Potential divider cct Vs Regulator/ buck converters etc - Page 1
Forum section: electronics / beginners

author: johndon2000
author_rank: Contributor
timestamp: June 13, 2013, 11:27:52 am
content: 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)

author: Unknown
author_rank: Unknown
timestamp: June 13, 2013, 11:40:38 am
content: 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.

author: digsys
author_rank: Unknown
timestamp: June 13, 2013, 01:05:31 pm
content: 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).

author: johndon2000
author_rank: Contributor
timestamp: June 13, 2013, 01:54:50 pm
content: ok thanks guysso, 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!

author: c4757p
author_rank: Super Contributor
timestamp: June 13, 2013, 02:03:10 pm
content: 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.

author: c4757p
author_rank: Super Contributor
timestamp: June 13, 2013, 02:07:14 pm
content: Quote from: digsys on June 13, 2013, 01:05:31 pmAt which point you have made a regulator...

author: digsys
author_rank: Unknown
timestamp: June 13, 2013, 10:50:55 pm
content: Quote from: johndon2000Not would,could. I added it as anexampleof what youCOULDdo, given that you had started with a Voltage divider example.Quote from: c4757pSome say Potatoe some say Potato ... :-) .... see above

author: c4757p
author_rank: Super Contributor
timestamp: June 13, 2013, 10:52:25 pm
content: Quote from: digsys on June 13, 2013, 10:50:55 pmPerfect analogy - the ones who say "potato" are spelling it right...