Safety heating circuit and electric blanket equipped with this circuit

Abstract

This invention provides a safe heating circuit, comprising: a PTC heating element that generates heat when energized; a first switching element coupled to the grounding circuit of the PTC heating element and configured to connect or disconnect the power supply circuit of the PTC heating element based on a switching control signal; a first voltage acquisition circuit for sampling a first temperature voltage based on the grounding current of the PTC heating element; an NTC element disposed between the PTC heating element and a sensing element; a sensing element for receiving leakage current from the PTC heating element conducted by the NTC element; a second voltage acquisition circuit for sampling a second temperature voltage based on the leakage current; and a controller configured to compare the first temperature voltage or the second temperature voltage with a set temperature voltage and output the switching control signal based on the comparison result. This safe heating circuit can accurately control the heating temperature and promptly detect faults and cut off the power supply to ensure user safety.

Description

Technical Field

[0001] This invention relates to electric heating and heat preservation equipment, and more particularly to a safe heating circuit and an electric blanket equipped with the circuit. Background Technology

[0002] Electric blankets are common household appliances, mainly used to raise the temperature inside the blankets while people sleep for warmth. They consume little electricity, have adjustable temperature, are easy to use, and are widely used, with a history of over 100 years.

[0003] However, improper maintenance during the use of electric blankets may lead to electric leakage or fire, posing a threat to the user's life. Such situations usually occur due to inaccurate temperature control of the heating wire, or aging of key components such as the heating wire, switching elements, or temperature sensing elements, resulting in short circuits or open circuits. This causes the electric blanket to overheat in certain areas. If the fault is not detected and the power is not cut off in time, it can easily cause a fire.

[0004] Therefore, the inventors of this invention have worked to solve these problems based on their many years of practical experience. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a safe heating circuit with PTC+NTC temperature control mode, and to configure a short circuit or open circuit detection and protection circuit for key components, which can accurately control the heating temperature and detect faults in time and cut off the power supply to ensure the safety of users' lives and property.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] One aspect of the present invention discloses a safe heating circuit, comprising:

[0008] PTC heating elements generate heat when energized;

[0009] A first switching element, coupled to the grounding circuit of the PTC heating element, is configured to turn the power supply circuit of the PTC heating element on or off based on a switching control signal.

[0010] The first voltage acquisition circuit is used to sample the first temperature voltage based on the grounding current of the PTC heating element;

[0011] An NTC element is disposed between the PTC heating element and the sensing element;

[0012] A sensing element for receiving leakage current from the PTC heating element conducted by the NTC element;

[0013] The second voltage acquisition circuit is used to sample the second temperature voltage based on the leakage current;

[0014] The controller is configured to compare the first temperature voltage or the second temperature voltage with a set temperature voltage and output the switching control signal based on the comparison result.

[0015] In some embodiments, the first switching element is a silicon controlled rectifier (SCR) element, and the controller outputs a continuous trigger pulse as a switching control signal to control the SCR element to turn on.

[0016] In some embodiments, the first voltage acquisition circuit includes a first sampling resistor coupled between a first switching element and a power supply ground, and a first filter circuit coupled to the first sampling resistor, wherein a signal input terminal of the controller is coupled to the first filter circuit to receive a sampled signal.

[0017] In some embodiments, the second voltage acquisition circuit includes a voltage divider circuit coupled to the current output terminal of the sensing element, and a second filter circuit coupled to the voltage divider circuit, wherein a signal input terminal of the controller is coupled to the second filter circuit to receive a sampling signal.

[0018] In some embodiments, the safe heating circuit of the present invention further includes a gear adjustment circuit, which is coupled to a signal input terminal of the controller for generating a gear adjustment signal, and the controller is further configured to adjust the set temperature voltage based on the gear adjustment signal.

[0019] In some embodiments, the safe heating circuit of the present invention further includes a display circuit, which is coupled to at least one signal output terminal of the controller and configured to display the current set gear based on a display control signal output by the controller.

[0020] In some embodiments, the safe heating circuit of the present invention further includes a third voltage acquisition circuit coupled to the power supply terminal of the first switching element; the controller is further configured to detect the open-circuit voltage acquired by the third voltage acquisition circuit when the first switching element is disconnected; if the open-circuit voltage is high, it is determined that the PTC heating element and the first switching element are in normal condition; if the open-circuit voltage is low, it is determined that the PTC heating element or the first switching element is faulty.

