Particle 3.3V to 6V


This is probably a typical question but i would like to know which transistor is best to use to power a 6V fan. The transistor is obviously acting like a switch to allow the fan to turn on and off. I have attached a diagram of the circuit.

@chuckie, I didn’t see what amps the fan will draw. That is a need to know if you want the transistor to be hefty enough to handle it.

Do you plan to control the speed of the fan, with PWM, or just turn it on, and off? I notice a waveform in your schematic, so leads me to believe you want to use PWM.

I see nothing wrong with your schematic. Just some values may still need tweeking.

BTW: I like your schematic. How did you achieve that. Photo of a paper, or some web/computer program?

I’m going to agree with @Jack. Some more data on the fan’s electrical properties would be nice.

If you have a multimeter (or a benchtop power supply!) put it in Current Measure mode and then put it inline with the fan (So, connect 6V to Multimeter +, then Multimeter - to Fan + and finally Fan - to GND) and measure the current draw and report back!

If you can find specs on the fan (motor), it may give max (startup) amps, and running amps.

Just a quick thought @chuckie: if you only need on/off control a relay might be easier!

1 Like

I usually prefer to use an electronic relay, especially if it is an inductive load. It seems to provide good protection to the processor. A bit more expensive than a mechanical relay tho.

Hey guys,

so this is the fan i am currently using to test my project. This one is a 5V :

I would like to do my initial testing on the 5V fan because the 6V is more expensive and do not really want to risk anything. So the fan will operate to keep the humidity of an enclosure at certain limits. For example, lets say the humidity sensor reads 60% humidity and i would like to increase till 70% or lower to 50%, the fan will operate until the above mention humidity is reached.




A couple of things:

@chuckie, I don’t think a fan (airflow) will reduce humidity. It is good to reduce mold and mildew tho.

If your fan draws MAX 210 ma, then a 2n2222 NPN transistor should do the trick.

Okay, so in the 5V case i just basically need to power the fan on for a certain period of time till a humidity is reached then it turns off that’s all. So my idea was that the spark core will output current that will turn on a transistor which then from the circuit i have attached, allows the fan to operate until a certain humidity is reached. So @Jack the 2n2222 will work? I currently tried it with a 2n3904 and it didn’t work. I have read that 2n3904 isn’t really capable of this.

Why do you think it is not capable of this?

I don’t think the 2n3904 are capable because i read online that they are low current gain transistors. They won’t have enough current to drive the fan.

I am going to order some 2n2222 any other transistors you guys suggest before i go ahead and purchase?

Maybe it is not as much the “current gain” as much as the max current.
It looks like the 2n3904 has a max current of 200 ma, while the 2n2222 has a max current of 600 ma.
Just my opinion, check the specs before you commit.

What value resistor are you using on the base of the transistor?

1K ohm for the base

What does that mean? How did it not work? Any current flow at all?

The base resistor of 1k should be ok.

You may want to use the “blink LED” example, but send it to your transistor. See what the voltages, and currents are doing.

In about an hour or so i will do it, i will keep you guys posted. I hope it works lets see. It didn’t work when i first initially tried it.

1 Like

If the 2n3904 is a low gain transistor, it may be worth trying a lower value on the base resistor (like half of 1k).

1 Like