im trying to make a circuit that boosts the input 'Signal' of the pwm for a fan
say the fan is running at 1000rpm i want the circuit to increase that speed by 30%, so
so bassically this
Input pwm--> +%30-->output pwm

a lot of people are making pwm controllers using 555 timers with Pots and i was wondering if i could replace a pot and just have the other pwm going straight in ?

thanks guys

 

Why not just turn it up? A bit more detail of what you are doing would help.

A "one shot" 555 circuit might work for you. It would generate a pulse of the time you choose from each input pulse. It wouldn't care about the width of the PWM input setting though, only it's own timing settings. Its setting would need to be matched up with the PWM frequency, so that the one shot ends before the next pulse comes along.

 

basically i want to make a duty cycle booster for my ps3 fan,
ive seen people make them but i want to know about them and to make one for myself

i feel the ps3 fan runs too slowly and want to increase the speed by 30%
now i could easily do this with a standard pot but i still want the speed to change when the system changes it aswell so thats where my idea of increasing the duty cycle came from

 

I'll bet there's a software hack for this?

 

sort of like this !!!
http://www.circuitsurgery.com/PS3/clearprog.html
but that a bit over kill for what i want, i only need a simple design and 25-30% increase

 

there is a software hack but i requires jailbreaking and i dont have an e3 flasher or a progskeet for it and i also want to keep this online as i have a heavily modified xbox anyway

 

A pulse stretcher won't do it. This needs a PWM modifier. Sounds like a pin 5 job, but I don't know how to do it. Does this need a sawtooth wave input and a way to adjust the frequency close enough to "lock in" to the input frequency?

 

i honestly thought it would be a squarewave frequency and im not sure by what you mean with the 'lock in'

 

i do really like the idea of this one aswell how it can be constantly adjusted with the knob but still the system can take over if required
http://www.circuitsurgery.com/PS3/yellowext.html

 

Isn't there a potentiometer you can adjust...
Seems like it..
http://kentb.blogspot.com/2010/05/adjusting-aggressiveness-of-your-ps3.html

And why do you "feel" its too slow.. Have you done temperature datalogging?

 

thats fake that pot doesnt exist !!!!
and by the time it gets to 80-90c is not speeding up then 92 it speeds up fast as hell then the damage is already done !

 

I really think your best move would be to purchase one of the modules you linked to.
Trying to build your own you would for the most part have to duplicate one of those units. I dont think you could do it for less than the cost of one of those.

 

im not so bothered about the cost as to i would like to know how its built how it works and why, many people have used 555 chips on theirs then 556 and even some other 12 leg ic

 

such as this !
http://www.cd24-7.co.uk/shop.php?sec=prod&prod=232

 

ANymore help guys ??

 

i honestly thought it would be a squarewave frequency and im not sure by what you mean with the 'lock in'

The principle I was working with is that you use the original PWM signal to make a DC level that is not very well filtered. Then you use that to modify the switching point of a 555 by altering pin 5. Then I lose it. I don't know if you are supposed to set the 555 up as a square wave oscillator and modify the time(on) with the DC level or feed the 555 a ramp and let the DC signal modify when it switches compared to the level of the ramp signal. The end result is a DC controlled PWM generator. Problem is, I don't know specifically how to do it.

 

If the PWM frequency is known, design of a circuit to do this would be simplified. What is the frequency?

 

i have no idea what the frequency is, and i don't have access to and oscilloscope to test it

 

The fans are a standard sized package. Just replace it with a fan of high CFM rating and/or higher RPM per volt.

You will get exactly the same result, ie high air flow for the same PWM setting.

If it was me I would just rig the fan direct to the power supply, so it runs at full speed all the time. The only down side is slightly higher audible noise, and reduced fan bearing life (but you can get ceramic bearing fans anyway with many times longer life).

 

As has already been mentioned; PWM to voltage and then voltage to PWM is probably the best way to go.

PWM to voltage can be achieved simply by integrating the pulses using a capacitor. Then compare this voltage with a triangular wave (it does not have to be perfect) using a comparator to provide a new PWM signal.