Hi reader,
I'm trying to control a pc fan speed by giving PWM to the gate of a n-mosfet.
1) generation of a clock with a 555 timer (~ 1,5 kHz, as seen in the datasheet, fig.12) (Vcc = 6V).
Output to TRIG of second timer (pin 2) + red led
2) generation of a PWM with a second 555 timer (as seen in the datasheet, fig.18), CONT (pin 5) modulated by a variable 10k resistor (Vcc)
3) Using output of second timer to "pulse" n-mosfet gate (MDP13N50) + yellow led
4) pc fan (12V, 0.18A) in series in drain-source of mosfet (with another 12V power supply)
(see circuit diagram attached, circuit made on a breadboard)
Looks like it works at least partially : I can see the second led (yellow) becoming brighter/dimmer when I change potentiometer value but the fan isn't doing anything...
BUT : fan spins only if I touch the ground of first power supply (Vcc=6V, suppplying both timers) and the drain (= the case) of the mosfet, then and only then, speed change if I change potentiometer.
Sometimes, when I remove my hand from ground, it spins even faster (not much though), sometimes not...
Nothing burns, nothing is hot...
What am I doing wrong ?
I'm trying to control a pc fan speed by giving PWM to the gate of a n-mosfet.
1) generation of a clock with a 555 timer (~ 1,5 kHz, as seen in the datasheet, fig.12) (Vcc = 6V).
Output to TRIG of second timer (pin 2) + red led
2) generation of a PWM with a second 555 timer (as seen in the datasheet, fig.18), CONT (pin 5) modulated by a variable 10k resistor (Vcc)
3) Using output of second timer to "pulse" n-mosfet gate (MDP13N50) + yellow led
4) pc fan (12V, 0.18A) in series in drain-source of mosfet (with another 12V power supply)
(see circuit diagram attached, circuit made on a breadboard)
Looks like it works at least partially : I can see the second led (yellow) becoming brighter/dimmer when I change potentiometer value but the fan isn't doing anything...
BUT : fan spins only if I touch the ground of first power supply (Vcc=6V, suppplying both timers) and the drain (= the case) of the mosfet, then and only then, speed change if I change potentiometer.
Sometimes, when I remove my hand from ground, it spins even faster (not much though), sometimes not...
Nothing burns, nothing is hot...
What am I doing wrong ?
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