Temperature protection circuit and electronic device

Abstract

The application discloses a temperature protection circuit and electronic equipment, the temperature protection circuit comprises a temperature detection module, which is used for outputting a detection voltage according to a heat source temperature change; a first comparison module, which is used for outputting a low level when the detection voltage is greater than a first voltage threshold and outputting a high level when the detection voltage is less than a second voltage threshold, the first voltage threshold being greater than the second voltage threshold; a second comparison module, which is used for outputting a low level when the detection voltage is less than a third voltage threshold, the third voltage threshold being less than the second voltage threshold; and a power supply control module, which is used for turning off the power supply when any comparison module outputs a low level and turning on the power supply when both comparison modules output a high level. The application can realize over-temperature shutdown, temperature recovery and temperature sensor abnormal shutdown without the participation of MCU and software, and improves the protection reliability.

Description

Technical Field

[0001] This application relates to the field of electronic technology, and in particular to a temperature protection circuit and electronic device. Background Technology

[0002] Projection equipment (especially those using LCD technology) suffers from light source efficiency loss, resulting in a significant amount of electrical energy being converted into internal heat within the optical engine. This poses a risk of thermal runaway, which can severely damage components and even cause safety accidents. Currently, the industry commonly employs two protection solutions: one involves connecting a traditional thermal protector in series in the light source power supply circuit, but its trigger and recovery temperatures are fixed, making it difficult to flexibly adapt to the heat dissipation strategies of different models; the other is a software protection solution based on analog-to-digital conversion detection by the microcontroller unit. This solution is highly dependent on the main control unit's operating status and has a protection blind spot when the main control unit is not running or has crashed. Furthermore, remote negative temperature coefficient thermistor sensors are prone to failures such as open circuits, short circuits, or connector detachment. Without effective sampling and judgment, the system may misjudge the temperature as normal, thus losing its protection function.

[0003] Therefore, the current technology needs further improvement. Summary of the Invention

[0004] The purpose of this application is to provide a temperature protection circuit and electronic device that can alleviate the technical problems of poor flexibility of thermal protectors, blind spots in software protection, and lack of effective protection when temperature sensors malfunction in current temperature protection schemes.

[0005] To achieve the above objectives, this application adopts the following technical solution: This application provides a temperature protection circuit, which is applied in an electronic device. The electronic device includes a heat source and a power supply module. The temperature protection circuit includes: Temperature detection module: The temperature detection module is used to output a corresponding detection voltage according to the temperature change of the heat source; A first comparison module is connected to a temperature detection module; the first comparison module is used to output a first level signal when the detected voltage is greater than a first voltage threshold, and to output a second level signal when the detected voltage is less than a second voltage threshold; the first voltage threshold is greater than the second voltage threshold. The second comparison module is connected to the temperature detection module; the second comparison module is used to output a second level signal when the detected voltage is greater than the third voltage threshold, and to output a first level signal when the detected voltage is less than the third voltage threshold; the third voltage threshold is less than the second voltage threshold. The power supply control module is connected to the first comparison module, the second comparison module, and the power supply module. The power supply control module is used to control the power supply of the power supply module to be disconnected when either the first comparison module or the second comparison module outputs a first level signal, and to control the power supply of the power supply module to be turned on when both the first comparison module and the second comparison module output a second level signal.

[0006] In some embodiments of the temperature protection circuit, the first comparison module includes a first comparator, a reference voltage divider unit, and a hysteresis control unit, and the output terminal of the first comparator is connected to the power supply control module. The reference voltage divider unit is connected to the non-inverting input terminal and the ground terminal of the first comparator. The reference voltage divider unit is used to provide a reference voltage to the non-inverting input terminal of the first comparator. The hysteresis control unit is connected to the non-inverting input and output of the first comparator. The hysteresis control unit is used to enable the first comparison module to have a second voltage threshold when the first comparator outputs a first level signal; and to enable the first comparison module to have a first voltage threshold when the first comparator outputs a second level signal.

[0007] In some embodiments of the temperature protection circuit, the reference voltage divider unit includes a first resistor and a second resistor. One end of the first resistor is connected to the power supply terminal, and the other end of the first resistor and one end of the second resistor are both connected to the non-inverting input terminal of the first comparator. The other end of the second resistor is grounded.

[0008] In some embodiments of the temperature protection circuit, the hysteresis control unit includes a third resistor, one end of which is connected to the non-inverting input of the first comparator, and the other end of which is connected to the output of the first comparator.

[0009] In some embodiments of the temperature protection circuit, the second comparison module includes a second comparator, a fourth resistor, and a fifth resistor. One end of the fourth resistor is connected to the power supply terminal, and the other end of the fourth resistor and one end of the fifth resistor are both connected to the inverting input terminal of the second comparator. The other end of the fifth resistor is grounded. The output terminal of the second comparator is connected to the output terminal of the first comparator, and the non-inverting input terminal of the second comparator is connected to the inverting input terminal of the first comparator.

[0010] In some embodiments of the temperature protection circuit, the power supply control module includes a sixth resistor, a seventh resistor, a first capacitor, a first switching transistor, a second switching transistor, a third capacitor, and a tenth resistor; one end of the seventh resistor is connected to the first comparator module, the other end of the seventh resistor and one end of the first capacitor are both connected to the first end of the first switching transistor, the other end of the first capacitor and the second end of the first switching transistor are both grounded, the third end of the first switching transistor is connected to the first end of the second switching transistor through the sixth resistor, the second end of the second switching transistor is connected to the power supply module, and the third end of the second switching transistor is connected to the power supply output terminal; one end of the third capacitor and one end of the tenth resistor are both connected to the first end of the second switching transistor.

[0011] In some embodiments of the temperature protection circuit, the temperature protection circuit further includes a pull-up module connected to the output terminal of the first comparator, and the pull-up module is used to pull up the output terminal of the first comparator to a preset level.

[0012] In some embodiments of the temperature protection circuit, the pull-up module includes an eighth resistor, one end of which is connected to the power supply terminal, and the other end of which is connected to the output terminal of the first comparator.

