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Pin 9 ULN2003 for unipolar steppers

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Hi all,just a quick question. i'm designing a drive system with 2 unipolar motors: **broken link removed**

Is there any particular current requirements for pin 9 of the ULN2003 chip which is connected to the 12V supply? Will a 12V 0.5A or 1A be fine? Thanks
 

COM pin should be connected to the power supply.
Yes you can connect microcontroller pin direct to ULN.
If you want to increase collector current you can connect 2 input pin(ULN) together at the same pin at uC and the collector pins (ULN) the same together

---------- Post added at 23:37 ---------- Previous post was at 23:32 ----------

Usually you connect one end of the coils of a stepper motor to the outputs of the driver IC (OUT1-OUT7), right? Usually the other end of the coils is connected to the positive supply, right? Now if you connect the COMMON FREE WHEELING DIODES pin ALSO to the positive power supply, then you have just connected all the built-in free wheeling diodes as they are needed to protect the IC from voltage spikes coming back from the motor coils at switch-off, ok?
So by connecting the COM to the positive supply where all the other ends of the motor coils are also connected, you have simply placed the built-in diodes in parallel with the motor coils and the diodes will protect the IC.
 

ckshivaram said:
COM pin should be connected to the power supply.
Yes you can connect microcontroller pin direct to ULN.
If you want to increase collector current you can connect 2 input pin(ULN) together at the same pin at uC and the collector pins (ULN) the same together

---------- Post added at 23:37 ---------- Previous post was at 23:32 ----------

Usually you connect one end of the coils of a stepper motor to the outputs of the driver IC (OUT1-OUT7), right? Usually the other end of the coils is connected to the positive supply, right? Now if you connect the COMMON FREE WHEELING DIODES pin ALSO to the positive power supply, then you have just connected all the built-in free wheeling diodes as they are needed to protect the IC from voltage spikes coming back from the motor coils at switch-off, ok?
So by connecting the COM to the positive supply where all the other ends of the motor coils are also connected, you have simply placed the built-in diodes in parallel with the motor coils and the diodes will protect the IC.
Click to expand...

Thanks for the info,really helpfull but what i wanted to know is if the two steppers have a current rating of 0.16A per phase (four phase motors) would the current for the positive supply have to be at least 0.16A * 4 phases = 0.64A * 2 motors = 1.28A?
 

You will never activate more than two out of four coils for a motor, so you have 0.32 A per motor maximum current.

Regarding connection of free-wheeling diodes in ULN2803, connecting COM to positive supply is generally recommended, but it will reduce the maxiimum step frequency of the motor. If you are heading for maximum speed, you should connect COM to voltage twice the motor supply, respectively add a zener diode, that allows COM to swing above the supply.
 
Pin 9 doesn't carry the motor operating current. The current flow is from the supply, through the motor to the ULN2003 output pins then via pin 8 to ground.
You should connect pin 9 to a voltage no lower than the motor supply voltage, usually it is connected directly to the motor supply. It only carries short current bursts generated by back EMF in the motor coils so you shouldn't worry about its current rating.

Brian.
 
Hi shivaram,

Is it necessary to connect supply to COM pin for non inductive loads like LEDs?
 

Hi,
For non inductive loads it is not necessary.
 

Is it necessary to connect supply to COM pin for non inductive loads like LEDs?
Click to expand...

No it is not, the COM pin is the common of the free wheeling diodes, you can leave it unconnected if you want.

Alex
 

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