[0021] In some embodiments, the controller is further configured to detect the first temperature voltage and compare it with a first preset threshold when the circuit breaker voltage is detected to be low when the first switching element is open; if the first temperature voltage is less than the first preset threshold, the PTC heating element is determined to be faulty; if the first temperature voltage is greater than the first preset threshold, the first switching element is determined to be faulty.

[0022] In some embodiments, the third voltage acquisition circuit includes a first comparator, the positive input terminal of which is coupled to the power supply terminal of the first switching element via a third filter circuit and a first current limiting circuit, the inverting input terminal is used to receive a reference voltage, and the output terminal is coupled to a signal input terminal of the controller.

[0023] In some embodiments, the safe heating circuit of the present invention further includes a fuse protection circuit, the fuse protection circuit including a fuse coupled between a power supply terminal and a PTC heating element, and a second switching element coupled between the fuse current outlet and the power supply ground, the controller being further configured to output a control signal to control the second switching element to turn on to blow the fuse when the first switching element is determined to be faulty.

[0024] In some embodiments, the safe heating circuit of the present invention further includes a sensing element detection circuit, the sensing element detection circuit including a second current limiting circuit and a fourth voltage acquisition circuit; the current inflow terminal of the second current limiting circuit is coupled to a power supply terminal, and the current outflow terminal is coupled to the current inflow terminal of the sensing element and the sampling terminal of the fourth voltage acquisition circuit; the fourth voltage acquisition circuit is used to sample the load voltage of the current inflow terminal of the sensing element, and the controller is further configured to receive the load voltage and compare it with a second preset threshold, and when the load voltage is higher than the second preset threshold, disconnect the first switching element.

[0025] In some embodiments, the fourth voltage acquisition circuit includes a second comparator, the positive input terminal of the second comparator is coupled to the current output terminal of the second current limiting circuit via a fourth filter circuit and a third current limiting circuit, the reverse input terminal is grounded, and the output terminal is coupled to a signal input terminal of the controller.

[0026] In some embodiments, the safe heating circuit of the present invention further includes a power supply circuit, which is coupled to an external power source to provide AC voltage to the PTC heating element, and is configured with a voltage conversion circuit that is configured to convert the AC voltage into a low-voltage DC power source.

[0027] In some embodiments, the safe heating circuit of the present invention further includes a power supply voltage detection circuit, which is coupled between the power supply terminal of the PTC heating element and a signal input terminal of the controller, for detecting the power supply terminal voltage of the PTC heating element. The controller is further configured to adjust the set temperature voltage based on the power supply terminal voltage of the PTC heating element detected by the power supply voltage detection circuit.

[0028] In some embodiments, the safe heating circuit of the present invention further includes a zero-crossing detection circuit, which is coupled between the power supply terminal of the PTC heating element and a signal input terminal of the controller, and includes at least one current-limiting resistor and a filter capacitor, as well as a clamping switch diode.

[0029] Another aspect of the invention also discloses an electric blanket, comprising:

[0030] blanket;

[0031] And a safe heating circuit as described in the first aspect above, wherein the PTC heating element is a heating wire with PTC characteristics arranged within the blanket.

[0032] In some embodiments, the PTC heating element, NTC element, and sensing element are integrated into one unit. The PTC heating element is a heating wire spirally wound on a core, the NTC element is an NTC material layer covering the heating wire, and the sensing element is a sensing wire spirally wound on the NTC material layer, with a shielding layer and an insulating layer covering the sensing wire on the outside.

[0033] The safe heating circuit of this invention adopts a PTC+NTC temperature control mode, which can accurately control the heating temperature. At the same time, it is further configured with a short circuit or open circuit detection and protection circuit for key components, which can cut off the power supply in time when the local temperature of the heating wire is too high or the key components are open / short circuit, to prevent fire and ensure the safety of users' lives and property. Attached Figure Description

[0034] Figure 1 This is a schematic block diagram of an exemplary embodiment of the safe heating circuit of the present invention.

[0035] Figure 2 This is a circuit diagram of an exemplary embodiment of the safe heating circuit of the present invention.

[0036] Figure 3 This is a pin diagram of the controller in an exemplary embodiment of the safe heating circuit of the present invention.

[0037] Figure 4 This is a schematic diagram of the display circuit and the gear adjustment circuit in an exemplary embodiment of the safe heating circuit of the present invention.

[0038] Figure 5 This is a schematic block diagram of another exemplary embodiment of the safe heating circuit of the present invention.

[0039] Figure 6 This is a circuit diagram of another exemplary embodiment of the safe heating circuit of the present invention.

[0040] Figure 7 This is a circuit diagram of the power supply circuit in an exemplary embodiment of the safe heating circuit of the present invention.

