Hi everyone,
I want to control a relay (SRD-03VDC-SL-C) using the teensy 4.1. However the current limit on the teensy GPIO pins is 4mA (or not?) and the minimum current required to energize the coil in the relay according to the datasheet is about 150mA. It's obvious that I cant control the relay directly from the GPIO pins so I found this guide as a solution: https://www.electronics-tutorials.ws/transistor/tran_4.html
Since I had all the components on hand I assembled the circuit with the following components:
2N2222 transistor
1N4007 diode
SRD-03VDC-SL-C relay
Rb = 650ohm (for a current limit of 4mA I used the formula : Rb = (Vin - Vbe)/Ib, Vin = 3.3, Vbe = 0.7, Ib = 0.004)
R = 10k ohm
link to the circuit simulation:
https://tinyurl.com/2jypqwgr
According to the simulation, the transistor should saturate at Rb = 650ohm, however in reality it doesn't. The transistor will saturate at a value of Rb ≈ 470ohm, which means a current draw ≈ 5.5mA from the GPIO pin. My question is what am I doing wrong? I want to use a higher value resistor to minimize the current draw from the teensy but after testing the circuit with multiple Rb value it only seems to work with Rb = 470ohm. Why is there an extra resistor R in the circuit? apart from drawing extra current and sinking it, I don't see the use of this extra resistor (R). Maybe there is a better way of solving my problem?
Thanks for the help
I want to control a relay (SRD-03VDC-SL-C) using the teensy 4.1. However the current limit on the teensy GPIO pins is 4mA (or not?) and the minimum current required to energize the coil in the relay according to the datasheet is about 150mA. It's obvious that I cant control the relay directly from the GPIO pins so I found this guide as a solution: https://www.electronics-tutorials.ws/transistor/tran_4.html
Since I had all the components on hand I assembled the circuit with the following components:
2N2222 transistor
1N4007 diode
SRD-03VDC-SL-C relay
Rb = 650ohm (for a current limit of 4mA I used the formula : Rb = (Vin - Vbe)/Ib, Vin = 3.3, Vbe = 0.7, Ib = 0.004)
R = 10k ohm
link to the circuit simulation:
https://tinyurl.com/2jypqwgr
According to the simulation, the transistor should saturate at Rb = 650ohm, however in reality it doesn't. The transistor will saturate at a value of Rb ≈ 470ohm, which means a current draw ≈ 5.5mA from the GPIO pin. My question is what am I doing wrong? I want to use a higher value resistor to minimize the current draw from the teensy but after testing the circuit with multiple Rb value it only seems to work with Rb = 470ohm. Why is there an extra resistor R in the circuit? apart from drawing extra current and sinking it, I don't see the use of this extra resistor (R). Maybe there is a better way of solving my problem?
Thanks for the help