How to reduce the voltage of a laptop power supply without reducing amperage?

Hi guys, I have a laptop power supply with an output of 19V, 5.6A. I want to use it to power a small stereo amplifier that needs 12V. I want to make an adapter or something that will reduce the voltage without affecting amperage for use with the small amplifier, but I also need it supplying 19V for the laptop. Is it possible to make do it this way: [19V power brick] --> [adapter/transformer] --> [amplifier]?

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Jack A Lopez4 months ago

Hey I was thinking: If you like challenges, maybe you could take apart your 19V power brick, and rewire it, so that its voltage output is 12 volts, instead of 19 volts.

You know, if could open it up, and discover what IC is doing the voltage regulating, and maybe look up the data sheet, and discover how the feedback works for that.

You might be able to re-wire its little voltage sense network, and make it into a brick that supplies regulated 12 V DC, instead of 19 V DC.

Tristan GianP (author)  Jack A Lopez4 months ago

I'll probably take the power brick apart then buy another power supply. For learning stuff while making sure I can use the amp. Thanks for the idea!

Tristan GianP (author) 4 months ago

The amp needs 2amps. It is rated for 30watts output. I haven't uses the amp yet since I have yet to reduce the voltage of the laptop power brick (chinese cheap amps based on TDA7297 don't come with a wallwart. :(( )

By the way, where did you find your, what you call "chinese cheap amps based on TDA7287"?

If the answer to that question is you bought them from somebody on eBay,

https://www.ebay.com/sch/i.html?_nkw=TDA7297+audio...

Then the answer to question of how to find a matching power supply for it, is maybe also, "eBay"

https://www.ebay.com/sch/i.html?_nkw=12v+3a+power+...

Also, I am not sure how you arrived at the answer of 2 A, from a rated power of 30 W. The usual formula for power is, power = voltage*current

So the current needed at 30 W, would be (30 W)/(12 V) = 2.5 A

When shopping for this new power supply, it would not hurt to choose one that could supply a little more power than what you need; i.e. a current rating greater than 2.5 A.

Also depending what the used junk market is like in your town, you might be 12V DC, at {3A , 5A, etc}, adapter, cheap locally.

In the town nearest to where I live, there are these places called "thrift stores"

https://en.wikipedia.org/wiki/Charity_shop

and those are the places where people donate old junk, like stray DC adapters, and the thrift store sells it at cheap prices.

seandogue4 months ago

I'm in agreement with some of the others who've answered and would suggest buying another supply for the audio amp.

It IS (likely) possible, but power supplies are so cheap as to make cost for a proper audio amp power supply a near non-issue.

Jack A Lopez4 months ago

I humbly suggest finding a similar, black brick, power supply, except one designed to supply a regulated 12 volts DC.

I recall the power supply for the old Xbox(r) 360, was regulated 12 volts DC, with rather hefty maximum current rating, like 12A to 16 A, (e.g. 12.1 A, 15.0 A, 16.1 A) depending on the exact hardware version.

There was a trick to turning it on. Essentially one of the wires in the cable was an enable input, and that had to be connected to the +5 V rail. Did I mention this thing also has a regulated 5V DC rail too? It does, but this 5V rail is only rated for 1 A of current max, similar to USB. I found a tutorial, one of many out there, that shows how to do this, here:

http://yetanotherpointlesstechblog.blogspot.com/20...

Come to think of it, those metal box enclosed, switching power supplies, found in the back of any desktop computer (ATX might be the actual name of this form factor), all of those have a 12 V DC rail, and many of them capable of supplying big current, circa 10 A max, on that DC rail. You'll have to look at the name plate to tell you what the exact max current rating is.

And again, for the ATX power supply, there is a wire that is an enable input. Only this time that enable pin wants to be pulled to ground, to make the power supply turn on.

rickharris4 months ago

As Steve says a lot depends on how much current you need to draw from the PSU.

Using simple methods you will normally effectively be dropping the extra voltage across a "resistor" (may be a FET) which may generate a lot of heat.

What is the wattage of the amp or better it's current consumption.

steveastrouk4 months ago

What current does the amp need ? It will draw what it needs, but the part you need to convert the voltage has to handle it.