DC-DC Fundamentals 1.3 Switching Regulator XIANG FANG: Hello, everyone. Welcome to the DC-DC Fundamentals. I'm Xiang. In this section, we'll talk about a switching regulator.

What is a Switching Regulator? The switching regulator is a DC-DC converter that delivers power by using switcher components. It offers high power conversion efficiency and design flexibility So what is a switching regulator? It is a DC-DC converter that delivers power by using switcher components. As you can see in this graph, it usually contains a switcher network and an L-C component tank. It can offer high power conversion efficiency and design flexibilities.

Pros and Cons Advantages Disadvantages High efficiency Good thermal performance High power density Allow wide input voltage range Vout can be smaller or larger than Vin Isolation possible with transformer Multiple outputs possible with transformer Switching produces higher output ripple & noise Slow transient response High complexity as more external components and design variables The advantage of using switching regulators is you can offer high efficiency and have good thermal performance. And it has high power density to allow wire input voltage range. And the Vout can be smaller or be larger than Vin. And it has the option to provide isolation. And it also can create multiple outputs by using transformer. The disadvantage of using a switching regulator is that the switching actually creates high output ripples and noise. The transient response is relatively slow. And it has high complexity as more external components are used. And there are many more design variables to consider.

How Does a Switching Regulator Work? The inductor stored and released energy to output load get energy from the input source which is controlled by the switches. An example of Buck converter: When switched to position 1, the inductor is storing energy; when switched to position 2, the inductor is releasing energy The average voltage over the inductor is zero: D(Vin-Vo)-D’Vo=0 => Vout = D*Vin D = Duty Cycle (% of time switch in the position for charging L) D’ = 1-D So how does a switching regulator work? As you can see, the inductors store and release energy to output low. And it gets the energy from the input source. And the switching is controlled by the controller. As an example, we show a Buck converter here in the bottom graph. When the switcher is in position one, the inductor is actually storing energy. And when the switch is switched to position two, the inductor is releasing the energy to the output. And the average voltage over an inductor is actually zero. So by doing some equation derivation, we can get that Vout is actually equal to the D times Vin, which the D is the duty cycle. It's the percent on time divided by the total switching time. Since D is smaller than 1, that means in the Buck converter, your Vout is always smaller than your Vin.

Basic Topologies Three basic types of switching converter topologies: Buck, Boost and Buck-boost VIN VOUT Boost Vout = Vin/(1-D) VIN VOUT Buck Vout = D*Vin VIN VOUT Buck-boost Vout = -DVin/(1-D) And in these slides, we show three basic topologies of the switching DC-DC converters. There are Buck converters, Boost converters, and Buck-Boost converters. For the Buck converter, you can only step down the voltage from Vin. For the Boost converter, the Vout can be higher than your Vin. And for the Buck-Boost, your Vout can be either higher or lower than your Vin, depends how you configure your duty cycle.

Synchronous vs. Non-Synchronous Non-Synchronous Buck Non-synchronous Diode voltage drop is fairly constant with output current Less efficient Less expensive Used with higher output voltages Synchronous MOSFET has lower voltage drop More efficient Requires additional control circuitry Costs more Synchronous Buck So when we talk about the switching converters, there are usually people talking about synchronous switching converters and non-synchronous. So what's the difference of these two types of switching regulators? For a non-sync regulator, usually one of the switches are diode, as you can see on the graph here. The bottom switch is replaced by a diode. The diode voltage job is fairly constant with the output current. So it's less efficient. But using the diode, it's less expensive. And it's easier to control. On the bottom graph, there's a synchronous Buck converter. As you can see, the bottom switch is using a MOSFET switch, rather than a diode. So the MOSFET has lower voltage drop than a diode. So it's more efficient. But it requires additional control to control these two switches. So it costs more. And it's more complex to configure.

Isolated vs. Non-isolated Isolated has no DC current flow between input and output. Transformer couples energy from primary to secondary through magnetic fields Isolated typically used in medical and offline applications requiring primary to secondary isolation Not typical for standard point of load solutions Transformer coupling AC input And there's isolated and non-isolated switching regulators. The isolated switching regulator has no DC current flowing between the input and the output. It's achieved by using transformer. The transformer couples energy from the primary to secondary through the magnetic field. The isolated typically is used in medical and offline applications, which requires safety requirements. But it's not typical for this type of isolation to be used in the standard point of low solution. As you can see in these typical graph here, the transformer to couple the energy from the input to the output and the feedback signals is going through this output coupler. So there's no direct connection between the output and input. Feedback across isolation boundary Typically an optocoupler Primary Side Switched Mode Power Supply with Power Factor Correction (PFC)

Controller vs. Regulator Discrete MOSFETs Provides the “brains” to control the power stage More complicated to design Full control over FET selection, switching frequency, overcurrent, compensation, softstart Can tailor the power supply to meet your specific needs Fully integrated regulator Integrated switches “plug and play” design Limited range of output filter components Limited control over functionality Partially integrated regulator May offer full or partial feature set , internal or external compensation Internal Power FET, external sync-FET or catch diode Limited control over frequency, overcurrent, softstart, etc. Allows wider range of output filter components Also, there's controller type and regulator type of switching regulator. For controller type, it usually uses discrete MOSFETs. That means the MOSFET is external. So the controller is only providing the brain to control the power stage. It's more complicated to design. But you have more flexibility. You can choose which FET to use, depends on your needs. And for the regulator, it usually indicates that the switching FETs is integrated in the power IC. There's fully integrated regulator-- that means your outside FET and the bottom FET are both integrated. So it's easier because both FETs that are inside, you don't need to worry about the selection. But it has a limited range of the filter components since the FETs are set. And it's limited control of the functionality. Also there's partially integrated regulator, like in the non-synchronized Buck converter, you can have diode outside, but you can integrate the outside FETs inside your regulator. And it's similar to the fully integrated regulator.

Summary Introduction to switching regulator The operation of switching regulator Types of switching regulator Basic topologies Synchronous vs. Non-synchronous Isolated vs. Non-isolated So in summary, in this section, we gave you an introduction of the switching regulator. We talked about operation and some basic concepts of the switching regulators.

Thank you! Thank you.