[0013] In some embodiments of the temperature protection circuit, the temperature detection module includes a thermistor, a ninth resistor, and a second capacitor. One end of the thermistor is connected to the power supply terminal, and the other end of the thermistor and one end of the ninth resistor are both connected to the first comparison module and the second comparison module. The other end of the ninth resistor and one end of the second capacitor are grounded, and the other end of the second capacitor is connected to the first comparison module and the second comparison module.

[0014] This application also provides an electronic device, which includes: a heat source, a power supply module, and a temperature protection circuit as described above.

[0015] This application provides a temperature protection circuit and electronic device. The temperature protection circuit sets independently adjustable shutdown and recovery thresholds through a first comparison module, and restores power supply only after ensuring that the heat source is sufficiently cooled, avoiding repeated switching on and off at critical temperatures. At the same time, the second comparison module detects anomalies in real time. When the temperature detection module exceeds the effective range due to open circuit or short circuit, it is immediately forcibly shut down, reducing the blind spot risk of software solutions. Thus, it balances the flexibility, reliability and anti-interference capability of temperature protection without the need for MCU intervention. Attached Figure Description

[0016] Figure 1 This is a block diagram of an existing temperature protection circuit.

[0017] Figure 2 This is a first structural block diagram of a temperature protection circuit provided in an embodiment of this application.

[0018] Figure 3 This is a second structural block diagram of the temperature protection circuit provided in the embodiments of this application.

[0019] Figure 4 This is a first circuit diagram of a temperature protection circuit provided in an embodiment of this application.

[0020] Figure 5 A second circuit diagram of a temperature protection circuit provided in an embodiment of this application.

[0021] Figure 6 The equivalent circuit diagram of the temperature protection circuit provided in the embodiment of this application, in which the first comparator outputs a first level signal and then lags back to the control unit.

[0022] Figure 7 The equivalent circuit diagram of the control unit when the first comparator outputs the second level signal in the temperature protection circuit provided in the embodiment of this application lags back to the control unit.

[0023] Figure 8 This is a schematic diagram of the structure of the thermistor in the temperature protection circuit provided in the embodiment of this application.

[0024] Figure 9 This is a schematic diagram showing the input-output relationship between the detection voltage and output voltage Vout of the first comparator in the temperature protection circuit provided in this application embodiment.

[0025] Figure 10 This is a schematic diagram showing the input-output relationship between the detection voltage and the output voltage Vout after superimposing a second comparator in the temperature protection circuit provided in the embodiments of this application.

[0026] Figure 11 This is a waveform diagram of the detection voltage, output voltage Vout, and power supply output voltage Vpwr_out in the temperature protection circuit provided in the embodiments of this application. Detailed Implementation

[0027] To make the objectives, technical solutions, and effects of this application clearer and more explicit, the following detailed description of this application is provided with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining this application and are not intended to limit this application.

[0028] Please see Figure 1 , Figure 1A circuit diagram of a conventional thermal protector application is shown. The thermal protector 11 is directly connected in series in the power supply circuit of the LED light source 12. Utilizing the difference in thermal deformation coefficients between different metals, when the temperature reaches the trigger temperature specified in the device specifications, the moving and stationary contacts disconnect due to the difference in deformation, thereby cutting off the current circuit of the LED light source 12 to stop heating and prevent further temperature increases. However, the thermal protector 11 is relatively large, requiring manual soldering. Its installation location, size, and wiring arrangement are limited by the internal space of the compact optomechanism. Its trigger and recovery temperatures are fixed by the device specifications, resulting in low accuracy, generally between a few degrees Celsius and a dozen degrees Celsius, making it difficult to flexibly adjust according to the overall structure, optomechanism temperature distribution, and recovery strategy. When the remote temperature sampling device experiences an open circuit, short circuit, or connector detachment, the thermal protector 11 itself lacks the ability to judge the validity of the sampling, which may lead to the system misjudging the temperature as normal and losing its protective function.

[0029] This application provides a temperature protection circuit and electronic device that can achieve over-temperature shutdown protection of the heat source, cooling recovery control, and failure safety protection when temperature detection is abnormal, without relying on MCU software control. The following detailed description of the temperature protection circuit and electronic device is provided in conjunction with specific embodiments.

[0030] Please see Figure 2 This application provides a temperature protection circuit for use in an electronic device. The electronic device includes a heat source 10 and a power supply module 20, which provides operating power to the heat source 10. The electronic device can be a projector, television, monitor, mobile phone, tablet computer, portable gaming device, or smart wearable device, or it can be a projection optical engine module, LED light source module, or display module. The heat source 10 can be a component in the electronic device that generates heat due to the conversion of electrical energy into heat energy, such as a light source (e.g., LED light source) in a projector, an LCD display screen, a polarizer, or optical path structural components. The power supply module 20 can be a power supply unit that provides operating power to the heat source 10, such as a DC power supply, a switching power supply, or a battery module, or it can be a power supply circuit integrated on a circuit board.

[0031] The temperature protection circuit includes a temperature detection module 100, a first comparison module 200, a second comparison module 300, and a power supply control module 400. The first comparison module 200 and the second comparison module 300 are both connected to the temperature detection module 100, and the first comparison module 200 and the second comparison module 300 are also connected to the power supply control module 400, which is also connected to the power supply module 20.

[0032] The temperature detection module 100 outputs a corresponding detection voltage based on the temperature change of the heat source 10. The detection voltage can be a sampling voltage that changes with the measured temperature, and it can be the voltage division value of a voltage divider network composed of a temperature sensing element and a fixed resistor. For example, the temperature sensing element can be a negative temperature coefficient thermistor (NTC), whose resistance decreases as temperature increases, thus causing the detection voltage output by the voltage divider network to increase with temperature. Alternatively, the temperature sensing element can be a positive temperature coefficient thermistor (PTC), whose resistance increases with temperature; in this case, the detection voltage can be increased with temperature by adjusting the connection method of the voltage divider network.

