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August 20, 2001

How do I design ...?

Question: Can you help me design a power supply to these specifications?

Original Question: I am requesting you to guide me in designing a 5 V, 1 A step-down regulator with an input voltage of 18 V using a PWM. I'll be very thankful if you help me out.

Answer: This type of question, that basically asks me to design a power supply that meets some requirement, is one that I frequently receive. The answer is always the same, a modified no, -- so don't ask. There is really no way I can design your power supply for you in a short email reply. The best I can do is to find a reference design or application note close to what you want so you can study it, and then modify it to your design. But this takes time, and it is something you can do for yourself. Your best sources of information on the web are the application notes and reference designs of the vendors who make the parts you need --- the makers of power semiconductors and controllers. You can find a partial list of these vendors on my vendor page at www.smpstech.com/vendors.htm. Do a page search on the key word semiconductors and dig what you need out of their websites. An alternate is to use a good power supply design book as a guide. This approach takes a little time to search for a design close to what you want, but is one of your best approaches to beginning a design.

The reason for this response is simple. If you are a student, you are not going to learn much if I do your design for you. If you are a working engineer, you have to take responsibility for your own design, and you can't ethically do this if you don't know in detail how it was done. So what good am I? If you have given it a good shot and are stuck, I can sometime help you over a rough spot. Therefore, ask a questions if you think I can help in a ten minute email answer, but don't ask me to do the research or design your power supply for you.

Posted by Jerrold Foutz at August 20, 2001 03:03 PM