Protection circuit for an electric appliance

Abstract

A protection circuit for an electrical appliance configured to control the supply of power to an electrical component, such as a heater device, a lamp or a motor, of an associated appliance in case an unsafe condition is detected such that the continued supply of power can be dangerous. The protection circuit comprises a first comparator module configured to compare an operating parameter input signal with a threshold value and to output a first control signal to a first switching circuit configured to control the power flow to the associated electrical component. The first comparator module is configured to receive an enable / disable signal from a first state change latching device, wherein the first state change latching device is responsive to a state change of the first control signal from the first comparator module, in response to which the state change latching device changes the enable / disable signal from an enabled state to a disabled state, thereby setting the first control signal to an off state. Advantageously, the protection circuit provides a hardware solution for the electrical circuit breaking system used in the appliance, thus the circuit does not use conventional thermal fuses and does not require the implementation of safety critical software. Thus, the protection circuit of the invention provides a particularly cost and space saving solution which is well suited for unconventional electrical appliances with a small form factor.

Description

Technical Field

[0001] This invention generally relates to a protective control circuit for use in appliances, and more specifically, but not exclusively, to a personal care appliance, such as a hair dryer or curling iron. The invention also relates to appliances incorporating such a protective control circuit. Background Technology

[0002] Electrical appliances containing electric heaters are common in ordinary households and can include personal beauty devices such as hair dryers, hair straighteners, and space heaters. To ensure the safe use of such appliances, household appliances are regulated by safety standards that specify how to operate them in case of malfunction. An example of such a standard is IEC / EN / UL 60730.

[0003] A typical requirement is that the appliance must include protective controls to ensure that power is disabled in the event of a detected safety fault. Furthermore, the power disablement should be a non-resettable control, ensuring that power remains disabled even after a restart. The user of the device should also have no way to reset the appliance to restore operation.

[0004] In appliances incorporating electric heaters, a non-resettable safety function can be provided by a thermal shut-off device that utilizes a thermal fuse, which is operable to disable the appliance when its operating temperature reaches an unsafe level. Examples of such electrical appliances incorporating this safety function are described in WO2015 / 005024A1 and WO2018 / 130832A1.

[0005] One design challenge associated with these electrical appliances is making them more ergonomic by reducing their weight and size, thus making them easier for users to hold and operate. This compromises the ability to design their electrical control systems to incorporate additional safety features (such as thermal fuses) within a reduced package size. Therefore, an alternative approach is desired that provides the same safety functionality that meets the relevant safety standards, but in a smaller package. It is in this context that embodiments of the present invention were designed. Summary of the Invention

[0006] According to a first aspect of the invention, a protection circuit for an electrical appliance is provided. The protection circuit is configured to control the power supply to an associated electrical component (e.g., a heater, lamp, or motor) of the electrical appliance when an unsafe condition is detected that would pose a danger if continued power supply were to occur. The protection circuit includes a first comparator module configured to compare an operating parameter input signal with a threshold and output a first control signal to a first switching circuit configured to control the power flow to the associated electrical component. The first comparator module is configured to receive an enable / disable signal from a first state change latching device, wherein the first state change latching device, in response to a state change of the first control signal from the first comparator module, changes the enable / disable signal from an enable state to a disable state, thereby setting the first control signal to a closed state, and thus locking the appliance in a non-operating safe state.

[0007] Advantageously, this protection circuit provides a 100% hardware solution for permanent electrical disconnection systems used in electrical appliances, and similarly, it does not use conventional thermal fuses and does not require the implementation of safety-critical software. It is worth emphasizing that the protection circuit still disconnects the system, even after a restart. Therefore, the protection circuit of this invention provides a particularly cost- and space-saving solution, which is well-suited for unconventional electrical appliances with a small form factor.

[0008] Restarting means turning the device off and then on again. When the protection circuit is in use and the first control signal is set to the off state, the device will not function when the user subsequently attempts to turn it on because it is disabled and locked in a non-operating state. It is possible to repair the device, resolve the safety issues, and have a technician reset the latch, but this requires disassembly.

[0009] In one example, the state change latching device may be a digital potentiometer with a wiper position that provides an enable / disable signal. In some examples, the enable / disable signal may be configured to also provide a predetermined threshold against which the operating parameter input signal is compared.

[0010] As part of the protection circuit, the monitor or "control" module can be configured to monitor the first control signal of the first comparator module and output a trigger input to the state change latching device in response to the state of the first control signal.