[0033] The first comparison module 200 is used to output a first level signal when the detected voltage Vs is greater than a first voltage threshold VH, and to output a second level signal when the detected voltage Vs is less than a second voltage threshold VL. The first voltage threshold VH is greater than the second voltage threshold VL. The first voltage threshold can be an upper limit threshold for triggering over-temperature protection, i.e., an over-temperature trigger threshold; the second voltage threshold can be a lower limit threshold for releasing over-temperature protection, i.e., a cooling recovery threshold; the first level signal can be a low-level signal indicating that power supply needs to be shut off, and the second level signal can be a high-level signal indicating that power supply is allowed to be turned on.

[0034] The second comparison module 300 is used to output a second-level signal when the detection voltage Vs is greater than a third voltage threshold, and to output a first-level signal when the detection voltage Vs is less than the third voltage threshold. The third voltage threshold is less than the second voltage threshold. The third voltage threshold can be a lower validity threshold used to determine whether the temperature sampling is valid; it can be set to be greater than the detection voltage when the temperature sampling path fails (e.g., NTC is open-circuited) and less than the detection voltage corresponding to the lowest normal operating temperature of the electronic device.

[0035] The power supply control module 400 is used to control the power supply of the power supply module 20 to be disconnected when either the first comparison module 200 or the second comparison module 300 outputs a first level signal; and to control the power supply of the power supply module 20 to be turned on when both the first comparison module 200 and the second comparison module 300 output a second level signal.

[0036] Specifically, when the temperature of the heat source 10 is within the normal range, the detection voltage is between the third voltage threshold and the first voltage threshold. The first comparison module 200 outputs a second level signal, and the second comparison module 300 also outputs a second level signal. The power supply control module 400 controls the power supply of the power supply module 20 to be turned on, and the heat source 10 works normally.

[0037] When the temperature of heat source 10 rises, causing the detection voltage to rise and exceed the first voltage threshold, the first comparison module 200 outputs a first-level signal. The power supply control module 400 controls the power supply module 20 to disconnect, the heat source 10 stops heating or its heating power decreases, and the temperature gradually drops, thereby preventing thermal runaway. Since the first voltage threshold is greater than the second voltage threshold, when the temperature drops to below the second voltage threshold, the first comparison module 200 resumes outputting the second-level signal, and the power supply control module 400 controls the power supply module 20 to turn on, allowing the heat source 10 to resume normal operation. In other words, the threshold corresponding to over-temperature shutdown (first voltage threshold VH) is different from the threshold corresponding to cooling recovery (second voltage threshold VL), with VH being higher than VL. This creates a hysteresis window, preventing repeated power supply interruptions when the temperature fluctuates near the shutdown threshold. It also avoids switching jitter caused by circuit noise interference, ensuring that the equipment cools down to a safe temperature before power is restored.

[0038] When an abnormality occurs in the temperature sampling path, such as a short circuit in the temperature detection element of the temperature detection module 100, causing the detection voltage to approach the supply voltage and exceed the first voltage threshold, the first comparison module 200 outputs a first-level signal, the power supply is shut off, and the system is in a safe state. Conversely, if the temperature detection element is open-circuited, the detection voltage is pulled down to near 0V, below the third voltage threshold, the second comparison module 300 outputs a first-level signal, the power supply is also shut off, and the system enters a safe state. Therefore, regardless of whether temperature sampling is normal or not, as long as there is a risk of over-temperature or sampling failure, the power supply control module 400 will shut off the power supply, achieving fail-safe operation. Fail-safe operation can be a protection mechanism whereby the circuit automatically enters a preset safe state (e.g., shutting down the controlled power supply path) under abnormal conditions such as an open circuit or short circuit in the temperature detection element, abnormal control signal, or unstable power supply.

[0039] The temperature protection circuit provided in this embodiment defines a temperature protection window using a third voltage threshold as the lower limit and a first voltage threshold as the upper limit. Power supply is allowed when the detected voltage falls within this window, and power supply is cut off when it exceeds this window (above the upper limit or below the lower limit). The second voltage threshold used to restore conduction is located inside this window and is lower than the first voltage threshold, making the trigger boundary and recovery boundary asymmetrical. This temperature protection circuit can be called an asymmetrical window-type temperature protection circuit. An asymmetrical window can be a protection window defined by an over-temperature trigger threshold (first voltage threshold) and a lower limit effectiveness threshold (third voltage threshold) as the upper and lower boundaries, respectively, with the cooling recovery threshold (second voltage threshold) located within this window and lower than the over-temperature trigger threshold, thus creating an asymmetrical voltage (temperature) boundary between the trigger condition and the recovery condition.

[0040] In this embodiment, the temperature protection circuit sets independently adjustable shutdown and recovery thresholds through the first comparison module 200. Power is restored only after the heat source 10 has been sufficiently cooled, avoiding repeated switching on and off at critical temperatures. At the same time, the second comparison module 300 detects anomalies in real time. When the temperature detection module 100 exceeds the effective range due to open circuit or short circuit, it is immediately forcibly shut down, reducing the blind spot risk of the software solution. Thus, the circuit balances the flexibility, reliability, and anti-interference capability of temperature protection without the need for MCU intervention.

[0041] Please see Figure 3 In some embodiments, the first comparison module 200 includes a first comparator U1, a reference voltage divider unit 210, and a hysteresis control unit 220, and the output of the first comparator U1 is connected to the power supply control module 400.

[0042] The reference voltage divider unit 210 is connected to the non-inverting input terminal and the ground terminal of the first comparator U1. The reference voltage divider unit 210 is used to provide a reference voltage to the non-inverting input terminal of the first comparator U1. The hysteresis control unit 220 is connected to the non-inverting input terminal and the output terminal of the first comparator U1. The hysteresis control unit 220 is used to enable the first comparison module 200 to have a second voltage threshold when the first comparator U1 outputs a first level signal; and to enable the first comparison module 200 to have a first voltage threshold when the first comparator U1 outputs a second level signal.