[0041] Figure 8 This is a schematic block diagram of another exemplary embodiment of the safe heating circuit of the present invention.

[0042] Figure 9 This is a circuit diagram of another exemplary embodiment of the safe heating circuit of the present invention.

[0043] Figure 10 This is a schematic diagram of an exemplary embodiment of the electric blanket with a safety heating circuit according to the present invention.

[0044] Figure 11 This is a schematic diagram of an integrated structure of the PTC heating wire, NTC layer, and temperature-sensitive wire in an exemplary embodiment of the electric blanket with a safety heating circuit according to the present invention. Detailed Implementation

[0045] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are for illustrating the general principles of the present invention and should not be considered limiting.

[0046] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0047] The term "coupled" in the specification and claims of this invention includes both direct and indirect connections, such as connections via an electrical conductive medium, like a conductor, which may contain parasitic inductance or capacitance. It may also include connections via other active or passive devices that achieve the same or similar functional purpose, such as connections via circuits or components like switches or follower circuits.

[0048] Figure 1 A schematic block diagram of a safe heating circuit according to an exemplary embodiment of the present invention is shown. (Refer to...) Figure 1A safe heating circuit includes: a PTC heating element 10 that generates heat when energized; a first switching element 11 coupled to the grounding circuit of the PTC heating element 10 and configured to turn the power supply circuit of the PTC heating element 10 on or off based on a switching control signal; a first voltage acquisition circuit 12 for sampling a first temperature voltage based on the grounding current of the PTC heating element 10; an NTC element 13 disposed between the PTC heating element 10 and a sensing element 14; the sensing element 14 for receiving leakage current from the PTC heating element 10 conducted by the NTC element 13; a second voltage acquisition circuit 15 for sampling a second temperature voltage based on the leakage current; and a controller 16 configured to compare the first temperature voltage or the second temperature voltage with a set temperature voltage and output the switching control signal based on the comparison result.

[0049] Specifically, the PTC heating element 10 is made of a heating material with PTC properties. It generates heat when energized and its resistance changes with temperature (the higher the temperature, the greater the resistance). One end is coupled to the power supply circuit 20, and the other end is coupled to the power ground 17 via the first switching element 11. Thus, when the first switching element 11 is turned on or off, current flows through the PTC heating element 10, causing it to heat up. When the first switching element 11 is turned off or off, no current flows through the PTC heating element 10, and it stops heating. The NTC element 13 is made of a material with NTC properties. Its resistance decreases as the temperature rises, resulting in a larger leakage current flowing into the PTC heating element in contact with it. The sensing element 14 is made of a conductive material and is in contact with the NTC element 13, receiving the leakage current flowing into the PTC heating element.

[0050] Reference Figure 2 In some embodiments, the first terminal H1 of the PTC heating element 10 is coupled to a power supply circuit to receive AC voltage, and the second terminal H4 is grounded via a first switching element (T1). An NTC element 13 is disposed between the PTC heating element 10 and the sensing element 14, which is used to receive leakage current from the PTC heating element 10 conducted by the NTC element 13.

[0051] Reference Figure 2 In one illustrative embodiment, the first switching element is a silicon controlled rectifier (SCR) T1, whose control signal input terminal is coupled to a signal output terminal of the controller via a resistor R30 and a capacitor C18, for receiving a switch control signal S110. Optionally, the switch control signal S110 is a continuous trigger pulse; the SCR T1 is turned on when it receives the continuous trigger pulse output by the controller, otherwise it is in an off state.

[0052] Reference Figure 2In one illustrative embodiment, the first voltage acquisition circuit includes sampling resistors R32 and R33 connected in parallel between the silicon controlled rectifier (SCR) element T1 and the power supply ground, and a first filter circuit coupled to the sampling resistors R32 and R33, the first filter circuit including a resistor R1 and a capacitor C1. A signal input terminal of the controller is coupled to the first filter circuit to receive the sampled signal S120.

[0053] Reference Figure 2 In one illustrative embodiment, the second voltage acquisition circuit includes a voltage divider circuit coupled to the current output terminal H2 of the sensing element 14, and a second filter circuit coupled to the voltage divider circuit. The voltage divider circuit consists of resistors R64 and R16, and the second filter circuit consists of resistor R15 and capacitor C6. A signal input terminal of the controller is coupled to the second filter circuit to receive the sampling signal S150. Furthermore, to protect the controller, a clamping diode D3 is also configured on the second voltage acquisition circuit.