[0011] The first state-change latching device may include a latching mechanism activated by a trigger input. This allows the control module to control the state of the latching device and, consequently, the state of the control signals input to the switching circuit. The latching mechanism can be configured to change its state when a trigger input is detected to be in a triggered state for a predetermined time period. For example, the latching mechanism can be implemented using the vernier position of a digital potentiometer, whose value decreases when the trigger signal actuates the "decreasing vernier position" pin. The trigger signal can be actuated for a predetermined period to ensure that the vernier position decreases to its minimum value.

[0012] The first state-change latching device may have a storage module for storing the state of the latching mechanism. For example, the control module may control the memory module to save the state of the latching mechanism by outputting a save input for a predetermined duration. Once the state of the latching mechanism is saved in the memory module, the device will remain in a non-operating state, even after the device is restarted.

[0013] In one example, the first comparator module may include a comparator that outputs a logic high signal to a first logic element when the operation parameter input signal exceeds a threshold, and wherein the first logic element outputs a first control signal as a logic high state when the first comparator output signal and the enable / disable signal are in the same logic state.

[0014] In another example, the first comparator module may include a comparator that outputs a first control signal to a logic high state when the operating parameter input signal exceeds a threshold, and wherein the threshold may be provided by an enable / disable signal of the first state change latching device when the signal is enabled.

[0015] Conveniently, the protection circuit can be configured to be fault-tolerant, such that any signal failure in the circuit will cause the switching circuit to be unable to reach a safe state, thereby cutting off the power supply to the relevant electronic components. Thus, the protection circuit can further include a second comparator module configured to receive an operating parameter input signal and compare it with a threshold, and in response, output a second control signal to a second switching circuit configured to control the power flow to the associated electrical appliance, wherein the second comparator module is configured to receive an enable / disable signal from a second state-change latching device. The second state-change latching device can also respond to a state change of the second control signal from the second comparator module, thereby changing the enable / disable signal from an enable state to a disable state, thus locking the second control signal to an off state.

[0016] In other words, the protection circuit includes first and second circuit branches, each of which controls the power flow to the associated switching circuit in a very similar manner.

[0017] A first switching circuit can be connected to a power control relay, wherein the power control relay is connected to a power source. Similarly, a second switching circuit can be connected to the power control relay. The power control relay can be configured to disable the power supply when one or both of the first and second switching circuits operate to de-energize the relay.

[0018] Within the scope of this application, it will be apparent that the various aspects, embodiments, examples, and alternatives set forth in the preceding paragraphs, in the claims, and / or in the following description and drawings, particularly their individual features, may be employed independently or in any combination. That is, all embodiments and / or features of any embodiment may be combined in any manner and / or combination unless such features are incompatible. The applicant reserves the right to amend any initially filed claim or accordingly file any new claim, including the right to modify any initially filed claim to be subordinate to and / or combine with any feature of any other claim, even though it was not initially claimed in this manner. Attached Figure Description

[0019] The above and other aspects of the invention will now be described by way of example only, with reference to the accompanying drawings, in which:

[0020] Figure 1 This is a schematic diagram of a circuit configuration according to an example of the present invention;

[0021] Figure 2 yes Figure 1 A more detailed schematic diagram of the circuit configuration shown;

[0022] Figure 3 yes Figure 2 The circuit configuration shown is a schematic diagram, but includes additional circuitry to provide fault tolerance;

[0023] Figure 4 This is an explanation Figure 2 The timing diagram of the circuit configuration shown, and

[0024] Figure 5 Is to provide and Figure 1-3 The diagram shows another example of a circuit configuration with equivalent functionality.

[0025] In the accompanying drawings, the same reference numerals are used to indicate features common to all elements in the drawings. Detailed Implementation

[0026] refer to Figure 1The protection circuit 2 includes various components installed within the electrical appliance 4 to provide appropriate safety functions for the appliance. In the example below, the protection circuit 2 provides control over the power supplied to component 6 of the electrical appliance 4. For example, component 6 could be a lamp, motor, or heater, although these are merely indications of component types relevant to this discussion. By controlling the power supplied to component 6, the component can be disabled if its continued operation is deemed unsafe.