[0043] The inverting input of the first comparator U1 is connected to the temperature detection module 100 to receive the detected voltage. When the detected voltage is greater than the reference voltage at the non-inverting input, the first comparator U1 outputs a low level (i.e., a first level signal); when the detected voltage is less than the reference voltage at the non-inverting input, the first comparator U1 outputs a high level (i.e., a second level signal). Since the hysteresis control unit 220 is connected between the non-inverting input and the output, forming a positive feedback loop, the reference voltage at the non-inverting input changes with the output state of the first comparator U1: when the output is high, the positive feedback raises the reference voltage to the first voltage threshold (VH); when the output is low, the positive feedback lowers the reference voltage to the second voltage threshold (VL). Thus, the first comparator module 200 outputs a low level (over-temperature shutdown) when the detected voltage is greater than VH, and only resumes outputting a high level (cooling recovery) when the detected voltage is less than VL. The difference between VH and VL is the hysteresis width. Without hysteresis (i.e., VH=VL), when the temperature repeatedly crosses the threshold near the shutdown point due to heat dissipation fluctuations or noise interference, the power supply will be repeatedly switched on and off. Frequent switching of the switching devices will not only cause switching bounce and noise, but also accelerate device wear and tear and affect the user experience. With hysteresis, once the power supply is turned off, it will not be restored until the temperature drops below the safe temperature of VL. This reduces the risk of repeated switching on and off and ensures that the device operates within the safe temperature range.

[0044] Please see Figure 4 In one embodiment, the reference voltage divider unit 210 includes a first resistor R1 and a second resistor R2. One end of the first resistor R1 is connected to the power supply terminal, and the other end of the first resistor R1 and one end of the second resistor R2 are both connected to the non-inverting input terminal of the first comparator U1. The other end of the second resistor R2 is grounded. The first resistor R1 and the second resistor R2 form a series voltage divider network, and the voltage divider node is connected to the non-inverting input terminal of the first comparator U1. The power supply voltage is divided to provide a reference voltage to the non-inverting input terminal. By adjusting the resistance ratio of the first resistor R1 and the second resistor R2, the static operating point of the reference voltage can be adjusted, thereby shifting the hysteresis window as a whole and achieving coarse adjustment of the protection temperature range.

[0045] As one embodiment, the hysteresis control unit 220 includes a third resistor R3, one end of which is connected to the non-inverting input terminal of the first comparator U1, and the other end of the third resistor R3 is connected to the output terminal of the first comparator U1.

[0046] The third resistor R3 serves as a positive feedback resistor, with one end connected to the voltage divider node and the other end connected to the output of the first comparator U1. When the output is high, the third resistor R3 injects current into the voltage divider node, raising the reference voltage at the non-inverting input to the first voltage threshold. When the output is low, the third resistor R3 draws current from the voltage divider node, pulling the reference voltage at the non-inverting input down to the second voltage threshold. By adjusting the value of the third resistor R3, the difference between VH and VL can be adjusted, i.e., the hysteresis width can be adjusted; a larger resistance value results in a smaller hysteresis width, and a smaller resistance value results in a larger hysteresis width. In practical applications, the hysteresis width is usually determined comprehensively based on the allowable temperature fluctuation range, noise level, and allowable switching frequency of the switching devices; this application does not impose specific limitations on this.

[0047] In this embodiment, the first comparison module 200 adopts a hysteresis comparator structure, which can automatically complete over-temperature shutdown and cooling recovery without the participation of MCU. The trigger threshold and recovery threshold can be flexibly adjusted through the hysteresis control unit 220. The reference voltage divider unit 210 uses only two resistors, which is simple in structure and low in cost. The hysteresis window level can be easily set by adjusting its resistance value. The hysteresis control unit 220 uses only one feedback resistor, which is the simplest to implement. The hysteresis width can be independently adjusted by adjusting its resistance value, which is convenient for adapting to the optomechanical temperature distribution and heat dissipation strategy of different models.

[0048] In some embodiments, the second comparison module 300 includes a second comparator U2, a fourth resistor R4, and a fifth resistor R5. One end of the fourth resistor R4 is connected to the power supply terminal, and the other end of the fourth resistor R4 and one end of the fifth resistor R5 are both connected to the inverting input terminal of the second comparator U2. The other end of the fifth resistor R5 is grounded. The output terminal of the second comparator U2 is connected to the output terminal of the first comparator U1, and the non-inverting input terminal of the second comparator U2 is connected to the inverting input terminal of the first comparator U1.

[0049] Therefore, the fourth resistor R4 and the fifth resistor R5 form a series voltage divider network. The voltage divider node is connected to the inverting input of the second comparator U2, providing a third voltage threshold (i.e., the lower limit validity threshold) to the inverting input. The non-inverting input of the second comparator U2 receives the detected voltage. When the detected voltage is greater than the third voltage threshold, the second comparator U2 outputs a high level (second level signal); when the detected voltage is less than the third voltage threshold, the second comparator U2 outputs a low level (first level signal). Since the output of the second comparator U2 is directly connected to the output of the first comparator U1, when either comparator outputs a low level, their common output node is pulled low, and the power supply control module 400 shuts off the power supply. In other words, the second comparator module 300 performs hardware-level monitoring of the validity of the temperature sampling path. Once the detected voltage is abnormally low, it determines that the sampling has failed or the temperature is too low, and immediately shuts off the power supply.

[0050] In this embodiment, the third voltage threshold is set to be greater than the detection voltage when the temperature sampling path fails (e.g., the detection voltage is pulled down to 0V when the temperature detection module 100 is open-circuited), and less than the detection voltage corresponding to the lowest normal operating temperature of the device. For example, when the lowest normal operating temperature of the electronic device is -10℃, the third voltage threshold can be set to a value greater than 0V and less than the detection voltage corresponding to -10℃ (e.g., 0.76V), specifically, 0.5V. With this setting, within the normal operating temperature range of the device (e.g., -10℃ to 110℃), the detection voltage is always greater than the third voltage threshold, and the second comparator U2 always outputs a high level, without affecting normal power supply; however, when the NTC fails in an open-circuit or short-circuit condition, the detection voltage drops to near 0V, less than the third voltage threshold, and the second comparator U2 immediately outputs a low level, shutting off the power supply. This avoids the problem of the system misjudging abnormal temperatures as normal temperatures and losing its protection function when the remote sensor fails.

