Allows wider input voltage range Isolation possible (with transformer) Multiple O/Ps possible (with transformer) Switching current into and out of an inductor: Generates Electromagnetic Interference (EMI) Causes the output to respond slower to transients in load Produces higher output ripple & noise More external components and design variables make switching power supplies difficult to design Inductive switcher-- we call it inductive because there is an inductor in this type of converter. As you can see, in this graph, we show example of a buck-boost converter. That's an inductor in the middle. And there's a switch going on and off by pumping through the inductor and the capacitance. So in this way, the energy can be delivered to the output load. For this type of off switcher, it's widely used in all kinds of applications and it's usually for its high performance about efficiency and for those applications that requires high power density and have heat dissipation problems. So the advantage of this type of converter-- it can give you a high performance and also can create isolation if that's required. And it can generate multiple output by using one DC-DC converter. The disadvantage of this type of switcher is that a switch in current, since its in and out, is kind of discontinuously. So there's EMI issues. Also, the output noise and ripple is relatively high comparing to a linear regulator. And it's more difficult to design, and more external components is required to configure such type of converter. Charge pump-- charge pump, we also call it up inductive release DC-DC converter because there's no inductor in this type of converter.

7 Charge Pump VIN VCF Vo - Applications Advantages Disadvantages Q1 Q3
LOAD + VIN Co Vo - Io VCF Applications requiring a low output current Applications with moderate input to output voltage difference Applications that have space constraints Advantages Disadvantages Moderate Efficiency Since charge pumps switch voltages across capacitors in and out of the output: No inductor is needed VOUT>=<VIN Fewer components make the charge pump easier to design Switching of the capacitor in and out of the circuit generates EMI Since the output of the charge pump is dependent on the charging and discharging of a capacitor, it has limited current capability The application of charge pump is that, for those of application that requires low output currents, moderate input or output voltage difference. And it's suitable for those applications with space constraints. The advantage of using this type of converter is, it can give you moderate very efficiency, and it's slightly less costly than the inductor type of switcher. And also, since the charge pump switches voltage across capacitors, so we all can be a larger, and can be smaller than your input voltage. And fewer components is needed to make this charge pump converter. The disadvantage is also related to the EMI issue. And since the charge pump depends on the charging and discharging of a capacitor, it has the limit of the current capacities.

8 Converter Comparison The choice of converter type depends on the power design priorities. Linear Regulator Switching Regulator Inductive Charge Pump Efficiency 20-60% 90-95% 75-90% Ripple Very low Low Moderate EMI Noise PCB Area Very small Largest Medium Cost Lowest Highest So in this slides, we show a summary of the comparison between these three types of the DC-DC converters. As you can see here, the linear regulator has a relatively low efficiency, but you can achieve low ripple and low EMI noise. And the solution size is usually small. And the cost, it's the lowest comparing to the other type. And the inductive type has the highest efficiency, but the ripple, it's kind of larger than the linear regulator. And it takes the largest PCB area and has the highest cost. And the charge pump has the moderate ripples, has the moderate efficiency, and the PCB size, and the cost is medium.

9 Summary Types of DC-DC converter Basic characteristics of a converter
Converter comparison So in this section, we give you an introduction of different types of the DC-DC converters.

10 Thank you! Thanks for watching.

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