Heating control circuit of thermal printing head and thermal printer

Abstract

The utility model provides a heating control circuit of a thermal printing head and a thermal printer, and relates to the technical field of printers. The thermistor in the thermal printing head is connected with the voltage dividing unit in series, meanwhile, the first reference voltage is preset, and whether the thermistor is in the normal-temperature environment or the low-temperature environment is judged by comparing the first reference voltage with the voltage dividing value of the voltage dividing unit and the thermistor; when the thermistor is in a normal temperature environment, the power supply of the power supply to the thermal printing head is switched to high voltage power supply, and when the thermistor is in a normal temperature environment, the power supply of the power supply to the thermal printing head is switched to low voltage power supply. That is, high voltage is adopted to supply power to the thermal printing head in the low-temperature environment, low voltage is adopted to supply power to the thermal printing head in the normal-temperature environment, it can be guaranteed that the thermal printer can present the same printing effect in the normal-temperature environment and the low-temperature environment, and the situation that the thermal printing head is prone to being overheated in the normal-temperature environment can be avoided. And the reliability of the circuit is improved.

Description

Technical Field

[0001] The present application relates to the technical field of printers, and in particular, to a heating control circuit for a thermal print head and a thermal printer. Background Art

[0002] A thermal printer records information by heating a thermal print head to a high temperature. During the operation of the thermal printer, overheating of the thermal print head often occurs. If the thermal printer works in an overheated state for a long time, it will inevitably damage the thermal print head, and ultimately cause the thermal printer to be unable to perform its own printing function. Especially for thermal printers used in medical scenarios, it is more necessary to ensure the reliability of their operation. Therefore, it is very necessary to control the heating of the thermal print head. Usually, a thermistor is provided inside the thermal print head. The thermistor has a remarkable characteristic, that is, its resistance value changes with the change of the ambient temperature. This characteristic is the main basis for the heating control of the thermal print head.

[0003] In the related art, the heating control scheme for the thermal print head basically uses the thermistor for voltage division sampling. The MCU (Micro Control Unit) collects this divided voltage value in real time, and through calculation, converts this divided voltage value into the current working temperature value. Subsequently, the MCU determines whether the thermal print head is overheated based on this working temperature value. Once the MCU determines overheating, it will disconnect the power supply for heating the thermal print head, thereby realizing the protection of the thermal print head. For this heating control scheme of the thermal print head, it is necessary for the MCU to collect the divided voltage value of the thermistor in real time and perform corresponding calculations to draw a conclusion on whether it is overheated. The delay is relatively long, the cost is relatively high, and the peripheral circuit of the MCU is relatively complex, and the circuit failure rate is relatively high. Since the calculation of the MCU is carried out through software, it requires the designer to have a certain software foundation. However, when the circuit fails, not only the hardware needs to be replaced, but also the corresponding software needs to be updated, which makes the later maintenance more difficult. In addition, regardless of whether the thermal print head works in a normal temperature environment or a low temperature environment, the voltage output by the power supply for heating the thermal print head in the existing heating control scheme is fixed. This not only causes the thermal print head to be prone to overheating at normal temperature, but also causes the thermal printer to be unable to present the same printing effect in normal temperature and low temperature environments. Summary of the Utility Model

[0004] The present application provides a heating control circuit for a thermal print head and a thermal printer, aiming to solve the problem that the thermal print head is prone to overheating when working at normal temperature in the related art.

[0005] To solve the above technical problems existing in the related art, a first aspect of the present application provides a heating control circuit for a thermal print head. The heating control circuit includes a power supply, a voltage dividing unit, a first comparison unit, and a voltage switching unit. The power supply is electrically connected to the thermal print head of the thermal printer. The voltage dividing unit is connected in series with the thermistor in the thermal print head. The first comparison unit is electrically connected to the voltage dividing unit, and the voltage switching unit is electrically connected to the first comparison unit. Specifically, the power supply is used to supply power to the thermal print head to heat the thermal print head when the thermal printer is performing a printing operation. The first comparison unit is used to access the first reference voltage and the divided voltage value of the voltage dividing unit and the thermistor, and compare the first reference voltage with the divided voltage value to determine whether the thermistor is in a normal temperature environment or a low temperature environment. Among them, when the thermistor is in a normal temperature environment, the first comparison unit outputs a low-voltage power supply signal, and when the thermistor is in a low temperature environment, the first comparison unit outputs a high-voltage power supply signal. The voltage switching unit is used to respond to the low-voltage power supply signal to switch the power supply of the power supply to the thermal print head to low-voltage power supply, or respond to the high-voltage power supply signal to switch the power supply of the power supply to the thermal print head to high-voltage power supply.