[0054] In some embodiments, the controller 16 may be a CPU, MCU, or other programmable device. (See reference...) Figure 3 In one illustrative example, the controller employs a microcontroller (MCU) 160, which has multiple signal input / output pins (pins 1-16). It can receive signals through the signal input pins and output signals through the corresponding signal output pins based on the configured program. In this illustrative example, pin 2 (PC0) of the MCU 160 is used to output the switch control signal S110, and pins 10 (PA6 / AN5) and 11 (PA5 / AN4) are used to receive sampled signals S120 and S150, respectively. In subsequent embodiments, the signals received or output by the controller will be identified in the same manner.

[0055] Reference Figure 1 In some embodiments, the safe heating circuit of the present invention further includes a gear adjustment circuit 18, which is coupled to a signal input terminal of a controller 16 for generating a gear adjustment signal. The corresponding controller 16 is also configured to adjust the set temperature voltage based on the gear adjustment signal.

[0056] Reference Figure 4 In one illustrative example, the gear adjustment circuit 18 includes a switch SW1 and a grounding resistor R13. By pressing the switch SW1, a gear adjustment signal S180 is generated, which allows the controller 16 to adjust the set temperature voltage based on the gear adjustment signal S180.

[0057] Reference Figure 1In some embodiments, the safe heating circuit of the present invention further includes a display circuit 19, which is coupled to at least one signal output terminal of the controller 16 and configured to display the current set gear based on the display control signal output by the controller.

[0058] Reference Figure 4 In one illustrative example, the display circuit 19 includes light-emitting diodes L1-L4 and LED5, which receive display control signals S190-S192 from the controller and then display the currently set gear through different combinations.

[0059] The working principle of the safe heating circuit in this embodiment will be further explained below with reference to the above illustrative embodiments:

[0060] At startup, the controller 16 outputs continuous trigger pulses to the first switching element (SCR element T1) to turn it on, at which point the PTC heating element 10 is powered on and begins heating. Resistors R33 and R32 in the first voltage acquisition circuit form a sampling resistor. The sampled voltage signal is filtered and current-limited by the first filter circuit composed of resistors R1 and capacitor C1, forming a sampling signal S120 that enters the controller. As the temperature rises, the resistance of the PTC heating element 10 increases, causing the sampling voltage of the first voltage acquisition circuit to decrease. When the controller detects that this sampling voltage is lower than the set temperature voltage corresponding to the current configuration level, it stops outputting trigger pulses to the first switching element (SCR element T1), thereby disconnecting the first switching element (SCR element T1) and stopping heating. Subsequently, as the temperature decreases, the resistance of the PTC heating element 10 gradually decreases; when its resistance decreases, the sampling voltage acquired by the first voltage acquisition circuit increases. When the controller detects that the sampled voltage is higher than the set temperature voltage corresponding to the current configuration level, it outputs a continuous trigger pulse to the first switching element (SCR element T1) to turn it on, thereby connecting the power circuit of the PTC heating element 10 and resuming heating. During the heating process, the two processes alternate, and the cyclic control achieves the purpose of constant temperature.

[0061] On the other hand, when the PTC heating element 10 is powered on and heating, the AC voltage flowing through it forms a leakage current through the NTC element 13 and enters the sensing element 14. This current is then sampled by the voltage divider circuit (resistors R64 and R16) in the second voltage acquisition circuit, filtered by the second filter circuit (resistor R15 and capacitor C6), and forms a sampling signal S150 which enters the controller, thus acquiring the NTC temperature voltage. When this NTC temperature voltage is lower than the set temperature voltage corresponding to the current configuration level, the controller outputs a continuous trigger pulse to the first switching element (thyristor element T1) to turn it on. At this time, the PTC heating element 10 remains powered on and heating. When the overall or local temperature sensed by the NTC element exceeds the NTC protection setting value, the leakage current entering the sensing element 14 through the NTC element 13 increases, which in turn causes the voltage signal (NTC temperature voltage) acquired by the second voltage to rise. When the controller detects that the NTC temperature voltage is higher than the set temperature voltage corresponding to the current configuration level, it stops outputting trigger pulses to the first switching element (thyristor element T1) to disconnect it, thereby disconnecting the power supply circuit of the PTC heating element 10 and stopping heating.

[0062] Based on the above principles, the safe heating circuit in the above-shown embodiment can achieve precise control of the heating temperature, while avoiding local overheating of the heating wire that could lead to safety accidents.