[0027] In the following discussion, component 6 can be considered as a heater device, although these terms are used interchangeably. This heater device can be a wire element type heater device, such as those found in typical hair dryers, or a ceramic element type heater device, which is commonly found in, for example, hair straighteners and curling irons, but is also found in hair dryers manufactured by the applicant.

[0028] It should be noted that Figure 1 The circuit diagram in the diagram is at a high functional level to provide an introduction to the architecture and functionality provided by protection circuit 2. The accompanying figures and related discussion provide a more detailed understanding of the specific circuit components used in the protection circuit.

[0029] In general, the protection circuit 2 includes a comparator module 10 that communicates with the switching circuit 12. The switching circuit 12 controls the operation of the power supply 14, which provides voltage / current to the heater assembly 6.

[0030] The comparator module 10 receives an input signal 16 from the temperature sensor 18 and compares the input signal 16 with a predetermined threshold 20. As those skilled in the art will understand, the input signal 16 can be a suitably calibrated voltage or current output by the temperature sensor 18, proportional to the sensed temperature. Although not shown here, the temperature sensor 18 can be integrated into the electrical appliance 4 in a manner that ensures accurate measurement of the parameter in question. For example, the temperature sensor 18 can be mounted next to or embedded in the heating element of the heating device. It is also contemplated that the temperature sensor signal 16 can be provided via current feedback from the heater device 6. Note that in this example, the comparator receives a signal from the temperature sensor, but in other applications, the input signal could represent another operating parameter.

[0031] It should be understood that the predetermined threshold 20 can be a stored value or it can be provided by the input signal. Figure 1 In this context, the predetermined threshold 20 is displayed as a single value, but other checks can be performed. For example, additional checks can be performed to ensure that the input temperature signal is within an acceptable voltage range.

[0032] Temperature comparator module 10 provides output signal 22 to switching circuit 12. In this example, output signal 22 is a digital output signal that can be in a high or low state, thereby activating or deactivating switching circuit 12 and thus controlling the power flowing to heater device 6 accordingly. Here, switching circuit 12 includes switching device 24, which is operatively connected to relay 26 to control its operating state. Relay 26 thus provides a reliable mechanism by which the power flow from power source 14 to heater device 6 can be controlled.

[0033] As described above, to comply with safety regulations, it is important that the protection circuit be able to disable power supply to component 6 in such a way that the user cannot resume operation of appliance 4 even after the appliance has been restarted. Therefore, for this purpose, protection circuit 2 includes a state change latching device 30 that interfaces with comparator module 10. State change latching device 30 is configured to respond to the output signal 22 of comparator module 10 and has the function of latching the output signal 22 to a low state if the output signal 22 transitions from a high state to a low state by issuing an enable / disable signal 31 to comparator module 10. For example, if comparator module 10 detects that the temperature at sensor 18 exceeds a predetermined threshold 20, thereby indicating a potential hazardous condition of appliance 4, the output signal 22 will transition from a high state to a low state to configure switching circuit 12 to disable power supply to heater device 6. In response, state change latching device 30 will detect the signal state transition and configure comparator module 10 such that even if the sensed temperature drops below the predetermined temperature threshold 20, the output signal 22 remains in a low state. For this purpose, state change latching device 30 sets the enable / disable signal 31 to a disabled state. Therefore, this function keeps the appliance in a safe state, allowing for proper investigation without the user turning on the return appliance.

[0034] like Figure 1 As shown, the state change latch device 30 operates under the control of the control module 32. The control module 32 receives the output signal 22 from the temperature comparator module 10 and provides appropriate control inputs 34 to the state change latch device 30. Figure 1In this document, the state change latch device 30 and the control module 32 are described as independent functional blocks; however, it should be noted that this is merely for convenience, and therefore, the state change latch device 30 and the control module 32 can be a single hardware module. It should be noted that all circuit components described herein as part of the protection circuit are preferably configured as hardware components. Thus, those hardware components can be configured as discrete components on a circuit board, or more preferably, those hardware components can form part of an integrated circuit. This means that the functionality provided by the protection circuit can be implemented in a particularly space-saving package that can be integrated into the existing PCB layout of the appliance. This contrasts with existing solutions that tend to be based on thermal fuses, which occupy a significant amount of package space within the appliance and are therefore unsuitable for personal appliances with novel layouts and limited package volumes, such as hair dryers.

[0035] Another advantage is that the hardware-based solutions provided by the examples of the invention discussed herein do not require the implementation of a software processing environment, which typically comes with significant requirements for security level certification.

