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What obvious thing am i missing?

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breadboardguy

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I need to get my h-bridge up and running for my robot, but i cant even make a simple n-channel fet to work!

Can someone tell me what is the obvious thing that i am missing in the circuit below, its what afrotechmod said to do on youtoube.

I have heard that low voltage on fet can cause issues, but i tryed with 6volts on the drain and ... nothing.

Need help.Quick please.

https://www.youtube.com/watch?v=Te5YYVZiOKs
 

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You're using it as a source follower so the gate to source voltage will only be 3.5V which isn't enough to turn it on.
 
Swap the motor and fet positions. Also connect the negatives of the batteries together.

Mike.
 
If you want to switch a motor with a fet it's like this the 5 k and 20k may not be needed if you get the right fet
 

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I did'nt knew that, must be my newbieness.

So i will drive the two n-channel on the high drive side with two 2sa684 at 9 volts, i tested it and it works. Its just more complicated.

If i use a pic mcu at ttl levels for the gate input, should i connect the two batteries(of the dc motors and of the pic mcu) ground together?

You really helped me, i was going crazy.

(is it normal that the irf511 floats high if i dont ground the gate?)
 
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One that's no h-bridge If it was would look like this **broken link removed**
Read this H-bridge secrets part 1
The high side MOSFETs on that circuit either need to be bootstrapped, be P channel or receive the gate drive from a higher voltage than the motor.
 
Hero the OP said H-bridge he posted a fet being used to switch a motor. I didn't draw that I just posted it to show what one looks like. If you or OP wants to know how to make one then please read here H-bridge secrets part 1
 
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Completly random question: Can i source an rc servo motor with a 5 volt regulator? (7805)

My circuit (with the2SA684 and the irf511) works very well, whats is only left now is to solder 8 irf511 fet, 4 2SA684, 2 7805, 3 ic socket, 10 screw connectors, 2 big caps and a lot of diodes and resistors on a 2 inches by 3,5 inches veroboard... It should take me at least two days for a such small thing.

Thanks for the help.
 
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