How to choose an LDO or switching regulator

How to choose an LDO or switching regulator

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I remember when I first started working with power management devices over 15 years ago.  Quite frankly, I didn't even know what an ‘LDO’ was, or even a switching regulator for that matter, since those terms weren't covered in the electrical engineering courses I took.  Because of that, I waited until the last minute to do the point-of-load power management design.  It made sense to wait until I knew how much power I needed before I started the design, I figured. 

Boy was I in for a few surprises! 

Lucky for me, there weren't as many options as there are today.  On the other hand, there weren't as many tools to help my design, either. After knowing the input voltage, output voltage, and output current for each rail, the solutions that were available seemed like a confusing collection of tools in a toolbox.  I ended up using the LM317 linear regulator for most of my power rails since it was easy to use and the output currents were not that high. 

Looking back, I could have done better (no offense to LM317 users!). 

If I could go back in time with today’s toolbox, I would select the TPS54061, a wide input voltage, step-down DC/DC converter that is smaller in size by integrating both power FETs, it’s  more efficient, and doesn't need as much copper on the board to dissipate heat… AND I wouldn't have the fear of magnetics anymore, since that was a tough class as I recall.  

However, I learned over time that there is no right answer.  It depends.  Whether designing for low noise, high efficiency, small size, or a fast transient response, I learned that each tool, or part, has its own unique purpose. Each voltage level has a special consideration and may have a trade-off. 

If you are new to designing with point-of-load power management devices, this Fundamentals of choosing LDO and switching regulators course will explain power trade-offs to help you choose the best solution.  If you have done many power designs, you will learn about some new tools that can make designing your power architecture more quickly.

Other resources:

How to pick an LDO based on your application - Video 

How to pick a Linear Regulator for Noise-Sensitive Applications - Analog applications journal (AAJ) article

Low-dropout regulators - quick reference guide

The Right LDO for your application - LDO's by applications webpage

  • I want to select a switching regulators for 4000 watts for a UAV that inputs 500Volts and output 25 volts

  • A switching regulator like the analog control UCC28950 or even the digital control UCD3138 in a full bridge-phase shifted topology can probably support a 4kW requirement with 500V to 25V conversion.  I will check with my collegues and ask them to comment, as this is out of my area of expertise.  

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