[0036] The extensive functions of protection circuit 2 have already been described; now refer to Figure 2 A more detailed discussion follows, in which a possible implementation example is shown.

[0037] exist Figure 2 In this circuit, comparator module 10 includes multiple logic gates that interface with enable / disable signals 31 from state change latch device 30. It can be seen that state change latch device 30 is implemented as a digital potentiometer, and enable / disable signals 31 are provided by the vernier output of the digital potentiometer, which will become more apparent in the following discussion.

[0038] In general, comparator module 10 includes a pair of comparators labeled 102 and 104, and a pair of AND gates labeled 106 and 108. Comparators 102 and 104 provide temperature comparison functionality provided by comparator module 10. Referring first to the first comparator 102, it receives a temperature signal 16 from temperature sensor 18 and a voltage reference signal 110 that implements a predetermined temperature threshold 12 as described above. Therefore, it should be understood that comparator 102 provides temperature comparison functionality for a single temperature value.

[0039] To provide further value verification, a second comparator 104 compares two input values: a temperature signal 16 from the temperature sensor 18 and a voltage reference signal 112 indicating a lower limit value. Those skilled in the art will understand that this value can be set to indicate an error reading, such as a negative temperature value. For example, the indicated temperature value could be -150 degrees Celsius, which could correspond to a signal voltage of 0.6V or less.

[0040] Therefore, the two comparators 102 and 104 together check whether the temperature signal is within a predetermined range determined by the two reference voltage values ​​110 and 112.

[0041] The outputs 102' and 104' of the two comparators 102 and 104 are fed as input signals to the first AND gate 106, which outputs signal 106' to the second AND gate 108. Therefore, when the outputs of both comparators are also in a logic high state, the output signal 106' will be logic high, indicating that the sensed temperature is within the acceptable temperature range defined by the voltage reference values ​​110 and 112.

[0042] The second AND gate 108 receives the output signal 106 from the first AND gate 106' and also receives an enable / disable signal 31 from the state change latch device 30 (hereafter referred to as a "digital potentiometer" for simplicity). Therefore, the second AND gate 108 will only configure its output signal 108 to a logic high state when both input signals of the second AND gate 108 are in a logic high state. It should be noted that the output signal 108' of the second AND gate is equivalent to the one referenced above. Figure 1 The output signal 22 of the comparator module 10 under discussion, and from now on, shall be referred to as such.

[0043] As discussed, the output signal 22 is input to the switching circuit 12, which includes a switching device 24. The switching device 24 includes a semiconductor switch 120 and a pull-up resistor 122 connected between its source and gate terminals. The drain terminal of the semiconductor switch 120 is connected to the coil contact of the relay 26. Here, the semiconductor switch 120 is shown as a PMOS, although other switch configurations can be used.

[0044] As can be understood from the above, the output signal 22 is connected to the gate terminal of the switch 120 via the inverter NOR gate 124. Therefore, when the output signal 22 from the comparator module 10 is in a logic high state, the inverter 124 converts the signal to a logic low state, which means that the gate terminal is at a low voltage, thus putting the semiconductor switch 120 into the on state. This means that current can flow between the source and drain of the semiconductor switch 120, thereby activating the relay 26 and ensuring that component 6 remains in the enabled state.

[0045] As described above, if the sensed temperature is not within the acceptable range defined by the voltage reference, then the two AND gates 106 and 108 will switch their outputs to logic low, which means that the output signal 22 from the comparator module 10 will change from a logic high state to a logic low state, thereby turning off the switching unit 120 and de-energizing the relay 26.

[0046] exist Figure 2 The details of the digital potentiometer 30 and control module 32 are shown more clearly in the image. It can be seen that the enable / disable signal 31 is generated due to the "wiper" pin (Rw) being connected to the second AND gate 108. As an initial condition, since the sensed temperature is within an allowable range (or at least below a predetermined temperature threshold), the protection circuit 2 operates under the enabled condition, and the voltage on the Rw pin will be at its highest position, corresponding to the input voltage pin Vcc of the digital potentiometer.

[0047] Control module 32 operates digital potentiometer 30 to pull the Rw pin from its highest position to its lowest position, which has the effect of changing the enable / disable signal from an enabled state to a disabled state. Once this occurs, control module 32 operates digital potentiometer to configure the Rw pin to its lowest position, thereby maintaining the enable / disable signal in the disabled state.

