Patent Application
20130088832
1. Technical Field
The disclosure generally relates to electronic devices, and particularly to a thermal protection circuit and an electronic device using the thermal protection circuit.
2. Description of the Related Art
A plurality of integrated circuits and chips are employed in an electronic device to satisfy multiple requirements. When the electronic device has been operating for an exceedingly long time, the integrated circuits and chips generate a great deal of heat. Much of the generated heat cannot be dissipated in real-time and may cause irreversible damage to the electronic device.
Therefore, there is room for improvement within the art.
Many aspects of the present embodiment can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present embodiment. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. Wherever possible, the same reference numbers are used throughout the drawings to refer to the same or like elements of an embodiment.
Also referring to
In the present embodiment, the first resistor R1 is a negative temperature coefficient (NTC) resistor, and has a resistance that is inversely proportional to the internal temperature of the electronic device 100. Therefore, the temperature detecting circuit 11 outputs the voltage signal decreasing proportionally with the internal temperature of the electronic device 100 increasing.
The comparing circuit 12 can be a hysteresis comparing circuit, and includes a first comparator A1. The first comparator A1 can be a LM393 comparator. A negative input of the first comparator A1 is connected to the output of the temperature detecting circuit 11 (i.e., the common node of the first resistor R1 and the second resistor R2). A positive input of the first comparator A1 is connected to the power supply VCC through a third resistor R3, and also connected to ground through a forth resistor R4. An output of the first comparator A1 is connected to the power supply VCC via a fifth resistor R5. The output of the first comparator A1 is also connected to a common node J of the positive input of the comparator A1, the third resistor R3 and the fourth resistor R4 through a sixth resistor R6.
Referring to
Therefore, by setting the high triggering voltage UP1 and the low triggering voltage UP2 respectively equal to the high voltage threshold and the low voltage threshold, the comparing circuit 12 compares the voltage signal to the predetermined thresholds (i.e., the high triggering voltage UP1 and the low triggering voltage UP2), thereby comparing the internal temperature of the electronic device 100 to the lower temperature value and the upper temperature value to output a first driving signal (e.g., a signal of logic 1) or a second driving signal (e.g., a signal of logic 0) to the anti-interference 13. For example, when the internal temperature of the electronic device 100 exceeds the upper temperature value (i.e., the output voltage of the temperature detecting circuit 11 is below to the low triggering voltage UP2), the output of the first comparator A1 is high-impedance. Accordingly the comparing circuit 12 outputs the first driving signal. In other embodiments, when the internal temperature of the electronic device 100 is below to the lower temperature value (i.e., the output voltage of the temperature detecting circuit 11 is greater than the high triggering voltage UP1), the comparing circuit 12 outputs the second driving signal.
The signal processing circuit 13 is connected between the comparing circuit 12 and the switching circuit 14. It should be understood that direct and continuous output of the first and second driving signals by the comparing circuit 12 to the switching circuit 14, which will correspondingly lead to constant switching on/off of the switching circuit 14, which may damage the switching circuit 14. Thus, the signal processing circuit 13 receives and processes the first driving signal or the second driving voltage to output a steady first driving voltage (e.g., logic 1) or a steady second driving voltage (e.g., logic 0) to the switching circuit 14, thereby preventing the switching circuit 14 from damage due to turning on/off constantly.
In detail, the signal processing circuit 13 includes a second comparator A2. The second comparator can be a LM393 comparator. A positive input of the second comparator A2 is connected to the output of the comparing circuit 12 (i.e., the common node of the fourth resistor R5 and the fifth resistor R6). A negative input of the second comparator A2 is connected to the common node J (i.e., the positive input of the first comparator A1). An output of the second comparator A2 is connected to the power supply VCC through a seventh resistor R7, and also connected to the switching circuit 14.
When the comparing circuit 12 outputs the first driving signal, the first driving signal is transmitted to the positive input of the second comparator A2, and the negative input of the second comparator A2 receives a voltage lower than the voltage of the output of comparing circuit 12 from the positive input of the first comparator A1. In this way, the output of the second comparator A2 is high-impedance, which leads to the disconnection between the output of the second comparator A2 and the seventh resistor R7, thereby causing the power supply VCC to output the first driving voltage (e.g., logic 1) to the switching unit 14 through the seventh resistor R7. In other embodiments, when the comparing circuit 12 outputs the second driving signal, the second driving signal is transmitted to the positive input of the second comparator A2. Since the negative input of the second comparator A2 is connected to the positive input of the first comparator A1, thus the negative input of the second comparator A2 receives a voltage from the positive input of the first comparator A1. In this way, according to a performance of the second comparator A2, the second comparator A2 outputs the second driving voltage (e.g., logic 0) to the switching circuit 14.
