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Voltage Drop Problem with ULN2803 n Stepper Motor

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sith108

New Member
Okay...My ULN2803 doesnt heat up anymore but therez this new problem now.

And again.....I've connected the Mitsumi M35sp-8 Unipolar Stepper motor to the Port B of my ATmega 8 microcontroller via ULN2803 IC.
I'm running the motor at 12V.
The Problem : The moment i switch on the Power Supply , the Voltage drops down to 3.5V at the power Supply and even if i try n increase the power Supply , it doesn't go up ( i used a 0-25 V variable Regulated Power Supply ). The motor however runs fine but a lot slower than itz rated speed.
Another problem is that the the Current reading at the o/p pins of the ULN2803 is 110mA which actually should have been 280 mA.

Why is this happening ? Whatz with the voltage drop at the power source ?
 

Ubergeek63

Well-Known Member
what is the rating on the power supply? if it is supposed to supply enough current try power the atmega separately and bring up the supply on the motor slowly. make sure it is set to max current out as well.
 

ecerfoglio

New Member
The Problem : The moment i switch on the Power Supply , the Voltage drops down to 3.5V at the power Supply and even if i try n increase the power Supply , it doesn't go up ( i used a 0-25 V variable Regulated Power Supply ). The motor however runs fine but a lot slower than itz rated speed.
Another problem is that the the Current reading at the o/p pins of the ULN2803 is 110mA which actually should have been 280 mA.

Why is this happening ? Whatz with the voltage drop at the power source ?
Maybe the power supply has a current limit. If this limit is set at 110 mA it will behave as you say it does
 
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