I need to simulate a class B push pull amplifier with center tapped transformers to get 1A load current.

Thread Starter

Mustaqeem Tariq

Joined Oct 30, 2019
21
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.
And no he did not built an audio amplifier or RF amp using these specifications as far as I know.
 

ronsimpson

Joined Oct 7, 2019
449
I have never seen a "push pull" NPN&PNP transformer output circuit with out a center tap.
I have seen and built many with a center tap and matched transistors, MOSFETs, or tubes. RF and Audio

Now that I said I never saw: I made many of these to drive a grid at several thousand volts using the "gain" in a tapped transformer. I stand corrected; no one in their right mind would build a not center tapped amp.
1577941357731.png
Bias circuit not shown.
 

MisterBill2

Joined Jan 23, 2018
5,206
I own a stack of Bogen PA amplifiers that all have output transformers, but the transformers are for impedance matching. The direct coupled complementary pair with the TIP31 and TIP32 can also use an output transformer for load matching. But split supplies will also be needed to keep the biasing simple.
Exactly like I stated earlier, transformers can be added to that circuit on the output strictly for load matching, and a center-tapped transformer to the input, with the tap tied to the emitters. That model will work quite well as a servo amplifier, where a bit of crossover distortion will not matter at all. You can use the TIP31 and TIP32 models and select the conditions to provide the output POWER to put 1 amp through a 16 ohm load, which is reasonable for a medium servo-motor. The model will then provide the base current and voltage needed to have that output, and the input transformer can match the specified input signal to what the transistors need.
And since you have studied both types, you can then use the two simulations to compare the efficiency and stability of each kind of circuit. That should get a decent grade. And if it comes that the request was for that center tapped circuit first presented, you can have that one ready to submit as well, using the TIP31 transistors and their model..
Not all designs are perfect at the first try, but the great engineer catches the flaws while th design is still only a drawing. Errors are simpler and much less expensive to correct at that stage. And even cheapr to fix when they are at the free-hand sketch stage.
 

ronsimpson

Joined Oct 7, 2019
449
No. You should at least "run" simulation on a circuit before posting. If you need to know how just ask. Not the first time.
Bottom transistor B-C short so it can not work.
I know it is hard when your helpers post the circuit wrong. But it was corrected down a post or two.
 

MisterBill2

Joined Jan 23, 2018
5,206
The only flaw is/was the common (ground) connection at the bottom of the base driver transformer secondary.

Why did you change from a split power supply to a single power supply?
 

ronsimpson

Joined Oct 7, 2019
449
OK, that means that the input signal amplitude is far too large. I suggest reducing the amplitude as an experiment.
Did you get a good sine wave with the other connection? and was the no-signal current?
Bill 2.0: The other circuit works. Has crossover distortion but I think that is ok for this home work.

Connecting a signal from B-E on a transistor causes the transistor to be on or off with little linear region. It is temperature instable. Usually in a amplifier there is a emitter resistor and collector resistor. There should be a Base resistor to limit the input current if no emitter resistor. With out Emitter resistors you will have very unpredictable gain, and large distortion.
Please build your circuit.
 

MisterBill2

Joined Jan 23, 2018
5,206
It reaIy matters a whole lot as to the amplitude of that BE signal applied to the transistor. That is what the linear portion of transistor operation is all about. Certainly if a signal is applied that drives the transistor into both saturation and cutoff there will be a lot of distortion. Thus I suggested reducing the amplitude of the drive signal. I believe that I also suggested initially that the amplitude of the drive signal should be calculated. That should not be so difficult since the transistors are operating as emitter followers. The appearance of flattened tops of the waveform should have made it immediately obvious that the stage was over driven.
 

ci139

Joined Jul 11, 2016
1,187
"center" tap to emitters sets a positive feedback
center tap to common requires a "high power" input signal
// No one tells you can't experiment with both ...

? is there any good options to this . . .
-- adding attenuation(emitter feedback + series base) resistors to emitter tapping would give more_linear drive_current

/// but it's TF drive ... "di/dt" - means no steady DC levels . . . ? can the output of the TF held at DC offset -- unlikely . . .
/// ? can the square wave with large duty have it's longer offset dominating the output . . . probably
/// -- e.g. -- no matter center tapping to emitters or to SGND -- there is absolute offset mismatch for I/O of the transformer . . . that is -- you drive your primary TF with a different signal than it's output will drive the 2-ry -- the output of which is the 4-th variant of the input signal . . .

TF - lab - ofz - T-0.png
 
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