I enjoyed the lecture, taking me back to the mid eighties to start nineties, when I designed bipolar integrated circuits. We used to adjust the bias current in the bias diodes in the diver stage so that we had a class A current flowing in the output transistors. This way we got a lower cross over distortion. We also put a small resistor in series with the npn emitter. This was a part of a protection circuit for limiting the short circuit current. One of the drawbacks of this classic class AB output stage is the need for a high voltage supply. If you make a bipolar output stage where the output is at the collectors it is possible to get as close to rails as a saturation voltage. I am still in IC design and as a famous designer said in the nineties: ‘ Someday the mos devices will get so small that they will go directly from sub threshold into velocity saturation and we will be back at bipolars’, not to mention the leak in the gate :-) Thanks for your lecture.
00:02 Driving a resistive load is necessary for circuits to deliver energy. 02:10 Driver stages and output stages in amplifiers 06:53 Lowering voltage reduces current through the output stage. 09:12 The problem with driving an amplifier to push a speaker to full power 14:32 Class A amplifier operation and limitations 17:06 Combining current sink and source for effective operation 21:43 Understanding the need for a dead zone due to transistors' VBE on requirement. 24:00 Tug-of-war between currents in driver stages 28:42 Efficiency defined as power delivered to the load vs. DC power. 31:00 Power delivered to the transistor causes heat 35:41 Bipolar transistors have specific junctions and characteristics Crafted by Merlin AI.
You prolly dont give a damn but does any of you know of a way to get back into an instagram account?? I was stupid lost my login password. I would love any tricks you can offer me
@Davion Cullen thanks for your reply. I got to the site on google and I'm waiting for the hacking stuff now. Looks like it's gonna take quite some time so I will reply here later when my account password hopefully is recovered.
29:00 When finding the efficiency of a class AB amplifier, is the biasing current not taken into account? Is it because the bias current is much smaller than the DC current in the amplifier such that the bias current can be ignored? 33:45 is this circuit topology (PMOS on top, NMOS in the bottom) intended to be a switching converter? Can the negative terminal of a class B/AB amplifier connected to the ground instead of the negative supply voltage? If so, then the output of the amplifier must have a non-zero DC value? Is it correct to say that the max time-averaged efficiency happens when the amplitude of the output voltage is closest to the supply voltage? On the other hand, the max instantaneous efficiency happens when Iq = Imax (i.e. when the transistor operates at the edge of the saturation region)?
It depends on the load and the power you want to be available to the load. On single ended RC-coupled class A stages, the theorectical efficiency is 25% as stated in the lecture, or 50% if the load is driven with an output transformer. Say you want to drive a load with 10 W of power, the input power will be 40 W, and 30 W are always wasted as heat. So the DC bias is the one that makes the stage draw from the supply 30 W while idling. This assumes load matches the output impedance, for best power transfer. The less bias current, the less power available.
I enjoyed the lecture, taking me back to the mid eighties to start nineties, when I designed bipolar integrated circuits. We used to adjust the bias current in the bias diodes in the diver stage so that we had a class A current flowing in the output transistors. This way we got a lower cross over distortion. We also put a small resistor in series with the npn emitter. This was a part of a protection circuit for limiting the short circuit current. One of the drawbacks of this classic class AB output stage is the need for a high voltage supply. If you make a bipolar output stage where the output is at the collectors it is possible to get as close to rails as a saturation voltage. I am still in IC design and as a famous designer said in the nineties: ‘ Someday the mos devices will get so small that they will go directly from sub threshold into velocity saturation and we will be back at bipolars’, not to mention the leak in the gate :-) Thanks for your lecture.
interesting thanks for sharing
00:02 Driving a resistive load is necessary for circuits to deliver energy.
02:10 Driver stages and output stages in amplifiers
06:53 Lowering voltage reduces current through the output stage.
09:12 The problem with driving an amplifier to push a speaker to full power
14:32 Class A amplifier operation and limitations
17:06 Combining current sink and source for effective operation
21:43 Understanding the need for a dead zone due to transistors' VBE on requirement.
24:00 Tug-of-war between currents in driver stages
28:42 Efficiency defined as power delivered to the load vs. DC power.
31:00 Power delivered to the transistor causes heat
35:41 Bipolar transistors have specific junctions and characteristics
Crafted by Merlin AI.
Awesome, this is where my uni stopped with the lectures on this topic. Really looking forward to 50 more videos of new content :)
Incredible lectures prof. Hajimiri ! Thank you very much.
You prolly dont give a damn but does any of you know of a way to get back into an instagram account??
I was stupid lost my login password. I would love any tricks you can offer me
@Davion Cullen thanks for your reply. I got to the site on google and I'm waiting for the hacking stuff now.
Looks like it's gonna take quite some time so I will reply here later when my account password hopefully is recovered.
@Davion Cullen It did the trick and I finally got access to my account again. I'm so happy!
Thank you so much, you saved my ass!
@Axel Ali happy to help :D
29:00 When finding the efficiency of a class AB amplifier, is the biasing current not taken into account? Is it because the bias current is much smaller than the DC current in the amplifier such that the bias current can be ignored?
33:45 is this circuit topology (PMOS on top, NMOS in the bottom) intended to be a switching converter?
Can the negative terminal of a class B/AB amplifier connected to the ground instead of the negative supply voltage? If so, then the output of the amplifier must have a non-zero DC value?
Is it correct to say that the max time-averaged efficiency happens when the amplitude of the output voltage is closest to the supply voltage? On the other hand, the max instantaneous efficiency happens when Iq = Imax (i.e. when the transistor operates at the edge of the saturation region)?
What is the minimum value of the DC biasing current in class A output stage? Explain you answer.
Why do we subtract VBE_ON in these equations?
You did not finish your very last subject. Do bjts latach up like SCRs? SCRs are used in power circuits. Please upload your follow up lecture. Thanks
Hi, I have a question
What is the minimum value of the DC biasing current in class A output stage
It depends on the load and the power you want to be available to the load. On single ended RC-coupled class A stages, the theorectical efficiency is 25% as stated in the lecture, or 50% if the load is driven with an output transformer. Say you want to drive a load with 10 W of power, the input power will be 40 W, and 30 W are always wasted as heat. So the DC bias is the one that makes the stage draw from the supply 30 W while idling. This assumes load matches the output impedance, for best power transfer. The less bias current, the less power available.
Great !
うちの親父は「100Vだと肘まで、200Vだと肩まで感電する」と言ってました。