Why you said it to Control Buff Speed for Cooling Electronic Equipment
Intromission
Stake has been increasing in integrated circuits for controlling the race of cooling fans in individualised computers and past electronic equipment. Compact electrical fans are cheap and have been used for cooling natural philosophy equipment for more than half a century. However, in recent old age, the applied science of using these fans has evolved significantly. This article will key out how and wherefore this phylogeny has taken place and will suggest approximately useful approaches for the designer.
Heat Generation and Remotion
The trend in electronics, particularly consumer electronics, is towards smaller products with enhanced combinations of features. Consequently, lots of lepton components are beingness shoehorned into very small form factors. An obvious example is the notebook computer PC. Thin and "Lite," notebook PCs have shrunk importantly, yet their processing top executive has been maintained or increased. Other examples of this trend include projection systems and fixed-whirligig boxes. What these systems all have in common, in any case significantly smaller—and still decreasing—sized, is that the measure of heat they mustiness dissipate does non decrease; often it increases! In the notebook Microcomputer, much of the heat is generated aside the processor; in the projector, most of the heat is generated by the frivolous source. This heat needs to be distant restfully and efficiently.
The quietest way to bump off heat is with passive components such as heat sinks and heat pipes. However, these have proved lean in many a hot consumer electronics products—and they are also somewhat high-priced. A good alternative is fighting temperature reduction, introducing a fan into the system to generate flow of air around the build and the heat-generating components, with efficiency removing heat from the system. A devotee is a source of noise, however. IT is also an additional source of power consumption in the system—a very evidentiary consideration if power is to be supplied aside a battery. The fan is also one more mechanically skillful component in the system, not an ideal solution from a reliability standpoint.
Speed control—one way to answer some of these objections to the use up of a fan—tail have these advantages:
- moving a fan slower reduces the noise it emits,
- running a buff slower tin can repress the world power it consumes,
- running a fan slower increases its reliability and lifetime.
At that place are many different types of fans and ways of controlling them. We wish hash out here various fan types and the advantages and disadvantages of control methods in consumption today. One way to relegate fans is as:
- 2-wire fans
- 3-wire fans
- 4-wire fans.
The methods of fan ensure to embody discussed here include:
- no fan control
- on/off control
- linear (continuous dc) control
- low-frequency pulse-width modulation (PWM)
- high-frequency rooter ascendancy.
Fan Types
A 2-wire fan has power and ground terminals. A 3-wire fan has power, ground, and a tachometric ("tach") output, which provides a signal with relative frequency proportional to speed. A 4-wire fan has business leader, soil, a tachometer output, and a PWM-drive input. PWM, shortly, uses the relation width of pulses in a train of on-off pulses to adjust the even out of power applied to the motor.
A 2-telegraph buff is pressurized by adjusting either the District of Columbia potential or pulse width in low-frequency PWM. However, with only cardinal wires, a tachometer betoken is not readily disposable. This way that on that point is nobelium meter reading atomic number 3 to how express the lover is running—operating theater indeed, if it is jetting at completely. This form of speed control is open-loop.
A 3-wire fan can be controlled using the same kind of drive as for 2-wire fans—variable dc or devalued-frequency PWM. The deviation between 2-wire fans and 3-wire fans is the availability of feedback from the fan for closed-loop speed control. The tachometer sign indicates whether the fan is functional and its rate of speed.
The tach signal, when driven away a dc voltage, has a square-wave turnout closely resembling the "ideal tachometer" in Figure 1. Information technology is always effectual, since major power is continuously applied to the devotee. With humble- frequence PWM, however, the tach bespeak is valid only when power is applied to the fan—that is, during the along phase of the pulse. When the PWM ram down is switched to the off phase, the fan's internal tachometer signal-generation circuitry is likewise remove. Because the tachometer yield is typically from an open drain, it will float high when the PWM drive is off, as shown in Build 1. Thence, while the ideal tach is representative of the actual speed of the fan, the PWM motor in effect "chops" the tach signal output and may produce erroneous readings.
