I think i found the problem.. Line for changing PWM frequency is ok, it looks like my FET and transistor are not capable of switching at this frequency. I am driving fan with P-Channel FET and transistor. FET is SUD50P04 and transistor is 2n3904.
If i run this testing code with line "TCCR0B = TCCR0B & 0b11111000 | 0x01;" in setup it looks like fan is always on 100% (255). The same was with LED diode, but when i tried to put LED directly on output port of ATtiny i can easily saw fading.
So that probably means that this combination of FET and transistor is not capable of running PWM at this frequency?
Testing code:
analogWrite(fet, 128);
delay(3000);
analogWrite(fet, 255);
delay(3000);
