Using delicate 5V IC to toggle 12V device with MOSFET, Diode, resistor

[NotASmurf]

Hey all, I have a 5v IC that is triggered by a sensor to unlock the 12v lock, I am using a NPN transistor as a switch with the 5v VCC as the gate, I need it to sink back to the GND of the IC without blowing it, is this safe? If not what changes would you suggest, it has been years since I've had to do this, and I'm used to using H-Bridges for such things, any help appreciated.

 

[berkeman]

You don't show the emitter position in the NPN transistor, but I assume it points to ground since you are using it as a low-side switch.

What IC is driving this transistor base through the base resistor Rb? Is it a CMOS IC (so its output swing to the 0V, 5V rails), or does it have TTL outputs (so the low output is not really to the 0V rail)?

 

[NotASmurf]

It is an arduino uno, and yes to the emitter position

 

[berkeman]

It is an arduino uno, and yes to the emitter position

What are Vol @ Iol and Voh @ Ioh for that Arduino?

 

[NotASmurf]

max 80ma and 5.5v

 

[berkeman]

Wow, it can source 80mA? Impressive. What is the Vol @ Iol spec?

 

[NotASmurf]

technically 40ma on both, but in practice runs 80ma most of the time

 

[berkeman]

My reason for asking about Vol is that if it doesn't reliably go down to 0V (which you typically get with CMOS outputs), then you may want to add a base pulldown resistor like this:

https://www.electronics-tutorials.ws/wp-content/uploads/2014/04/switch1.gif?fit=273%2C245

 

[Tom.G]

If the V_OL of the Arduino is 0.5V or more, I suggest adding a diode in series with the 1k resistor of the circuit that @berkeman suggested; Anode towards the Arduino, Cathode towards the transistor.