H3LIO

I mean Right. I'm using the ones you told me BC338. I was think the same, that the specs in the fan would affect the way it works with dutycycle. It's working nice, but i will try different fans to know why it happens. Thank you

Your calculations are Roth, I was using a different resistor 160 Ohm as R3 when I was doing I only notice now.

Hi Hero999, I change R3 for 67 Ohm and I have ib of 24mA and vbe = 1.6V and it works with a min duty cycle of 3.13%. I will send the file to Mixos. Thank you for that it will have a faster switching time and it's cheaper to make.

"How did you measure Ib?" I didn

Hi Hero999, It works but only with a duty cycle higher than 70%, ib = 12mA. Tomorrow I'm going to change the resistors, let you know.

Hi Hero999, " found the datasheet for the MCU you're using and noticed that the I/O pins probably won't be abe to supply enough current to ensure a transistor driving a 300mA load will saturate properly so I used two transistors rather than one. Tr2 will deliver between 17mA and 21mA to T1's base but the impedance seen by the MCU's I/O pin will be about 10k so hardly any current will flow out of it." I try but doesn't work because I need a transistor to be able to drive +/-400mA Load. but this weekend I will do the calculations to see if the values are matching. Using a mosfet driver will increase the price it will be twice more expensive then the LM358. It is useful if you need a faster switching time.

Thanks Hero999, I will try this weekend or next week and then I will let you know how it works. I'm attaching the code some part of the code is comment because I'm testing a few things. the code is in basic. H PWM.txt

In my project PWM fan controller, I'm seeing people complain because my choose of components. I use a LM358 because it's a general purpose Am-pop, probably it's a common component most off us have. The typ SR of LM358 it's 0.6 V/