I designed the modified circuit. It is attached below:
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Did you actually get your circuit to work?My work is complete.
Nope. It just gives 1A load current and I think it is not correct as they are not biased correctly.Did you actually get your circuit to work?
In my attachment in post #2 I explained how the transistors are biased so that they do not produce crossover distortion. But class-B always has crossover distortion. Real audio amplifiers use class-AB with the transistors biased a little.Can you please explain the bias circuit to get to class B operation?
suppose ... the ohmic (electro-dynamic) speakers . . . seem to be parametrized at their lowermost frequency usually 20 or 40 HzMy work is complete.
This circuit is no longer a complementary circuit, it is a regular push pull power stage withforward bias applied to both bases. A TIP31 would work quite well here but the bias may need to be adjusted a bit. A complementary stage driven from a transformer will be more complex in that the PNP will need a negative forward bias while the NPN side will need a positive forward bias. I can do it with the collectors tied and using an LM301 op-amp, but at that point it would be rather clear that outside help was involved. And since this is a take-home exam that may not be allowed.I think you are to compare the two circuits. (use the right transistors)
View attachment 195816
I do not have SPICE models for the two transistors you want. I think you can do that. If not ask questions.
I never really understood the home work request. I got: input and output transformers. After that I got lost.It does look like not many read that post that described what was actually requested
The end of the input transformer SECONDARY that is shown commoned must instead connect to the junction of the two emitters. And why has the negative supply shown earlier been replaced with a common connection? Wishing it would work will not make it work!Circuit on the right desperately needs a capacitor in-between the input transformer and the two Bases. OR The bottom end of the input transformer could be set at 1/2 supply.
View attachment 195847
This circuit is not the same as the complementary circuit shown in post #15 That post shows two supplies, one positive and one negative. That does make quite a difference. In fact, it makes a very big difference in the idling current, and in how the bias must be set, and how the load must be connected. The result is that it becomes quite a challenge to bias both the NPN and the PNP transistors slightly into conductionwhen both the bases and the emitters are tied to each other. Adding capacitors makes it possible but then it may not be direct coupled.I never really understood the home work request. I got: input and output transformers. After that I got lost.
Most people think center tapped transformer but the following circuit with two transformers would work. (add bias?)
View attachment 195840
The teacher just gave the question which I posted earlier. And he did not give the load resistance. But just said to build a class B push pull amplifier with transformer coupled at both input and output with a load current of 1A using TIP 31 and TIP 32. I think now the question is quite clear. I said center tapped earlier because I thought it was the only way to incorporate a transformer in the circuit. I am sorry if it misguided you.Not knowing what is in the teachers head, causes me to not want to work on this any more.
From experience:
The teacher said in class some thing that we did not hear at AllAboutCircuits.
The teacher thought he said ……. but he did not say that.
The student thought he heard …….. but was texting at the time.
The hand out contradicts what the teacher said.
The question is clear only to the teacher.
We can not remember who said "center tapped transformer" first.
Push Pull has too many versions. Which one?
After spending 50 hours on this question the teacher through out the question because no one got it right.
Teacher never really built one of these.
Audio amp or RF amp? Never said. Implied? Did the teacher ever say "50 or 75 ohms = RF, 8 ohms=audio"?
This list could go on, but I need to stop thinking on this!
by Duane Benson
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