Electrical – Voltage regulator drop

stepper motorvoltage-regulator

First off I'm a beginner at electronics I don't understand much so bear with me.

I've just constructed my first bipolar stepper motor circuit today on a breadboard. I've actually extracted the stepper motor from an old Epson printer. I've used an lm317t adjustable voltage regulator to power the motor driver. Input is a 9v battery and I give 5v as motor power supply to the l293d motor driver. There is a separate microcontroller and its power and ground which is 5v as well.

Now I've used a pot to adjust and multimeter to check the output motor voltage of the lm317 regulator. I have set the pot such that the output is at 5v

Now my question is when the stepper motor runs successfully, the multimeter reading drops from 5v down to 4v. Why does this happen?

Best Answer

9V batteries can only source a small amount of current. You are likely exceeding the current that the battery can comfortably source (or, to phrase it differently, you are drawing enough current that the battery's internal resistance causes too large of a voltage drop).

If you measure the battery voltage, you will likely see it dropping below ~8V, which is the drop-out voltage of the LM317 when you are operating it at 5V output. The LM317 may need an input voltage of up to 8V (5V + 3V) to provide a stable 5V output (the recommended Vi-Vo is 3V).

Use several AA batteries in series, or a wall-wart that can supply a decent amount of current.