use of capacitors and inductors in buck converter [closed]

Question

For stepping down voltages, why can't we use a simple resistive circuit and the voltage division rule for the output? Why do we use a buck converter instead? What role do a capacitor and an inductor play in a buck converter?

Answer 1

There are two primary motivations for using the converter:

1. The resistor divider will not provide regulation. The more current you draw from it, the lower the output will become. If the input voltage changes, the output will change proportionally. The converter will work to keep the output voltage the same over a wide range of source and load conditions.

2. The resistor divider dissipates most of the power it takes. You have to choose resistors with low enough resistance that you can supply operating current to the load. Those small resistors will dump a significant current to ground, wasting power. Converters are designed for efficiency in the 75-95% range, which will be difficult to obtain with a voltage divider.

Shortcuts exist to use a voltage divider to obtain a certain supply, but they are themselves usually used with regulated supplies as sources, and buffers such as emitter followers or op amps to keep the load current from having much effect on the divider.

Answer 2

Short answer: you need the ability to store energy to actively regulate the voltage or current. You can use a variable resistor in the form of a transistor to regulate the voltage which is essentially what an LDO does, but resistive dividers are lossy.

And capacitor or inductor allows you to store energy for a short amount of time and then give it back allowing you to regulate the voltage or current. Another nice thing about storing energy is you can add additional switches and get more voltage than you started with which is not possible with a resistor divider.