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Author Topic: Make an adjustable small power supply.  (Read 1205 times)

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Geek-9pm

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Make an adjustable small power supply.
« on: November 27, 2017, 12:03:37 AM »
If you like DIY, you might  want a small adjustable power supply.

But a professional service bench supply can be very pricey. At the other extreme, the changers for cell phones only give a single voltage.

Take a look ant the up-down voltage regulator r that has a modern chip that does what your want. You could use an old power block from a laptop as a DC source and wire it to this  device and get whatever DC you need. Up to about 20 volts.

I found it on eBay and checked  the data sheet. It is real product that represents state of the art in small regulators. So forget about using those old analog regulators you use twenty years ago. (Somebody had asked about 7805.)

Here one of may links on eBay to this little thing:
DC-DC Buck Step-down Regulator Converter
This thing is sold at a very low cost, you could not build one yourself for that price.
Photo attached ...    ;D

[attachment deleted by admin to conserve space]

DaveLembke



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Re: Make an adjustable small power supply.
« Reply #1 on: November 27, 2017, 06:09:24 AM »
Depends on what your current draw is to note also. This might work fine for small projects, but wont be a replacement for a laptop power supply for 4.16 amps at 19 volts. Looks like peak current is 3 amps and it likely gets warm at that current draw through that small regulator that has no heatsink. If you need more amperage a heavier power supply would be needed, and hopefully one with passive cooling and voltage regulator mounted to a heat sink to avoid melt down of the VRM.

I myself still prefer the 7800 series voltage regulators for quick projects because I can heat sink away heat and keep the voltage regulator cool.

The chip based voltage regulators that lack heat sinking are fine for low current needs, however I bought a phone charger that runs off of 2 x AA 1.5V batteries that takes 3 Volts and ramps it up to 5 Volts out of a USB port to charge a phone requiring 5 Volts from a 3 Volt supply and the VRM which was a small chip like the one in the picture of this power supply was roasting hot. I pointed my IR gun at it and it peaked at 218F it got my attention when I was feeling for heat and my finger touched it. The unit was getting warm and so I opened it up to see why it got so warm when charging my small LG smartphone with 3.5" display. I expected heavier duty electronics for passive cooling and what I found was that there was nothing to draw heat away from the voltage regulator. They had a voltage doubler circuit that brought the 3 Volts to 6 volts and then a voltage regulator to maintain the 5 Volts off of the 6 volt doubler circuit. The device is not economical for use because AA Batteries are not cheap and it will completely drain 2 Brand New Alkaline AA batteries and only get me 80% charge before batteries are spent from a phone battery that is drained to charged to 80%. These days I use the device as one last final drain for AA batteries before tossing them out. When the device they normally powered starts to show that it needs new batteries such as my wifes wireless keyboard and mouse which runs on AA batteries, the batteries are at say 70% life left but starting to make these devices act up, I will put the batteries into this cell phone charger and drain out the last of their juice to squeeze 20% charge into my phone then toss the batteries out completely spent.

I found this 2 x AA Battery Cell Phone Charger at a local Dollar Store and bought it out of curiosity for $1.00. Took my oscilloscope to it probing around to see what they are exactly doing with some chips unknown identification, then saw the doubler circuit bringing the 3 volts to 6 volts and the regulator with a clean 5 volt output. It pulls very heavy on those AA batteries but it does work! Makes you wonder how they make any money on it at $1.00 when the parts and labor to make it ourselves would go way over.  ;D

Geek-9pm

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Re: Make an adjustable small power supply.
« Reply #2 on: November 27, 2017, 02:47:37 PM »
For many small project 3 amps is more than enough. The data sheet for that chip shows that you will need a heat sink if you plan on using it at its maximum current and voltage leve4ls. But that chip does work well even at high temperatures.
Here is a link:
http://www.datasheets360.com/part/detail/mp1484en/2593044454316269448/
Thee you have to download the PDF to see what the limits are. It does good enough to run a typical notebook computer. They say it  will work up to 85 C. That is more than warm. Hot enough to cook an egg.



kemakara



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Re: Make an adjustable small power supply.
« Reply #3 on: March 29, 2018, 10:17:06 AM »
Quote
If you need more amperage a heavier din rail power supplies would be needed, and hopefully one with passive cooling and voltage regulator mounted to a heat sink to avoid melt down of the VRM.

A power supply converts alternating current from the outlet on the wall into direct current. There are several ways to do this. We are going to look at one of the simplest, but also most illustrative.

Electricity passes through several stages in a voltage regulator type power supply like this one, or like the common wall-wart. The ways in which it is altered by each stage are explained.

patio

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Re: Make an adjustable small power supply.
« Reply #4 on: March 29, 2018, 05:47:14 PM »
Re-read Dave's comments above...already explained.
   
 
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Geek-9pm

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Re: Make an adjustable small power supply.
« Reply #5 on: March 29, 2018, 08:04:44 PM »
To clarify, the device I mentioned is very suitable for small battery powered projects. It is not intended for direct conversion of power from the mains.

The data sheet shows it works well with 12 volt input and delivers output good for a smartphone or USB device.

For the price, one could not build anything from basic components with the stability and power rating of this device. Fir example, using a legacy LM7805 would only give 2.5 watts and would need heat sink. Of course, using a 7805 would be a very minimalist project.

And using a LM7805 would mark yh0ou as an old school DIY person and might cause a time warp if you put it in your rocket ship.



« Last Edit: March 29, 2018, 08:15:30 PM by Geek-9pm »