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H bridge

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my motor is 12V and consumes 150mA

150mA??? baby FETs....

in that case Hero999's circuit is more than adequate... it is the same as the bottom schematic you posted but with Hero's reduced Q count, look at where your motor is in that one, plus it has the back EMF diodes Hero999 was talking about. You may even be able to reduce the FET size.

and REPLACE RL (R load) with the motor... in this case, the motor IS R load... + or - to either side, the only difference it will make is which way the motor spins per which input you turn on. Do NOT turn both inputs on at the same time. L = OFF, H = ON.
 
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the problem is that I look at this circuit and do not know where to start the engine, I do not know where it feeds this circuit!
 
no. you feed it 12V, and it turns that 12V on to the LOAD. The control inputs are labeled as A and B.

if you put motor + as the left of R Load, and motor - as the right of R Load, then A HI and B LO = spin forward, and A LO with B HI = spin reverse.

Before I had stated not to turn both A and B on at the same time, but I see D1 takes care of that. D1 keeps both sides from turning on at the same time by clamping the base of M2 to the drain of M1, which, if it's on, will be ground preventing M2 from coming on.
 
The IRF7204 has a maximum drain voltage of 20V but I made a mistake when I said the maximum voltage rating of this circuit is 20V. It's really 12V because it is the maximum gate voltage for the IRL7204.

Anyway, don't use exactly the same parts as I have done in the schematic, it's just an example not a final design; you should find parts which suit your application.
 
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by pulling A or B HI. Like Hero999 said he was going to do, he re-wired your posted schematic to have the bottom FETs turn on the top FETs, and thus eliminates one pair of transistors.

In a previous post I had stated "if you put motor + as the left of R Load, and motor - as the right of R Load, then A HI and B LO = spin forward, and A LO with B HI = spin reverse". THIS IS BACKWARDS. A HI = reverse, and B HI = Forward. A and B HI = reverse for the MOTOR(+) to be on the left.


Let's say you want to go reverse. Set A = HI. M1 turns on and puts the motor(+) to ground. It also pulls the base of M4 LO turning it on automatically, which applies +12V to the motor(-).
 
this is annoying .. because I already wanted to build this circuit to apply in my car! how do I know the components that precizē? : |
 
The IRF7204 has a maximum drain voltage of 20V but I made a mistake when I said the maximum voltage rating of this circuit is 20V. It's really 12V because it is the maximum gate voltage for the IRL7204.

Anyway, don't use exactly the same parts as I have done in the schematic, it's just an example not a final design; you should find parts which suit your application.


I think the part selection is pretty good, except that, as mentioned, the Gate/Source max voltage is only 12V. AND it's running a motor, not a resistive load. The only thing I would change is to put a 1K between each 7204 gate and the corresponding drains.

The n channel FETs have a pretty low turn on threshold, so I think they're well suited for a logic driven application. Both FETs are pretty cheap and readily available.
 
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I think the part selection is pretty good, except that, as mentioned, the Gate/Source max voltage is only 12V. AND it's running a motor, not a resistive load. The only thing I would change is to put a 1K between each 7204 gate and the corresponding drains.

The n channel FETs have a pretty low turn on threshold, so I think they're well sutied for a logic driven application. Both FETs are pretty cheap and readily available.


means that if I feed the 12V instead of 20V, the mosfet will work the same?
 
this is annoying .. because I already wanted to build this circuit to apply in my car! how do I know the components that precizē? : |

moonstreat, do your homework. Go to a catalog or manufacturer's website and do a parametric search. Or Digikey.com.
do a search on mosfet, then enter in the currents/voltages/gate thresholds values of what you need for your circuit
 
Mike odom I am very weak, like a lot of electronic, but I'm very new and still do not understand many things! I have seen things in this forums a lot of chips! and I will be a pleasure to tar to learn from you! I still can not make circuits for myself! how to calculate values of resistors or capacitors to a circuit! I learn with time!
 
The MOSFET can be rated for anything higher than the voltage you're using.

No offence but I don't think you have enough experience to build this.

My advice is, study MOSFETs, Ohm's law and the absolute maximum ratings system before building it.
 
I walk to take a course in electronic and automation! and this is my last year! I'll build a mini truck headed! and want to control your car from this circuit! = P. . .
 
means that if I feed the 12V instead of 20V, the mosfet will work the same?
The max allowed drain-source voltage of the Mosfet is 20V. It works the same with a 12V or even a 3V supply voltage for its load.
The circuit shown uses a 12V supply so the 20V Mosfets will not have a voltage that is too high for them.
 
I walk to take a course in electronic and automation! and this is my last year! I'll build a mini truck headed! and want to control your car from this circuit! = P. . .


I think your lecturer needs to teach you about voltage ratings.

In my experience some courses tend to poorly teach practicalities such as component ratings and focus too much on passing the exams.

AND it's running a motor, not a resistive load.
It's standard practise on schematics to replace the device being driven with RL.

It might not be driving a motor, it could be a latching relay coil or even a speaker.


The only thing I would change is to put a 1K between each 7204 gate and the corresponding drains.
Why do you suggest that?

The n channel FETs have a pretty low turn on threshold, so I think they're well suited for a logic driven application. Both FETs are pretty cheap and readily available.

They're SMT which might not bother you or me but will be difficult for a nube to solder.

I also got it the wrong way round by putting the logic level devices on the high side rather than the low.

I didn't think about actually building it, it's just a proof of concept, I just picked some MOSFETs models from LTSpice which looked good. I think I'll remove the part numbers before posting it, the next time I do this.
 
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