In the ever-evolving world of power electronics, switching power supplies have become a cornerstone of modern design. As energy efficiency becomes a top priority, the traditional linear power supply market is gradually shifting towards more efficient switching solutions. This transition has pushed the industry to explore higher switching frequencies, enabling smaller and more compact power systems that meet the demands of today’s ultra-thin devices.
This article focuses on the fundamentals of selecting an inductor for non-isolated switching power supplies (SMPS), particularly for applications like voltage regulation modules (VRM) and point-of-load (POL) power supplies. While these guidelines are ideal for small form factor designs, they may not apply directly to larger backplane-based systems.
Figure 1: Typical buck topology power supply
The buck topology is one of the most commonly used configurations in power conversion, especially where the output voltage is lower than the input. In a standard buck circuit, when the switch (Q1) turns on, current flows through the inductor, increasing at a rate determined by the inductance value. According to Lenz’s Law, the change in current is proportional to the applied voltage and the time it's applied, divided by the inductance. As the current increases, so does the output voltage across the load resistor.
When the control IC detects a threshold, it turns off the switch, allowing the inductor to release stored energy through the diode D1. This process continues cyclically, with the control IC adjusting the switching frequency to maintain the desired output voltage. Figure 2 illustrates the voltage and current waveforms over several cycles.
Figure 2: Switching waveform of a buck topology power supply
The inductance value plays a crucial role in maintaining continuous current flow during the off-time of the switch. To ensure stable operation under all conditions, the minimum inductance must be calculated based on several key parameters:
- Input voltage range
- Output voltage and its tolerance
- Operating frequency
- Inductor ripple current
- Continuous or discontinuous conduction mode
Table 1: Typical Step-Down Power System Specifications
Using the data from Table 1, the minimum inductance can be calculated as follows:
L1(min) = Vo(min)(1 - Vo(min)/(Vin(min) - Von)) / (f(min) × dI)
Substituting the values:
L1(min) = 4.95V × (1 - 4.95V/(20V - 0.7V)) / (693,000Hz × 0.5A)
L1(min) = 10.6 μH
Therefore, the selected inductor must have at least 10.6 μH of inductance, with a current rating above 20A to ensure reliable performance and a safety margin. Using an inductor with a lower value could lead to instability and failure in maintaining the output voltage within specifications under maximum load.
Once the inductance is determined, the actual component must also meet electrical standards, size constraints, and installation requirements. While many manufacturers offer standard inductors, custom solutions from specialized suppliers like CoEv Magnetic Components can provide tailored performance, ensuring optimal design and faster time-to-market. By leveraging industry expertise, engineers can reduce development time and enhance product reliability.
For Nokia Glass,Mobile Front Glass Oca,Oca Front Glass,Oca Front Glass For Nokia
Dongguan Jili Electronic Technology Co., Ltd. , https://www.jlglassoca.com