cpu fan controller using pic

[ttuyen04hanhle04]

hi all, i am designing a cpu fan controller using pic, i create a pwm pulse by using pic then connect directly pin4 (pwm) of fan, power supply of fan is 12Vdc, pin3 (tach) : not connect. the problem is the fan doesn't work match with pwm pulse, pls show me the problem. thx all

 

[THINKER_KAM_MAN]

hi all, i am designing a cpu fan controller using pic, i create a pwm pulse by using pic then connect directly pin4 (pwm) of fan, power supply of fan is 12Vdc, pin3 (tach) : not connect. the problem is the fan doesn't work match with pwm pulse, pls show me the problem. thx all

just a suggestion

what is the circuit?
is it a dc 12V fan?
is pin 4 the a pin on the pic?
are you using one of open output?