[SOLVED] Getting high Vce in ULN2803

[Murugesh_89]

Hi,
I have switched some loads previously using a single npn transistor in saturation region. At those time the value i got Vce as 0.1 - 0.2 V.

But now i am using ULN 2803 for switching and i tried with some 10k, 22K, 47K resistors between supply and output(collector). I am just giving 12V at the input of base. But i am getting the Vce as 0.6V for the three different value of resistors. Why is it so?

Is there any way to make Vce as 0.1 - 0.2 V.

Thanks,
Murugesh

 

[FvM]

ULN2803 is a darlington driver. It can't achieve 0.1 to 0.2 V saturation voltage.

 

[Murugesh_89]

Why is it so?

 

[schmitt trigger]

Because you have the Vce of the first transistor in series with the Vbe of the second transistor...

At full load (500mA), the total voltage drop could be as high as 1.6V (per the Texas Instruments datasheet), although on average would be around 1.2V