I am using Arduino Due to control BJT switch array.
Schematic is as follow (attachment):

I am able to get 3.3v output voltage from Arduino. The problem is that once I connect it as schematic shows, the output voltage drops to 0.6v.
Arduino Due pins can give output current as high as 40mA, but this circuit gives me only 0.0266mA (by calculation).
When using 3.1V battery, the circuit works fine and gives 1.23mA current.

Can anyone help me?
Thank you

 

hi,
Are you sure you have the MCU pin set as an Output and not an Input.?
If the internal pulls ups are enabled its possible that the pin is pulling High off load.

 

If the collector load is an LED inside of an optical isolator then it might be that when the Arduino output pin goes high, the current through the transistor's collector pulls the power supply out of regulation, the result being that the power supply and therefore the output of the Arduino will be regulated at a voltage that is just enough to drive the transistor at the level that pulls the supply out of regulation.

You can check for this condition by measuring the voltage between VCC and VSS of the Arduino or by disconnecting the optical isolator.

 

To make sure that you connected to the right pins of transistor.

 

Is that .6V measured at the output pin or at the transistor base? In the second case, it would be correct.

 

hi,
Are you sure you have the MCU pin set as an Output and not an Input.?
If the internal pulls ups are enabled its possible that the pin is pulling High off load.

Thanks for your reply.
I only used "digitalWrite(xx, HIGH);" to set pin to 3.3V.
I will try it right now.
Do I have to use "pinMode(xx, OUTPUT);" to set it as output? Why I still can get 3.3V without this?

 

If the collector load is an LED inside of an optical isolator then it might be that when the Arduino output pin goes high, the current through the transistor's collector pulls the power supply out of regulation, the result being that the power supply and therefore the output of the Arduino will be regulated at a voltage that is just enough to drive the transistor at the level that pulls the supply out of regulation.

You can check for this condition by measuring the voltage between VCC and VSS of the Arduino or by disconnecting the optical isolator.

Thanks for your reply, sir.
The problem is that the circuit works with a 3.1 battery.

 

hi,
Are you sure you have the MCU pin set as an Output and not an Input.?
If the internal pulls ups are enabled its possible that the pin is pulling High off load.

It works now.
Thanks so much for your help.

 

Hello,
From circuit you posted change 71.5K to 10K and base 2K to 440 ohms will delivery maximum current!