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Topic: Basic question about L293D (Read 447 times) previous topic - next topic

angel6700

Hello,

I'm new on this so this is probably a very simple question but I could not find the answer.

I'm making a bipolar stepper driver with a L293D IC. OK ir works as expected, but I discovered something that cannot understand.

I'm powering the motor with a power supply (+5V) to pin 8 of the L293D. And the IC itself with the +5V of the arduino (to pin 16).

The code in the arduino make the motor rotate continuously. But, if I unplug the power supply for the motor, it still rotates! Why? I suppose that if there is no voltage in pin 8 (Vs) it uses the voltage in the pin 16 (Vss). In that case this is something not to do, I suppose...

So if I want to switch off the motors I should disconnect the 5V in the pin 16 (the logic part). Or better bring low the enable signals.

What is correct?

Thanks for your help.

dc42


I'm powering the motor with a power supply (+5V) to pin 8 of the L293D. And the IC itself with the +5V of the arduino (to pin 16).

The code in the arduino make the motor rotate continuously. But, if I unplug the power supply for the motor, it still rotates! Why? I suppose that if there is no voltage in pin 8 (Vs) it uses the voltage in the pin 16 (Vss). In that case this is something not to do, I suppose...


It's not uncommon to find that, because of the manufacturing process, there are extra diodes in the chip between the power or ground pin and other pins. There might be a diode in the L293D between the logic power pin (Vcc2) and the motor power pin (Vcc1), and current is flowing through this diode (although I would expect the datasheet to specify that Vcc2 must not be greater than Vcc1 - and it doesn't). But these diodes are not intended to take current. So if you keep doing that, you may damage the L293D.


So if I want to switch off the motors I should disconnect the 5V in the pin 16 (the logic part). Or better bring low the enable signals.

What is correct?


Bring the enable signals low.
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angel6700

Quote
Bring the enable signals low.


Hello, thank you very much. I will do that.

I supose I can use the same PWM pin from the arduino to both enable pins.

Best regards.

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