[0048] exist Figure 2 An example of the function implemented in control module 32 can be observed. As already discussed, control module 32 transitions from a logic high state to a logic low state in response to control signal 22 from comparator module 10. For this purpose, control module 32 includes a falling edge detector 130, which triggers the operation of negative pulse generator 132. Negative pulse generator 132 sends a logic low signal to the Pd pin of digital potentiometer 30, causing the cursor position to decrease from its current highest value. Note that the pin assignment of digital potentiometers may vary; in other devices, the Pd pin is also referred to as the Ud pin, or more generally, the pin that decrements the cursor position. Those skilled in the art will recognize such other pin assignments. For example, UC, or "up control," is used to increase the cursor position, and DC, or "down control," is used to decrease the cursor position. Those skilled in the art will also understand that different types of digital potentiometers are commercially available, and any of these types, when properly configured, can be used in this application.

[0049] The duration of the negative pulse generated by the negative pulse generator 132 is configured sufficient to pull the value of the Rw pin from its highest position to its lowest position, and this duration can vary depending on the specifications of the digital potentiometer used, particularly the number of steps between the highest and lowest positions of the vernier. However, for the purposes of this discussion, the negative pulse can be considered to be on the order of 3 seconds, corresponding to a 32-step vernier. For further context, the enable / disable signal is configured to provide a digital input that, given a circuit voltage Vcc of 5V, provides enable / disable at, for example, a value of 0.7*Vcc and a value of, for example, 0.3*Vcc. Therefore, for a 32-step potentiometer, the enable / disable signal is positive when the voltage is greater than 3.5V, corresponding to vernier position 23, and negative when the voltage is less than 1.5V, corresponding to vernier position 9.

[0050] Once the cursor position of the digital potentiometer 30 is pulled low, triggering the enable / disable signal to switch to the disabled state, the cursor position must be set or "saved" to that position. The control module 32 achieves this through a delay block 134 and another negative pulse generator block 136.

[0051] As shown in the figure, the negative pulse signal generated by the negative pulse generator 132 is also input to the delay block 134. The delay block 134 responds to the transition of the negative pulse signal from a low state to a high state, in this example after a 3-second period has elapsed. Once the transition is detected, the delay block implements a short delay period, in this case 10ms, and then triggers another negative pulse generator 136 to generate a negative pulse signal, which is input to the ASE pin of the digital potentiometer. The other negative pulse generator 136 generates a negative pulse of a predetermined duration to keep the ASE pin in the low state for a sufficient time so that the digital potentiometer 30 saves the cursor position to the non-volatile memory (NVM) 138 of the digital potentiometer 30. Once the low state of the cursor position is saved to the NVM 138, the enable / disable signal 31 will remain in the disabled state, thereby keeping the switching circuit 22 in the disabled state.

[0052] It should be noted that the specific function of control module 32 is configured to operate the digital potentiometer in the desired manner, so other digital potentiometers may require different control functions. Specifically, the 10ms delay implemented by delay block 134 is configured to ensure that the negative pulse signal has explicitly transitioned back to a high state before triggering another negative pulse generator 138 to generate the NVM save signal at the ASE pin, because the save function will only succeed if the Pd pin is high when the save function is implemented.

[0053] From the above discussion, it can be understood that Figure 2The circuit configuration implements an elegant hardware solution for permanent protection of electrical appliances that must be in a safe state when critical parameters exceed thresholds. Because this solution is hardware-based, it is very space-efficient and can be integrated into the existing PCB space within the appliance.

[0054] Now go to Figure 3 An example of an enhanced protection circuit 200 is shown, which is related to the above regarding Figure 2 The circuit topologies discussed share commonalities. Figure 3 In the middle, you can see at the top of the image. Figure 2 Protection circuit 2, the replication circuit can be seen in the lower part of the figure. For the purposes of discussion, the upper circuit section will be referred to as the first circuit branch 202, and the lower circuit section will be referred to as the second circuit branch 204. It should be noted that the configuration and operation of the first circuit branch 202 are as described above. Figure 2 Therefore, further discussion will not be repeated here.

[0055] and Figure 2 Compared to the protection circuit, Figure 3 The protection circuit 200 provides fault tolerance because the function of the first circuit branch 202 is replicated by the second circuit branch 204. Therefore, if one circuit branch fails and fails to de-energize the relay 26, the other circuit branch will still function correctly, de-energizing the relay and thus cutting off the power supply to the heater device 6.