[0051] Understandably, when the NTC is short-circuited, the detected voltage is close to the supply voltage and exceeds the first voltage threshold. At this time, the first comparator module 200 outputs a low level to shut off the power supply, and the system remains in a safe state. Conversely, when the NTC is open-circuited, the detected voltage is 0V, and the second comparator module 300 outputs a low level to shut off the power supply. Therefore, regardless of whether the NTC is short-circuited or open-circuited, the temperature protection circuit can reliably shut off the power supply, achieving failover safety.

[0052] In this embodiment, independent hardware monitoring of the effectiveness of the temperature sampling path can be achieved through the second comparator U2 and two voltage divider resistors. The structure is simple and the cost is low. When the remote NTC sensor is open-circuited, the circuit can automatically enter the safe shutdown state, eliminating the protection blind spot caused by sensor failure in the existing solution and significantly improving the reliability of the system.

[0053] Please continue reading. Figure 4 In some embodiments, the power supply control module 400 includes a sixth resistor R6, a seventh resistor R7, a first capacitor C1, a first switch Q1, a second switch Q2, a third capacitor C3, and a tenth resistor R10; one end of the seventh resistor R7 is connected to the first comparison module 200, and the other end of the seventh resistor R7 and one end of the first capacitor C1 are both connected to the first end of the first switch Q1. The other end of the first capacitor C1 and the second end of the first switch Q1 are both grounded. The third end of the first switch Q1 is connected to the first end of the second switch Q2 through the sixth resistor R6. The second end of the second switch Q2 is connected to the power supply module 20, and the third end of the second switch Q2 is connected to the power supply output terminal; one end of the third capacitor C3 and one end of the tenth resistor R10 are both connected to the first end of the second switch Q2.

[0054] The first switching transistor Q1 can be an N-channel MOSFET, with its first terminal being the gate, the second terminal being the source, and the third terminal being the drain. The output terminals of the first comparator U1 and the second comparator U2 serve as a common control signal node, connected to the gate of the first switching transistor Q1 via the seventh resistor R7. The seventh resistor R7 acts as a gate current-limiting resistor, used to limit the gate drive current and suppress ringing. The first capacitor C1 is connected in parallel between the gate and the source of the first switching transistor Q1, used to filter out high-frequency interference in the gate drive signal and to provide a soft-start effect during the gate voltage establishment process.

[0055] The second switch Q2 can be a P-channel MOSFET, which acts as the main switch for power supply on / off. The first switch Q1 is the driver. When the common control signal node is high, the first switch Q1 is turned on, and the control node is pulled low to near ground potential. The gate-source voltage of the second switch Q2 is approximately the negative of the controlled power supply input voltage, and its absolute value is greater than the turn-on threshold voltage of the second switch Q2. The second switch Q2 is turned on, and the power supply module 20 supplies power to the heat source 10. When the common control signal node is low, the first switch Q1 is turned off, and the common control signal node is pulled up to near the controlled power supply input voltage through the sixth resistor R6. The gate-source voltage of the second switch Q2 is close to 0V, and the second switch Q2 is turned off. The power supply module 20 stops supplying power to the heat source 10.

[0056] In this embodiment, the comparator output has limited driving capability. If it directly drives the high-power main switch, it may cause losses and interference due to insufficient driving current or excessive switching speed. However, the small signal transistor (first switch transistor Q1) first performs level conversion and amplification, and then drives the main switch transistor (second switch transistor Q2). The two-stage switching structure of first switch transistor Q1 driving second switch transistor Q2 can achieve reliable power supply on / off control with less driving power consumption. At the same time, the switching speed can be regulated by the cooperation of gate resistor and capacitor, and electromagnetic interference can be suppressed.

[0057] In some embodiments, the temperature protection circuit further includes a pull-up module 500, which is connected to the output of the first comparator U1. The pull-up module 500 is used to pull up the output of the first comparator U1 to a preset level. Specifically, the pull-up module 500 includes an eighth resistor R8, one end of which is connected to the power supply terminal, and the other end of which is connected to the output of the first comparator U1.

[0058] In this embodiment, the output stages of the first comparator U1 and the second comparator U2 can adopt an open-drain output structure. An open-drain output can be an output structure where the output stage of a comparator (or other device) is led out only by the open drain of the switching transistor and lacks internal pull-up capability; it requires an external pull-up resistor to form a high level at the output terminal. When both the first comparator U1 and the second comparator U2 adopt an open-drain output structure, their output terminals can be directly connected and pulled up to the power supply terminal together through the eighth resistor R8, forming a wired-AND logic. A wired-AND logic can be a logic connection method where multiple open-drain output terminals are directly shorted and connected to the power supply through a pull-up resistor. This is equivalent to a logic AND: when any output terminal outputs a low level, the common node is pulled low; only when all output terminals are in a high-impedance (off) state is the common node pulled up to a preset level (high level).

[0059] Since the outputs of the first comparison module 200 and the second comparison module 300 are connected to the same control node (common control signal node) via wired-AND logic, when the first comparison module 200 outputs a low level due to over-temperature or the second comparison module 300 outputs a low level due to sampling failure, this control node is pulled low, and the power supply control module 400 shuts off the controlled power supply path. Only when both output a high level does the control node remain high, and the power supply is turned on. Therefore, the fail-safe logic of shutting off due to any abnormality can be implemented using hardware wiring, without any software intervention, resulting in high reliability.

[0060] Please see Figure 5 As another embodiment, if the selected comparator is a push-pull output structure, a direct wired-AND connection cannot be performed. Instead, a diode (such as diode D1 and diode D2) can be connected in series at the output terminals of the first comparator U1 and the second comparator U2, respectively, before connecting them. The unidirectional conduction characteristic of the diodes isolates the output terminals, preventing abnormal current sinking when one comparator outputs a high level while the other outputs a low level, thus achieving an equivalent wired-AND logic. Diodes D1 and D2 should ideally be selected with low on-state voltage drop. The voltage drop of D1 needs to be considered in the calculation of the feedback circuit parameters at the non-inverting input of U1 and the selection of the on-state voltage of Q2.

