Amplifier class D error schematic

[ArnaudMARTIN]

Hello,

I am trying to simulate an class D amplifier, to try it on board after.
When i add 50 Ohms Serial Resistance of Vcc+(12V) , the output of CMOS isn't very nice.

Could you help me to improve the schematic of these amplifier ?

Thank you for your help.

Arnaud

 

[KlausST]

Hi,

I don't open .zip files with unknown content. Upload a screenshot / .png using the [insert image] button

Explain more, maybe in the screenshot, about the resistor.
Explain what "output of CMOS" means.
Explain what "isn't very nice" means. Draw a sketch.

Klaus

 

[ArnaudMARTIN]

Sorry, for the last upload.
Here, my schematic :

And the scope of Vinv et Voutb without Rser on V3 :

And the same simulation with Rser :

 

[KlausST]

Hi,

May I ask why you added Rser at all? It makes no sense in my eyes.

Klaus

 

[BigBoss]

Rser should be around few milliohm, not 50 Ohm.

 

[FvM]

The desigh flaw is to drive complementary MOSFET by the same gate signal without generating any dead time. Massive cross conduction expected.

 

[Easy peasy]

indeed - user should look at currents in U3, U4 ....

 

[ArnaudMARTIN]

Tank you for your answers.
I change Rser to 1 Ohm, but it's right that the current is too high in MOSFET during commutation.

Can i improve that ?

Thank you for your help.

 

[KlausST]

Hi,

as already mentioned: This is cross conduction because of unsuitable circuit.
--> use a complementary N-Ch MOSFET driver including dead time.

I recommend to read some "class D design" application notes, to avoid re-inventing the wheel and loosing much time and performance.
Many years ago I´ve read some good IR (International Rectifier) ones, now Infineon.

Or even simpler: Use ready to buy power stages. (includes: driver, dead time, bootstrap, MOSFETs, maybe some protection features)

Klaus

 

[ArnaudMARTIN]

Thank you vert much for your answers.
Si if i understood, I must choose an other driver with dead time) and maybe use only 2 mosfet N if thé driver have an inverting and no-inverting output.

Have you got an référence of à driver like that ?


Have a good day

Arnaud

 

[KlausST]

Hi,

usually it´s the other way round: you choose the MOSFETs and according them combined with the applications´s requirements you choose the driver.

I guess there are several thousands of drivers. Which one to choose depends on the application. If there was a "one for all", then there was no need for thousands others.

Again: Read/watch application notes and tutorials (or consider to pay someone to designing it for you)
At least this is what I´d do if I were on your place.

Klaus

 

[ArnaudMARTIN]

I found a new mosfet driver for half bridge application with dead time. I would like simulate it, but i have an error during simulation : time step too small.
My new schematic :

Adn the start of waveform before error :

 

[KlausST]

Hi,

please read the IR2108 datasheet carefully. It shouldn´t be that hard, because it just needs a couple of external components.
--> it needs a bootstrap capacitor

--> also D1 needs to be defined.

Since the simulation is not realistic according power supplies, I strongly recommend adding the power supply capacitors in the simulation, otherwise there is a risk to forget to include them in the real circuit. The real circuit won´t work reliably without power supply capacitors.

Klaus

 

[BradtheRad]

error during simulation : time step too small.

Alter time step so a reasonable number fit into one cycle of operation.
Say you have a clock at frequency 1 kHz. Try time step 1 uSec.