ULN2803A / sink current

ACGUY

Hi all,

I have a question about ULN2803A.
When the input pin of the device has been pulled up by 3.3V and 1kohm, does this device, can sink the how many of the current?

Regards,
Nagai

over 7 years ago

0 Michael J Schultis over 7 years ago

TI__Mastermind 24485 points

Hello Nagai-san,

Please refer to the ULN2803 functional block diagram. You can calculate the expected input current based on the internal resistance values. If we assume that the base current into each transistor is small, we can calculate the voltage and current based on a resistor divider.

Does this make sense? Let me know if you have additional questions.

Best,
Michael

0 ACGUY over 7 years ago in reply to Michael J Schultis

Guru 11170 points

Hello Michael-san,

I'm sorry to ask a lot.
I tried calculate.
I attached a calculation result file.
Could you give me your advice then refer the file?

Best regards,
Nagai

ULN2803A_Calculation.pdf

0 Michael J Schultis over 7 years ago in reply to ACGUY

TI__Mastermind 24485 points

Hello Nagai-san,

The beta curve was provided in a previous post:

http://e2e.ti.com/support/interface/industrial_interface/f/142/p/528543/1923270#1923270

If you take the Beta curve and the I(in) expected based on your input voltage and the resistor divider then you can see what the maximum output current the device can manage is.

Based on 3.3V input, your input current is 237uA. Based on what you want your output current to be, you can see if the device can manage this output current based on the corresponding Hfe at that output current.

Best,
Michael

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ULN2803A / sink current