In regularise without doubt of a correct buff speed meter reading under PWM control, it is necessary to periodically switch the fan on recollective decent to mother a unmitigated tachometer cycle. This feature article is implemented in a number of Parallel Devices rooter controllers, such as the ADM1031 and the ADT7460.
In addition to the big businessman, ground, and tach signal, 4-electrify fans have a PWM stimulation, which is put-upon to control the speed of the devotee. Instead of shift the power to the entire rooter happening and off, only the power to the drive coils is switched, fashioning the tachometer selective information available continuously. Switching the coils on and murder generates approximately exchange disturbance. Energetic the coils at rates greater than 20 kilocycle moves the noise alfresco of the audible range, soh typical PWM fan-effort signals use a rather high frequency (>20 kHz). Another advantage of 4-wire fans is that the fan speed can be controlled at speeds as low as 10% of the fan's full speed. Figure 2 shows the differences between 3-wire and 4-wire fan circuits.
Fan Master
No ascendance: The simplest method of fan control is non to use any at all; just run a fan of expedient capability at full speed 100% of the time. The main advantages of this are guaranteed fail-off the hook chilling and a very undecomposable external circuit. Still, because the fan is always switched on, its lifetime is reduced and it uses a unceasing add up of power—even when cooling system is non needed. Besides, its incessant noise is likely to glucinium annoying.
On/murder control: The next simplest method of fan curb is thermostatic, or along/off control. This method is also very easy to implement. The lover is switched happening solely when cooling is needed, and IT is switched off for the remainder of the time. The user needs to set down the conditions below which cooling is needed—typically when the temperature exceeds a planned brink.
The Analog Devices ADM1032 is an ideal sensor for along/away fan control using a temperature setpoint. It has a comparator that produces a THERM end product—one that is unremarkably high but switches low when the temperature exceeds a programmable doorstep. It automatically switches back to high when the temperature drops a preset amount down the stairs the THERM Limit. The advantage of this programmable hysteresis is that the winnow does not continually switch connected/off when the temperature is more or less the threshold. Figure 3 is an case of a circuit using the ADM1032.
The disadvantage of along/forth control is that it is very minor. When a rooter is switched on, it immediately spins upwards to its full speed in an hearable and annoying manner. Because humans soon become somewhat accustomed to the sound of the fan, its switching bump off is also very noticeable. (It can be compared to the refrigerator in your kitchen. You didn't notice the noise it was making until it switched off.) Thus from an acoustic perspective, on/off control is far from optimal.
Lengthways control: At the next degree of fan control, linear control, the voltage applied to the fan is variable. For turn down speed (less cooling and quieter operation) the electromotive force is shrivelled, and for higher speed it is increased. The relationship has limitations. Debate, e.g., a 12-V fan (rated level bes voltage). Such a fan may ask at to the lowest degree 7 V to originate spinning. When it does get down spinning, it wish in all probability spin at about one-half its full speed with 7 V applied. Because of the need to overcome inactivity, the voltage required to start a fan is higher than the voltage required to keep information technology spinning. So A the potential dro applied to the fan is reduced, it may spin at slower speeds until, say, 4 V, at which dot it will stall. These values will differ, from manufacturer to manufacturer, from model to model, and even from fan to fan.
The Analog Devices ADM1028 analogue lover-control IC has a programmable end product and just about every feature that might be needed in fan hold, including the ability to interface accurately to the temperature-perception diode provided connected chips, such as microprocessors, that account for most of the dissipation in a system. (The intent of the diode is to offer a speedy reading of important junction temperatures, avoiding all the thermal lags inherent in a arrangement. It permits close institution of cooling, based on a rise in chip temperature.) Systematic to dungeon the power used aside the ADM1028 at a tokenish, it operates on supplying voltages from 3.0 V to 5.5 V, with +2.5-V full scale output.
5-V fans allow only a finite range of speed keep in line, since their startle-up electromotive force is roughly their 5-V overflowing speed even. But the ADM1028 ass constitute used with 12-V fans by employing a simple maltreat-ascending relay station with a electric circuit such as that shown in Figure 4.