[0056] In summary, the first circuit branch 202 includes a first comparator module 210, a first state change latch device 212, a first control module 213, and a first switching circuit 214 connected to the relay 216. The operation of these circuit elements is related to the above-mentioned... Figure 2 The description of protection circuit 2 is the same.

[0057] The second circuit branch 204 is very similar to the first circuit branch 202, and also includes the second comparator module 230, the second control module 231, the second state change latch device 232, and the second switching circuit 234. These circuit elements will be discussed further below.

[0058] It is worth noting that the second comparator module 230 is somewhat simplified compared to the first comparator module 210, and has a single comparator element 236 and a single AND gate 238. Comparator element 236 receives a temperature signal 16 from the temperature sensor 18 and a voltage reference signal 240 defining a temperature threshold. Therefore, in practice, because comparator element 236 receives the same temperature signal and the same voltage reference, comparator element 236 implements the same functionality as described above. Figure 2The protection circuit discussed is similar to the temperature checking function of comparator module 10.

[0059] When appliance 2 is operating normally and the temperature signal 16 from temperature sensor 18 is below a predetermined threshold, the output signal 242 of comparator element 236 is logic high and is fed to AND gate 238. In the same manner as in the first circuit branch 202, in the second circuit branch 204, AND gate 238 also receives an enable / disable signal 244 from the second state change latch device 232, which is initially in a logic high state.

[0060] Optionally, AND gate 238 can also receive an enable / disable signal 239 from the state change latch device 212 of the first circuit branch 202, as shown by the dashed line labeled 239' in the figure. Similarly, an enable / disable signal 244 from the second state change latch device 232 can also be input to the first comparator 210, as shown by the dashed line 244'. This configuration ensures that either state change latch device 212, 232 can disable the operation of the relay device 26, thus effectively improving the fault tolerance of the circuit. Furthermore, since the operation of either state change latch device 212, 232 triggers the AND gate, a failure in either device will not affect the result, because the two state change latch devices 212, 232 are effectively cross-linked, so the triggering of either will cause the operation of both switching devices, thereby de-energizing the relay. This prevents tolerances in the comparator from, for example, tripping only one of the state change latch devices 212, 232, because in this case, both AND gates 108 and 238 will be triggered.

[0061] When appliance 2 is working normally, the input signal of AND gate 238 will be logic high, and therefore the output signal 246 of AND gate 238 will also be logic high.

[0062] Output signal 246 is input to second switching circuit 234, which is connected to relay 216 in the same manner as first switching circuit 214. Optionally, as shown here, output signal 246 can be filtered by filter element 247, which applies an appropriate time constant to output signal 246 to filter out any transient fluctuations in the signal. As a further option, latching element 248 can be included in the circuit, and... Figure 3In the diagram, latch element 248 is shown located after filter element 247. One advantage of latch element 248 is that, if the outputs of comparators 108 and 238 are pulled high before the 3-second period required to activate state change latch devices 212 and 232 expires, latch element 248 ensures that the signal remains in a low state for a sufficiently long period to allow state change latch devices 212 and 232 to become low-state enable / disable signals.

[0063] Here, each of the switching circuits 214 and 236 must provide a positive voltage to the relay 216 in order to energize the relay 216, and thus also to the heater device. Figure 3 (Not shown in the diagram) Power supply. In the second circuit branch 204, the second switching circuit 234 includes a semiconductor switching device 250, shown as an NMOS transistor, whose source terminal S is connected to ground GND, its drain terminal D is connected to a relay 216, and its gate terminal G receives the output signal 246 from the AND gate 238. A pull-down resistor 252 is connected between the gate terminal G and ground GND to ensure that the logic low signal is at ground potential.

[0064] Using this configuration, it can be understood that when the output signal 246 from AND gate 238 is logic high, this will cause the gate terminal G of switching device 250 to enter a high state, which will connect the drain terminal D and the source terminal S, thereby energizing the coil connection of the relay 216 connected thereto. The first switching circuit 224 is connected to another coil connection of relay 216, and when both switching circuits are active, relay 216 is energized.

[0065] Conversely, if the output signal 246 from AND gate 238 transitions to a logic low state, pull-down resistor 252 ensures that the gate terminal G is grounded, thus turning off the switching device and de-energizing relay 216.

