Potential divider cct Vs Regulator/ buck converters etc

[johndon2000]

Am I correct in thinking it is feasible to use a potential divider circuit to convert a 12V power supply to 5V, but it is just not practical?

And the reasons its not practical is because it's not efficient, excessive heat loss, melting resitors etc & there are much better alternatives (regulators, buck converters etc)

[alm]

The current you draw from a voltage divider should be small compared to the quiescent current. If you want to draw 1 A from a voltage divider that divides 10 V down to 5 V, then you might want the quiescent current an order of magnitude higher, so 10 A for example. This divider will consist of two 0.5 ohm resistors. Drawing 1 A through these resistors will reduce the voltage to 4.5 V instead of 5 V due to loading (bad load regulation), and in the mean time you will convert 50-60 W to heat in each of the resistors, even when not drawing any power. A linear regulator will be an order of magnitude more efficient under load, and maybe four orders of magnitude when idle, and a buck converter might be two order of magnitude more efficient under load.

For tiny currents, like the base current of a small signal transistor, the current drawn from the divider is negligible, so you can use much larger value resistors. This is where voltage dividers are commonly used.

[digsys]

Also, IF for some reason you didn't want to use a regulator, and only needed say up to 10mA, you can make your resistive divider,
with say 0.1mA Q, and feed that straight into a Op-Amp Buffer (which can be as small as a SOT23-5).

[johndon2000]

ok thanks guys

so, in a nutshell, you would use a potential divider in low current (mA) applications, but for higher current you should use a regulator etc?

Thanks again!

[c4757p]

As a rule of thumb, voltage dividers are used for signals, not power. (There are notable exceptions - hair dryers, for example, use the heating element as a voltage divider to get a lower voltage for the motor.) Even if a circuit uses less than a milliamp, it's quite rare to power it through a voltage divider. They can be used to configure a regulator, but the power isn't actually going through the voltage divider in that case.

[c4757p]

Also, IF for some reason you didn't want to use a regulator, and only needed say up to 10mA, you can make your resistive divider,
with say 0.1mA Q, and feed that straight into a Op-Amp Buffer (which can be as small as a SOT23-5).

At which point you have made a regulator...

[digsys]

  so, in a nutshell, you would use a potential divider in low current (mA) applications ...

Not would, could. I added it as an example of what you COULD do, given that you had started with a Voltage divider example.

  At which point you have made a regulator... 

Some say Potatoe some say Potato ... :-)  .... see above

[c4757p]

Some say Potatoe some say Potato ... :-)  .... see above

Perfect analogy - the ones who say "potato" are spelling it right...