[0006] A second aspect of the present application provides a thermal printer. The thermal printer includes a thermal print head and the heating control circuit mentioned in the first aspect of the present application. The heating control circuit is used to control the power supply of the power supply to the thermal print head to control the heating of the thermal print head by controlling the power supply.

[0007] It can be understood that through the implementation of the above technical solutions of the present application, a voltage dividing unit is connected in series with the thermistor in the thermal print head, and a first comparison unit and a voltage switching unit are provided. The first comparison unit can access the preset first reference voltage and the divided voltage value of the voltage dividing unit and the thermistor, and judge whether the thermistor is in a normal temperature environment or a low temperature environment according to the comparison result of the two. When it judges that the thermistor is in a low temperature environment, it will output a high-voltage power supply signal to the voltage switching unit to guide the voltage switching unit to switch the power supply of the power supply to the thermal print head to high-voltage power supply. When it judges that the thermistor is in a normal temperature environment, it will output a low-voltage power supply signal to the voltage switching unit to guide the voltage switching unit to switch the power supply of the power supply to the thermal print head to low-voltage power supply. It can be seen that different from the traditional solution of using a fixed voltage to supply power to the thermal print head in both low temperature and normal temperature environments, the present application can switch the voltage provided by the power supply to the thermal print head between low temperature and normal temperature environments, that is, use a high voltage to supply power to the thermal print head in a low temperature environment and a low voltage to supply power to the thermal print head in a normal temperature environment. This can not only ensure that the thermal printer can present the same printing effect in both normal temperature and low temperature environments, but also avoid the thermal print head from overheating easily in a normal temperature environment, improving the reliability of the circuit. Description of the Drawings

[0008] To more clearly illustrate the related art or the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required in the description of the related art or the embodiments of the present application. Obviously, the drawings in the following description are only some embodiments of the present application, rather than all embodiments. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0009] Figure 1 The first structural block diagram of the heating control circuit provided by the embodiment of the present application;

[0010] Figure 2 The second structural block diagram of the heating control circuit provided by the embodiment of the present application;

[0011] Figure 3 The third structural block diagram of the heating control circuit provided by the embodiment of the present application. Detailed implementation manners

[0012] In order to make the purpose, technical solutions and advantages of the present application more obvious and understandable, the following will clearly and completely describe the present application in combination with the embodiments of the present application and the corresponding drawings, where the same or similar reference numerals represent the same or similar elements or elements with the same or similar functions from beginning to end. It should be understood that the various embodiments of the present application described below are only used to explain the present application, and are not used to limit the present application. That is, based on the various embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present application. In addition, the technical features involved in the various embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0013] In the related art, when a thermal printer controls the heating of its own thermal print head, the MCU of the thermal printer will collect the divided voltage value of the thermistor in the thermal print head in real time, and calculate based on this divided voltage value to obtain the current working temperature value of the thermal print head. Then, the obtained working temperature value is compared with a preset safe temperature threshold to draw a conclusion on whether it is overheated. It can be understood that since the MCU needs to perform calculations when judging whether the thermal print head is overheated, its delay is relatively long, the cost is relatively high, and the peripheral circuit of the MCU is relatively complex, and the circuit failure rate is very high. Moreover, the calculation of the MCU is carried out through software, which requires the designer to have a certain software foundation. However, when the circuit fails, not only the hardware needs to be replaced, but also the corresponding software needs to be updated, which makes the later maintenance more difficult. In addition, whether the thermal print head is operating in a normal temperature environment or a low temperature environment, the voltage output by the power supply for heating the thermal print head in the existing heating control scheme is fixed. This not only causes the thermal print head to be prone to overheating at normal temperature, but also causes the thermal printer to be unable to present the same printing effect in normal temperature and low temperature environments. Therefore, in the embodiments below, the present application proposes a heating control circuit for a thermal print head. This heating control circuit can be applied in a thermal printer. The thermal printer can control the power supply to the thermal print head through this heating control circuit (that is, control the heating of the thermal print head by controlling the power supply), and can effectively solve the above-mentioned drawbacks existing in the related art, thereby improving the reliability of the operation of the thermal printer.

