Hi.
I like to learn all sorts of things, and the latest is some electric theory. I have decided to learn using a rather common project, a fan controller for cpu 12v dc fans.
At this point, I have poured over sites and schematics and datasheets looking at examples, as well as scads of tutorials and the like to learn a bit. I feel I have an OK understanding of linear models as well as pulsed analog ones. I am using multisim 10 for now until I graduate to a "non-frying of components" level.
For the basic linear voltage circuit, I am going to pick a bit of a challenge. Designing circuits to handle a 12v source off a psu has been done. There is plenty of current available and only the control circuit needs to handle the heat generated by the load on the fan. So, I choose to control 3 fans with a motherboard 3pin fan header. Research is rather sketchy on the actual max load the motherboard headers can handle. I have seen an average of 6 watts per all headers, as well as 3watts per header, as well as some documentation stating that a single header is capable of up to 6watts.
So, not knowing what the actual upper threshold of current is for a motherboard fan header, erring on side of caution. In a linear voltage output from a mobo header, I have been playing with a very simple circuit that uses a pair of transistors, specifically a 2n3904 and TIP32a. Simply, 12V source is applied to collector of TIP32a. 2N3904 collector to TIP32a base. 2N3904 base to V from fan header. Both transistors emitters go to the fan V in. This effectively opening the TIP32a linearly, with the slight voltage drop, while isolating the acutual load from the fan header.
This is fairly straight forward, as one can calculate the load on both sides. However, there is also the trend to include PWM circuits into the fan headers. Research has shown both low and high side circuits. The low side is generally what is seen for the DIY PWM circuit. Understanding that a transistor or FET is being induced to allow the voltage from the fan to ground, at a rate, is not too hard to grasp. The reverse where the voltage is actually modulated is also not too terribly hard to grasp.
But here is where most of the grasping really starts.
For instance, on my motherboard, the Intel 975xbx2, I have the Andigilog aSC7621 chip onboard. This particular chip has 4 fan outputs (PWM). All 4 are capable of utilizing the newer 4pin configuration, where the 12v is fed continuous, and the fan itself uses the 4th pin, the SIGNAL, to modulate the duty cycle. The problem here is that while in the datasheets, the example shcematic tells of simply using an external MOSFET to convert to 3pin configuration, it does not state implicitly that it is a high or low side circuit. I am assuming low side, but it is hard to tell, because there is no schematic. The PWM signal, as stated in the datasheet is up to 5.5v. To make matters worse, or better, the frequency of the PWM is adjustable. Using SpeedFan, one can have a fan header @ 10Hz, up to 30kHz. While I find that 10Hz can run my 120mm 12v .30A fan down at 5% duty cycle, there is a definiate rotor click, as well as LED fan "blink". Tuning the frequency to 23kHz fixes the rotor click and the LED "blink", but forces the fan to stall at 5%. 10% duty and it starts and maintains.
Now, heh, do a voltage reading. On the 4pin header, reading the 12v is solid 12v, no matter the duty. Reading the SIGNAL, @10Hz, with neg lead on the case, and there are from 32 to 0 mV. Read the same SIGNAL @23kHz, and it is 0 to 180 mV. Now also read the 3pin voltage. Here it is a bit different, @10Hz, jumping around like crazy, @23kHz, solid 12v. Now put pos lead on pos 3pin, neg lead on ground of 3pin, and you will see @10Hz jumping around, @23kHz linear voltage looking, 12 - 0v.
Assuming that Intel has already used a MOSFET in converting the PWM Signal to a 3pin configuration, how does one tell if it a high or low side PWM signal? Couple that to this little issue, that the 4pin header is (assuming data sheet is correct) only @5.5v max, while the 3pin is @12v.
Ah, more learning. I have some circuits now that use an OP AMP to drive a 12v fan using a 5v feed. There is a MOSFET in it, a BUZ71L. I have tried other MOSFET's as well as transistors and found lot's of working designs.
But we have not only a voltage difference, but also a possible method of PWM implementation. Assume we deal with the 12v 3pin header. It is pulsing the voltage or the ground path. The modulation is already there. A quick changing MOSFET should mimic this. I have that working in sim now. NOTE: Please bear in mind that my project goal is to LEARN, in this case, how to isolate the actual load to 3 fans and protect the origin from overload, while maintaining the source "speed". With that in mind, ahem, the MOSFET chosen should handle the load of 3 fans, arbitrarily let's say a 3A model. So, the PWM signal is put to a MOSFET, high or low side, and it replicates the gate signal, pulse on @ % duty.