[0061] In this embodiment, the pull-up module 500 uses only one resistor to ensure that the common control signal node in the open-drain output structure has a clear effective level. The circuit is simple and low in cost. By forming a wired-AND logic with the pull-up resistor and the open-drain output, a hardware failure safety mechanism of "shutdown upon any abnormality" is realized, which does not require software intervention and has high reliability. At the same time, adjusting the resistance value of the eighth resistor R8 can adjust the pull-up level and pull-up strength of the control node, which is convenient for matching with the driving requirements of the subsequent switching circuit.

[0062] Please see Figure 6 and Figure 7 To facilitate understanding of the upper limit hysteresis characteristic of the first comparison module 200, the following is combined with... Figure 6 and Figure 7 This describes the equivalent circuit of the non-inverting input terminal (reference voltage divider node Vref_H) of the first comparator U1 in two output states.

[0063] When the output of the first comparator U1 is low, the output potential of the first comparator U1 is close to 0V. Since one end of the third resistor R3 (hysteresis positive feedback resistor) is connected to the output of the first comparator U1, its other end is equivalent to ground in this state. At this time, the component connections on the reference voltage divider node Vref_H are as follows: one end of the first resistor R1 is connected to the power supply (+5V), and the other end is connected to the reference voltage divider node Vref_H; one end of the second resistor R2 is connected to the reference voltage divider node Vref_H, and the other end is grounded; one end of the third resistor R3 is connected to the reference voltage divider node Vref_H, and the other end is equivalent to grounded because the output is 0V. Therefore, the second resistor R2 and the third resistor R3 form a parallel grounded branch at the reference voltage divider node, and the first resistor R1 is a pull-up branch.

[0064] When the first comparator U1 outputs a high level, the output voltage of the first comparator U1 is pulled up to near +5V by the eighth resistor R8 (open-drain pull-up resistor). Since the other end of the third resistor R3 is connected to the output, this end is effectively connected to +5V. The component connections at the reference voltage divider node Vref_H become: one end of the first resistor R1 is connected to +5V, and the other end is connected to the reference voltage divider node Vref_H; one end of the second resistor R2 is connected to the reference voltage divider node Vref_H, and the other end is grounded; one end of the third resistor R3 is connected to the reference voltage divider node Vref_H, and the other end is connected to +5V via the eighth resistor R8. Therefore, the first resistor R1 and the eightth resistor R8 and the third resistor R3 form two pull-up branches in parallel at Vref_H, pulling up to +5V, while the second resistor R2 is the only grounded branch.

[0065] As one embodiment, the temperature detection module 100 includes a thermistor R0, a ninth resistor R9, and a second capacitor C2. One end of the thermistor R0 is connected to the power supply terminal, and the other end of the thermistor R0 and one end of the ninth resistor R9 are both connected to the first comparison module 200 and the second comparison module 300. The other end of the ninth resistor R9 and one end of the second capacitor C2 are grounded, and the other end of the second capacitor C2 is connected to the inverting input terminal of the first comparator U1.

[0066] The thermistor R0 can be a negative temperature coefficient thermistor, whose resistance decreases as temperature increases. The thermistor and the ninth resistor R9 form a voltage divider network. Thermistor R0 is located on the upper arm of the voltage divider network (closer to the power supply side), and the ninth resistor R9 is located on the lower arm (closer to the ground side). The connection point between them is the sampling node, and the voltage at the sampling node is the detection voltage. When the temperature rises, the thermistor resistance decreases, the voltage division ratio changes, and the detection voltage increases; conversely, when the temperature decreases, the detection voltage decreases. By changing the selection of the thermistor (e.g., different resistance values) and adjusting the resistance of the ninth resistor R9, the voltage division ratio and the range of change of the detection voltage can be adjusted to adapt to different protection temperature settings. The second capacitor C2 is connected in parallel between the sampling node and the ground terminal to filter out high-frequency interference in the detection voltage and ensure the stability of the threshold comparison.

[0067] Please see Figure 8 In one embodiment, the thermistor R0 includes a thermistor terminal 1, a transmission line 2, and a connection terminal 3. Thermistor terminal 1 can be flexibly placed inside the optomechanical cavity or close to special detection points such as LED light sources and LCD displays to sense the temperature of the target area. The sensed temperature signal is output through transmission line 2 and then directly connected to the main board of the first comparator module 200, the second comparator module 300, and the power supply control module 400 via connection terminal 3, which is equivalent to thermistor R0 in the temperature protection circuit. It should be noted that connection terminal 3 can be set with two pins, one pin connected to the power supply terminal (e.g., +5V) and the other pin connected to the ninth resistor R9. When the detected temperature exceeds the set threshold, the hardware circuit directly cuts off the power supply output without the need for MCU or software judgment, thereby effectively preventing thermal runaway in the back end. This solution allows for precise setting of the protection temperature, flexible placement of the thermistor terminal 1, convenient adjustment of circuit parameters, and does not rely on software control. Combined with fail-safe design, it has high reliability.

[0068] Please refer to the following: Figure 9 , Figures 10 to 11 To illustrate the structure of this temperature protection circuit in detail, the following specific embodiments are provided for further explanation: In this embodiment, the over-temperature trigger protection temperature is 110℃, the cooling recovery temperature is 90℃, and the low temperature limit temperature is -10℃, which covers the normal operating temperature range of the equipment. When the temperature exceeds the above-mentioned normal operating range and triggers the corresponding limit threshold, the circuit performs shutdown protection.

[0069] The ninth resistor R9 can be a fixed resistor with a resistance of 10kΩ; the thermistor can be an NTC device with a resistance of 10kΩ and a B value of 3950K at room temperature (25℃); the comparator power supply voltage can be 5V.