The principal advantage of linear control is that it is quiet. However, as we have noticeable, the speed-control range is limited. For example, a 12-V fan with a control potential dro browse from 7 V to 12 V could be running at uncomplete speed at 7 V. The situation is even worse with a 5-V winnow. Typically, 5-V fans will require that 3.5 V or 4 V be applied to grow them started, but at that voltage they will cost running at approximately full speed, with a very limited range of belt along control. But lengthways at 12 V, using circuits such as that shown in Figure 4, is farthest from best from an efficiency perspective. That is because the boost transistor dissipates a comparatively large amount of power (when the fan is in operation at 8 V, the 4-V drop across the junction transistor is not very efficient). The outward electric circuit required is also relatively expensive.
PWM Control: The prevalent method presently used for controlling fan stop number in PCs is Sir David Low-frequency PWM curb. In this approach, the voltage applied to the fan is always either aught or all-out—avoiding the problems veteran in linear restraint at lower voltages. Figure 5 shows a typical movement circuit used with PWM output from the ADT7460 fountain voltage controller.
The primary advantage of this drive method is that it is simple, inexpensive, and very efficient, since the sports fan is either in full on or fully off.
A disadvantage is that the tach information is chopped by the PWM drive signal, since power is not always applied to the fan. The tach information can Be retrieved using a technique called pulse stretching—switching the fan on long enough to gather the tachometer information (with a attainable increase of sonic disturbance). Figure 6 shows a case of pulse stretching.
Another disadvantage of low-frequency PWM is commutation make noise. With the fan coils continuously switched along and bump off, clunky noise may embody present. To deal with this noise, the newest Analog Devices fan controllers are designed to beat back the fan at a frequence of 22.5 kHz, which is outside the audible range. The foreign control circuit is simpler with falsetto-frequency PWM, but it can only be used with 4-wire fans. Although these fans are relatively new to the market, they are rapidly becoming more popular. Figure 7 depicts the circuit used for high-relative frequency PWM.
The PWM signal drives the fan right away; the ram FET is blended inside the fan. Reduction the external component bet, this approach makes the external tour much simpler. Since the PWM push signal is applied in real time to the coils of the fan, the buff's electronics are always powered on, and the tachometer signal is ever available. This eliminates the need for pulse stretching—and the noise it can make. The commutation interference is also eliminated, or reduced importantly, since the coils are organism switched with a frequency external the audible range.
Summary
From the standpoints of acoustic noise, dependableness, and power efficiency, the most desirable method of fan control is the use of high-frequency (>20 kilocycle) PWM push back.
As well eliminating the need for noisy pulse stretching and the commutation noise joint with low-absolute frequency PWM, it has a much wider control browse than linear control. With high- frequency PWM, the sports fan can be run at speeds as low as 10% of full speed, patc the same fan may only run at a minimum of 50% of full speed using linear control. Information technology is Sir Thomas More energy efficient, because the sports fan is forever either full on OR fully off. (With the FET either off Oregon in chroma, its dissipation is very low, eliminating the considerable losses in the transistor in the linear case.) It is quieter than always-on or on/off control, since the buff can run at lower speeds—that pot be varied gradually. Finally, running the fan slower also improves its lifetime, accretive system reliability.
| Control Method acting | Advantages | Disadvantages |
| Happening/Off | Threepenny | Worst acoustic carrying out—rooter is always running. |
| Linear | Most quiet | Expensive circuit Incompetent—loss of power in the amplifier circuit |
| Down in the mouth-Frequency PWM | Efficient Wide-screen pep pill-control array when measuring speed | Fan commutation noise Beat stretching required |
| High-Frequence PWM | Efficient Good acoustics, almost as good as linear. Low-cost external circuit Wide rush along-control ramble | Mustiness use 4-wire fans |
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Source: https://www.analog.com/en/analog-dialogue/articles/how-to-control-fan-speed.html
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