Hbridge design

[ahmedragia21]

Hi , i wanna your opinion on this design before doing it on a PCB, whethere it has something wrong or not , also i added the 2n2222 to make an ENABLE like pin to use it for PWM ..

 

[Hayato]

It makes no sense to me.
Those NAND gates, they will do nothing.

And the 2n2222? Will you ground the ground with that? Or, try to control the power side of the mosfets with a very low power transistor?

 

[ahmedragia21]

Those NAND gates prevent the h-bridge from damage ...
for the 2n2222, i wanna do an enable pin for PWM

 

[Hayato]

IRF540 can handle up to 33A.
A 2N2222 cannot handle more than 500mA, your circuit will not work.

And I cannot understant how the NAND are supposed to "protect" the H-BRIDGE.

 

[ahmedragia21]

So what is the subistiute for the 2n2222 ?
for the nand gate when there are two high inputs , the h-bridge will be short circuited

 

[Hayato]

But your design will never have 2 high inputs. Your H-Bridge is just dynamic as a statue.

And you must control it with the NAND gates, you don't need to add a 2N2222.

 

[ahmedragia21]

so how do i put an enable pin in the NAND ?

 

[Hayato]

Just configure the NAND gates the way that when you have a HIGH input, one optocoupler is driven HIGH and another LOW, and vice-versa.

 

[ahmedragia21]

and the other pin is direction DIR ?

 

[Hayato]

Take a look:


When A = 0, then #Q = 1 and Q = 0
When A = 1, then #Q = 0 and Q = 1

A is where your signal comes from.

Then you know what you should do.

 

[ahmedragia21]

Hi, i've modified the circuit as you suggested .
any corrections needed ?

 

[Hayato]

Still not right.
The A from my schematic is the direction. If you just connect PWM where it should be VCC it will malfunction.
You should add 2 more NAND gates to make some sort of MUX, with the Outputs and "PWM".

Then, in your power section, probably the MOSFETs gates capacitances will interfere your output waveform, you should drive them with push-pull or totem-pole drivers.

 

[ahmedragia21]

Tried to do it but couldnt figure it out unless using a Tri-state buffer ...

 

[Hayato]

You don't need a tristate.
Try to evolve that last schematic.
Then you'll get something like this:

 

[ahmedragia21]

Thanks hayato,
well how about the other problem you said , i couldnt understand it ??
why i need to drive the mosfets in totem pole form ?

 

[ahmedragia21]

any other suggestions guys before making it as a PCB ?

 

[blueroomelectronics]

Build a prototype first.