# what do you mean by biasing?

Discussion in 'Electronics Homework Help' started by diaryrashid, Nov 25, 2012.

1. ### diaryrashid

10
0
Nov 25, 2012
hello everyone
i have some question

1- what do u mean by biasing in transistor??

2-list the different types of biasing?

3- what is the operating point or Q point of transistor?

4-why it necessary to have a CAPACITOR between the input and the base of the transistor?

thanx

2. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

25,449
2,809
Jan 21, 2010
Did you try googling for any of these?

OK, OK, it's pretty hard. LMGTFY.

3. ### Raven Luni

798
8
Oct 15, 2011
#4 might need a hint before googling. Look for 'coupling capacitor' (and in case you get confused, note that this is also very different from a DEcoupling capacitor)

10
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Nov 25, 2012
yup.thx

5. ### CiaranM

74
1
May 19, 2012
1) 'biasing' means applying voltage to the base for the TR to switch on. typically 0.6-0.7V.
2)I guess you mean forward bias and reverse bias? you'd usually hear these terms when talking about diodes (do remember that the transistor is, in effect, two diodes joined back-to-back). Forward bias means the appropriate polarity of voltage (at least 0.7V for an NPN TR) has been applied and current is going in the typical direction. Reverse bias means that the opposite polarity of voltage to what is usual has been applied, and so current goes in the other direction. this is actually quite useful for zener diodes or using TRs as noise sources.
4) this is called a 'coupling capacitor' and it serves to remove a DC offset. imagine that you have a sine wave which cycles around 0V. Its positive peak is at 1V, and its negative peak is at -1V. Now, say that there is a DC offset of 2V. This moves the sine up 2V on the axis, so now it cycles from 1V to 3V! Note that the since wave is now direct current. This is bad, though I forget why. Basically, a coupling cap removes this offset and brings the wave back down to where it should be. You'll also see coupling caps on the outputs of circuits.