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How to make a Variable/Adjustable Power Supply ? Answered

Hi Everyone,

I am having (12 - 0- 12)V and 1.6A AC to DC Transformer, and I would like to make Adjustable power supply, How I can do that? and on reducing the voltage amp would be same ? or amp also reduces ?

and Also want to add a USB port to charge my mobile devices..

Transformer image
http://blogspot.tenettech.com/wp-content/uploads/2014/07/x-0-x-500x500.jpg



Edited.
I want to build my own Custom circuit using bridge rectifier and some Capacitor and resisters. Alhtough @-max- answer is very good and thinkable, Can you recommend some Good ready-made adjustable circuit which having the capability to control Amp and also volts ? Please provide link or Name/Model#


Please guide me..

Thanks

Discussions

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Nematic!

2 years ago

Built a rectifier and use it with LTC 3780 module

with this module you can controle volts and amps

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-max-

2 years ago

"I want to build my own Custom circuit using bridge rectifier and some Capacitor and resisters. Alhtough @-max- answer is very good and thinkable, Can you recommend some Good ready-made adjustable circuit which having the capability to control Amp and also volts ? Please provide link or Name/Model#"

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How a Regulator works (basics): A typical power supply works by using a switch sorta like a dimmer control, but with some smart circuitry that monitors the output voltage / current

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A: Google is your friend. There are many schematics that exist out there, it is not too hard to find one that fits your criteria.

B: For the most rudimentary DIY power supply: A single transistor (preferably darlington) and a zener diode can be combined. It really does not get any simpler. Connect the collector of an NPN device to the positive, the base to some voltage reference (for this crude design, a few series LEDs or a zener diode is fine) and the emitter (output) to capacitor bridging to ground. Because the transistor turns on when the voltage between the base and emitter exceeds 0.6V, the transistor will be turned off and not allow any current to flow until the voltage on the emitter falls 0.6V below the voltage present at the gate, at which point it starts to deliver power, and the voltage is regulated. This can be built and messed with in 5 minutes time, and is "good enough" for many non-critical applications, and was quite popular before the much better 3 pin regulators became commonplace.

C: Better "simple" regulator: Just use a classic chip, like the LM7805. 3 pins: Input, Ground, Output. The wiring is also that dead simple. For more robust design you would add some bypass capacitors as close to the pins as possible, some filter capacitors to buffer the input and output, and maybe some reverse-biased diodes for some protection, but that is generally unnecessary. LM317T is a bit more difficult, requiring a resistor divider and external feedback, but it's still very simple. The problem with most of these designs is that they typically have a 1.25V bandgap voltage reference in series with the feedback, so you have to get the adjust voltage to -1.25V to get the output to go down to zero. A second LM317 current limiting circuit can be connected in series to the input of the voltage reg to limit current. That is also not perfect, but it's simple and works.

D: EEVblog did a power supply design, using a very flexible LT chip and he had some requirements that as you will learn, are hard to accomplish. Took him like 5 videos to get to a final design.

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Yonatan24

2 years ago

You've come to the wrong part of the right site...

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rickharris

2 years ago

LOADs of projects to do just that on the right >>>>>>>>>>

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-max-

2 years ago

The question is far to vague for a unique answer. Do you want a current limit function? DO you want a fully adjustable supply, or only down to ~1.2V? Dual rail? Any electrical noise or efficiency requirement? without any precise requirements, below are the 2 main directions you can take your project:

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1) Build your own supply: There are lots of chips available, switching regulators (like the LM2596), which are "better," or if you want simple, a 3 pin linear regulator would suffice. A little extra circuitry can add a current limiting mode (like CC mode) When designing your own, you can get as advanced as you want. From copying an already existing design, all the way up to designing your own from scratch w/ transistors and opamps!

a) While building your own is the "harder" option, it allows you to get exactly what you want, and optimize your design for your need. I personally recommend this to do as a learning experiment.

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2) Just buy a DC to DC module. Amazon sells a wide variety of cheap DC to DC converters for fairly cheap. Some can reduce, boost, and/or invert voltage, some offer a basic CC mode, some are very powerful, and some even have displays and knobs which allow you to set the voltage and current limits separately. The last one is probably the best generic option for an easy "DIY lab power supply"

Just MAKE SURE to to rectify your transformer's output using a full wave bridge rectifier and to use a substantial smoothing capacitor.

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Downunder35m

2 years ago

1. A transformer won't provide DC by itself, either infos are missing or missed some vital details.
2. What happens to the amps largely depends on how you reduce the output voltage.
3. My best suggestion would be two buck convertes, one for the adjustable output, the other (or a car charger) for the USB charging.
If you need more then 12V you can also use step-up-down-converters.

Last but not least you can find a lot of Instructables about this, some are listed on the right.