BC547 collector current when base voltage is 3.3V

Submitted by Pefey on Wed, 04/01/2020 - 08:04

Hi,

I am controlling a 5V relay using a microcontroller (NodeMCU) operating on 3.3V. So the GPIO pins will only provide 3.3V. Hence I have used a BC547 to control the relay. But I am confused if the BC547 transistor will be fully closed when i give 3.3V and deliver enough current to trigger the relay 

I have attached the graph below that shows the collector current value for different base voltage. If my VBE is 3.3V then there is no collector current at ambient temperature. I think I am missing something here. Can some one pls help 

Capture.PNG

Use proper base resistor.

  Joined February 12, 2018      696
Monday at 02:11 PM

thanks for answer gupta, but how can it be done? What value of resistor should i use? Also resistor is only used to control the current right? 

  Joined December 12, 2019      8
Thursday at 04:07 PM

Transistor is a current control device. Use proper resistor to control the base current.

  Joined February 12, 2018      696
Monday at 02:11 PM

Thanks for the answer i am slowy getting to understand this.

So the above graph is useless? I also did not find a graph for base current vs collector current.

So how much base current should i provide to base pin of bc547 if my collector current should be 70mA. Please help me with this. I also want to know formulae for calculating resistor value if my base voltage is 3.3V

  Joined December 12, 2019      8
Thursday at 04:07 PM