Heating device having heating transistor unit

A heating device is provided. A temperature sensing unit is configured to sense an ambient temperature and accordingly output a temperature sensing voltage. A driving unit is coupled to a heating transistor unit and the temperature sensing unit, and configured to drive the heating transistor unit for performing heating based on the temperature sensing voltage. An activating unit is coupled to the temperature sensing unit, configured to output an activating signal based on the temperature sensing voltage when a temperature of the printed circuit board has risen up to a preset temperature. The heating device as provided can assure that the activating signal can be normally outputted by the heating device under an ambient at an extremely low temperature.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of China application serial no. 201510523698.X, filed on Aug. 24, 2015. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to an electronic apparatus, in particular, to a heating device.

2. Description of Related Art

In general, when the electronic apparatus is used, its ambient temperature as required for operation is about consisting with the living ambient temperature, without need of specific control on temperature. At most, a thermal dissipation device such as a fan may be additionally installed to allow the electronic apparatus to normally work. However, in some special areas or working environments, the temperature may be extremely low, such as −40° C. or less, resulting in that electronic apparatus cannot be normally activated. In this situation, the electronic apparatus needs to be first heated up to a certain temperature, and then electronic apparatus is activated, so as to assure the electronic apparatus to be normally turned on and working.

Usually, the heating device of electronic apparatus is controlled by the micro controller or the central processing unit. However, when the micro controller or the central processing unit is at extremely low temperature, abnormal situation may occur. In manufacture, a heater board may usually be configured to perform heating but the heater board has the disadvantage of high cost and this issue needs to be further solved.

SUMMARY

The invention provides a heating device, in which the production cost for the heating device can be reduced.

A heating device of the invention includes a heating transistor unit, a temperature sensing unit and a driving unit. The temperature sensing unit is configured to sense an ambient temperature and accordingly output a temperature sensing voltage. The driving unit is coupled to the heating transistor unit and the temperature sensing unit, and configured to drive the heating transistor unit to perform heating based on the temperature sensing voltage.

As to the foregoing descriptions, an embodiment of the invention uses the driving unit to drive the heating transistor unit to perform heating based on the temperature sensing voltage. By use of the heating transistor unit to perform heating, it can effectively reduce the production cost of the heating device. In another embodiment, the heating device can further have an activating unit. The activating unit outputs an activating signal based on the temperature sensing voltage when the driving unit drives the heating transistor unit to perform heating based on the temperature sensing voltage until a sensed temperature (for example, a sensed temperature of a printed circuit board or the ambient temperature) has risen to a preset temperature. Since the driving unit's low-temperature tolerance is higher than micro controller or central processing unit, it can be assured that the activating signal can be normally outputted by the heating device under an extremely low temperature.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1is a drawing, schematically illustrating a heating device according to an embodiment of the invention. Referring toFIG. 1, the heating device100includes a heating transistor unit102, a temperature sensing unit104and a driving unit106. The driving unit106is coupled to the heating transistor unit102and the temperature sensing unit104. The temperature sensing unit104is configured to sense a temperature and output a temperature sensing voltage based on the sensing result. The driving unit106is configured to drive the heating transistor unit102based on the temperature sensing voltage to perform heating. The heating transistor unit102can be implemented by bipolar transistor as an example, such as PNP bipolar transistor, so that the heating transistor unit102replacing the heater board to server as the heating element can greatly reduce the production cost and decrease the layout space of the printed circuit board.

FIG. 2is a drawing, schematically illustrating a heating device according to another embodiment of the invention. Referring toFIG. 2, in detail, implementation of the heating transistor unit102, the temperature sensing unit104and the driving unit106can be the way shown inFIG. 2. In the heating device200, the temperature sensing unit104can be implemented by a negative temperature coefficient thermistor NTC1, which is coupled between the driving unit106and a ground. The driving unit106in the embodiment includes a NPN bipolar transistor Q1, a resistor R1and a resistor R2. The resistor R1is coupled in series with the resistor R2between an operation voltage VCC and a base of the transistor Q1. A common connection node of the resistor R1and the resistor R2is coupled to a collector of the transistor Q1. An emitter of the transistor Q1is coupled to the ground. In addition, the heating transistor unit102in an embodiment includes three PNP bipolar transistors Q2-Q4, coupled in series between the operation voltage VCC and the ground. The base of the transistor Q2is coupled to the collector of the transistor Q1. The bases of the transistors Q2and Q3are coupled to their own collectors thereof, respectively.

