### Author Topic: How does one allocate different voltages to different circuits from one supply?  (Read 420 times)

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##### How does one allocate different voltages to different circuits from one supply?
« on: March 18, 2019, 07:54:25 pm »
I am a beginner, and I am wondering about how to power different circuits with one supply.

Let's say we have a car battery with like 14v, how does that volatge get spread across the various radio, screen, and audio circuits. I'm assuming they don't all run off 14v.

I know you can use voltage dividers, but wouldn't that result in power losses if you use resistors?

Also with high power circuits, you would need high power dissipation resistors right?

If anyone can explain this to me that would be amazing! Also if anyone has any schematics or anything that would be really great.

#### Benta

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##### Re: How does one allocate different voltages to different circuits from one supply?
« Reply #1 on: March 18, 2019, 08:06:16 pm »
You use local voltage regulators, meaning each circuit has its own.

#### jeroen79

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##### Re: How does one allocate different voltages to different circuits from one supply?
« Reply #2 on: March 18, 2019, 08:23:21 pm »
Depending on the application there are several options.
-Linear regulator.
Low efficiency but little noise.
-Switching DC-DC converter.
More efficient but switching adds noise.
-Charge pump.
For low current applications.
-Voltage divider.
Most useful if you need some reference voltage with no load.

#### IanB

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##### Re: How does one allocate different voltages to different circuits from one supply?
« Reply #3 on: March 18, 2019, 08:40:54 pm »
I am a beginner, and I am wondering about how to power different circuits with one supply.

Let's say we have a car battery with like 14v, how does that volatge get spread across the various radio, screen, and audio circuits. I'm assuming they don't all run off 14v.

This tends to happen with modern computer boards.

For an analogy, think about the mains supply in your house. Most items need a lower voltage, so you have various "wall wart" or "plug pack" adapters like cellphone chargers that you plug into the mains and get a low voltage out the other side. All of these adapters are various kinds of voltage step-down converter.

Similarly, a modern computer board may have a 12 V supply coming in and have it routed around the board like a 12 V "mains". Various chips that need lower voltages, like 5 V, or 3.3 V, or 2.5 V have local voltage step-down converters that take the 12 V "mains" coming in, and produce the required lower voltage going out.

The mode of operation of mains adapters and local voltage step down converters on a computer board is very similar. They all tend to be a kind of "transformer" with special circuitry to control and regulate them.
I'm not an EE--what am I doing here?

#### rstofer

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##### Re: How does one allocate different voltages to different circuits from one supply?
« Reply #4 on: March 18, 2019, 11:25:13 pm »
Let's say we have a car battery with like 14v, how does that volatge get spread across the various radio, screen, and audio circuits. I'm assuming they don't all run off 14v.

Sure they do! Even the engine control unit (ECU) connects to the battery voltage.  If anything needs a lower voltage internally then it uses some kind of voltage regulator.  But they will all start out by being connected to battery voltage.

Others have explained about linear versus switching power supplies and either will work.

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##### Re: How does one allocate different voltages to different circuits from one supply?
« Reply #5 on: March 18, 2019, 11:32:21 pm »
Thanks everyone!!

Smf