# Buck Converter vs Voltage Divider

Why would I prefer to use a buck converter over a voltage divider, and vice-versa?

I know that voltage dividers are less complex and cheaper than buck converters, given that voltage dividers are simply two resistors.

What are other pros and cons of using a buck converter?

• Which application(s) are you interested? Or are you asking about en-general? – calcium3000 Oct 11 '17 at 22:25
• yes, in-general – Shicon Wen Oct 11 '17 at 23:28
• Voltage dividers are 1) Far less stable, 2) Are generally very inefficient, and 3) Are affected by the load connected. Voltage dividers are fine if the output is connected to a very high impedance (i.e. the ADC input of a microcontroller) but when you try to drive an actual load it will become a part of the divider network (in parallel with the lower resistor) and will affect the output voltage – DerStrom8 Oct 11 '17 at 23:37
• voltage dividers are for tiny loads: instruments, voltage refs, FET driving, etc – dandavis Oct 12 '17 at 6:55

## 3 Answers

It's generally down to efficiency. For very small currents, a voltage divider can use very little power (by using high value resistors_, while a buck converter will use power just powering itself.

But at larger currents, a voltage divider can waste a lot of power as heat in the resistors. A buck converter might be ~80% efficient under load.

• The load on the output can be thought of as another resistor to ground that is in parallel with the other resistor defining the value, so anything but infinite load resistance will pull down the output. – Simon Richter Oct 11 '17 at 22:34

Keep in mind that voltage dividers have three legs, and the voltage in the junction is determined by all three.

Normally, two of these are resistors with a known value with one side connected to a supply rail (= low resistance), so the combination of voltage and resistance is known and fixed for these. The third leg, the "output", however also affects the voltage, and in a normal voltage divider, you want a high resistance here to minimize the effect.

If you have a high resistance on the output path, it is no longer usable as a supply rail, because that would need to be low resistance — try connecting a voltage divider behind a voltage divider.

A typical buck converter contains a voltage divider on the feedback path to select the output voltage. The feedback input is a high-impedance comparator input, while the output of the buck converter is connected to a large capacitor that acts as a low-impedance source, so the output of the voltage divider is well-defined.

Voltage dividers are not a good choice to source current to a load. If you draw significant current from it, then the voltage at the output of the divider drops.

simulate this circuit – Schematic created using CircuitLab

As you change the load value, you change the value of $V_{out}$. If you want to keep the voltage pretty much constant, the current through the load should a lot smaller than the one through $R_2$.

A dc-dc converter (buck, boost, etc) makes sure the voltage stays pretty much constant under different load conditions. If you find them to be too complex or an overkill for a specific application, you could instead choose an LDO.

A voltage divider would find an application, for example, as an input to an ADC, because the ADC only needs to measure the voltage level to translate that into a binary number, while drawing little current and therefore does not disturb the output voltage.