[0063] Figure 5 A schematic block diagram of a safe heating circuit according to another exemplary embodiment of the present invention is shown. (Refer to...) Figure 5 A safe heating circuit includes: a PTC heating element 10 that generates heat when energized; a first switching element 11 coupled to the grounding circuit of the PTC heating element 10 and configured to turn the power supply circuit of the PTC heating element 10 on or off based on a switching control signal; a first voltage acquisition circuit 12 for sampling a first temperature voltage based on the grounding current of the PTC heating element 10; an NTC element 13 disposed between the PTC heating element 10 and a sensing element 14; the sensing element 14 for receiving leakage current from the PTC heating element 10 conducted by the NTC element 13; a second voltage acquisition circuit 15 for sampling a second temperature voltage based on the leakage current; and a controller 16 configured to compare the first temperature voltage or the second temperature voltage with a set temperature voltage and output the switching control signal based on the comparison result. The controller 16 is also configured to detect the open-circuit voltage collected by the third voltage acquisition circuit 21 when the first switching element 11 is disconnected. If the open-circuit voltage is high, it is determined that the PTC heating element 10 and the first switching element 11 are in normal condition. If the open-circuit voltage is low, it is determined that the PTC heating element 10 or the first switching element 11 is faulty.

[0064] As a further improvement, in this exemplary embodiment, the controller 16 is further configured to detect the first temperature voltage sampled by the first voltage acquisition circuit 15 and compare it with a first preset threshold when the first switching element 11 is in the open state and the above-mentioned open circuit voltage is detected to be low. If the first temperature voltage is less than the first preset threshold, the PTC heating element 10 is determined to be faulty (open circuit). If the first temperature voltage is greater than the first preset threshold, the first switching element 11 is determined to be faulty (short circuit).

[0065] Reference Figure 6 In one illustrative embodiment, the third voltage acquisition circuit includes a first comparator U3B. The positive input of the first comparator U3B is coupled to the power supply terminal of the first switching element (SCR element T1) via a third filter circuit consisting of resistor R40, capacitor C3, and diode D8, and a first current limiting circuit consisting of resistors R27 and R28. The inverting input is coupled to a voltage divider circuit consisting of resistors R4 and R7 for receiving a reference voltage. The output is coupled to a signal input terminal of the controller for outputting a circuit-breaking voltage signal S210. Examples of the first and second voltage acquisition circuits are similar to those in the foregoing embodiments and will not be described in detail here.

[0066] The working principle of the safe heating circuit in this embodiment will be further explained below with reference to the above illustrative embodiments:

[0067] When the first switching element 11 is open, the controller 16 detects the open-circuit voltage (i.e., the open-circuit voltage signal S210 output by the output terminal of the first comparator U3B) collected by the third voltage acquisition circuit 21. If the open-circuit voltage is high, it indicates that the first switching element 11 is open normally, thus determining that the PTC heating element 10 and the first switching element 11 are in normal condition. If the open-circuit voltage is low, it may indicate that the PTC heating element 10 has an open circuit, or that the first switching element 11 has malfunctioned and cannot open normally, thus determining that either the PTC heating element 10 or the first switching element 11 has malfunctioned.

[0068] At this time, the controller 16 further detects the first temperature voltage sampled by the first voltage acquisition circuit 12 and compares it with the first preset threshold. If the first temperature voltage is less than the first preset threshold, it indicates that the PTC heating element 10 has an open circuit, causing its ground terminal H4 to be at a low level, thus determining that the PTC heating element 10 is faulty (open circuit). If the first temperature voltage is greater than the first preset threshold, it indicates that the first switching element 11 has a fault and cannot disconnect normally. Usually, the first switching element 11 fails and short-circuits, causing a voltage to be generated at its ground terminal, thus determining that the first switching element 11 is faulty (short circuit). The first preset threshold can be set according to the actual situation.

[0069] Reference Figure 1 and Figure 5 In some embodiments, the safe heating circuit of the present invention further includes a power supply circuit 20, which is coupled to an external power supply to provide AC voltage to the PTC heating element 10, and is configured with a voltage conversion circuit that is configured to convert the AC voltage into a 5V low-voltage DC power supply.

[0070] Reference Figure 7 In one illustrative embodiment, the power supply circuit includes a live wire terminal L and a neutral wire terminal N for coupling to an external power source, and a fuse F1 connected in series after the live wire terminal L. A protection circuit consisting of a varistor (surge receiver) ZNR1, a filter capacitor CX1, and resistors RX1 and RX2 is provided after the fuse F1, and then coupled to a PTC heating element 10 for power supply. Simultaneously, a voltage conversion circuit is also coupled, which includes a current-limiting resistor R38, a capacitor C16, a Zener diode ZD1, a diode D2, and filter capacitors C17 and C7. After passing through a voltage regulator chip U2 and being filtered by capacitors C26 and C25, a stable 5V low-voltage DC power supply is generated.

