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Buck converter design

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pradipmagar001@gmail.com

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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%.
 

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

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.
 

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.
 

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
 

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