Double checking H-Bridge Circuit

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Spanky09

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*Updated schematic in last post*

Hi guys,

New to making home circuits. I made a thread on it before, but for some reason it didn't bump when I posted the picture of the schematic and its stuck on the third page.

This is the motor I'm using:
10RPM 12V DC Motor with Gearbox [RKI-1035] - $5.00 : Robokits World, Easy to Use, Versatile Robotics Kits...

This is my schematic I came up with:
ImageShack® - Online Photo and Video Hosting

I'm using this as my PMOS and this as my NMOS transistors. I couldn't find a DC motor on PSpice so I just put in a resistor and a inductor to represent it. The motor used in the bridge is the one in the first post in the thread.

Should this H-Bridge work? Any feedback is appreciated.
 
Last edited:
Your circuit will not work because it uses a negative power supply and most of its Mosfets are shown connected upside-down.

Please post your schematic to your post HERE instead of over at Image-Shack that takes hours to wake up.
 
audioguru said:
Your circuit will not work because it uses a negative power supply and most of its Mosfets are shown connected upside-down.
Click to expand...

Is it possible he simply put the battery upside-down? Judging by some of the labels (GND=0V) it appears that this was a mistake. Then again, I have no experience with H-Bridges
Der Strom
 
Hell, I can't view stuff hosted on image shack from work. Per AG I wish people would just post the images here rather than link to image shack. Additionally, since people don't leave their images on image shack eventually the threads here end up meaningless for people researching old threads.

Ron
 
I'll redo the schematic. PSpice didn't have the transistor drawings that make sense to me from the Electronics course I did... The 12V at the top should be +12V. The bottom two and outer top two are supposed to be the NMOS transistors with their drain at top and source at bottom. The two inner top transistors are PMOS with source at top and drain at bottom.

My inputs for all the gates are 3.3V high and 0V low. I'm using an Arduino Fio.
 
Ok attached is the new schematic. My logic is as follows:

When N1 and N4 are high, motor will go in one direction. When N1 is high, the gate of P1 will be grounded, allowing current to pass through P1. Motor goes in other direction by same logic when N2 and N3 are on.

The resistors need to be there to avoid a short circuit.

Not sure if I'm even on the right track. Any advice would be appreciated.
 

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  • Circular Fan H-bridge.png
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Again, you showed the P-channel Mosfets connected upside-down. Simply look at their datasheet to see which terminals are source and drain and see the body-diodes. The resistors turn off the P-channel Mosfets and have nothing to do with a short-circuit.
Here is the corrected schematic that is still covered with Multisim chicken-pox dots:
 

Attachments

  • H-bridge.PNG
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I get now about the notation of the PMOS. I didn't really look at which way the source and drain were on the data sheet.

However, my big question is whether or not the circuit will work to turn the direction of the motor. I'm not sure if the transistor's specifications will allow the motor to turn the way I want it to. I have difficulty understanding how the specifications on their datasheets are applied. My budget is small and I'd like to know before ordering the transistors that they will work.

Also do I still need schottky diodes with these specific transistors? If what I understand from the datasheet, there is a built in diode?
 
The fixed H-bridge circuit will make the motor run forward or backwards as you want. The motor should be allowed to stop first before it changed direction to avoid stripping the gears and causing a high current.
The body diode in a Mosfet is in the wrong position to protect it and is very slow because it is not "designed into a Mosfet", it is part of the structure of a Mosfet. Use four 1N5817 1A Schottky diodes.
 
Spanky09 said:
Other than the four diodes I have to put in, all is ok?
Click to expand...
The circuit will be fine for occasionally changing the motor's directon or occasionally starting and stopping the motor.
But the circuit is too slow for PWM motor speed control.
 
That's the extent to what I want to use the motor for so thanks! I take it if I wanted to use PWM, I would need transistors that could support higher frequency rates?
 
For high speed PWM motor speed control you must quickly charge and discharge the high capacitance of the gates of the Mosfets with a fairly high current driver circuit.
 
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