[0071] Reference Figure 7 In one illustrative embodiment, the power supply circuit further includes a fuse protection circuit, which includes a second switching element SCR1 coupled between the current outlet of the fuse F1 and the power ground.

[0072] Accordingly, in some embodiments, the controller 16 is also configured to output a control signal S220 to control the second switching element SCR1 to turn on when the first switching element 11 is determined to be faulty. At this time, the AC power introduced into the live wire terminal L is grounded through the second switching element SCR1, thereby blowing the fuse F1 to cut off the power supply and achieve the protection effect.

[0073] Reference Figure 1 In some embodiments, the safe heating circuit of the present invention further includes a power supply voltage detection circuit 25. (See also...) Figure 7 In one illustrative embodiment, the power supply voltage detection circuit is coupled between the power supply terminal of the PTC heating element 10 and a signal input terminal of the controller. It includes a resistor R36 coupled to the power supply terminal of the PTC heating element 10 (the current outlet of fuse F1), and a resistor R19, a diode D1, and a capacitor C4 connected in parallel with the resistor R36 and grounded. This power supply voltage detection circuit samples and generates a power supply voltage detection signal S250. Upon receiving this signal, the controller can detect the power supply voltage of the PTC heating element and adjust the set temperature voltage to avoid the influence of power supply voltage fluctuations on the heating temperature control.

[0074] Reference Figure 1In some embodiments, the safe heating circuit of the present invention further includes a zero-crossing detection circuit 24. (See also...) Figure 7 In one illustrative embodiment, the zero-crossing detection circuit is coupled between the power supply terminal of the PTC heating element 10 and a signal input terminal of the controller 16, and includes two current-limiting resistors R39 and R22, a filter capacitor C9, and a clamping switching diode D6. The zero-crossing detection circuit outputs a sampling signal S240 to a signal input terminal of the controller 16, so that the controller 16 can detect zero-crossing anomalies of the power supply based on the sampling signal S240.

[0075] Figure 8 A schematic block diagram of a safe heating circuit according to another exemplary embodiment of the present invention is shown. (Refer to...) Figure 8 A safe heating circuit includes: a PTC heating element 10 that generates heat when energized; a first switching element 11 coupled to the grounding circuit of the PTC heating element 10 and configured to turn the power supply circuit of the PTC heating element 10 on or off based on a switching control signal; a first voltage acquisition circuit 12 for sampling a first temperature voltage based on the grounding current of the PTC heating element 10; an NTC element 13 disposed between the PTC heating element 10 and a sensing element 14; the sensing element 14 for receiving leakage current from the PTC heating element 10 conducted by the NTC element 13; a second voltage acquisition circuit 15 for sampling a second temperature voltage based on the leakage current; a controller 16 configured to compare the first temperature voltage or the second temperature voltage with a set temperature voltage and output the switching control signal based on the comparison result; and a sensing element detection circuit including a second current limiting circuit 22 and a fourth voltage acquisition circuit 23. The second current limiting circuit 22 has its current inflow terminal coupled to a power supply terminal, and its current outflow terminal coupled to the current inflow terminal of the sensing element 14 and the sampling terminal of the fourth voltage acquisition circuit 22. The fourth voltage acquisition circuit 22 is used to sample the load voltage at the current inflow terminal of the sensing element 14. Correspondingly, the controller 16 is also configured to receive the load voltage sampling signal and compare it with a second preset threshold. When the load voltage is higher than the second preset threshold, the first switching element 11 is disconnected.

[0076] Reference Figure 9 In one illustrative embodiment, the second current limiting circuit 22 includes current limiting resistors R21 and R29 connected in series, one end of which is coupled to a power supply terminal, and the other end of which serves as a current outflow terminal coupled to the current inflow terminal of the sensing element 14.

[0077] Reference Figure 9In one illustrative embodiment, the fourth voltage acquisition circuit includes a second comparator U3A. The positive input terminal of the second comparator U3A is coupled to the current output terminal of the second current limiting circuit via a fourth filter circuit consisting of capacitor C2, resistor R23, and diode D9, and a third current limiting circuit consisting of resistors R37 and R66. The inverting input terminal is grounded via resistor R3 and coupled to the output terminal via resistor R2. The output terminal is coupled to a signal input terminal of the controller for outputting the load voltage signal S230. Additionally, to protect the comparator and controller chip, a clamping diode D4 is also coupled to the fourth voltage acquisition circuit.