[0014] Figure 1It is the first structural block diagram of the heating control circuit. In some embodiments, the heating control circuit includes a power supply 104, a voltage dividing unit 101, a first comparison unit 102, and a voltage switching unit 103. The power supply 104 is electrically connected to the thermal print head of the thermal printer. The voltage dividing unit 101 is connected in series with the thermistor in the thermal print head. The first comparison unit 102 is electrically connected to the voltage dividing unit 101, and the voltage switching unit 103 is electrically connected to the first comparison unit 102. During the actual heating control process of the thermal print head, when the thermal printer is performing a printing operation, the power supply 104 can supply power to the thermal print head to heat the thermal print head. The first comparison unit 102 can access the first reference voltage and the divided voltage value of the voltage dividing unit 101 and the thermistor, and compare the first reference voltage with the divided voltage value to determine whether the thermistor is in a normal temperature environment or a low temperature environment. When the thermistor is in a normal temperature environment, the first comparison unit 102 can output a low voltage power supply signal to the voltage switching unit 103, and when the thermistor is in a low temperature environment, the first comparison unit 102 can output a high voltage power supply signal to the voltage switching unit 103. The voltage switching unit 103 can respond to the low voltage power supply signal in a normal temperature environment to switch the power supply of the power supply 104 to the thermal print head to low voltage power supply, or respond to the high voltage power supply signal in a low temperature environment to switch the power supply of the power supply 104 to the thermal print head to high voltage power supply. Preferably, the voltage dividing unit 101 includes a voltage dividing resistor, that is, the voltage dividing resistor is used to divide the voltage with the thermistor.

[0015] It can be understood that different from the traditional solution that uses a fixed voltage to supply power to the thermal print head in both low temperature and normal temperature environments, in this application, the voltage provided by the power supply 104 to the thermal print head can be switched between low temperature and normal temperature environments, that is, a high voltage is used to supply power to the thermal print head in a low temperature environment, and a low voltage is used to supply power to the thermal print head in a normal temperature environment. This can not only ensure that the thermal printer can present the same printing effect in normal temperature and low temperature environments, but also avoid the thermal print head from overheating easily in normal temperature environments, thereby improving the reliability of the circuit.

[0016] As one of the embodiments, the first reference voltage is set according to the resistance value of the thermistor in the first critical environment, which has a first critical temperature. When the temperature of the environment where the thermistor is located is less than the first critical temperature, it means that the thermistor is in a low-temperature environment, and when the temperature of the environment where the thermistor is located is greater than the first critical temperature, it means that the thermistor is in a normal-temperature environment. That is to say, the first critical temperature is the critical point for dividing the low-temperature environment and the normal-temperature environment at the temperature level. Usually, the resistance value of the thermistor is not fixed and is closely related to the temperature of the environment where it is located. When the temperature of the environment changes, the resistance value of the thermistor also changes. Correspondingly, the voltage division value of the voltage division unit 101 and the thermistor also changes, which indicates that the voltage division value of the voltage division unit 101 and the thermistor can be used to indirectly represent the temperature value of the environment where it is located. At the same time, since the first reference voltage is set according to the resistance value of the thermistor at the first critical temperature, the first reference voltage is actually the critical point for dividing the low-temperature environment and the normal-temperature environment at the voltage level. In this way, the present application can determine the low-temperature environment and the normal-temperature environment by comparing the first reference voltage and the voltage division value of the voltage division unit 101 and the thermistor. Preferably, the first critical temperature for dividing the low-temperature environment and the normal-temperature environment is 0°C.

