Hi all!
I made a simple BJT switch to control an array of LEDs with a uC. In attachment you find the simple schematic.
I have to control a current of about 510mA and the BJT I am experimenting with is a BCP53. uC supply is 5V.
I made two different version of the circuit:
1) If V+ is 5V and Rb is 220R the circuit works perfectly. When port is high LEDs are off and vice-versa.
2) Then I hade to raise V+ to 15V. uC supply is indipendent from V+ and it is still 5V. This time the circuit does not work: if uC port is high the LEDs are ON and if uC port is low the LEDs are still ON. Resistor is still 220R but I also tried to raise and lower it. No change. It start working if base voltage is raised too to 15V but I must control the base with 5V from the uC.
I made this test with one only led ad 17mA of current.
I think BCP53 beta of 25 could be too low for my application but I cannot figure why it works if V+ is 5V and it stop working if V+ raised to 15V.
Do you think I can try with a Darlington pair? Something like a BSP 60
Many thanks for your kind reply!
I made a simple BJT switch to control an array of LEDs with a uC. In attachment you find the simple schematic.
I have to control a current of about 510mA and the BJT I am experimenting with is a BCP53. uC supply is 5V.
I made two different version of the circuit:
1) If V+ is 5V and Rb is 220R the circuit works perfectly. When port is high LEDs are off and vice-versa.
2) Then I hade to raise V+ to 15V. uC supply is indipendent from V+ and it is still 5V. This time the circuit does not work: if uC port is high the LEDs are ON and if uC port is low the LEDs are still ON. Resistor is still 220R but I also tried to raise and lower it. No change. It start working if base voltage is raised too to 15V but I must control the base with 5V from the uC.
I made this test with one only led ad 17mA of current.
I think BCP53 beta of 25 could be too low for my application but I cannot figure why it works if V+ is 5V and it stop working if V+ raised to 15V.
Do you think I can try with a Darlington pair? Something like a BSP 60
Many thanks for your kind reply!