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voltage regulators vs resistors?

what are the benefits of voltage regulators over resistors and vice versa? why to use voltage regulators if resistors can limit the voltage?

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Ignore Mpilch, sadly he's wrong. A voltage regulator drops EXACTLY the same amount of power as a resistor !! Where the regulator wins is that it automatically adjusts controls the output VOLTS irrespective of the CURRENT, within the limits of the device, and the output resistance of a voltage regulator is effectively ZERO.

Reasons to use a regulator over a resistor
1.Low voltage cutoff -> Self resume after voltage 'within tollerance'
2.Efficiency - more efficient for large current setups.
3.Harmonics cancellation- I.E. Ripple rejection as mentioned here.
4.Not limited to 1/4w and 1/2w - yes you can parallel but you might need banks of them.
5. Other custom feature such a thermal cutoff.
Reasons to use a resistor over a regulator
1. Cost - Resistors are cheap.
2. Low load(cost) - Somthing like 20ma 5v as an example
3. Complex balanced circuit - by creating a resistor bridge one can measure the draw of things 'nearby'/'linked' in/around the circuit.
4. Kustom - Its basically a non IC version of a regulator and costs more too.

Couple of points wrong.

Item 2. Since we are talking linear regulators. How can it be more efficient ? The same energy is dissipated in the two devices. Granted, in some low load, low drop applications, a linear reg can be surprisingly efficient, but the energy dissipated, once again, is the same.

Item 4. Not heard of a power resistor ?

TL:DR. A resistor is not a replacement for a regulator, when the voltage or current in a load must be controlled to a high precision.


Tell them they are all wrong steveastrouk

It is about ripple.

Joe
Resistors are great for limiting voltage if there is very little current drawn by the circuit. But when you get up to hundreds of mA being needed by a circuit a regulator is best.

For instance, if you want to make a decent USB charger for your smart phone. Many phones are looking for a voltage on the data pins of the USB connector which tells them it's safe to charge thinking it's attached to a PC. It's only looking for around 2V at only a few micro amps, so adding a couple of resistors in a voltage divider configuration is a great way to take the 5V down to 2V.

But when you need more then a few micro amps from the power source you will need large resistors that can handle the power through them. The thing about resistors is they are very inefficient compared to a voltage regulator. When you are using resistors in a voltage divider configuration of say taking 9V down to 5V, your basically loosing that extra 4V to heat. In the case of a battery your are wasting about 1/3rd of the battery life to heat. Voltage regulators are able to use more of that access voltage towards the output and loose less of it to heat. Though it still burns off a good bit of that access power to heat. Just not as much as resistors do.
@mpilchfamily "Resistors are great for limiting voltage if there is very little current drawn by the circuit. But when you get up to hundreds of mA being needed by a circuit a regulator is best."

--Ok, so if i'm powering a chip which is rated to draw +/-50mA, then heat would not be an issue with a resistor?

@Josehf Murchison "Ripple comes through with resistors and not regulators. Ripple is caused when you rectify AC and convert it to DC."

So, if i'm dividing V from a battery, then i do not need to worry about ripple, correct?
It is about ripple.

Ripple comes through with resistors and not regulators.

Ripple is caused when you rectify AC and convert it to DC.

First when you run your AC through a rectifier it comes out as a bunch of humps.

Next you add a capacitor to the circuit.

This keeps the voltage up but it drops a little between the tops of the humps this is called ripple and it comes through in some circuits.

Voltage regulators work at 2 volts below the ripple minimum thus eliminating the ripple.

Joe
A resistor limits voltage in exact proportion to how much current is flowing through it.  Supposing the voltage on one side of the resistor is Vin, the voltage on the other side is Vout,  and the current flowing through it is I, then the voltage drop across it is: 

Vin-Vout = I*R 

or

Vout = Vin - I*R

A typical linear voltage regulator
http://en.wikipedia.org/wiki/Linear_regulator
has three pins, {Vin, Vout, Vground}, and it has some magic wired into it so that it tries to regulate Vout,  actually (Vout-Vground), in such a way that this number stays constant.

If you like, you may imagine this magic is accomplished by way of a tiny demon living inside the voltage regulator who has a voltmeter connected between pins Vout and Vground, and also a variable resistor Rvar connected between Vin and Vout.    So, now:

Vout  = Vin - I*Rvar  = constant

Then the demon watches Vout-Vground, (which really is Vout, assuming Vground=0).  When this voltage is too low, the demon turns a knob to decrease Rvar.  When this voltage is too high the demon turns the knob the other way to increase Rvar.
 
So now, Vout = constant,  independent of whatever current I is being drawn through the regulator, and it is all due to the efforts of this hard working little demon.  

If you are uncomfortable with idea of demons living in your electronic components, you could just as easily say the magic (or perhaps engineering if you don't like the word "magic") is due to an electronic circuit which uses feedback to regulate its output voltage.
http://en.wikipedia.org/wiki/Feedback#Electronic_engineering