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As the title suggests I am looking for a way to drop 12V to 5V**. Which circuit should I use? And if I am going to use one, Why can't I use the others in the list ? I am looking for: 1. If the current going in is the same as the current going out. 2. Least heat dissipation. My options : Voltage Divider ; DCDC Converter ; Zener Diode ; Voltage Regulator IC.

** I am trying to run 4-5 servos (5V) using a microcontroller (PIC 18F452) and also 4 DC motors(12V).

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  1. A Very Low drop of current. 2. Least heat dissipation.

First off, let's discuss your requirements. "Low drop of current" doesn't make much sense, typically you would specify something like "low dropout voltage", but that's not necessary in this case (12V is much more than 5V). Or perhaps you mean you want as much current out as goes in, which is easily met by a DC-DC converter. Regardless...

Voltage Divider

A voltage divider is not suitable for powering a load. As the current drawn by the load increases, the voltage decreases; and it will dissipate quite a lot of power.

Zener Diode

Again, not appropriate except for very small loads, which motors are not. Large power dissipation for high load currents, and not very stable regulation. Zener diodes are typically used for references rather than regulators.

DCDC Converter ; Voltage Regulator IC.

In the context of your question, these are the same thing. The distinction you are looking for is switching DC-DC converter vs. linear regulator (both of these are DC-DC regulators, and both are typically ICs). For your purposes, a switching converter is most appropriate as it will dissipate the least power, and will actually have more current out than in (a step down converter, 12V -> 5V, will be able to supply about twice as much current as the input current).

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A Very Low drop of current.

Meaningless unless you mean has the ability to drive a good amount of current or does not take too much current in standby. Both important.

Least heat dissipation

A DC-to-DC converter is your only option here. Specifically, you need to find a high efficiency buck regulator capable of supplying the current you need. All the other options will waste heat because that's what they do when they drop voltage from a higher voltage to a lower voltage.

When you have decided what current you need there are plenty of ways to find one.

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A Voltage Divider is only useful as a power supply if you are drawing very small amounts of current and can handle the heat/inefficiency, so I'd count that out right away. A Zener Diode has its uses, but you're likely to run into similar problems as the Voltage Divider.
A DC-DC buck converter is good on efficiency/heat and there are a wide number of choices out there. If you don't want to trouble yourself with all the passives connected to it, there are DC-DC modules available from places like TRACO Power.
The term "Voltage Regulator IC" is a little broad. Depending on your current requirements, a low-cost solution may be an LDO.

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Which circuit should I use?

in cases like this, you generally start with the power profile of your circuit, and its supply requirement, and go from there, with the understanding that any of the options can be made to work here.

assuming a typical always-run mcu circuit without heavy load, you are talking about 10ma of steady current consumption (towards the high end).

all linear solutions are comparable in terms of power dissipation - 70mw here, so not much to worry about.

a divider (more precisely ONE resistor) can be made to work but it is quite limiting and in my view doesn't offer much.

a dc/dc converter can be complex, expensive and ripple-rich, not a great choice if you have adc involved. but it can be efficient under heavy load.

I would go with a liner voltage regulator as it is of low cost and offers the most flexibility, with minimum downside.

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