L298 dc motor driver

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Scolioza

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Hi all.

I recentlly designed a full h bridge motor driver using L298.

I want to drive the motors using de PWM output on RC2 of a 16F877A uC.
I attached an interrupt on RB0, and in the interrupt routine, I increased the duty cycle by 50 units by pressing of a button.
The pwm freq. is 3kHz with 10 bit res.
The problem is that after 70% duty cycle the motor increases by itself the spining and then suddenly stops.
Reseting the uC fix this.
What can cause this?
 

Hello there,

Please check out these two pictures..

You should consider T5,T6,T7,T8 timming sections.
 

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  • edaboard1.bmp
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  • edaboard2.bmp
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Can you help me how to interpret those values?

If a i understood well i have to add some delay before start a new duty cycle?

- - - Updated - - -

And here is the circuit:
 

Tryed everything works fine with a led but when I connect the L298 is like someone is pushing the button and increments the duty cycle.The uC doesnt resets
 

I use 3KHz
The problem is with uC it seems that over 70% duty RB0 is pulldown
I changed the motor and it works fine
 
Last edited:

Hi again.
I dont give up so easy. So i made another board with optocouplers to isoltate the pic from the motor ground. But with the first motor its the same story.

Any idea of what is going on?
What is the tipically voltage drop across L298? Because at full pwm with a 4.5 voltage the output of L298 is 1.8 V.
thanks
 

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