[0078] In this illustrative embodiment, the examples of the first voltage acquisition circuit and the second voltage acquisition circuit are similar to those in the previous embodiments, and will not be described in detail here.

[0079] The working principle of the safe heating circuit in this embodiment will be further explained below with reference to the above illustrative embodiments:

[0080] When the sensing element 14 is working normally, the current introduced from the second current limiting circuit is divided into two paths. One path flows into the sensing element 14 through the current inflow terminal H3 and out through the current outflow terminal H2, entering the second voltage acquisition circuit composed of resistors R64, R16, R15 and capacitor C6. The other path enters the aforementioned fourth voltage acquisition circuit. At this time, the load voltage signal S230 sampled by the fourth voltage acquisition circuit received by the controller is a relatively stable voltage value. When the sensing element 14 is disconnected due to a fault, the voltage at its current inflow terminal H3 will increase, thereby causing a corresponding change in the load voltage sampled by the fourth voltage acquisition circuit. When the controller detects this change, it can determine that the sensing element 14 has failed (open circuit), thereby disconnecting the first switching element (thyristor element T1) and issuing an alarm signal through the display circuit.

[0081] Figure 10 Another exemplary embodiment of the present invention is shown, which is an electric blanket configured with the safety heating circuit of one or more of the above embodiments. The electric blanket includes:

[0082] Blanket 1; and a safety heating circuit as shown in one or more of the above embodiments. The PTC heating element in the safety heating circuit is a PTC heating wire arranged in the blanket 1. An NTC element and a sensing element are arranged parallel to the PTC heating wire and coupled to the control box 3 via a wire 4. The controller, the first switching element, the gear adjustment circuit, and the display circuit are all housed within the control box 3. The power supply circuit is also integrated within the control box 3 and is powered via a plug 5.

[0083] Reference Figure 11In one exemplary embodiment, the PTC heating wire, NTC element, and sensing element are integrated into a single unit. The PTC heating wire 100 is spirally wound around a core 101. The NTC element is an NTC material layer with NTC properties covering the PTC heating wire 100. The sensing element is a conductive wire 103 spirally wound around the NTC material layer. A shielding layer 104 covers the conductive wire 103, and an insulating layer 105 is provided on the outermost layer. Optionally, the core 101 is made of PET, and the shielding layer 104 is made of a tin-copper alloy. The materials of the PTC heating wire, NTC element, and sensing element can be selected according to actual needs.

[0084] It should be noted that in some embodiments, the electric blanket of the present invention can be configured with one of the safety heating circuits shown in the foregoing embodiments, or it can be configured with a combination of several safety heating circuits shown in the foregoing embodiments to achieve better temperature control and protection, and thus better safety. Since the implementation methods and working principles of the several safety heating circuits have been described in detail in the foregoing embodiments, they will not be described again.

[0085] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. A safety heating circuit, characterized in that, The application relates to a temperature control system for a PTC electric heating element, comprising: a PTC electric heating element generating heat when powered; a first switching element coupled in a ground loop of the PTC electric heating element and configured to turn on or off a power loop of the PTC electric heating element based on a switching control signal; a first voltage acquisition circuit configured to sample a first temperature voltage based on a ground current of the PTC electric heating element; an NTC element arranged between the PTC electric heating element and a sensing element; a sensing element configured to receive a leakage current from the PTC electric heating element conducted by the NTC element; a second voltage acquisition circuit configured to sample a second temperature voltage based on the leakage current; a third voltage acquisition circuit coupled to a power terminal of the first switching element, comprising a first comparator having a positive input coupled to the power terminal of the first switching element, a negative input configured to receive a reference voltage, and an output coupled to a signal input of a controller; and the controller configured to compare the first temperature voltage or the second temperature voltage with a set temperature voltage and output the switching control signal based on the comparison result; the controller further configured to detect an open circuit voltage sampled by the third voltage acquisition circuit when the first switching element is turned off, and determine that the PTC electric heating element and the first switching element are in normal state if the open circuit voltage is high, or determine that the PTC electric heating element or the first switching element is faulty if the open circuit voltage is low; and when the open circuit voltage is detected to be low when the first switching element is turned off, the first temperature voltage is detected and compared with a first preset threshold, and it is determined that the PTC electric heating element is faulty if the first temperature voltage is less than the first preset threshold, or it is determined that the first switching element is faulty if the first temperature voltage is greater than the first preset threshold.

