Week #8: (10/22-26) Transistor Biasing

[rjagodowski]

This week we will discuss various transistor biasing schemes for bipolar junction transistors. The lecture will be based upon the circuits built in the lab exercise. This week's lab will be Experiment #5 handouts on Transistor Bias Circuits. A copy will be provided for you during Tuesday's class on 10/23. A pdf of this lab can be found in the Registered Users Only area here. You must be registered and logged in to view content in this area.)

You may find this link to Transistor Biasing handy from Electronics-Tutorials.ws, which has tutorials on many electronics topics. Here's a link to introduction to Amplifiers from Electronics-Tutorials.ws.

Here's an additional link you might find helpful: BJT DC Biasing. It's also available directly as a pdf here:

BJT Biasing Circuits.pdf

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You will perform the calculations, build and test the four circuits in Part 1 of the lab sheets. We won't be discussing the circuits in Part 2 yet.

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Part 1: Build & verify all 4 circuits. You may substitute a 2N2222 for the 2N3904. Suggestion: Use your multi-meter to check each transistor BEFORE putting it in the circuit. Here is a pdf of the procedure:

Transistor DMM Check.pdf

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You will make the measurements for each of 3 transistors for each circuit. This will help demonstrate the stability of the Q-point with respect to transistor variations.

Here are the formulas required for each circuit:

Fig. 5-1:
VRB=VCC-0.7V
IB=(VCC-0.7V)/RB
IC=(beta)*IB (assume beta around 150-200)
VRC=IC * RC
VC=12V-VRC
VCE=VC-VE=VC-0=VC


Fig. 5-2:
IB=(VCC-0.7)/(RB+beta*RE)
VRB=IB*RB
IC=beta*IB
VRC=IC*RC
VC=VCC-VRC
VCE=VC-VE=VC-VRE where VRE=IC*RE

Fig. 5-3:
VB=VCC(R2/(R1+R2))
VE=VB-0.7
IE=IC=(VE-0)/RE
VRC=IC*RC
VC=VCC-VRC
VCE=VC-VE

Fig. 5-4:
VB=0.7
IE=IC= (VCC-VBE)/(RB/beta+RC)=(VCC-0.7)/(RB/beta+RC)
VRC=IC*RC
VC=VCC-VRC

And here's a pdf of the above forumulas and the pinouts shown below. A printout of this was distributed in class on 10/23.

Biasing Formulas v18.1.pdf

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Transistor Pinouts:

Transistor Pinouts.jpg (150.78 KiB) Viewed 1418 times