What is ULN2003 IC?

A logical circuit with Darlington transistor (NPN) was used to control the High DC load approximately equal to 50V and 500mA. This circuit could only be used for a single load. To solve this issue an IC name ULN2003 was introduced.

What is the voltage range of ULN2003 output pins?

Output pins are the common ground within the ULN2003. Attach any load within 50V and 500mA from the outside to the Output to make the load functional. It comes in another version with a voltage range of 100V. The current handling system is also 500mA for each input.

Why are the open collector outputs of ULN2003 not working?

In proteus it doesn’t behave as expected, the open collector outputs of ULN2003 are not pulled high through the LED as they are supposed to be, this is a simulation model misbehavior. The solution you can use it to add pull up resistors (I have used a resistor network) like shown below:

How to use ULN2003 to connect different loads to a device?

Just attach the different loads with a different power source with ULN2003. Then Connect each load with a different power source. After that Common the ground with IC. Each Input pin controls each output. Now turn that device on which need to be on by applying High Logic on that input.