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Amplifier class D error schematic

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ArnaudMARTIN

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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
 

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  • classeD.zip
    8.3 KB · Views: 105

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
 

Sorry, for the last upload.
Here, my schematic :
1649879887363.png


And the scope of Vinv et Voutb without Rser on V3 :
1649879981877.png


And the same simulation with Rser :
1649880039575.png
 

Hi,

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

Klaus
 

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

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.

1649921722143.png


Can i improve that ?

Thank you for your help.
 

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
 

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
 

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
 

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 :

1649944820173.png


Adn the start of waveform before error :
1649944869510.png


1649944920572.png
 

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
 

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