Hi Guys,
Stuck on a little problem (or several problems).
I'm working on a project to PWM control a couple of PC fans from a PIC18F4550 and as there will be 4 fans wired in parallel I thought the best option would be to use a MOSFET rather than an NPN transistor due to the higher current requirements.
So, I've used the attached circuit however It seems that I dont get full control of the fan speed, it seems to be achieving full speed with only about a 50% PWM duty cycle, now I wasnt sure if this was just due to the fan itself so i've tried a few different ones with the same result.
Can someone please just have a glance over my circuit (attached) and see what they think and if there is something wrong, what I might be able to try to resolve the problem. The PWM frequency is 25KHz which should be well within the capabilities of the STP36NF I am using.
Thanks
Stuck on a little problem (or several problems).
I'm working on a project to PWM control a couple of PC fans from a PIC18F4550 and as there will be 4 fans wired in parallel I thought the best option would be to use a MOSFET rather than an NPN transistor due to the higher current requirements.
So, I've used the attached circuit however It seems that I dont get full control of the fan speed, it seems to be achieving full speed with only about a 50% PWM duty cycle, now I wasnt sure if this was just due to the fan itself so i've tried a few different ones with the same result.
Can someone please just have a glance over my circuit (attached) and see what they think and if there is something wrong, what I might be able to try to resolve the problem. The PWM frequency is 25KHz which should be well within the capabilities of the STP36NF I am using.
Thanks
Attachments
-
180.1 KB Views: 109