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Figure: 3.20 circuit diagram of Buck regulator
The circuit for the buck regulator operates by varying the amount of time
in which inductor receives
energy from the source.
In the basic block diagram the operation of the buck converter or buck regulator can be seen that the
output voltage appearing across the load is sensed by the sense / error amplifier and an error voltage is
generated that controls the switch.
Typically the switch is controlled by a pulse width modulator, the switch remaining on of longer as more
current is drawn by the load and the voltage tends to drop and often there is a fixed frequency oscillator to
drive the switching.
Buck converter operation
When the switch in the buck regulator is on, the voltage that appears across the inductor is Vin - Vout.
Using the inductor equations, the current in the inductor will rise at a rate of (Vin-Vout)/L. At this time
the diode D is reverse biased and does not conduct.
Figure: 3.21 circuit diagram of Buck regulator during switch on condition
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When
the switch opens, current must still flow as the inductor works to keep the same current flowing. As
a result current still flows through the inductor and into the load. The diode, D then forms the return path
with a current Idiode equal to Iout flowing through it.
With
the switch open, the polarity of the voltage across the inductor has reversed
and therefore the current
through the inductor decreases with a slope equal to -Vout/L.
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