[0017] Further, the first comparison unit 102 includes a first comparator. The reverse input terminal of the first comparator is connected to the first reference voltage, and the forward input terminal of the first comparator is connected to the voltage division value of the voltage division unit 101 and the thermistor. The output terminal of the first comparator is electrically connected to the voltage switching unit 103. That is to say, in this embodiment, the first comparator is used to compare the first reference voltage and the voltage division value to determine whether the thermistor is in a normal-temperature environment or a low-temperature environment. Usually, the thermistor has a negative temperature coefficient, that is, the resistance value of the thermistor is negatively correlated with the temperature of the environment where it is located (the higher the temperature of the environment where it is located, the smaller the resistance value of the thermistor; the lower the temperature of the environment where it is located, the larger the resistance value of the thermistor). Based on this characteristic of the thermistor, it can be known that in the normal-temperature environment, the first reference voltage is greater than the voltage division value of the voltage division unit 101 and the thermistor, and the first comparator outputs a low-voltage power supply signal (low level) to the voltage switching unit 103. During the process of the environment changing from normal temperature to low temperature, the temperature of the environment gradually decreases, and the voltage division value of the voltage division unit 101 and the thermistor gradually increases. As time goes by, the voltage division value of the voltage division unit 101 and the thermistor will increase to be greater than the first reference voltage, indicating that it has changed from a normal-temperature environment to a low-temperature environment, and the first comparator will output a high-voltage power supply signal (high level) to the voltage switching unit 103.

[0018] As one of the embodiments, the power supply 104 is configured with a feedback resistor. The resistance ratio of the feedback resistor is closely related to the voltage output by the power supply 104, that is, closely related to the voltage provided by the power supply 104 to the thermal print head. Therefore, by adjusting the resistance ratio of the feedback resistor, the voltage provided by the power supply 104 to the thermal print head can be changed. That is to say, when the voltage switching unit 103 in this embodiment switches the power supply of the thermal print head by the power supply 104, it can be achieved by switching the resistance ratio of the feedback resistor. That is, the function of the voltage switching unit 103 in this embodiment is to switch the resistance ratio of the feedback resistor. In some implementation manners of this embodiment, the voltage switching unit 103 includes MOS transistors, that is, the resistance ratio of the feedback resistor is switched by MOS transistors.

[0019] Figure 2 It is the second structural block diagram of the heating control circuit. In some other embodiments, in addition to the structures listed above, the heating control circuit further includes a second comparison unit 105 and a switch unit 106. The second comparison unit 105 is electrically connected to the voltage dividing unit 101, and the switch unit 106 is electrically connected to the second comparison unit 105. During the actual heating control process of the thermal print head, the second comparison unit 105 can access the second reference voltage and the divided voltage value of the voltage dividing unit 101 and the thermistor, and compare the second reference voltage with the divided voltage value, aiming to determine whether the thermistor is overheated (that is, the temperature is too high). When the thermistor is overheated, the second comparison unit 105 will output a disconnection signal to the switch unit 106, and when the thermistor is not overheated, the second comparison unit 105 will output a connection signal to the switch unit 106; the switch unit 106 can respond to the disconnection signal to disconnect the electrical connection between the power supply 104 and the thermal print head when overheated, or respond to the connection signal to make the electrical connection between the power supply 104 and the thermal print head when not overheated.

[0020] It can be seen that in this application, the second comparison unit 105 is used to compare the second reference voltage and the divided voltage value of the voltage dividing unit 101 and the thermistor to determine whether the thermistor is overheated, and when it is determined that the thermistor is overheated, the electrical connection between the power supply 104 and the thermal print head is disconnected through the switch unit 106, thereby realizing overheat protection for the thermal print head. It can be understood that when realizing overheat protection for the thermal print head in this application, it is not necessary to perform complex operations using an MCU like in traditional solutions. The response speed of the circuit is faster, and at the same time, the complex peripheral circuits of the MCU are avoided, reducing the failure rate of the circuit. It is not necessary to require the designer to have a certain software foundation, and the later maintenance is simpler. Moreover, the second comparison unit 105 of this application can adopt a comparator commonly used in the art (such as a comparator with the model number LM393), and compared with the MCU, the cost will be lower.

