自動化專業(yè)外文翻譯----基于嵌入式處理器的vlsi芯片的溫度自動控制-預(yù)覽頁
【正文】 ed chip, but can be significantly lower and the difference between measured temperature and the actual die temperature increases as the power dissipation increases. So, the temperature of the circuit board or heat sink must be correlated to the die temperature of the high speed chip. Of course a better alternative is possible with a number of high speed chips. Many CPUs, FPGAs and other high speed ICs include a thermal diode which is actually a diode connected bipolar transistor, on the die. Using a remote diode temperature sensor connected to this thermal diode, the temperature of the high speed IC’s die can be measured directly with an excellent accuracy. This not only eliminates the large temperature gradients involved in measuring temperature outside the target IC’s package, but it also eliminates the long thermal time constants,from several seconds to minutes, that cause delays in responding to die temperature changes. 12 There is also a drawback in fan speed control. Normally the fan speed is controlled by adjusting the power supply voltage of the fan. This is done by a lowfrequency PWM signal, usually in the range of about 50 Hz, whose duty cycle is varied to adjust the fan’s speed. This is inexpensive and also efficient. But the disadvantage of this method is that it makes the fan somewhat nosier because of the pulsed nature of the power supply. The PWM waveforms fast edges cause the fans mechanical structure to move, which is easily audible. In some systems, it is also important to limit the rate of change of the fan speed. This is critical when the system is in close proximity to users. Simply switching a fan on and off or changing speed immediately as temperature changes is acceptable in some environments. But when users are in nearby, the sudden changes in fans noise are highly annoying. So to avoid these effects the fan’s drive signal must be limited to an acceptable level. 5. Future Scope of the Work In the present work temperature is sensed using the temperature sensor LM35 and the speed of the motor is controlled by varying the width of PWM generated by the processor. But the temperature sensed by the IC LM35 is not very accurate even though we keep the IC very near to the processor orVLSI chip. So, we can use a remote diode temperature sensor connected to the thermal diode which measures the temperature of the high speed ICs directly with excellent accuracy. Another important aspect is a variety of remote temperature sensors with up to five sensing channels is available that can detect the die temperature of the high speed chip and transmit temperature data to a speed regulators with multiple channels of fan tachometer monitoring can provide reliable control of fan RPM or supply voltage based on mands from an external microcontroller. For this simple ICs are provided by MAXIM MAX6660 and MAX6653. The first IC can sense the remote temperature and controls the fan speed based on that temperature. It 13 produces a DC supply voltage for the fan through an internal power transistor. The second IC also performs a similar function but drives the fan with a PWM waveform through an external pass transistor. Both include plete thermal fault monitoring with over temperature outputs, which can be used to shut down the system if the high speed chips get too hot. So, the present work can be improved further by using the above mentioned techniques.
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