When the ambient temperature is lower, the resistance of the thermistor NTC1would be greater and the cross voltage of the thermistor NTC1is larger. After proper design for the resistances of the resistor R1, the resistor R2and the thermistor NTC1, the cross voltage of the thermistor NTC1can conduct the transistor Q1when ambient temperature has dropped to a preset value, such as −40° C. Then, voltage on the base of the transistor Q1is increased, and further the voltage on the base of the transistor Q2is drawn down to conduct the transistors Q2-Q4. The transistors Q2-Q4as conducted can generate heat to bring up the temperature of the printed circuit board. As the transistors Q2-Q4gradually bring up the temperature of the printed circuit board, the resistance of the thermistor NTC1and the base voltage of the transistor Q1are gradually dropping, and then the transistor Q1is turned off The transistors Q2-Q4are also turned off, thereby, it can avoid the heating time being too long, which causes over-temperature or wasting power.

The heating transistor unit102of an embodiment includes three PNP bipolar transistors Q2-Q4, which can be respectively configured at different locations where the heating are needed, so to improve the heating effect. In an example, when the heating device200is applied to electronic apparatus, the PNP bipolar transistors Q2-Q4can be respectively configured at the locations, at which nearby components of the electronic apparatus are poor for low-temperature tolerance, and then can assure the electronic apparatus to be normally turned on and working. In addition, since the PNP bipolar transistor serving as the heating element can be directly coupled to the ground, such as the transistor Q4, the PNP bipolar transistor as the heating element can transmit the thermal energy to the ground surface of the printed circuit board through grounding route, and then perform heating with better efficiency. The embodiment uses three PNP bipolar transistors Q2-Q4as the example for description, however, the designer can determine the number of the PNP bipolar transistors according to the actual need.

FIG. 3is a drawing, schematically illustrating a heating device according to another embodiment of the invention. Referring toFIG. 3, as comparing with the heating device100inFIG. 1, the heating device300can further include a hysteresis unit302, coupled between the temperature sensing unit104and the driving unit106. The hysteresis unit302can be configured to hysteresis the switch time for switching the voltage level of the temperature sensing voltage output from the temperature sensing unit104, so to prevent the driving unit106from frequently switching the states when the temperature swings at the vicinity of critical temperature for enabling the driving unit106. The hysteresis unit302as an example can output a first voltage based on the temperature sensing voltage to enable the driving unit106when the temperature rises up to a first temperature and output a second voltage based on the temperature sensing voltage to disable the driving unit106when the temperature drops to a second temperature, wherein the first temperature is higher than the second temperature.

As an example, the temperature sensing unit104of an embodiment can include a negative temperature coefficient thermistor NTC2and a resistor R3, wherein a terminal of the thermistor NTC2is coupled to the operation voltage VCC. The resistor R3is coupled between another terminal of the thermistor NTC2and the ground. The hysteresis unit302can include a comparator A1and a feedback unit304. The comparator A1has a positive input terminal coupled to a reference voltage Vref1, and a negative input terminal coupled to a common connection node of the thermistor NTC2and the resistor R3. The feedback unit304is coupled between an output terminal and the positive terminal of the comparator A1, configured to produce a feedback voltage to the positive terminal of the comparator A1based on a voltage at the output terminal of the comparator A1. The feedback unit304in the embodiment is implemented by the resistor R4.

The driving unit106in an embodiment can include metal-oxide-semiconductor (MOS) field effect transistor (FET) M1, coupled between the heating transistor unit102and the ground. A gate of the MOSFET M1is coupled to the output terminal of the comparator A1. Further, the heating transistor unit102in an embodiment includes a PNP bipolar transistor Q5, of which an emitter is coupled to the operation voltage VCC. A collector of the transistor Q5is coupled to the ground. A base of the transistor Q5is coupled to a drain of the MOSFET M1.

In the embodiment, when the ambient temperature is getting lower, then the resistance of the thermistor NTC2is getting greater, causing the voltage at the negative input terminal of the comparator A1to be smaller. When the voltage at the negative input terminal of the comparator A1is smaller than the reference voltage Vref1, the comparator A1would output a high voltage to conduct the MOSFET M1. The MOSFET M1as conducted can pull down the voltage at the base of the transistor Q5and conduct the transistor Q5, so the transistor Q5starts to generate heat and bring up the temperature of the printed circuit board. As the temperature of the transistor Q5is gradually rising, the resistance of the thermistor NTC2is gradually dropping, and then the voltage at the negative input terminal of the comparator A1is gradually increasing. When the voltage at the negative input terminal of the comparator A1is greater than the reference voltage Vref1at the positive input terminal, the output voltage of the comparator A1changes to a low voltage, causing the MOSFET M1to be turned off, and further turning off the transistor Q5to stop heating.

It is noted that, in the embodiment, the resistor R4is configured to feedback the output voltage from the comparator A1to the positive input terminal, so the time for the MOSFET M1to be conducted or turned off can be delayed. For example, the MOSFET M1is turned on when the temperature of the printed circuit board has dropped down below 6° C., causing the transistor Q5to start heating. The MOSFET M1is turned off when the temperature of the printed circuit board has risen up above 22° C., causing the transistor Q5to stop heating. The delay time for the MOSFET M1to be conducted or turned off can be adjusted by changing the resistance of the resistor R4according to the actual need.

