Basic question about L293D

[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.

[angel6700]

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.