[0066] It should be noted that the operation of the second control module 231 and the second state change latch device 232 is related to the already established... Figure 2 The operation of the equivalent component described in protection circuit 2 is the same as that of the first circuit branch 202. Therefore, no further description will be provided here.

[0067] From the above discussion, it will be understood that the first circuit branch 202 and the second circuit branch 204 operate in parallel to provide a watchdog function for the operation of the heater device 6. Both circuit branches 202 and 204 respond to the temperature sensor 18 detecting that the temperature at the heater device 6 is higher than a predetermined temperature threshold, which is considered to define the safe upper limit of the heater device. If the temperature signal exceeds the predetermined threshold, the state change of the output signal propagates through comparators and AND gates to disable the switching circuits 214 and 234 and de-energize the relays. Simultaneously, in response to the state changes from the comparator modules 210 and 230, the state change latching devices 212 and 232 in the first and second circuit branches 202 and 204 are operated respectively to latch their respective enable / disable signals 239 and 244 to the disabled state, thereby locking the appliance 2 in a non-operating safe state. Therefore, even if the temperature drops to an acceptable level, the latched enable / disable signals 239 and 244 issued by the state change latching devices 212 and 232 will ensure that operation of the appliance 2 is impossible.

[0068] Figure 4 It shows Figure 2 and Figure 3 A series of timing diagrams or waveforms of various signals in the protection circuit. Regarding... Figure 3 The timing diagram relates to components in the first circuit branch 202, but it should be understood that the same information applies to the second circuit branch 204. For clarity, waveforms are labeled 4(a) to 4(g), where waveform 4(a) represents the main power supply to the product containing the heater device 6; waveform 4(b) represents the voltage supplied to the relay; waveform 4(c) represents the temperature profile detected by the temperature sensor 18; waveform 4(d) indicates the voltage of the output signal 22 from the comparator module 10; 210; waveform 4(e) represents the trigger signal generated by the control module 32; 213; waveform 4(f) represents the voltage on the ASE pin of the state change latch device; and waveform 4(g) represents the state of the enable / disable signal 31; 239 from the state change latch device 30; 212 to the comparator module 10; 210.

[0069] Referring first to waveform 4(c), it can be seen that the temperature starts at t=0 with a value below a predetermined threshold, as indicated by the dashed line marked VREF1, and rises above that threshold at t=T1. Due to the filtering applied by filter element 247, there is a 150ms time period before any signal transition occurs. At t=T2, as can be seen from waveform 4(d), the voltage at switching device 12;214 transitions from logic high to logic low. Similarly, as shown in waveform 4(e), at t=T2, a negative pulse is generated by negative pulse generator 132. As mentioned above, the negative pulse is generated with a 3-second period, which causes the enable / disable signal 31;239 to decrease in steps from its highest value to its lowest value, as shown in waveform 4(g).

[0070] Once the 3-second negative pulse ends and the negative pulse transitions back to logic high, the delay block 134 implements a 10ms delay period before the second negative pulse generator 136 generates a short negative pulse of 50ms at the ASE pin of the state change latch device 30; 212. This causes the cursor position of the state change latch device 30; 212 to be stored in the NVM.

[0071] This function can be further understood by considering waveforms 4(a) and 4(b), which respectively represent the main power supply and the circuit voltage Vcc from the wall plug. It can be seen that when the main power supply is interrupted, this also interrupts the positive circuit voltage Vcc, indicating that as a safety measure, the user shuts off the appliance at the wall plug once they realize it has tripped. It can also be seen that when the main power supply is re-established, this also re-establishes the circuit voltage Vcc, and although the temperature is at a safe level, this does not change the state of the enable / disable signal of the state change latching device, as can be seen by comparing waveforms 4(a), 4(d), and 4(g).

[0072] Those skilled in the art will understand that the above references Figures 1 to 4 The described circuit configuration is an example of a hardware implementation of a single-operation latching switch circuit for an appliance, optionally with single fault tolerance. A single-operation latching device is a device that retains latching even after a restart operation. For completeness, references will now be made to... Figure 5 Another example configuration of the protection circuit 300 is described.

[0073] Figure 5 and Figures 1 to 3 The circuit configurations in these circuits share some commonalities, so only the differences will be described here to avoid confusion regarding the basic working principles.