[0021] As one of the embodiments, the second reference voltage is set according to the resistance value of the thermistor in the second critical environment, which has a second critical temperature. When the temperature of the thermistor is less than the second critical temperature, it means that the thermistor is not overheated, and when the temperature of the thermistor is greater than the second critical temperature, it means that the thermistor is overheated. That is to say, the second critical temperature is the critical point for dividing overheating or not at the temperature level. Generally, the resistance value of the thermistor is not fixed and is closely related to its own temperature. When its own temperature changes, its own resistance value also changes. Accordingly, the voltage division value of the voltage division unit 101 and the thermistor also changes. This shows that the voltage division value of the voltage division unit 101 and the thermistor can be used to indirectly represent the temperature of the thermistor. At the same time, since the second reference voltage is set according to the resistance value of the thermistor at the second critical temperature, the second reference voltage is actually the critical point for dividing overheating or not at the voltage level. Thus, the discrimination of overheating or not can be carried out by comparing the second reference voltage and the voltage division value of the voltage division unit 101 and the thermistor.

[0022] Further, the second comparison unit 105 includes a second comparator. The inverting input terminal of the second comparator is connected to the second reference voltage, and the non-inverting input terminal is connected to the voltage division value of the voltage division unit 101 and the thermistor. The output terminal of the second comparator is electrically connected to the switch unit 106. That is to say, in this embodiment, the second comparator is used to compare the second reference voltage with the voltage division value to determine whether the thermistor is overheated. Generally, the thermistor has a negative temperature coefficient, that is, the resistance value of the thermistor is negatively correlated with its own temperature (the higher the temperature of the thermistor itself, the smaller the resistance value; the lower the temperature of the thermistor itself, the larger the resistance value). Based on this characteristic of the thermistor, when the temperature of the thermistor is at room temperature, the second reference voltage is less than the voltage division value of the voltage division unit 101 and the thermistor, and the second comparator outputs a connection signal (high level) to the switch unit 106. During the process of the temperature of the thermistor changing from room temperature to overheating, the temperature of the thermistor gradually increases, and the voltage division value of the voltage division unit 101 and the thermistor gradually decreases. As time goes by, the voltage division value of the voltage division unit 101 and the thermistor will decrease to be less than the second reference voltage, indicating that the thermistor has overheated, and the second comparator will output a disconnection signal (low level) to the switch unit 106.

[0023] As one of the embodiments, the switch unit 106 is electrically connected between the power supply 104 and the thermistor. The switch unit 106 has an open state and a closed state. When the switch unit 106 is in the open state, the power supply 104 and the thermistor are electrically connected through the switch unit 106. When the switch unit 106 is in the closed state, the electrical connection between the power supply 104 and the thermistor is cut off by the switch unit 106, and at this time, the power supply 104 no longer provides voltage to the thermistor. In this embodiment, when the thermistor overheats, the switch unit 106 will respond to the disconnection signal from the second comparison unit 105 and enter the closed state to disconnect the electrical connection between the power supply 104 and the thermistor. When the thermistor does not overheat, the switch unit 106 will respond to the connection signal from the second comparison unit 105 and enter the open state to enable the electrical connection between the power supply 104 and the thermistor. Preferably, the switch unit 106 of the present application can adopt common switching devices in the art, and this embodiment will not list them one by one.

