H-Bridge

501

06:34:25

The correct way to build an H-Bridge with only N MOSFETs.  
The upper two MOSFET gates must be driven with a voltage higher than the main supply (Vcc), or they will not saturate correctly. This is due to the fact that if we drive them with a voltage equal or, even worse, lower than Vcc, Vgs will be almost zero (tens to a thousand mV), and the FETs will work in their linear zone, allowing just a very little current to pass through the drain and source. This gate driver supply should be referenced to the load leads, and it must be at least 4 or 5V (see datasheets for specific Vgs-Id relation). This could be obtained with a switching power supply with a transformer, with the secondary winding of it (which is usually the ground) connected to the Source of the upper MOS. Obviously we need two of these converters (one for each high-side MOS). 
They also exist as ICs with the size of a small relay (phew.. ). 
Hope this could help you, SirCube. 

published 10 years ago

nikisalli

10 years ago

So i can do this with igbts?

rich11292000

10 years ago

Floating power supplies

sircube

10 years ago

Yes, it is correct

sircube

10 years ago

@nikisalli I don't know exactly how IGBTs work, but i suppose you can, although I suggest you FETs to have less voltage drop

sircube

10 years ago

@rich11292000 you can achieve floating power supplies with insulated switching comverters, I actually used this IRL

hurz

10 years ago

A little simplified, does not answers how the 10v for top MOS can float as static supply and not a dynamic boost cap. Would be nice if you present a practical solution at that point and we can call it "correct"!

sircube

10 years ago

The pratical solution would be bigger than the EC screen ahaha, but if you want you can contact me for the complete schematic!

hurz

10 years ago

EC is for all! And you promised a "correct" solution for all users. If you are clever enough, you can demonstrate at a half bridge how it works. Ahhh, and dont forget some dead time generator. Have correct fun!

sircube

10 years ago

I could do that, maybe in a few days. The idea for the dead time was to implement it via software (I originally designed this to be controlled by a uC).

hurz

10 years ago

Right, the interface is also missing and left room for judgment if correct or not.

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