2. A safety heating circuit as claimed in claim 1, characterized in that The first switching element is a thyristor, and the controller outputs a continuous trigger pulse as the switching control signal to control the thyristor to turn on.

3. The safety heating circuit of claim 1, wherein, The first voltage acquisition circuit comprises a first sampling resistor coupled between the first switching element and a power ground, and a first filter circuit coupled to the first sampling resistor, and a signal input of the controller is coupled to the first filter circuit to receive a sampling signal.

4. The safety heating circuit of claim 1, wherein, The second voltage acquisition circuit comprises a voltage dividing circuit coupled to a current outflow terminal of the sensing element, and a second filter circuit coupled to the voltage dividing circuit, and a signal input of the controller is coupled to the second filter circuit to receive a sampling signal.

5. The safety heating circuit of claim 1, wherein, The application further comprises a gear adjustment circuit coupled to a signal input of the controller and configured to generate a gear adjustment signal, and the controller is further configured to adjust the set temperature voltage based on the gear adjustment signal.

6. A safety heating circuit as claimed in claim 5, characterised in that, The application further comprises a display circuit coupled to at least one signal output of the controller and configured to display a current set gear based on a display control signal output by the controller.

7. The safety heating circuit of claim 1, wherein, The positive input of the first comparator is coupled to the power terminal of the first switching element via a third filter circuit and a first current limiting circuit.

8. The safety heating circuit of claim 1, wherein, The safety heating circuit further comprises a fuse protection circuit, the fuse protection circuit comprises a fuse coupled between the power terminal and the PTC heating element, and a second switching element coupled between a current outflow end of the fuse and a power ground, and the controller is further configured to output a control signal to control the second switching element to be turned on to fuse the fuse when the first switching element is determined to be faulty.

9. A safety heating circuit as claimed in any one of claims 1-6, characterized in that The safety heating circuit further comprises an inductive element detection circuit, the inductive element detection circuit comprises a second current limiting circuit and a fourth voltage acquisition circuit; a current inflow end of the second current limiting circuit is coupled to the power terminal, a current outflow end of the second current limiting circuit is coupled to a current inflow end of the inductive element and a sampling end of the fourth voltage acquisition circuit; the fourth voltage acquisition circuit is configured to sample a load voltage of the current inflow end of the inductive element, and the controller is further configured to receive the load voltage and compare the load voltage with a second preset threshold value, and when the load voltage is higher than the second preset threshold value, the first switching element is turned off.

10. A safety heating circuit as claimed in claim 9, characterised in that, The fourth voltage acquisition circuit comprises a second comparator, a positive input end of the second comparator is coupled to the current outflow end of the second current limiting circuit through a fourth filter circuit and a third current limiting circuit, a negative input end of the second comparator is grounded, and an output end of the second comparator is coupled to a signal input end of the controller.

11. A safety heating circuit as claimed in any one of claims 1 to 6, characterised in that, The safety heating circuit further comprises a power supply circuit, the power supply circuit is coupled to an external power supply to provide an alternating voltage for the PTC heating element, and the power supply circuit is configured with a voltage conversion circuit configured to convert the alternating voltage into a low-voltage direct current power supply.

12. A safety heating circuit as claimed in claim 11, characterised in that, The safety heating circuit further comprises a power supply voltage detection circuit, the power supply voltage detection circuit is coupled between a power terminal of the PTC heating element and a signal input end of the controller, and is configured to detect a voltage of the power terminal of the PTC heating element, and the controller is further configured to adjust the set temperature voltage based on the voltage of the power terminal of the PTC heating element detected by the power supply voltage detection circuit.

13. The safety heating circuit of claim 11, wherein, The safety heating circuit further comprises a zero-crossing detection circuit, the zero-crossing detection circuit is coupled between a power terminal of the PTC heating element and a signal input end of the controller, and comprises at least one current limiting resistor and a filter capacitor, and a clamping switching diode.

14. An electric blanket, characterized in that, The safety heating circuit comprises: a blanket; and the safety heating circuit according to any one of claims 1-13, wherein the PTC heating element is an electric heating wire with PTC characteristics arranged in the blanket.

15. The electric blanket of claim 14 wherein, The PTC heating element, the NTC element and the inductive element are integrally arranged, wherein the PTC heating element is an electric heating wire spirally wound on a core, the NTC element is an NTC material layer covering the electric heating wire, and the inductive element is an inductive wire spirally wound on the NTC material layer and externally provided with a shielding layer and an insulating layer covering the inductive wire.

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