Hi,
I was testing a small circuit I had which I intend to recreate on a larger scale once I had the basics down.
It involves using a micro controller and a P channel MOSFET to switch an LED on. And to later add a ULN2803 to sink the current.
What I found weird is that by adding the ULN2803, the current to the LED drops significantly (20mA to 1mA). I am aware there is a voltage drop across the NPN transistor and that I did not change the value of the resistor value between adding the ULN2803 but the current supplied seems to be a constant 1mA making me believe that the ULN2803 is acting as a constant current device.
Can anyone shine some light on this and maybe how I can get the load current back to around 20mA?
Thanks
I was testing a small circuit I had which I intend to recreate on a larger scale once I had the basics down.
It involves using a micro controller and a P channel MOSFET to switch an LED on. And to later add a ULN2803 to sink the current.
What I found weird is that by adding the ULN2803, the current to the LED drops significantly (20mA to 1mA). I am aware there is a voltage drop across the NPN transistor and that I did not change the value of the resistor value between adding the ULN2803 but the current supplied seems to be a constant 1mA making me believe that the ULN2803 is acting as a constant current device.
Can anyone shine some light on this and maybe how I can get the load current back to around 20mA?
Thanks
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