Next, we have the issue where we have a total of 5.5v, and the assumption is that on a 4pin header, the signal is NOT pulsing, but is a signal for a PWM fan. Now, I don't know, nor know how to detect if this 5.5v signal is linear or pulsed. Either way, learning both cannot be bad.
So let's say the 5.5v is pulsed. Again, probably low side. So, we use a MOSFET to control a 12v signal, and it should work. An intersting note is that many schemtics show a 'kick start' capacitor, as well as a pull-up resistor and some diodes. Lot's of different designs out there. In protecting the motherboard, how does one design such a circuit for protection?
And then we can guess that maybe the 5.5v is actually a linear voltage, designed to trigger the circuitry in a PWM fan. Now one must build a PWM circuit, and use the 5.5v through most likely an OP Amp, and output the PWM 12v according to the 5.5v input.
Whew. Hopefully that is enough detail to describe what I am dealing with. The actual reason for this post is to, obviously, glean some knowledge from those who know more than I.
Specifically, I wish to develop the following circuits, with each circuit capable of withstanding a 1.5A load, while protecting the signal (motherboard fan header):
1. 5.5v linear input to 12v PWM output
2. 5.5v PWM input to 12v PWM output
3. 12v PWM input to 12v PWM output (simply keep same, but isolate fan header)
4. 12v linear to 12v PWM output
5. 12v linear to 12v linear (simply keep same, but isolate fan header)
I am open to learning anything ATM. PIC I would like to learn, but first wish to understand these concepts. I welcome any advice or criticism that helps to learn. I welcome any reference to schematics or components that may work better.
Again, I am just wishing to learn something, and this is nothing new under the sun, but does present itself as a great project because I have access to many different computers with different chips, as well as many different fans. It would seem a logical choice.
Thank you to whomever may wish to divulge some info.
Respectfully,
MrWoo
I like to learn all sorts of things, and the latest is some electric theory. I have decided to learn using a rather common project, a fan controller for cpu 12v dc fans.
At this point, I have poured over sites and schematics and datasheets looking at examples, as well as scads of tutorials and the like to learn a bit. I feel I have an OK understanding of linear models as well as pulsed analog ones. I am using multisim 10 for now until I graduate to a "non-frying of components" level.
For the basic linear voltage circuit, I am going to pick a bit of a challenge. Designing circuits to handle a 12v source off a psu has been done. There is plenty of current available and only the control circuit needs to handle the heat generated by the load on the fan. So, I choose to control 3 fans with a motherboard 3pin fan header. Research is rather sketchy on the actual max load the motherboard headers can handle. I have seen an average of 6 watts per all headers, as well as 3watts per header, as well as some documentation stating that a single header is capable of up to 6watts.
So, not knowing what the actual upper threshold of current is for a motherboard fan header, erring on side of caution. In a linear voltage output from a mobo header, I have been playing with a very simple circuit that uses a pair of transistors, specifically a 2n3904 and TIP32a. Simply, 12V source is applied to collector of TIP32a. 2N3904 collector to TIP32a base. 2N3904 base to V from fan header. Both transistors emitters go to the fan V in. This effectively opening the TIP32a linearly, with the slight voltage drop, while isolating the acutual load from the fan header.
This is fairly straight forward, as one can calculate the load on both sides. However, there is also the trend to include PWM circuits into the fan headers. Research has shown both low and high side circuits. The low side is generally what is seen for the DIY PWM circuit. Understanding that a transistor or FET is being induced to allow the voltage from the fan to ground, at a rate, is not too hard to grasp. The reverse where the voltage is actually modulated is also not too terribly hard to grasp.
But here is where most of the grasping really starts.