[0070] According to the resistance-temperature characteristics of NTC devices, the following table shows that: at 110℃, the NTC resistance is 500Ω, and the calculated detection voltage is 5V×10kΩ / (500Ω+10kΩ)≈4.76V, which is recorded as the first voltage threshold VH; at 90℃, the NTC resistance is 904Ω, and the calculated detection voltage is 5V×10kΩ / (904Ω+10kΩ)≈4.59V, which is recorded as the second voltage threshold VL; at -10℃, the NTC resistance is 55.6kΩ, and the calculated detection voltage is 5V×10kΩ / (55.6kΩ+10kΩ)≈0.76V. This value is the upper limit of the reference for setting the third voltage threshold (lower limit validity threshold). The third voltage threshold can be set to a value greater than 0V and less than 0.76V.

[0071] In this example, the resistance values ​​of the second resistor R2 and the eighth resistor R8 are preset to 100kΩ. Based on this, the resistance values ​​of the first resistor R1 and the third resistor R3 are calculated.

[0072] Please continue reading. Figure 9 When the detected voltage is VL (4.59V), the output Vout of the first comparator U1 is approximately 0V, and it initiates a transition to a logic high level. At this time, according to Kirchhoff's current law, the node current equation for the non-inverting input of the first comparator U1 is: the current flowing through the first resistor R1 is equal to the sum of the current flowing through the second resistor R2 and the current flowing through the third resistor R3, that is: (5V-4.59V) / R1=4.59V / 100kΩ+4.59V / R4, denoted as Formula 1.

[0073] When the detected voltage is VH (4.76V), the output of the first comparator U1 is approximately 5V, and it initiates a transition to a logic low level. At this time, the eighth resistor R8 and the third resistor R3 are connected in series between the non-inverting input node and the power supply (i.e., the pull-up path is injected into the node through the eighth resistor R8 and the third resistor R3). The node current equation for the non-inverting input node is: the sum of the current flowing through the first resistor R1 and the current flowing through the series branch of the eighth resistor R8 and the third resistor R3 is equal to the current flowing through the second resistor R2, that is: (5V-4.76V) / R1+(5V-4.76V) / (100kΩ+R4)=4.76V / 100kΩ, denoted as Formula 2.

[0074] Solving the equations simultaneously using Formula 1 and Formula 2, we get: R3≈136.3kΩ, R1≈5.15kΩ. Matching commonly used resistor nominal values, we select R3=137kΩ and R1=5.15kΩ respectively. Substituting these values ​​into the above formulas for re-verification, we obtain VL≈4.591V and VH≈4.760V, which are basically consistent with the design target and meet the design requirements.

[0075] Based on the above parameters, the temperature protection process in this example is as follows: When the target device temperature rises to 110℃, the NTC resistance drops to 500Ω, the detection voltage rises to 4.76V, and the voltage at the inverting input of the first comparator U1 is about to exceed the reference voltage at the non-inverting input. The output of U1 changes from high to low, and through the wired-AND logic and switching circuit, the main switch is turned off, thereby cutting off the power supply to the target device and preventing further temperature rise. When the target device temperature drops back to 90℃, the NTC resistance rises to 904Ω, the detection voltage drops to 4.59V, and the voltage at the inverting input of the first comparator U1 is about to fall below the reference voltage at the non-inverting input. The output of U1 changes from low to high, the main switch is turned on again, and the power supply is restored. During this process, if the NTC circuit is open, the detection voltage drops to 0V, below the third voltage threshold, and the second comparator U2 outputs a low level, similarly cutting off the power supply to ensure safety in case of failure.

[0076] The second comparator U2 does not require hysteresis. Its main function is to implement temperature detection failure protection, which reduces circuit complexity, saves costs, and facilitates practical application. Given that Vs = 0.76V at -10℃, the reference voltage Vref_L at the inverting input of U2 is designed to be around 0.76V. Using R4 = 270kΩ and R5 = 49kΩ, Vref_L = (5*49) / (270+49) ≈ 0.768V. When the temperature drops to -10℃, Vs < 0.768V, meaning the non-inverting input voltage of U2 is less than the inverting input voltage. U2 outputs low, and after a logical AND with the high level output of U1 (open-drain output), the common control node Vout remains low. The main switch shuts off the power supply to the subsequent stage, entering a protection state (abnormal failure protection or low-temperature operation protection). When the fault is cleared or the temperature rises above -10℃, and Vs > 0.768V, the power supply to the subsequent stage is restarted.

[0077] Please continue reading. Figure 10 Based on the input and output states of U1 and U2 mentioned above, the overall circuit in this embodiment has the following input-output relationship between the detection voltage Vs and the common control node Vout: Vref_L = 0.768V, VL = 4.591V, VH = 4.760V, corresponding to temperature detection values ​​of approximately -10℃, 90℃, and 110℃, respectively. It can be clearly seen that when the temperature is below -10℃ or above 110℃, or when the temperature detection section experiences an abnormal failure (short circuit or open circuit), the common control node Vout outputs a low level, thus disconnecting the power supply to the subsequent stage and entering a protection state; when the temperature drops below 90℃ but above -10℃, Vout outputs a high level, the power supply to the subsequent stage is turned on, and the equipment resumes normal operation.

[0078] Please see Figure 11The green waveform represents Vs, the blue waveform represents Vout, and the red waveform represents PWR_OUT. When Vs rises to around 4.76V, it triggers Vout to output a low level, thus turning off PWR_OUT. When Vs drops to around 4.59V, it triggers Vout to output a high level, thus turning on PWR_OUT. When Vs further drops to around 0.76V, PWR_OUT turns off again. When Vs rises back above 0.76V, PWR_OUT turns back on.

[0079] The temperature protection circuit in this application forms an asymmetric window through upper limit hysteresis comparison and lower limit validity comparison. At the same time, the circuit is designed with corresponding failure protection measures, so that the light source is only allowed to be powered when the detection voltage is within the effective range. It does not rely on the main control software, the disconnection threshold and recovery threshold can be configured according to the target temperature, and it is suitable for compact space layout.

[0080] This application also provides an electronic device, which includes a heat source, a power supply module, and a temperature protection circuit according to any of the above embodiments. The temperature protection circuit is connected to both the heat source and the power supply module, and is used to control the switching on and off of power supply from the power supply module to the heat source based on temperature changes in the heat source.