[0024] As one of the embodiments, Figure 3 is the third structural block diagram of the heating control circuit. In addition to the structures listed above, the heating control circuit further includes an MCU and an AND gate unit 107. The AND gate unit 107 is electrically connected between the switch unit 106 and the second comparison unit 105, and the MCU is electrically connected to the AND gate unit 107. During the actual heating control process of the thermal print head, when the thermal printer is performing a printing operation, the MCU can send a print start signal to the AND gate unit 107. When the thermal printer is not performing a printing operation, the MCU can send a print stop signal to the AND gate unit 107. When the AND gate unit 107 receives both the print start signal and the connection signal at the same time, it controls the switch unit 106 to electrically connect the power supply 104 and the thermal print head. When the AND gate unit 107 does not receive both the print start signal and the connection signal at the same time, it controls the switch unit 106 to disconnect the electrical connection between the power supply 104 and the thermal print head. As for the situation where the AND gate unit 107 does not receive both the print start signal and the connection signal at the same time, such as receiving the print start signal and the disconnection signal at the same time, receiving the print stop signal and the connection signal at the same time, and receiving the print stop signal and the disconnection signal at the same time, etc. It can be understood that whether the power supply 104 and the thermistor are electrically connected, that is, whether the thermistor is powered, not only depends on whether the thermistor overheats, but also depends on whether a printing operation is performed. Therefore, this embodiment also takes whether a printing operation is performed as the basis for whether the power supply 104 and the thermistor are electrically connected. Only when a printing operation is performed and the thermistor does not overheat (that is, the AND gate unit 107 receives both the print start signal and the connection signal at the same time), will the power supply 104 supply power to the thermistor to heat the thermistor.

[0025] The above embodiments are only the preferred implementations of the present application, and they are not the only limitations on the content related to the heating control circuit; in this regard, those skilled in the art can make flexible settings based on the above embodiments according to the actual application scenarios. It can be understood that through the implementation of the above embodiments of the present application, the present application can switch the voltage provided by the power supply 104 to the thermal print head between a low-temperature environment and a normal-temperature environment, that is, a high voltage is used to supply power to the thermal print head in a low-temperature environment, and a low voltage is used to supply power to the thermal print head in a normal-temperature environment. This is different from the traditional solution in which a fixed voltage is used to supply power to the thermal print head in both low-temperature and normal-temperature environments. It can not only ensure that the thermal printer can present the same printing effect in normal-temperature and low-temperature environments, but also avoid the thermal print head from overheating easily in a normal-temperature environment, improving the reliability of the circuit. In addition, when implementing the over-temperature protection of the thermal print head in the present application, it is not necessary to perform complex operations using an MCU as in the traditional solution. The response speed of the circuit is faster, and at the same time, the complex peripheral circuit of the MCU is avoided, reducing the failure rate of the circuit. It is not necessary to require the circuit designer to have a certain software foundation, and the later maintenance is simpler. Moreover, the second comparison unit 105 of the present application can use a comparator commonly used in the art, and the cost is lower than that of the MCU.

[0026] It should be noted that several embodiments shown above in the present application are described in a progressive manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts among the embodiments can be referred to each other. It should also be noted that in the text description of the present application, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply such an actual relationship or order between these entities or operations. Further, the terms "comprising", "including" or any other corresponding variant are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes these elements, but may also include other elements not explicitly listed, or may also include elements inherent to this process, method, article or device; moreover, without further limitation, an element defined by the statement "including one..." does not exclude the existence of another identical element in the process, method, article or device including the said element.

[0027] In addition, by implementing the several embodiments shown above in the present application, those skilled in the art can implement or use the present application. For the several embodiments shown above in the present application, various modifications will be obvious to those skilled in the art, and the general principles defined in the present application can be implemented in other embodiments not shown without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the several embodiments shown above, but rather to the broadest scope consistent with the principles and novel features disclosed in the present application.

Claims

1. A heating control circuit for a thermal print head, characterized in that: include: A power source, electrically connected to a thermal print head of the thermal printer, for supplying power to the thermal print head to heat the thermal print head when the thermal printer performs printing; A voltage dividing unit connected in series to a thermistor in the thermal print head; a first comparison unit, electrically connected to the voltage division unit, for accessing a first reference voltage and a voltage division value of the voltage division unit and the thermistor, and comparing the first reference voltage with the voltage division value to determine whether the thermistor is in a normal temperature environment or a low temperature environment; wherein when the thermistor is in the normal temperature environment, the first comparison unit outputs a low voltage power supply signal; when the thermistor is in the low temperature environment, the first comparison unit outputs a high voltage power supply signal; A voltage switching unit is electrically connected to the first comparing unit, and is used to respond to the low voltage power supply signal to switch the power supply of the power supply to the thermal print head to low voltage power supply, or respond to the high voltage power supply signal to switch the power supply of the power supply to the thermal print head to high voltage power supply.

