Is this push pull amplifier wrong?

Question

Under the following tutorial:

They explain push pull operation. But should't negative terminal be separate with the ground? Dont we need +Vcc and -Vcc

Here is the push-pull from the tutorial:

EDIT: here is my simulation:

Green is input, red is output.

One of your transistors is upside down. And there's no base bias network. — , Jan 19 '16 at 15:06

Andy aka · Accepted Answer · 2016-01-19T14:31:20.057

4

But should't negative terminal be separate with the ground? Dont we need +Vcc and -Vcc

No, that would work providing the load is connected via an output coupling capacitor: -

Here's another: -

edited Jan 19 '16 at 14:31

answered Jan 19 '16 at 14:29

Andy aka

? Because I simulated without a cap and the result was a rectified sinusoid – user16307 Jan 19 '16 at 14:30
Yeah that might happen! – Andy aka Jan 19 '16 at 14:31
i edited my question. adding a cap didnt work for me. please see my schematics. just a cap is not enough? – user16307 Jan 19 '16 at 14:38
oh is that because mine is not biased?? – user16307 Jan 19 '16 at 14:43
Q2 is the wrong way round too. Yes, the transistors need decent biasing. – Andy aka Jan 19 '16 at 14:43
oh i both didnt bias and put Q2 wrong way. :(( thanks – user16307 Jan 19 '16 at 14:46
So the transistor Q3 is providing a current sink for the diodes to stabilise the voltage drop across them? – quantum231 Apr 27 '16 at 18:53

score 0 · Answer 2 · answered Jan 30 '17 at 04:26

Your output doesn't seem to have any (noticeable) DC offset so you can leave out the output capacitor for simulation sake.

You don't get a negative swing because the output is clipped between 0 and +Vcc. You can do one of two things to fix this:

Also, you would want to add a Vbias between the output stage inputs equal to 2*Vbe to keep both transistors at the verge of saturation.

2 Answers2