The switching unit 14 includes a bipolar junction transistor (BJT) Q1, and a eighth resistor R8. A base of the BJT Q1 is connected to the output of the signal processing circuit 13. An emitter of the BJT Q1 is connected to ground. A collector of the BJT Q1 is connected to the power supply VCC through the eighth resistor R8, and also connected to both the CPU 20 and the fan 30.
After receiving the first driving voltage or the second driving voltage from the signal processing circuit 13, the switching circuit 14 turns on or off, thereby controlling an operation of the CPU 20 and the fan 30. For example, when the internal temperature of the electronic device 100 exceeds the upper temperature value, such as 60° C., the switching circuit 14 receives the first driving voltage, and the BJT Q1 turns on. Then both the CPU 20 and the fan 30 are connected to ground through the BJT Q1 to obtain a low level (e.g., logic 0). Upon receiving the low level, the CPU 20 will slowdown, and the rotational speed of the fan 30 increases, thereby cooling down the internal temperature of the electronic device 100.
Alternatively, when the internal temperature of the electronic device 100 is less than the lower temperature value, such as 25° C., the switching circuit 14 receives the second driving voltage, and the BJT Q1 turns off. Then both the CPU 20 and the fan 30 are connected to the power supply VCC through the eighth resistor R8 to obtain a high level. Upon receiving the high level, the CPU 20 and the fan 30 would recover to normal operation.
In the present embodiment, when the internal temperature of the device 100 is below the upper temperature value, such as 60° C., the temperature detecting circuit 11 outputs the voltage signal not lower than the low triggering voltage UP2. In this way, the comparing circuit 12 outputs the second driving signal. Since the positive input of the second comparator A2 is connected to the output of the comparing circuit 12, so the positive input of the second comparator A2 receives a voltage less than the voltage of the negative input of the second comparator A2. Therefore, according to the characters of the second comparator A2, the second comparator A2 outputs the second driving voltage. Then the BJT Q1 receives the second driving voltage, and turns off. Obviously, both the CPU 20 and the fan 30 would connect to the power supply VCC through the eighth resistor R8 to obtain a high level, and respectively work normally.
When the internal temperature of the electronic device 100 exceeds the upper temperature value, the temperature detecting circuit 11 outputs the voltage signal lower than the low triggering voltage UP2. According to the performance of the comparing circuit 12, the first comparator A1 outputs a high impedance. Accordingly, the output of the first comparator A1 is disconnected from the fourth resistor R5. In this way, the output of the comparing circuit 12 outputs a voltage greater than the voltage of negative input of the second comparator A2. Therefore, the signal processing circuit 13 outputs the first driving voltage, and the BJT Q1 turns on. Obviously, both the CPU 20 and the fan 30 would connect to ground through the BJT Q1 to obtain a low level (e.g., logic 0). Upon receiving the low level, the CPU 20 will slow down, and the rotational speed of the fan 30 increases, thereby cooling down the internal temperature of the electronic device 100.
As the electronic device 100 cools down, the internal temperature falls and the voltage signal of the internal temperature rises proportionally. When the internal temperature of the electronic device 100 falls to below the lower temperature value, the voltage signal of the internal temperature signal rises to above the high triggering voltage UP1. Then the comparing circuit 12 outputs the second driving signal again. Accordingly, the signal processing circuit 13 outputs the second driving voltage, and the BJT Q1 turns off. Therefore, both the CPU 20 and the fan 30 obtain a high level again, and recover to work normally.
In the other alternative embodiments, the first resistor R1 is a positive temperature coefficient (PTC) resistor, and has a resistance directly proportional to the internal temperature of the electronic device 100 increasing. In detail, the first resistor R1 and the second resistor R2 are connected in turn between the power supply VCC and the ground. Thus, the temperature detecting circuit 11 also outputs the voltage signal decreasing proportionally with the internal temperature of the electronic device 100 increasing.
In the other alternative embodiments, the positive input and the negative input of the first comparator A1 are respectively connected to ground through capacitors C1, C2 for filtering the voltages of the positive input and the negative input of the first comparator A1.
In the present specification and claims, the word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. Further, the word “comprising” does not exclude the presence of elements or steps other than those listed.
It is to be understood, however, that even though numerous characteristics and advantages of the exemplary disclosure have been set forth in the foregoing description, together with details of the structure and function of the exemplary disclosure, the disclosure is illustrative only, and changes may be made in detail, especially in the matters of shape, size, and arrangement of parts within the principles of this exemplary disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 201110292897.6 | Oct 2011 | CN | national |
