35. Class B and Class AB Amplifiers 

The Best half an hour I have spent watching a RU-vid video.

Unlike some videos dealing with amplifier circuits, you dont leave out the basics and you lay out the algebra in a way that makes it easy to understand.

I'm glad you liked it and thank you for watching.

Thanks for the time you spend making these video's!!! I have learned more from you and others on youtube than I did in college. I find that making the output stage to be straight forward, it is the VAS stage of the amp that I have problems making, I like using a split power supply so I can use a op amp for the pre amp stage because finding matched transistors for a reasonable price is impossible.

Another great video. Thank you.

Thanks for this video and all your video's man, you explain everything really well and showing it on the scope makes it so easy to understand. Thanks a bunch.

For this title means "power amplifiers " i even studied fundementals of microelectronic in which we`ve got remarkable digestivable concepts but boldy none of them can reach to your great and increadible video lectures ...Thanks man .

This video is excellent and easy to understand. Kudos Sir!

Really like your videos. I'm a development engineer in the uk. Really needed to finally understand BJT amps. Now, much more confident. Thanks for the uploads..

Thank you so much, my teachers redesign the course and desing a wrong circuit schematic and all the people in the lab burn their arduino, so now we needed to design ourselves the amplifier but no one show the math behind it.

Love all your vids

Great video! How would you calculate the AC Gain (hFE), rE', Rin and Rout?

I got a basic understanding now. Thanks,

awesome content ! thank u

Excellent tutorial.

Love it! Thank you! Next you should do a video on bootstrapping techniques for a class AB amplifier. Not that I need help with that. :-)

This is a great effort to teach novices like me . Thank you very much

At the negative cycle, the npn transistor should be in its off state, therefore disconnecting the 10V source from the pnp transistor, so where does the current comes from that allow negative voltage to appear at the output?

That 4 resistor voltage divider is getting me confused... Shouldnt the voltage at first base be 10V-VR1? That in this case is 5.32

Very Very welll explanation.

When no input signal do transistor have current?

What is the minimum value of the DC biasing current in class A output stage? Explain you answer.

What is the most linear class of amplifier

U helped me so much I like it thank u

Thanks for this great video, now I can explain class ab to a baby

In your circuit diagram, you have a Vcc which forward biases the pn diode, how come that it doesn't conduct for the full cycle? Did you assumed that the Vcc is not present there?

great video and this is probably a stupid question but is the sine wave from a signal gen? if so at what frequency?

Cool video and tanks. I am doing my on ab amplifier but the redidtir krpp warm upp and búin. What am í doing rhong?

Great work sir

Hello: I have 2 questions with regard AB power amp circuits. (1) If you look at the Fairchild datasheet for a TIP29 power transistor, how do you determine the DC gain? It says that if Vce = 4V, Ic = 0.2A then the DC gain has a min value of 40. However, if Vce = 4V and Ic = 1A, the the DC gain has a min value of 15 and a max value of 75. (2) For power amplifiers how do you arrive at a value for r'e? Can you use 25mV / Icq? Thanks very much.

14:35 I realize that this circuit is mainly to exemplify a sort of class B (partly AB) output stage, but.... having two separate input caps raises some issues regarding the output transistors getting out of sync. One problem will occur at startup when C2 charging will lag C1, resulting in both Q1 and Q2 on at the same time, shorting the supply for some period of time.

Hey thanks for the video. Just a quick question about the design of the of the Class AB amplifier. How do i find the values of the two resistors and the capacitors. I have found the KVL around the Resistor and the diodes, which is; R = (Vcc - 1.4V)/(2*I) . But i dont know what to put for the current in the KVL. Also, my load resistor is 8 Ohms. Thanks you

I have noticed that most people don't include an emitter resistor in their Class AB Amplifier designs. I have found that it is really needed to eliminate thermal runaway. How do you determine the value of these emitter resistors?