[0081] In this embodiment, the electronic device can be a projection device, which may include an optical engine, also known as an optical imaging module in a projection display device. The optical engine typically includes a light source, optical components along the optical path, a display chip, and a heat dissipation structure. The heat source can be a light source (such as an LED light source) or a heat-generating component like the display chip within the optical engine. The power supply module can be a light source driver that supplies power to the light source. The thermistor in the temperature detection module of the temperature protection circuit can be placed in a specific detection location, such as inside the optical engine cavity or near the light source, to perform point-to-point monitoring of the internal temperature of the optical engine. Due to the compact internal space and uneven temperature distribution of the optical engine, the temperature protection circuit of this application can reliably shut off the power supply to the light source based on the actual internal temperature of the optical engine without relying on the main control software, preventing thermal runaway of the optical engine and thus avoiding safety accidents such as device deformation and fire.

[0082] Electronic devices can also be televisions, monitors, mobile phones, tablets, portable gaming devices, smart wearable devices, in-vehicle devices, and other electronic devices that contain heat sources and require temperature protection; this application does not limit the scope of such devices.

[0083] The electronic device in this application integrates the aforementioned temperature protection circuit, enabling over-temperature shutdown, cooling recovery, and sensor malfunction shutdown without MCU software intervention. It reliably protects the heat source and prevents thermal runaway even when the main control unit is not running, crashes, or experiences software malfunctions, significantly improving the device's safety, reliability, and lifespan. Furthermore, the flexible configurability of the protection threshold allows it to adapt to the heat dissipation strategies and structural layouts of different models. Since the temperature protection circuit has been described in detail above, it will not be repeated here.

[0084] The temperature protection circuit and electronic device provided in the embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the technical solutions and core ideas of this application. Those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A temperature protection circuit, characterized in that, The temperature protection circuit is used in an electronic device, which includes a heat source and a power supply module. The temperature protection circuit includes: A temperature detection module, which outputs a corresponding detection voltage based on the temperature change of the heat source; A first comparison module is connected to the temperature detection module; the first comparison module is used to output a first level signal when the detection voltage is greater than a first voltage threshold, and to output a second level signal when the detection voltage is less than a second voltage threshold; the first voltage threshold is greater than the second voltage threshold. A second comparison module is connected to the temperature detection module; the second comparison module is used to output a second level signal when the detection voltage is greater than a third voltage threshold, and to output a first level signal when the detection voltage is less than the third voltage threshold; the third voltage threshold is less than the second voltage threshold. A power supply control module is connected to the first comparison module, the second comparison module, and the power supply module. The power supply control module is used to control the power supply of the power supply module to be disconnected when either the first comparison module or the second comparison module outputs the first level signal, and to control the power supply of the power supply module to be turned on when both the first comparison module and the second comparison module output the second level signal.

2. The temperature protection circuit according to claim 1, characterized in that, The first comparison module includes a first comparator, a reference voltage divider unit, and a hysteresis control unit, and the output of the first comparator is connected to the power supply control module; The reference voltage divider unit is connected to the non-inverting input terminal and the ground terminal of the first comparator. The reference voltage divider unit is used to provide a reference voltage to the non-inverting input terminal of the first comparator. The hysteresis control unit is connected to the non-inverting input and output of the first comparator. The hysteresis control unit is used to enable the first comparison module to have the second voltage threshold when the first comparator outputs the first level signal; and to enable the first comparison module to have the first voltage threshold when the first comparator outputs the second level signal.

3. The temperature protection circuit according to claim 2, characterized in that, The reference voltage divider unit includes a first resistor and a second resistor. One end of the first resistor is connected to the power supply terminal, and the other end of the first resistor and one end of the second resistor are both connected to the non-inverting input terminal of the first comparator. The other end of the second resistor is grounded.

4. The temperature protection circuit according to claim 2, characterized in that, The hysteresis control unit includes a third resistor, one end of which is connected to the non-inverting input of the first comparator, and the other end of which is connected to the output of the first comparator.

5. The temperature protection circuit according to claim 2, characterized in that, The second comparison module includes a second comparator, a fourth resistor, and a fifth resistor. One end of the fourth resistor is connected to the power supply terminal, and the other end of the fourth resistor and one end of the fifth resistor are both connected to the inverting input terminal of the second comparator. The other end of the fifth resistor is grounded. The output terminal of the second comparator is connected to the output terminal of the first comparator, and the non-inverting input terminal of the second comparator is connected to the inverting input terminal of the first comparator.

6. The temperature protection circuit according to claim 1, characterized in that, The power supply control module includes a sixth resistor, a seventh resistor, a first capacitor, a first switching transistor, a second switching transistor, a third capacitor, and a tenth resistor. One end of the seventh resistor is connected to the first comparison module. The other end of the seventh resistor and one end of the first capacitor are both connected to the first end of the first switching transistor. The other end of the first capacitor and the second end of the first switching transistor are both grounded. The third end of the first switching transistor is connected to the first end of the second switching transistor through the sixth resistor. The second end of the second switching transistor is connected to the power supply module and to the power supply output terminal. One end of the third capacitor and one end of the tenth resistor are both connected to the first end of the second switching transistor.

7. The temperature protection circuit according to claim 2, characterized in that, The temperature protection circuit also includes a pull-up module, which is connected to the output of the first comparator and is used to pull up the output of the first comparator to a preset level.

8. The temperature protection circuit according to claim 7, characterized in that, The pull-up module includes an eighth resistor, one end of which is connected to the power supply terminal, and the other end of which is connected to the output terminal of the first comparator.

9. The temperature protection circuit according to claim 1, characterized in that, The temperature detection module includes a thermistor, a ninth resistor, and a second capacitor. One end of the thermistor is connected to the power supply terminal, and the other end of the thermistor and one end of the ninth resistor are both connected to the first comparison module and the second comparison module. The other end of the ninth resistor and one end of the second capacitor are grounded, and the other end of the second capacitor is connected to the first comparison module and the second comparison module.

10. An electronic device, characterized in that, The electronic device includes: a heat source, a power supply module, and a temperature protection circuit as described in any one of claims 1 to 9.

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