Ir2104+ Irf540

[Eva]

Very long dead time produces a characteristic type of distortion. You can make this very obvious by playing a pure tone in the low or midrange area and increasing the volume slowly from 0.

 

[Tekko]

Crossover distortion.

 

[zox2003]

I am currently thinking about inverter circuit for IR2011...What would be prefered circuit...Drive it with:

1.LT1016 directly
2.Use LM311 and CD4069
3.Use LM311 and Transistor inverter

Thanks

 

[Tekko]

LT1016 and a deadtime circuit to prevent/eliminate shoot through, usually an RCD circuit.

 

[zox2003]

Can you point to example of dead-time circuit.Thanks

 

[Tekko]

Search! It´s all over the class d forum.

 

[zox2003]

Don't you think that I have enuff deadtime internally in IR2011.

 

[Tekko]

I havent read the datasheet but i don´t think it has amny internal deadtime what so ever.

 

[zox2003]

IR original design does not have deadtime circuit incorporated in their design at all using IR2011S.

Is it really necessary?

 

[luka]

Hi

It depends on how good are your fets... if they are fast + fast diode then you don't need it, but if you use fets like I did, then you will need it

 

[zox2003]

Luka,

i have a plan to use IRF540 's (2X) in output with 50ohm gate resistors in parallel with 4148 diode.

 

[luka]

Hi

Lower the Qg is,higher Rg can be

 

[zox2003]

So Luka ,

Are we talking about resistor-diode dead-time on gates of output MOSFETS or circuit on input of driver (IR2011)?

IRF540 -do I need one for these MOSFET's?

 

[luka]

Hi

Input of driver and yes you will probably...

 

[Eva]

Depending on the amount of gate charge and on the particular components added between the outputs of the driver and the gates, you may easily find that those IR ICs actually provide too much dead time.

 

[zox2003]

New amp thread on:

http://www.diyaudio.com/forums/showthread.php?threadid=112696

 

[Gyula]

Oh, so you are asking me for the Ft of IRF540??? No, Ft is a bipolar-transistor thing meaningful only for linear amplifiers... MOSFETs in switching applications behave in another way, gate drive and package and circuit parasitistics are the limiting factors for switching speed.

Hi Eva! In electronics, everything works in the same way. The so-called mathematics. The MOSFETs also have Ft, despite you classified it for bipolar transistors. So there's another limiting factor for switching speed.

 

[zox2003]

Apsolutely,

MOSFET transistors have Ft.
Eva is really good person that knows a lot about switching aplications but needs to get some more informations about some certain things.

 

[JohnG]

You are both right. MOSFETs do have an Ft defined (see Baliga), which is a function of the internal gate resistance Rg, but usually it is not relevant to high-speed switching applications. Parasitic inductance in the source lead is an inherent limiting factor for voltage-drive gate drives. Generally, one desires to limit the speed of the MOSFET via external gate resistance, since relying on the source inductance is dangerous to devices!

The inherent response speed of the channel for Si-based vertical power MOSFETs is less than one nanosecond. Metal-gate MOSFETs can switch in a few nanoseconds, poly-Si gates in 10-20 nanoseconds. You should not use these types of speeds unless you know what you are doing, or don't mind smoking a lot of parts while you learn.

In general, what you gain by going to extreme switching speed, you lose with EMI problems and voltage overshoot. You can get away with more at low voltages, and less at high voltages. A low inductance package will also let you get away with more.

Ciao,
John

 

[Gyula]

Yes. As I know the power MOSFETs are made with polysilicon gate electrodes, which has higher resistance than it could be with metalization. So the "switching speed" can't be reduced to nanosecond range.