October 26, 2010 AT 12:07 pm

TUTORIAL TUESDAY! What is a power supply? Transformer-based AC/DC converters


A power supply is a device that supplies power to another device, at a specific voltage level, voltage type and current level. For example, when we talk about a 9VDC @ 500mA power supply can provide as much as 500mA of current and the voltage will be at least 9V DC up to that maximum current level. While it sounds simple, power supplies have a lot of little hang-ups that can be very tricky for the uninitiated. For example, unregulated supplies say they can provide 9V but really may be outputting 15V! The very common 7805 regulator datasheet claims it can regulate up to 1000 mA of current, but when you put a 15V supply on one side, it overheats and shuts down! This tutorial will try to help explain all about power supplies. Read “What is a power supply?” here!


The most common and inexpensive plugpack power supply type you’ll see is the chunky transformer based plug. Whenever you buy some consumer electronics you’ll be getting one of these – read more about Transformer-based AC/DC converters here!

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  1. Nice write-up!

  2. Your tutorials are awesome. I love tutorial Tuesday.


  3. Because of recent "green" regulations, it will become more and more difficult to find these types of wall warts. I think it may even be illegal to sell a product with them in California? I think all the ones you find on digikey are now switching.

  4. I havent seen a transformer based one come with new gear for a very long time, since they dont have the efficiency needed to meet regulations.

    What is more scary is how crap some of the switchmode ones are. Some dont even have overload or overheat protection in them which is quite worrying, and the amount of HF noise out of the cheapies is something you dont want to have to deal with either.

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