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is this bjt transistor hbridge right?

dragon

Oct 31, 2022
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Just like to ask is this basic h-bridge schematic right for a full left - full right all or nothing action?


YYeKwfS.png
 

danadak

Feb 19, 2021
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Yes. But transistor drive depends on what yiou use for top and bottom devices,
NPN, PNP, both.....

1668169580331.png

1668169661561.png

And dont forget you need deadtime switching, eg. no vertical par simultaneously on.

1668169869229.png



Regards, Dana.
 
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dragon

Oct 31, 2022
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Thanks.
As I trace the logic of the wires of my drawing, the top transistor actually doesnt turn on until
the bottom transistor does otherwise it doesnt make it to arduino ground, so the bottom one
turns on a nanosecond before the top one does, but its quite unmeasurable time delay.

Your not Garth from Wayne's World are you? That would be extremely trippy, and I'm starting to go crazy.
 

danadak

Feb 19, 2021
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You do not want top and bottom transistor in same leg to turn on at same
time, thats key. Otherwise you have a dead short on the power supply to
ground. Thats usually taken care of in embedded processor PWM settings
or in external driver chip.

Most scopes can measure that time delay.

No on garth :)


Regards, Dana.
 

crutschow

May 7, 2021
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You cannot control a 12V H-bridge directly from the Arduino.
The top transistors need a driver to generate the 12V base control signal required.
 

dragon

Oct 31, 2022
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its actually 24volt. (+12v - -12v) the arduino output is enough isnt it? transistors are really sensitive, you can set em off with 30k resistors in line with the base and they still fire fine cant you?
 

crutschow

May 7, 2021
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the arduino output is enough isnt it?
No, the Arduino output by itself is not sufficient.
you can set em off with 30k resistors in line with the base and they still fire fine cant you?
Yes, you can "set em off" with a 30k resistor, but that's when the emitter is at ground potential.
The base-resistor value is not a factor here, it's the base-emitter voltage that's critical not just the base voltage, so they won't "fire" from the Arduino low output voltage.
So if the top bridge transistor is at 12V, then the base voltage must be at 12V to turn it off, and within 0.7V of that to turn it on.
And to control the bottom transistor, its base must be a -12V.

Since your understanding of transistors seems to be a little fuzzy, methinks you need to read a little more about how transistors work.
 

danadak

Feb 19, 2021
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Low cost H Bridge that will interface to Arduino -


Ratings :

1668247511043.png





Regards, Dana,
 
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dragon

Oct 31, 2022
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that chip is in spec with what I need! and its 3 american dollars with what i was planning to buy for it other than the wire was the 4 transistors, they were 1.40 dollars each, so it was 5.60 dollars australian to buy, basicly the same f u dont take into account the wire, not sure if it would heat up more or less.
I think I need a resistor on the arduino ground too, just so i dont overdrive the transistor bases, but more like dont overdrive the arduino internals.
 
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danadak

Feb 19, 2021
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You can directly drive the L298N from Arduino, no R needed :

1668262624231.png

As you can see very small current needed by inputs.

What are your motor specs in terms of V and I ?


Regards, Dana.
 

dragon

Oct 31, 2022
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24volt and about 700 milliamps. they are 33 ohm. and they have 1 mm play on the gear box, they are 280 rpm. (very strong ones. hehe)
 
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