Voltage Divider Bias Circuit

This electronics video tutorial explains how to solve the voltage divider bias circuit. It explains how to use a formula to quickly calculate the base current of the NPN transistor and how to calculate the emitter and collector currents as well as calculating the emitter and collector voltages Ve, Vc, as well as Vb and Vce.

Transistors - NPN & PNP:

BJT Transistors - Electronic Switches:

Night Activated LDR Sensor Circuit:

Finding The DC Load Line & Q-Point:

Collector Feedback Bias Circuit:

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Emitter Feedback Bias Circuit:

Common Emitter Amplifier:

Common Collector & Base Amplifier:

Darlington Pair & Beta Current Gain:

Class A, AB, B, & C Amplifier Circuits:

Voltage Gain of Transistor Amplifier:

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Multistage Transistor Amplifier Circuit:

Transistor Audio Mixer Circuit:

Operational Amplifiers:

Summing Amplifiers:

LM386 Audio Amplifier:

LC Oscillator Tank Circuit:

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Final Exams and Video Playlists:

Full-Length Videos and Worksheets:

[PunmasterSTP]

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[sweetmendoza]

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[trelligan]

Just a comment to feed the YT algorithm.
Excellent review for those of us who used to work on this stuff.

[sagharzahedi]

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[seandempsey]

I've gotta say you have carried me through school and now university so thankyou!!

[arindambala]

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[dennisgonya]

This is a great piece showing Thevenin's equivalent and the biasing of a transistor. I am taking Cleveland Institute of Electronics Advanced Engineering Course and will add this to the transistor books. I will teach this is Asia. I was a staff engineer/scientist at IBM with patents and recognize the great work that you have shown here. Great job.

[kumargoldking]

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[rishiladdha]

Thank you so much.
PS: Would love it if you could organise your content in topic wise playlists. That'll amplify how useful they are :)

[billyd]

Very good explanation. +1 after beta was always omitted when I did this 40 odd years ago at college due to it being negligable.
Well done!

[jayeannetionetteabugan]

IF ONLY I COULD TREAT THIS MAN AS A SIGN OF GRATITUDE. THANK YOU FOR YOUR VIDS MAN!

[יוסיבןעזרא-רס]

why Vb is not the voltage divider between r1 and r2 ?

[corruptofficial]

Hi there, it's perfect explanation how to calculate parameters in a transistor circuit. Thank you.

[alohahoward]

Your videos are invaluable. Thanks so much.

[avishka-don]

You are amazing! I actually understand this now!

[Festus]

I'm not sure that the Base Voltage of 3.7 V is correct here, because it lacks the voltage input from the V-source/voltage divider. It seems that the BASE VOLTAGE is the Thevenin Equivalent voltage of 4.9V. It can't be both, and 4.9V satisfies the KVL loop for the Base-Emitter loop and represents the first entry into the big equation for Base current. The Thevenin equivalent voltage is the voltage produced by the source voltage and the voltage divider. The 3.7V value did not affect the other calculations, so I think this is a minor error. Any other input on this welcome.

[Yanga_Thami]

thank you i passed my Tutorials through this Video

[re.liable]

I've been trying to solve this without find the Thevenin equivalent as was done in the video.

Using KVL in the "finding the I_B" stage, I initially used:
V_CC = I_1R_1 + V_BE + I_ER_E

and from that have gotten as far as:
I_B = (V_CC(R_2/(R_1 + R_2)) - V_BE) / ((β + 1) R_E)

It's basically the same as the one that was used in the video, however I am missing a term in the denominator which is the equivalent parallel resistance between R_1 and R_2.

Can someone try to point out how I could fit that in this equation? I feel like I should have included it in the initial KVL equation I used, but I don't know where (and how) it should go.

EDIT: After searching a bit, I realize that the equation should've been:
V_CC = I_1R_1 + I_BR_B + V_BE + I_ER_E

R_B is the parallel resistance I'm missing. However, I'm still struggling to intuitively think of the *existence* of R_B along that path.

[successthruknowledge]

wow, is the formula for Ib given on exams or must you derive it? I doubt I could remember it. Also I'm glad he did another example with thevenin voltages and thevenin resistors. I was not sure how to apply them to a real example. So overall awesome lecture!!!!

[eggxecution]

Personal notes:

in voltage divider bias circuit Ve = Ie*Re
Ie = Ic if Rth < (1+B)Re if it is not, use Ie = Ib + Ic
also learned where Vb, Vc, Ve are positioned