Thanks heaps Jony130.

 

Why is the class D full bridge giving wrong results? I was expecting much amplified signal. Circuit and snapshots attached please.

 

What voltage do you think is the right result? You can't get more than a ±5Vpk signal if the bridge supply voltages are 5V.

 

The CD4030 isn't providing enough current to drive the FET gates properly. You can see that by looking at the gate waveforms.
The closer a match you get for the amplitudes of the triangle and sine wave inputs the greater will be the gain.

 

Alec_t & crutschow, thanks once again. What driver would you recommend? And should I use a double supply to get ±5V?

 

What driver would you recommend?

A transistor totem-pole arrangement (one NPN, one PNP per half-bridge) is commonly used, or there are dedicated H-bridge-controller ICs.
If you use dual-polarity supplies you will have to consider level-shifting circuits for driving the FETs.

Edit: But if you're thinking IC you might as well just buy a Class-D amp IC.

 

Alec_t, I did but didn't produce any better results. Is there anything I'm doing wrong?

 

What driver would you recommend?

I thought you were referring to a FET gate driver. You've got the totem-poles now, but they would normally be driving FET gates. Try re-instating the FETs. 2N3055s are not ideal for the totem poles; they have low gain.
I had a play with your sim. Attached is a mod of your circuit.

 

Alec_t & crutschow, thanks once again. What driver would you recommend? And should I use a double supply to get ±5V?

Dual supplies will complicate the driver requirements.

The bridge supply voltage determines the maximum output voltage and power. How much do you want?

Note that increasing the bridge voltage also increases the drive voltage requirements.

 

Hi Crutschow, I would like to have a ±5V on the output.
Alec_t: what transistor would you mind recommending?
No lucks at all folks.
Thanks.

 

Crutschow, I have also noted that you have recommended I download "circuit from AAC,with mods", could you kindly direct me where it's at. I have searched the forum but could not find it. Also, I have updated the circuit, but its behavior is getting stranger.

 

No lucks at all folks.

In what way? What isn't working as you want it to? The sim worked ok for me .
Why did you plot the voltage at one end of the load, instead of the voltage difference across the load?
As for recommending transistors, you haven't told us the output power required.
The circuit I think Crutschow was referring to is the one I attached in post #28.

 

Alec_t, got the point matey. Thanks. A question though: what transistor (BJT) pair are you recommending? It seems the ones on the circuit are ideal BJT, pardon my ignorance. It's my understanding that using any transistor may not work properly because of switching speed issue i.e. it takes more time to switch off a transistor than switch on.

Also, (pardon my ignorance)

1. why did you add an offset on the ac signal/input? And why is the signal (digital) out zer0 when I set the AC signal offset to 0 instead of 2.2V? Why did you set it to 2.2V less than the Virtual offset (i.e. 2.27V)
2. why did you choose virtual ground to 2.27V?

Appreciate your support in advance.

 

why did you add an offset on the ac signal/input?

Because the time constant of R8/C4 delays the time before the U2 non-inverting input reaches a stable DC level and I wanted to speed up the sim.

why is the signal (digital) out zer0 when I set the AC signal offset to 0

Because initially the U2 non-inverting input is centred on 0V whereas the inverting input is centred on PGND, i.e. 2.27V

what transistor (BJT) pair are you recommending?

That depends on what FETs and supply voltage you will ultimately use on the output stage.

Why did you set it to 2.2V less than the Virtual offset (i.e. 2.27V)

Just an approximation to get the two U2 inputs roughly balanced initially.

why did you choose virtual ground to 2.27V?

That was your choice, not mine .

 

Crutschow, I have also noted that you have recommended I download "circuit from AAC,with mods", could you kindly direct me where it's at. I have searched the forum but could not find it.......

In which post did I make that reference?

 

Thanks lot folks.
@crutschow, it was a comment on the circuit you attached and I thought you were asking me to download the file.