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Linux/L293D: Voltage Drop at Outputs

Piciu C
Prodigy 20 points
Part Number: L293D

Tool/software: Linux

Hi,

I'm a French student working on an RC autonomous car project. The first part of the project consists in controlling two DC motors using Pulse With Modulation. I use the L293D with a Raspberry Pi 3B+.

I have a 7.2 V battery for the VCC2 and 5V from the RPi for the VCC1. I tried using PWM with the EN1 pin then with the IN1/2 pin (respectively EN2 and IN3/4 for the second engine). However, I still have the same problem.

When I run my code, a significant voltage drop occurs (between 3 and 4V). I can measure it at VCC1, VCC2 and at the outputs, even with a PWM at 100%. Therefore, my engines do not turn fast enough and I don't know how this voltage drop can be avoided.

Is it possible to avoid this voltage drop? Is the code the only problem, even though I tried two methods (sending PWM to the EN pin and using IN1/IN2 for the directions, or setting EN to High and using PWM on IN1 or IN2 depending on the direction)?

Thank you,

Piciu

  • 0
    TI__Guru 56650 points
    Piciu,

    Where do you measure the voltage drop? When voltage drop occurs, what is the VCC2 voltage? And, what load current should be?

    If you can get some waveforms, it could speed up the debugging process.
  • 0 in reply to Wang5577
    Prodigy 20 points
    Hello Wang,

    Thank you for your quick reply. Sorry for answering so late, but I only had access to measure tools today at the laboratory.

    I can measure the voltage drop at all the output pins, but also at VCC2 and VCC1. When the voltage drop occurs, I measure 3.5-4V at VCC2 instead of 7.2 from my battery.

    I don't have any data about the current my DC motor needs, so I measured it: I think that this is the reason why the voltage drops, because the chip does not deliver enough current.

    Indeed, the motor needs about 1.2A to start rotating, and it barely keeps rotating at 600mA which is the output current of the L293D.

    Do you think this is the problem? Does Texas Instrument produce motor controllers that deliver more than 1A?

    Thank you again for your support,
    Best regards,

    Piciu
  • 0 in reply to Piciu C
    TI__Guru 56650 points
    Piciu,

    "the voltage drop at all the output pins, but also at VCC2 and VCC1. When the voltage drop occurs, I measure 3.5-4V at VCC2 instead of 7.2 from my battery"

    VCC1 and VCC2 are L293D's input pins. If the voltage drop was already happened on VCC2 and VCC1, the voltage drop was not caused by the L293D. We should check the voltage on battery terminal. If it was also 3.5~4V, that is battery issue. If the battery is 7V, then, it was the cable resistance issue between the battery and the L293D board.