For instance, on my motherboard, the Intel 975xbx2, I have the Andigilog aSC7621 chip onboard. This particular chip has 4 fan outputs (PWM). All 4 are capable of utilizing the newer 4pin configuration, where the 12v is fed continuous, and the fan itself uses the 4th pin, the SIGNAL, to modulate the duty cycle. The problem here is that while in the datasheets, the example shcematic tells of simply using an external MOSFET to convert to 3pin configuration, it does not state implicitly that it is a high or low side circuit. I am assuming low side, but it is hard to tell, because there is no schematic. The PWM signal, as stated in the datasheet is up to 5.5v. To make matters worse, or better, the frequency of the PWM is adjustable. Using SpeedFan, one can have a fan header @ 10Hz, up to 30kHz. While I find that 10Hz can run my 120mm 12v .30A fan down at 5% duty cycle, there is a definiate rotor click, as well as LED fan "blink". Tuning the frequency to 23kHz fixes the rotor click and the LED "blink", but forces the fan to stall at 5%. 10% duty and it starts and maintains.
Now, heh, do a voltage reading. On the 4pin header, reading the 12v is solid 12v, no matter the duty. Reading the SIGNAL, @10Hz, with neg lead on the case, and there are from 32 to 0 mV. Read the same SIGNAL @23kHz, and it is 0 to 180 mV. Now also read the 3pin voltage. Here it is a bit different, @10Hz, jumping around like crazy, @23kHz, solid 12v. Now put pos lead on pos 3pin, neg lead on ground of 3pin, and you will see @10Hz jumping around, @23kHz linear voltage looking, 12 - 0v.
Assuming that Intel has already used a MOSFET in converting the PWM Signal to a 3pin configuration, how does one tell if it a high or low side PWM signal? Couple that to this little issue, that the 4pin header is (assuming data sheet is correct) only @5.5v max, while the 3pin is @12v.
Ah, more learning. I have some circuits now that use an OP AMP to drive a 12v fan using a 5v feed. There is a MOSFET in it, a BUZ71L. I have tried other MOSFET's as well as transistors and found lot's of working designs.
But we have not only a voltage difference, but also a possible method of PWM implementation. Assume we deal with the 12v 3pin header. It is pulsing the voltage or the ground path. The modulation is already there. A quick changing MOSFET should mimic this. I have that working in sim now. NOTE: Please bear in mind that my project goal is to LEARN, in this case, how to isolate the actual load to 3 fans and protect the origin from overload, while maintaining the source "speed". With that in mind, ahem, the MOSFET chosen should handle the load of 3 fans, arbitrarily let's say a 3A model. So, the PWM signal is put to a MOSFET, high or low side, and it replicates the gate signal, pulse on @ % duty.
Next, we have the issue where we have a total of 5.5v, and the assumption is that on a 4pin header, the signal is NOT pulsing, but is a signal for a PWM fan. Now, I don't know, nor know how to detect if this 5.5v signal is linear or pulsed. Either way, learning both cannot be bad.
So let's say the 5.5v is pulsed. Again, probably low side. So, we use a MOSFET to control a 12v signal, and it should work. An intersting note is that many schemtics show a 'kick start' capacitor, as well as a pull-up resistor and some diodes. Lot's of different designs out there. In protecting the motherboard, how does one design such a circuit for protection?
And then we can guess that maybe the 5.5v is actually a linear voltage, designed to trigger the circuitry in a PWM fan. Now one must build a PWM circuit, and use the 5.5v through most likely an OP Amp, and output the PWM 12v according to the 5.5v input.
Whew. Hopefully that is enough detail to describe what I am dealing with. The actual reason for this post is to, obviously, glean some knowledge from those who know more than I.
Specifically, I wish to develop the following circuits, with each circuit capable of withstanding a 1.5A load, while protecting the signal (motherboard fan header):
1. 5.5v linear input to 12v PWM output
2. 5.5v PWM input to 12v PWM output
3. 12v PWM input to 12v PWM output (simply keep same, but isolate fan header)
4. 12v linear to 12v PWM output
5. 12v linear to 12v linear (simply keep same, but isolate fan header)
I am open to learning anything ATM. PIC I would like to learn, but first wish to understand these concepts. I welcome any advice or criticism that helps to learn. I welcome any reference to schematics or components that may work better.
Again, I am just wishing to learn something, and this is nothing new under the sun, but does present itself as a great project because I have access to many different computers with different chips, as well as many different fans. It would seem a logical choice.
Thank you to whomever may wish to divulge some info.
Respectfully,
MrWoo