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
In reply to It will work by Sourav Gupta
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?
Transistor is a current control device. Use proper resistor to control the base current.
In reply to Yes by Sourav Gupta
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
All information given by the datasheet is useful from different aspects.
https://circuitdigest.com/article/npn-transistors
Follow the above link. I hope this will provide all answers of your quarries.
Sourav Gupta
Joined February 12, 2018 696Monday at 02:11 PM
Use proper base resistor.