Thanks for the video I couldn't understand why to use the 2 capacitors that are connected to the source

the best !!! ⭐⭐⭐⭐⭐

Hello: I am back into electronics after a hiatus. Would you consider doing a video on a Class AB amplifier with a common-emitter driver. I have been searching for a good document or video that explains how to design and analyze such a circuit. I have a schematic in mind but I couldn't attach it to this comment.

29:20 "efficiency [of AB] goes up a little bit [compared to B]". Power consumption difference of the bias network is insignificant. The main difference in efficiency is due to the fact that in class AB the transistors are on for a larger proportion of the time, and conduct some current directly from one rail to the other, at least for part of the cycle. Hence AB is less efficient than B. (When comparing B and AB "push pull" amplifiers as shown in this video.)

Hi, The circuits are common collectors (emitter followers) so at best the gain is unity. Rout would be RE||RL AC resistance in to the base is r'e*beta. Overall input resistance would be r'e*beta||RB1||RB2. Hope that helps.

Love these videos. They are so well done! I am stil not sure how to use a transistor datasheet to arrive at a DC gain estimate. As there is such a great range. If you look at the Fairchild datasheet for a TIP29 power transistor, how do you determine the DC gain? It says that if Vce = 4V, Ic = 0.2A then the DC gain has a min value of 40. However, if Vce = 4V and Ic = 1A, the the DC gain has a min value of 15 and a max value of 75. Thanks

What could cause 0v output in the circuit for the class AB

What an explanation! But where is the amplification done by transistors?

Very nice video.. would u like to know what is the model number of pnp and non bjt ?

what is the least energy efficient class of amplifier

You should remake this video with better sound or just a better mic :)

I designed a class AB amplifier with dual voltage driving PNP and NPN transistor. The final was the amplifier works perfect but when the power is switched off the positive voltage gets drained but the negative voltage stays what's the solution. Pls

Although I listened to that part many times, I still don't understand how both nodes end up being equal to 318mV at 8:47. The lower node should be (10000/21360)*10=4.682V and the upper node should be (11360/21360)*10= 5.318V as far as I can see.

thankyou sir

RMS-power is a nonsensical name, what you mean is not the rms-value of p(t) (p(t) = the instantaneous value of the power) but the _average_ power of p(t). Also note you wrote on the board a formula for Pout with units V^2 which is incorrect.

Wow!

Sir please make a video to explain the circuitry of class b amplifier where you teach us the need of each and every component required... Please I would be exceptionally thankful to u.

Why do we need class AB?

3:40 no negative output? it do have , system is on Q point

plz explain curren tmirror using mosfet bulk driven

How can Power out can be .7Vout*.7Vce

ASMR starts at 17:56

24:55 "any current that goes through D2 is going to go into the transistor, be multiplied beta times...". That part of the explanation is wrong. The current through D2 does not go through Q2, nor vice versa. (The D2 current and the Q2 base current sum to make the current through RB4.) Instead, the current through D2 produces a particular voltage drop that is similar to the VBE required for a similar current in Q2. These amounts are not guaranteed to match exactly, so RB1 and RB4 would need to be adjusted to get a voltage across D1 and D2 that sets the desired ICE in the transistors. And at least the diode drop and required VBE will track with temperature, but only if the diodes and transistors are thermally connected (so not in the circuit as built, contrary to 27:06). It is indeed sort of a current mirror, though it's missing emitter resistors that would normally be used to set the current stablely.

alot easier to tell them Vrms squared divided by R load.

hello thanks for video. I have homework about ab amplifiers and i watched that video but i didnt find answer to my questions i need Rb1 and rb2 and my teacher gave me that formule rb1=(vcc-vd1)/(idmin + (iq+ILmax/1+b)) that formula gives me rb1=rb2 and i just dont know ILmax in that formula if i found it i can get rb1 thanks for helping me and if you give your mail adress i can show you my problems.

I do n't understand the significance of the Viking.