# Inductance dimensionning

Discussion in 'General Electronics Chat' started by Oussama Zaidi, Jul 18, 2016.

1. ### Oussama Zaidi Thread Starter Member

Mar 1, 2016
53
0
Hi
In the picture below I have a voltage regulator with an external inductance of 330uH of value, I want to know what is the role of the inductance in the circuit ? why do we need to use it ? and also how they calculate its value ? can I use for example just 150uH not 330uH? Thank you.
Datasheet:http://www.mouser.com/ds/2/405/lm2575-n-405736.pdf

2. ### bertus Administrator

Apr 5, 2008
18,682
3,633
Hello,

Did you see fig 31 on page 14 of the datasheet?
It has some graphs on the inductor ranges.
Also look at page 15 for the formulas to make the calculations.

Bertus

Oussama Zaidi likes this.
3. ### BobTPH Senior Member

Jun 5, 2013
1,214
243
And, yes, the inductor is the key component that makes a buck regulator work. Without it you would simply be PWMing the input voltage to the output.

Bob

Oussama Zaidi likes this.
4. ### DickCappels Moderator

Aug 21, 2008
5,000
1,517
But if you think about it the heart of a buck converter is PWM followed my a low loss LC low pass filter.

Oussama Zaidi likes this.
5. ### crutschow Expert

Mar 14, 2008
20,216
5,717
That is a switching regulator to give high efficiency conversion of a high voltage to a lower voltage.
The output of the IC is a PWM signal switched between 0V and the input voltage, with an average value equal to the desired output voltage.
This pulsed voltage could be smoothed with an RC filter but that would dissipate power in the resistor and give no better efficiency than a linear regulator.
Thus the "why" we need the inductor, is to losslessly absorb the pulse energy (stored energy = ½ LI²) and store some of it between pulses while transferring it to the output.
This, in conjunction with the output capacitor, give a steady DC output voltage with only a small ripple voltage.

Since, with proper design, this switching conversion process will have low losses, it is much more efficient (for significant differences the input and output voltages) than simply dumping the excess voltage across a variable resistance as heat, which a linear regulator does.

Oussama Zaidi likes this.