Issue link: https://read.uberflip.com/i/1444137
get off-the-shelf with the exact requirements that a custom power supply requires. MOST COMMON TOPOLOGIES WHEN ISOLATION IS NOT REQUIRED The most common nonisolated switch-mode power supply topology is the buck converter. It is also known as the step-down converter. It accepts a positive input voltage and generates an output voltage lower than the input voltage. It is one of the three most basic switch-mode power supply topologies that only require two switches, an inductor, and two capacitors. Fig- ure 3 shows the basic principle of this topol- ogy. The high-side switch pulses a current from the input and generates a switch node volt- age alternating between the input voltage and ground voltage. The LC filter takes that pulsed voltage on the switch node and generates a DC output voltage. Depending on the duty cycle of the PWM signal controlling the high-side switch, a different level of DC output voltage is generated. This DC-to-DC buck converter is very power efficient, relatively easy to build, and requires few components. The buck converter pulses current on the input side, while the output side has continuous cur- rent coming from the inductor. This is the reason why a buck regulator is very noisy on the input side and not so noisy on the output side. Under- standing this is important when low noise sys- tems need to be designed. Besides the buck topology, the second basic topology is the boost, or step-up, topology. It uses the same five basic power components as the buck converter, but rearranged, so that the inductor is placed on the input side and the high-side switch is placed on the output side. The boost topology is used to step up a certain input voltage to an output voltage that is higher than the input voltage. When selecting a boost converter, it is important to note that boost converters always specify the maximum rated switch current and not the maxi- mum output current in their data sheets. In a buck converter, the maximum switch current is directly related to the maximum achievable output current, independent of voltage ratio between the input voltage and the output voltage. In a boost regulator, the voltage ratio directly affects the possible max- imum output current based on a fixed maximum switch current. When selecting a suitable boost regulator IC, you need to not only know the desired output current, but also the input and output volt- age of the design in development. A boost converter is very low noise on the input side, since the inductor in line with the input con- nection prevents rapid changes in current flow. However, on the output side this topology is quite noisy. We only see pulsed current flow through the outside switch, and thus output ripple is more of a concern compared to the buck topology. The third basic topology, only consisting of the five basic components, is the inverting buck- Figure 3. Concept of a simple buck step-down converter. Figure 4. Concept of a simple boost step-up converter. 6 FEBRUARY 2022 | www.eetimes.eu Cover Story