Buck converter design

[pradipmagar001@gmail.com]

Please suggest me practical buck converter design, because i studied various designs available on internet but they gave me component values which vary design to design.My specifications for buck converters are.
Vin=12v, Vout=5v, load current=2A, Switching frequency=18Khz, Output voltage ripple 3%.

 

[goldsmith]

Hi
What are you exactly looking for ? how to design perhaps ? or a designed circuit ?

 

[pradipmagar001@gmail.com]

Thanks for reply sir...
I don't want designed circuit, just want design procedure formulas or any application note that gives some easy method for it.

 

[BradtheRad]

1.

You need to determine the coil's Henry value, based on the given switching frequency and load current.

The LR time constant is useful here. Start at switch-On time. Current ramps up from zero to, say, 2x your load current. Then you switch Off. Current ramps down to zero.

The cycle period is 1/18000 sec.

Your duty cycle prospectively is 5V / 12V, or 42 percent.

Assume a switch-On resistance of a few tenths of an ohm. What Henry value will ramp up to 4A during switch-On?

During switch-Off your load resistance is involved. It calculates to 2.5 ohms (5V divided by 2A). What Henry value will drop from 4A to zero A, through a resistance of 2.5 ohms, during switch-Off?

The above approach can only be approximate, because the smoothing capacitor adds its own dynamics to the mix.

 

[goldsmith]

Hi
Design formulas ? well ,
The method which Bradtherad mentioned is good too but there is another way too ( in addition with that )
For CCM buck converter where inductor current don't reach zero : L=[5*(vi-vo)/io]*[vo*t/io]
C=I/F*vrpp

Best Luck