Need Help with my Fan Controller Project

Thread Starter

Iago Pereira

Joined Oct 11, 2015
7
I've reached to this schematic, in wich I tent to have a pwm regulator in wich, as I increase the fan speed the lm3914 lights up more leds according to the fan's speed, and when I turn the turbo switch, the fans get a little 15v boost and the 555 on the left starts blinking 3 red leds, but im not sure of how functional this circuit is.Design_5 PWM.png
 

AnalogKid

Joined Aug 1, 2013
8,698
You have the raw IC4 555 PWM waveform driving the 3914 with no filtering. That won't work. The 3914expects an analog voltage input. Hang a capacitor on pin 5 to filter the pwm to an average DC value.

IC1 Vcc should not come through a 1.2 K resistor. It should be powered directly from either the +15 or the +12, and its operation controlled by the Reset input.

All ICs need power supply decoupling.s.

ak
 

AnalogKid

Joined Aug 1, 2013
8,698
R7 is not connected to pin 5, so I don't know what you are talking about. My suggestion is to add a capacitor from pin IC3 5 to GND. This works with R8 to form a crude lowpass filter.

Why is the output frequency of IC4 so low? 100 Hz is near the operating frequency of the fan motors. The PWM frequency should be much higher than this. Also, a higher PWM freq will be easier to filter at the input to IC3.

ak
 

Thread Starter

Iago Pereira

Joined Oct 11, 2015
7
R7 is not connected to pin 5, so I don't know what you are talking about. My suggestion is to add a capacitor from pin IC3 5 to GND. This works with R8 to form a crude lowpass filter.

Why is the output frequency of IC4 so low? 100 Hz is near the operating frequency of the fan motors. The PWM frequency should be much higher than this. Also, a higher PWM freq will be easier to filter at the input to IC3.

ak
what changes should I do to the IC4 then?
 

AnalogKid

Joined Aug 1, 2013
8,698
As I said:

1. Why is the output frequency of IC 4 so low?

Also:

2. What is the operating frequency an duty cycle at each end of the R10 adjustment range?

ak
 

Thread Starter

Iago Pereira

Joined Oct 11, 2015
7
As I said:

1. Why is the output frequency of IC 4 so low?

Also:

2. What is the operating frequency an duty cycle at each end of the R10 adjustment range?

ak
1- I don't know, i adapted a circuit i found on the internet...

2 I don't know also... I don't understand the pwm part of the circuit very well
 

Sensacell

Joined Jun 19, 2012
2,631
What kind of fans are you using? do they function correctly under PWM control?

DC brushless fans (the majority these days) have a controller chip inside that commutates the motor coils, if you interrupt the power to the fan, (PWM) this controller can reset or become unstable.

You need to test this.
 

Alec_t

Joined Sep 17, 2013
11,746
The supply to IC1 is always present (12V or 15V) so the LEDs will always be blinking.
Unless the LEDs are closely matched they will be uneven in brightness. It is better if they have individual current-limiting resistors.
 
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