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3a : Buck Converter

A DC-to-DC converter is a device that accepts a DC input voltage and produces a DC output voltage. Typically the output produced is at a different voltage level than the input. In addition, DC-to-DC converters are used to provide noise isolation, power bus regulation, etc. The following is a summary of some of the popular DC-to-DC converter topolopgies:

1)Buck converer                                     isolated                             single output

2)boost converter                                   non isolated                       multiple output

3)buck-boost conveter   


There may be only L and no C. If L and C both are there, then it is a 2nd order converter as its functioning will be described by a 2nd order differential equation. The plots of pulses to the main device (with ON time of 0.6 out of a cycle time of 1 pu), Vo and Iload with respect to time are as follows:


Vo=d Vin where δ= tON/T;  tON being the ON duration of the main switch and T being the period of the turn-ON and turn-OFF of the switch.

When s1 is on ,L accumulates energy during this time current increases.



((Vin-Vo)/L)t + i(o)= i(t)          where i ‘is the current flowing through the inductor

During off interval when D1 is on


i(t)=(-Vo/L)(t-dT) + i(dT)

These are the equations during turn on and turn off intervals.


The simulation circuit for a buck converter is given below:

The current at the output is continuous or not is decided by the value of filter inductance. The ripple content in the output voltage is decided by the capacitor. The minimum value of inductance for maintaining continuous conduction decided by the values of frequency, duty ratio, load current and the input voltage.


Cite this Simulator:

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