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Why dB scale preferred in Power Electronics?

Decibel(dB):


Decibel is logarithmic scale. It defines the ratio of two quantities. In electronics circuits and systems, it is used to define the power or voltage gain of the system or amplifier. In communication system decibel scale is used to represent attenuation.


When it is used to define power gain, factor 10 is multiplied with logarithmic scale and it is represented as


Gain in dB= 10 log (Gain)


When it is used to define Amplitude or voltage gain, factor 20 is multiplied with logarithmic scale and it is represented as


Gain in dB= 20 log (Gain)


Power is proportional to square of voltage therefore factor 20 is multiplied when voltage gain is calculated.


Power Gain:

For an amplifier power gain can be calculated as,

If pin=1w,pout=10 w and gain=10


Gain in dB=10 log (gain)


Gain in dB=10 log (10)


Gain =10 dB.





Above table shows some example of power gain which is calculated in dB.
If pin=1w,pout=0.1w and gain=0.1

Gain in dB=10 log(gain)

Gain in dB=10 log(0.1)

Gain= -10dB

Attenuation provided by system is 10dB.

Amplitude Gain:

For an amplifier amplitude can be calculated as,
If vin=1v,vout=100v, and gain=100

Gain in dB=20 log(gain)

Gain in dB=20 log(100)

Gain=40dB.



dBW:

when power is represented with respect to 1w of power in decibel scale then it is represented as dBW. 

For example:
If pi=10w then

Gain in dBW=10 log(10w/1w)

Gain=10dBW.

dBV:

when  voltage is represented with respect to 1v of voltage in decibel scale then it is represented as dBV.

For example:
If vi=100v then

Gain in dBV=20 log(100v/1v)

Gain=40dBV.

dBm:

when power is represented with respect to 1mW of power in decibel scale then it is represented as dBm.

For example:
If pi=100mW then

Gain in dBm=10 log(100mW/1mW)

Gain=20dBm

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