2. The heating control circuit according to claim 1, characterized in that: The first reference voltage is set according to the resistance value of the thermistor in a first critical environment, the first critical environment has a first critical temperature, when the temperature of the environment in which the thermistor is located is lower than the first critical temperature, the thermistor is in the low temperature environment; when the temperature of the environment in which the thermistor is located is higher than the first critical temperature, the thermistor is in the normal temperature environment; the thermistor has a negative temperature coefficient, when the thermistor is in the low temperature environment, the first reference voltage is lower than the voltage division value; when the thermistor is in the normal temperature environment, the first reference voltage is higher than the voltage division value.

3. The heating control circuit according to claim 1, characterized in that: The first comparison unit includes a first comparator, a reverse input terminal of the first comparator is connected to the first reference voltage, a forward input terminal of the first comparator is connected to the voltage division value, and an output terminal of the first comparator is electrically connected to the voltage switching unit.

4. The heating control circuit according to claim 1, characterized in that: The power supply is configured with a feedback resistor, and the voltage switching unit switches the power supply of the power supply to the thermal print head to low voltage power supply or high voltage power supply by switching the resistance ratio of the feedback resistor.

5. The heating control circuit according to claim 4, characterized in that: The voltage switching unit includes a MOS tube, and the resistance ratio of the feedback resistor is switched by the MOS tube.

6. The heating control circuit according to claim 1, characterized in that: Also includes: a second comparison unit, electrically connected to the voltage division unit, for accessing a second reference voltage and the voltage division value, and comparing the second reference voltage with the voltage division value to determine whether the thermistor is over-temperature; wherein when the thermistor is over-temperature, the second comparison unit outputs a disconnection signal; and when the thermistor is not over-temperature, the second comparison unit outputs a connection signal; The switch unit is electrically connected to the second comparison unit, and is used for responding to the disconnection signal to disconnect the electrical connection between the power supply and the thermal print head, or responding to the connection signal to electrically connect the power supply and the thermal print head.

7. The heating control circuit according to claim 6, characterized in that: The second reference voltage is set by the resistance value of the thermistor under a second critical environment, the second critical environment has a second critical temperature, when the temperature of the thermistor is lower than the second critical temperature, the thermistor is not over-temperature; when the temperature of the thermistor is higher than the second critical temperature, the thermistor is over-temperature; the thermistor has a negative temperature coefficient, when the thermistor is over-temperature, the second reference voltage is higher than the voltage division value; when the thermistor is not over-temperature, the second reference voltage is lower than the voltage division value.

8. The heating control circuit according to claim 6, characterized in that: It also includes an MCU and an AND gate unit, wherein the AND gate unit is electrically connected between the switch unit and the second comparison unit, and the MCU is electrically connected to the AND gate unit, wherein: The MCU is used to: send a print start signal to the AND gate unit when the thermal printer is printing; or send a print stop signal to the AND gate unit when the thermal printer is not printing; The AND gate unit is used to: control the switch unit to electrically connect the power supply to the thermal print head when the print start signal and the connection signal are received at the same time; or control the switch unit to disconnect the electrical connection between the power supply and the thermal print head when the print start signal and the connection signal are not received at the same time.

9. The heating control circuit according to claim 6, characterized in that: The second comparison unit includes a second comparator, the inverting input terminal of the second comparator is connected to the second reference voltage, the positive input terminal is connected to the divided voltage value, and the output terminal of the second comparator is electrically connected to the switch unit.

10. A thermal printer, characterized in that: The invention comprises a thermal print head and a heating control circuit as claimed in any one of claims 1 to 9, wherein the heating control circuit is used for controlling the power supply to the thermal print head, so as to control the heating of the thermal print head by controlling the power supply.

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