Search found 23 matches
- Wed Feb 25, 2009 9:30 pm
- Forum: General Discussion
- Topic: Help with comparator design
- Replies: 38
- Views: 14442
Re: Help with comparator design
1)First off, 0.0032v into 8 ohms only produces about 1.2 watts of power. I doubt you can hear this over the sound of the fan itself 2)Your new circuit isnt too bad either though, but again if you use a -2v Vgt for Q1 you might run into the problem of pin 7 not being able to go high enough to turn Q...
- Sat Feb 21, 2009 8:32 pm
- Forum: General Discussion
- Topic: Help with comparator design
- Replies: 38
- Views: 14442
Re: Help with comparator design
Hello The suggestion from MrAl about adding a bias voltage to the low-pass filter got me to thinking and I just may have arrived a the minimal configuration that meets my design goals. I originally chose a comparator to eliminate any offset voltage from the mother board output. If this new and hopef...
- Thu Feb 19, 2009 11:09 am
- Forum: General Discussion
- Topic: Help with comparator design
- Replies: 38
- Views: 14442
Re: Help with comparator design
You can most likely get away without using R5 and R6 (to get a min output) if you instead connect the 100k (R7) directly to pin 1 of the comparator and connect a 150k resistor from C2 to +3v. Hello If a 150K resistor is connected to C2 would this not change the cutoff frequency of the low-pass filt...
- Tue Feb 17, 2009 11:24 pm
- Forum: General Discussion
- Topic: Help with comparator design
- Replies: 38
- Views: 14442
Re: Help with comparator design
With an op amp like the one shown in the schematic (1/2 of LM392) the output will not be able to reach +12v ... so an idea might be to add a diode in series with the output of the op amp to force the output to always be one diode drop above the max output. Hello Switching the amp to negative negati...
- Mon Feb 16, 2009 12:22 pm
- Forum: General Discussion
- Topic: Help with comparator design
- Replies: 38
- Views: 14442
Re: Help with comparator design
http://www.postimage.org/Pq2lL12i.jpg After putting this project aside for some other priorities, I stumbled on to a data sheet for the LM392 amplifier/comparator dual. This got me thinking about the limitations of the discrete transistor circuit. A comparator input can give better noise immunity, ...
- Sat Jan 24, 2009 4:21 pm
- Forum: General Discussion
- Topic: Help with comparator design
- Replies: 38
- Views: 14442
Hello I occurs to me that I did not see the forest for the trees. I redrew the circuit including the motherboard and realized that the amplifier is sourcing current to the motherboard. Insert Homer Simpson d'oh! I believe what needs to be optimized is the low-pass filter and the pull-up resistor. Co...
- Fri Jan 16, 2009 6:23 pm
- Forum: General Discussion
- Topic: Help with comparator design
- Replies: 38
- Views: 14442
Hello everyone MrAl is this what you envisioned for the LM393 configuration? I have changed the threshold to 1.0 volts and reduced the hysteresis, from the original circuit. C2 was added per the data sheet. As I explained before, the LM4040 has a turn-on time of 10 microseconds and was misapplied in...
- Thu Jan 15, 2009 10:43 am
- Forum: General Discussion
- Topic: Help with comparator design
- Replies: 38
- Views: 14442
Hello sghioto I concur with Bigglez, very elegant solution. Correct me if I am misunderstanding. The AD822 you suggest has a slew of 3 volts per microsecond. With positive logic PWM, a 25 KHz square wave of 30% duty cycle would have a pulse width of 12 microseconds and a space width of 28 microsecon...
- Tue Jan 13, 2009 4:11 pm
- Forum: General Discussion
- Topic: Help with comparator design
- Replies: 38
- Views: 14442
Hello to All The fan control is single loop, when the temperature increases above threshold the software I am using, SpeedFan, increases the speed command to the fan. It does not check to see if fan speed increased. SpeedFan waits a time interval and checks the temperature again and adjusts the spee...
- Mon Jan 12, 2009 11:08 am
- Forum: General Discussion
- Topic: Help with comparator design
- Replies: 38
- Views: 14442
Hello Bigglez You have framed the problem well, what I require is a circuit that detects the duty cycle of the PWM signal and ignores the amplitude. Ideally it will give a 12 volt DC output for 100% duty cycle. My desired output range is 5 to 12 volts to the fan, assuming that the output is proporti...
- Sun Jan 11, 2009 7:29 pm
- Forum: General Discussion
- Topic: Help with comparator design
- Replies: 38
- Views: 14442
- Thu Jan 01, 2009 3:43 pm
- Forum: General Discussion
- Topic: Help with comparator design
- Replies: 38
- Views: 14442
Hello, sghioto The INTEL initiative is all well and good for motherboard designers, it eliminates the need for high current output transistors on fan headers. Many of the newer motherboards now only support four wire fans for the CPU. However if you are a person who wants you PC to be seen and not h...
- Mon Dec 29, 2008 5:12 pm
- Forum: General Discussion
- Topic: Help with comparator design
- Replies: 38
- Views: 14442
Help with comparator design
My goal for this project is to control a thee wire brushless fan with the PWM signal from a four wire fan header. I have looked at number motherboards and discovered implementation the control signal varies. The INTEL specification is mute on a logic hi value, but requires a maximum logic low of 0.8...
- Sun Nov 09, 2008 1:03 pm
- Forum: General Discussion
- Topic: help with op amp circuit
- Replies: 16
- Views: 7409
- Sun Nov 09, 2008 10:36 am
- Forum: General Discussion
- Topic: help with op amp circuit
- Replies: 16
- Views: 7409
Pin 4 of J1 cannot source more than 5mA with a supply voltage of 13.2 volts, the 2.2K pull up resistor [R2] takes care of that, but I am not certain how to factor in the zener voltage tolerance to size the shunt resistor [R3] for minimum supply voltage of 11.4 volts. Would it be: [11.4V - 3.5V] / [ ...