I would like to add to the wonderful answers provided here.

In general avoid the use of voltage dividers to power your circuits. But, even voltage regulators may be a bad choice in many cases.

Voltage regulators change the voltage level by dissipating the excess power as heat.

Example: You have a 9v input and you are using a regulator to change it to 5v. Consider you circuit requires 1A of current.

Now, in voltage regulators, the input current is slightly higher than the output. But it is small enough to be ignored for calculations. So, we have 1A of current as output and 1A of current as input.

Output power = 1A x 5v = 5W Input power = 1A x 9v = 9W

There is a difference of 4W between the output and input. This power difference is dissipated as heat that is why often a heat sink is required. This also means that the power is getting wasted. This is a huge issue for power conscious applications such as those battery powered.

Here comes the buck converters to the rescue. For a buck converter, the output and input powers are equal if you consider 100% efficiency. However, they are generally 80-90% efficient. That means for an output of 5W, the input will be 5/0.9 (90% efficiency) = 5.55W

This is a difference of 3.45W.

Similarly, boost converters step up the output DC voltage.

Hope it helps.

In general avoid the use of voltage dividers to power your circuits. But, even voltage regulators may be a bad choice in many cases.

Voltage regulators change the voltage level by dissipating the excess power as heat.

Example: You have a 9v input and you are using a regulator to change it to 5v. Consider you circuit requires 1A of current.

Now, in voltage regulators, the input current is slightly higher than the output. But it is small enough to be ignored for calculations. So, we have 1A of current as output and 1A of current as input.

Output power = 1A x 5v = 5W Input power = 1A x 9v = 9W

There is a difference of 4W between the output and input. This power difference is dissipated as heat that is why often a heat sink is required. This also means that the power is getting wasted. This is a huge issue for power conscious applications such as those battery powered.

Here comes the buck converters to the rescue. For a buck converter, the output and input powers are equal if you consider 100% efficiency. However, they are generally 80-90% efficient. That means for an output of 5W, the input will be 5/0.9 (90% efficiency) = 5.55W

This is a difference of 3.45W.

Similarly, boost converters step up the output DC voltage.