ULN2803 Question

@shahrul-Ex12xz • Oct 25, 2024

Oct 25, 2024

925

I tried to pull-down some device to 0V.
First, using transistor, it's successful. Then I need to interface more than one device, I using ULN2803, but there is a small problem. There are have small voltage drop at pin and ground.

Testing with transistor, when signal low, pin is 1.85V and when signal high, pin is 18mV (~0V)
Testing with ULN2803, when signal low, pin is 1.85V and when signal high, pin is 0.6V.
This 0.6V giving me problem, it should 0V.
Can anybody have propose circuit?

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sauravgoswami

@sauravgoswami-UAfTlI • Apr 24, 2010

0.6V is considered 0V in digital circuits I do not feel it should cause any problems,however you can connect the ground pin to circuit ground through a loading resistor,I hope it will give you 0V,by the way does this small voltage drop affecting your circuit operation.
shahrul

@shahrul-Ex12xz • Apr 24, 2010

Yes, this small voltage drop affecting my output result. That device converting PWM into current analog (0-25mA).
By using transistor, I can vary duty cycle and can get max 25mA. By using ULN, this value can't be achieve. It's max is 19mA.

I think to change GND reference. I want to make pin 9 ULN to become -0.6V, so that voltage at the pin become zero.
sauravgoswami

@sauravgoswami-UAfTlI • Apr 24, 2010

You can try that buddy, and let me know ur results however as far as i know you should be using pull-up transistors instead of resistors in case of PWM.