As known in the foregoing embodiments, the driving unit106is not implemented by the complicate circuit such as the micro controller or the central process unit and the low-temperature tolerance is high, so to assure that the heating control can still be precisely performed in normal operation under extremely low temperature.

FIG. 4is a drawing, schematically illustrating a heating device according to another embodiment of the invention. Referring toFIG. 4, as foregoing descriptions, the heating device can be applied to an electronic apparatus, that is, the heating device can also have the function to activate the electronic apparatus to assure that the electronic apparatus can still be normally turned on and working under low temperature. As the example in an embodiment, the heating device400can output the activating signal S1to activate the chip of the electronic apparatus, the central processing unit, or the micro controller, and so on. The electronic apparatus in an example can be computer, display, . . . , and so on. As shown inFIG. 4, in addition to the heating device100inFIG. 1, the heating device400in an embodiment further includes an activating unit402, coupled to the temperature sensing unit104. The activating unit402can outputs an activating signal Si based on the temperature sensing voltage when the temperature of the printed circuit board has risen up to a preset temperature.

To assure that the activation unit402does not output the activating signal S1to activate the electronic apparatus when the temperature in the printed circuit board has not risen up to the preset temperature yet, the implementation of the heating device can be the one shown inFIG. 5. InFIG. 5, the heating device500includes the activating unit402and the heating device300as shown inFIG. 3. The activating unit402in an embodiment can be implemented by an OR gate502. The first input terminal of the OR gate502is coupled to a common connection node of the thermistor NTC2and the resistor R3. The second input terminal of the OR gate502is coupled to the output terminal of the OR gate502and receives the reference voltage Vref2at a logic low level. The reference voltage Vref2in an example can be provided by coupling the second input terminal of the OR gate502to the ground through the resistor R5but this is not limited herein. When the ambient temperature is too low, which causes the voltage (i.e. the temperature sensing voltage) at the common connection node of the thermistor NTC2and the resistor R3to be at the logic low level, the output of the OR gate502is also at the logic low level. In this situation, the activating unit402does not output the activating signal S1.

On the other hand, the heating device300starts to perform heating and the temperature thereby starts to rise. The voltage at the common connection node of the thermistor NTC2and the resistor R3is then rising accordingly. When the voltage at the common connection node of the thermistor NTC2and the resistor R3has risen up to the logic high level, in which the temperature of the printed circuit board is rising up to the preset temperature at this moment, the OR gate502changes to output the voltage at the logic high level, in which the activating unit402then outputs the activating signal S1. The temperature corresponding to the condition that the activating unit402outputs the activating signal S1can be set by changing the resistance of the resistor R3. As a result, the temperature sensing voltage is configured to determine whether or not to trigger the activation. This can assure that the activation unit402does not output the activating signal S1to activate the electronic apparatus when the temperature has not risen up to the preset temperature yet. Further, it can avoid that the electronic apparatus is activated at the over-low temperature, resulting in the electronic apparatus being activated or operating abnormally.

It is noted that, the second input terminal and the output terminal of the OR gate502in the embodiment are coupled to each other. Thus, after the OR gate502outputs the voltage with logic high level, that is, after the activating signal S1is outputted, the voltage at the second input terminal of the OR gate502is also changed to the logic high level. As a result, no matter how the voltage at the first input terminal of the OR gate is changed after then, that is, no matter how the ambient temperature is changed, the output voltage of the OR gate502is still keeping at the logic high level. In other words, after the electronic apparatus is activated, the heating device500would not be turned off due to decrease of the ambient temperature after then, and the activating state for the electronic apparatus would be continuously maintained. In other embodiment, after the electronic apparatus is activated, the heating device500may be configured to stop outputting the activating signal S1when the ambient temperature drops to a value lower than the preset temperature, the coupling state between the second input terminal and the output terminal of the OR gate502can be removed.

As to the foregoing descriptions, the embodiments of the invention use the driving unit to drive the heating transistor unit to perform heating based on the temperature sensing voltage. Thereby, the activating unit outputs the activating signal based on the temperature sensing voltage when the sensed temperature has risen up to the preset temperature. Since the low-temperature tolerance of the driving unit is higher than that of the micro controller or the central processing unit, it can be assured that the heating device can still normally output the activating signal under extremely low temperature. In addition, the production cost of the heating device can be reduced by use of the heating transistor unit to perform heating. Further, since the heating transistor unit serving as the heating element can transmit the thermal energy to the other components through the ground surface of the printed circuit board, the heating can be performed with better efficiency and uniformity with respect to the heater board as usually used, which can only use the printed circuit board for conducting heat.