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### Topic: External Voltage supply (Read 945 times)previous topic - next topic

#### max891

##### Dec 29, 2011, 02:44 pm
I have some stepper motors to power so I need to use some external voltage source, I chose LM317 circuit from  datasheet and Li-po battery(1700 mAh 25C)
How I can put it into use ?  Positive wire to L293D leg which supply power for stepper motor , negative one to gnd of arduino ?
I tried this but It fail a bit... Where is mistake  ? How to connect them.

#### Grumpy_Mike

#1
##### Dec 29, 2011, 10:27 pm
Look at the data sheet and you will see it is more complex than this.
You need a potential divider and decoupling capacitors.

#### max891

#2
##### Dec 30, 2011, 09:15 am
I know, I build  1.2V-25V voltage  regulator from  typical application section. But I see my mistake right now ....
http://www.ti.com/lit/ds/symlink/lm117.pdf Input voltage should be more or equal 28V. I connected far less ...

#### Grumpy_Mike

#3
##### Dec 30, 2011, 09:41 am
No the input voltage must be a few volts more than the output voltage not more that 28V. That first diagram is for a regulator that goes up to 25V.

#### max891

#4
##### Dec 30, 2011, 11:58 am
Ok so I had circuit from this diagram except Resistor 240 ohms - I had only 220 ohms so I used it.
It works properly, using a pot I can change voltage. I set it to 3.3V and put positive terminal to leg on L293D corresponding for supplying motor. Negative one to GND of same IC and... nothing.

#### Grumpy_Mike

#5
##### Dec 30, 2011, 05:41 pm
Quote
I set it to 3.3V and put positive terminal to leg on L293D corresponding for supplying motor

This is because, according to the data sheet, the motor supply has to be at lease the same voltage as the chip's logic supply voltage. In other words it will not work with only 3V3.

#### dc42

#6
##### Dec 30, 2011, 07:13 pm
Bear in mind that the voltage supplied by the L293D to the stepper motor will be 2 to 3v less than the supply voltage you feed to its Vcc2 pin.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

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