 |
Zakładka z wyszukiwarką danych komponentów |
|
|
Zakładka z wyszukiwarką danych komponentów |
|
TC664EUN Arkusz danych(PDF) 10 Page - Microchip Technology |
|
||||||||||||||||||||||||||||||
TC664EUN Arkusz danych(HTML) 10 Page - Microchip Technology |
|
|
10 / 36 page  TC664/TC665 DS21737A-page 10 2002 Microchip Technology Inc. 4.1 Fan Speed Control Methods The speed of a DC brushless fan is proportional to the voltage across it. For example, if a fan’s rating is 5000 RPM at 12 V, it’s speed would be 2500 RPM at 6 V. This, of course, will not be exact, but should be close. There are two main methods for fan speed control. The first is pulse width modulation (PWM) and the second is linear. Using either method the total system power requirement to run the fan is equal. The difference between the two methods is where the power is con- sumed. The following example compares the two methods for a 12 V, 120 mA fan running at 50% speed. With 6 V applied across the fan, the fan draws an average cur- rent of 68 mA. Using a linear control method, there is 6V across the fan and 6V across the drive element. With 6 V and 68 mA, the drive element is dissipating 410 mW of power. Using the PWM approach, the fan is modulated at a 50% duty cycle, with most of the 12 V being dropped across the fan. With 50% duty cycle, the fan draws an RMS current of 110 mA and an average current of 72 mA. Using a MOSFET with a 1 Ω RDS(on) (a fairly typical value for this low current) the power dis- sipation in the drive element would be: 12 mW (Irms2 * RDS(on)). Using a standard 2N2222A NPN transistor (assuming a Vce-sat of 0.8 V), the power dissipation would be 58 mW (Iavg* Vce-sat). The PWM approach to fan speed control causes much less power dissipation in the drive element. This allows smaller devices to be used and will not require any spe- cial heatsinking to get rid of the power being dissipated in the package. The other advantage to the PWM approach is that the voltage being applied to the fan is always near 12 V. This eliminates any concern about not supplying a high enough voltage to run the internal fan components which is very relevant in linear fan speed control. 4.2 PWM Fan Speed Control The TC664/TC665 devices implement PWM fan speed control by varying the duty cycle of a fixed frequency pulse train. The duty cycle of a waveform is the on time divided by the total period of the pulse. For example, given a 100 Hz waveform (10 msec.) with an on time of 5.0 msec., the duty cycle of this waveform is 50% (5.0 msec./10.0 msec.). An example of this is shown in Figure 4-2. FIGURE 4-2: Duty Cycle Of A PWM Waveform. The TC664/TC665 devices generate a pulse train with a typical frequency of 30 Hz (CF = 1 µF). The duty cycle can be varied from 30% to 100%. The pulse train gen- erated by the TC664/TC665 devices drives the gate of an external N-channel MOSFET or the base of an NPN transistor (Figure 4-3). See Section 7.5 for more infor- mation on output drive device selection. FIGURE 4-3: PWM Fan Drive. By modulating the voltage applied to the gate of the MOSFET Qdrive, the voltage applied to the fan is also modulated. When the VOUT pulse is high, the gate of the MOSFET is turned on, pulling the voltage at the drain of Qdrive to zero volts. This places the full 12 V across the fan for the Ton period of the pulse. When the duty cycle of the drive pulse is 100% (full on, Ton = T), the fan will run at full speed. As the duty cycle is decreased (pulse on time “Ton” is lowered), the fan will slow down proportionally. With the TC664/TC665 devices, the duty cycle can be controlled through the analog input pin (VIN), or through the SMBus interface, by using the Duty-Cycle Register. See Section 4.5 for more details on duty cycle control. T Ton Toff T = Period T = 1/F F = Frequency D = Duty Cycle D = Ton / T FAN 12 V Qdrive TC664 TC665 VDD GND VOUT G D S |
Podobny numer części - TC664EUN |
|
Podobny opis - TC664EUN |
|
|
Link URL |
| Polityka prywatności |
| ALLDATASHEET.PL |
| Czy Alldatasheet okazała się pomocna? [ DONATE ] |
O Alldatasheet | Reklama | Kontakt | Polityka prywatności | Linki | Lista producentów All Rights Reserved©Alldatasheet.com |
| Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
|
Family Site : ic2ic.com |
icmetro.com |
Polish ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
