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1.1 DC-DC fundamentals - an introduction
Hello, everyone. I'm Xiang Fang. Welcome to the DC-DC fundamentals. In this section, we'll give you an introduction to the DC-DC converter. So what is a 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 device to provide the DC power from a source to a load. So there are different types of converters. In general, there's two basic types. One is called a linear type. In linear type converter, the power is delivered continuously from the source to the load. And the pass element, which regulates the current flow from the source to the load, operates in the linear region. And the other type, we call it switcher type. The power delivery in the switcher type converter is inversed from the source to the load. And the pass element of the switch is switching on and off cycle by cycle. And there are different basic converter characteristics to be reminded of. And in these systems, when you're doing converter design or power IC selections, these characteristics are better to keep in mind. For example, the system requirement, we want to know the output voltage level, the current rating, and input voltage range. And one key specification is the efficiency of the DC-DC converter. And that is the operation. It measures the performance of the DC-DC converter. And also sometimes the transient responses is very important. And always the size and cost matters. So in this slide, I will talk about a linear regulator. A linear regulator is usually used in the radio frequency and precise analog applications. It's usually using those applications where there's a narrow VIN to VOUT difference. And that requires a lot of precision and low noise. The advantage of using a linear regulator is it has a low output ripple and noise. And it has a fast transient response. And usually it has low cost, and fewer external components are needed to make a linear regulation work. Also there's some disadvantages of this linear regulator. It's the low efficiency, especially when your VIN is much larger than VOUT. And when using linear regulators, you can only generate VOUT lower than your VIN. Converter's characteristics-- so when you're doing DC-DC converter design or selection, there are 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 precision and low noise. As you can see in the slides, we release a 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 costs 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 VOUT, you have a very low efficiency. And the power generated from the regulator is dissipated through the whole regulator. So there will be heat dissipation problems. And you can only generate a VOUT lower than your VIN. That means you cannot push your voltage. Inductive switcher-- we call it inductive because there's an inductor in this type of converter. As you can see in this graph, we show an example of a buck-boost converter. There's an inductor in the middle. And there's a switch going on and off by pumping the energy through the inductor and the capacitance. So in this way, the energy can be delivered to the output load. For this type of switcher, it's widely used in all kinds of applications. And it's usually for its high performance about the efficiency. And for those applications that require high power density and have heat dissipation problems. So the advantage of this type of converter-- it can give you high performance and also can create isolation if that's required. And it can generate multiple outputs by using one DC-DC converter. The disadvantage of this type of switcher is that a switch in currents, since it's in and out, is kind of discontinuously. So there's EMI issues. So 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 are required to configure such type of converter. Charge pump-- we also call it inductiveless DC-DC converter, because there's no inductor in this type of converter. The application of charge pump is that for those applications that require low output currents and with moderate input or output voltage difference. And it's suitable for those implications with space constraints. The advantage of using this type of converter is it can give you moderate efficiency, and it's slightly less cost than the inductor type of switcher. And also since the charge pump switches voltage across capacitors, your VOUT can be larger and can be smaller than your input voltage. And fewer components are 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. So in this slide, we show a summary of the comparison between these three types of DC-DC converters. As you can see here, the linear regulator has the 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 types. And the inductive type has the highest efficiency. But the ripple is 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. So in this section, we give you an introduction of different types of DC-DC converters. Thanks for watching.
Watch the next video in the series:
DC-DC fundamentals - switching regulator overview
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Date:
April 29, 2013
This presentation provides an introduction to DC-DC converters.
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