Driving a high current load with an arduino nano

I have a bit of a dilemma and wanted to see if anyone can help out, I am using an arduino nano to control a npn transistor that is used as a switch to drive a load that needs about 200mA of current. The whole thing is powered externally, but both the arduino and the load are connected to the same power source. Now here's the issue. I am afraid that if the power supply is not turned on and I am programming the arduino will attempt to drive my 200 mA load and will die heroically in the attempt. Is this what I can expect to happen or am I overlooking something? Any ideas how to solve my issue?

Thx in advance!

A circuit diagram would help...but provided the load has a direct connection to the external power supply and isn't connected through the Arduino you should be fine. Switching a transistor which has no power to flow through it isn't going to create any problems.


I'll sketch out something real quick as soon as I get home, sorry for that. My fear is that because both the arduinos Vin and the load are connected to the same supply, once the supply is removed isn't the arduinos Vin providing the 5V to my load?

I threw his together just for better understanding

OPs diagram.

The circuit will not work as you think, the load should be in the collector circuit and a resistor fitted in the base circuit.
This circuit will work better, it is a generic file I have, but gives the basic configuration of load, transistor and controller.

R = 470R should be enough to saturate your transistor.
Tom.. :slight_smile:

Maybe I didn't state my doubt well enough, I am concerned about the arduino driving my load if VCC is not connected to my power source but the arduino is powered through USB

Then the resistor will prevent excess current flowing, all is fine.

But please say what the load actually is, details always matter.

The load is simply a resistor that will draw around 200 mA, i just need that much current to be drawn from my supply so it doesnt shut down. So no, the resistor does not limit the current because if 5V are applied to VCC by the arudino itself it has to provide 200 mA

Then you won’t need a free-wheel diode. In general the nature of the load may affect the circuit design - some loads are inductive and need a diode to snub them, some have high inrush currents, which affects what device you need to survive the initial pulse.