[0074] With similar Figures 1 to 3In the example circuit configuration, protection circuit 300 includes comparator module 302, state change latching device 304, and associated control device 306, which control the operation of switching circuit 308. As in the previous example, switching circuit 308 includes switching device 310, which controls the energization of relay 312, which in turn controls the operation of power supply 314, which regulates the power flow from main power supply 316 to appliance component 318.

[0075] It is worth noting that in this embodiment, the state change latch device 304 sends an enable / disable signal 322 to the comparator module 302, but the enable / disable signal serves as a voltage reference for the comparator module 302 to compare with the measured temperature signal 324 received from the temperature sensor 326.

[0076] As in the previous example, the state change latch device 304 is implemented as a digital potentiometer, and the enable / disable signal 322 is the output of the digital potentiometer's vernier pin. Since the digital potentiometer provides a voltage reference used by the comparator module 302, this voltage value must be accurate to ensure proper comparison with the temperature sensing signal. Therefore, the digital potentiometer is preferably configured with a vernier of 256 steps to provide appropriate resolution for the voltage reference.

[0077] The control device 306 and the switching circuit 308 operate in the same manner as discussed with reference to the preceding example, and therefore will not be discussed further. It should be understood that this example has a simpler implementation with fewer logic components.

[0078] Different examples of circuit configurations and some variations thereof have been described above. Those skilled in the art will understand that modifications may be made to those circuit configurations without departing from the inventive concept defined in the claims.

[0079] The circuit configuration discussed above has the advantage that the cut-off function is implemented as a hardware solution, providing an extremely compact package. Those skilled in the art will understand that the protection circuits discussed here operate on a one-time basis and cannot be reset by the user, thus ensuring that the electrical appliance remains in a safe state. However, conveniently, the protection circuits can be configured to allow them to be tested and reset in factory settings. One way to reset the protection circuit is to power the PU pin (or “pull-up pin”) of the digital potentiometer via an external test interface. This action pulls the cursor position high to its highest level, thus setting the enable / disable signal back to the enabled state. Once the cursor pin Rw returns to its highest level, the ASE pin of the digital potentiometer can be powered on for a period of time to retain the new cursor position.

Claims

1. A protective circuit for electrical appliances, comprising: A first comparator module is configured to compare an operating parameter input signal with a threshold and output a first control signal to a first switching circuit, the first switching circuit being configured to control the power flow to associated electrical components. The first comparator module is configured to receive an enable / disable signal from the first state change latch device. The first state change latching device responds to a state change of the first control signal from the first comparator module. In response, the first state change latching device changes the enable / disable signal from an enabled state to a disabled state, thereby setting the first control signal to an off state and thus locking the electrical appliance in a non-operating safe state. The control module monitors the first control signal of the first comparator module and outputs a trigger input to the first state change latching device in response to the state of the first control signal. The first state change latching device includes a latching mechanism activated by a trigger input and a storage module for storing the state of the latching mechanism. The control module controls the storage module to save the state of the latching mechanism by outputting a save input for a predetermined duration. Thus, once the state of the latching mechanism is saved in the storage module, the electrical appliance will remain in a non-operating safe state even after it is restarted.

2. The protection circuit according to claim 1, wherein, The latching mechanism is configured to change its state when a trigger input is detected to be in a trigger state for a predetermined time period.

3. The protection circuit according to claim 1 or 2, wherein, The first state change latching device is a digital potentiometer.

4. The protection circuit according to claim 1 or 2, wherein, The first comparator module includes a comparator that outputs a logic high signal to a first logic element when the operation parameter input signal exceeds the threshold, and wherein, when the output signal of the comparator and the enable / disable signal are in the same logic high state, the first logic element outputs the first control signal in a logic high state.

5. The protection circuit according to claim 1 or 2, wherein, The first comparator module includes a comparator that outputs the first control signal as a logic high state when the operation parameter input signal exceeds the threshold.

6. The protection circuit according to claim 5, wherein, When the enable / disable signal of the first state change latching device is in the enabled state, the threshold is provided by the enable / disable signal.

7. The protection circuit according to claim 1 or 2, further comprising: The second comparator module is configured to receive an operating parameter input signal, compare the operating parameter input signal with a threshold, and, in response, output a second control signal to a second switching circuit configured to control the power flow to an associated electrical appliance. The second comparator module is configured to receive an enable / disable signal from the second state change latch device. In response to a state change of the second control signal from the second comparator module, the second state change latch device changes the enable / disable signal from the enabled state to the disabled state, thereby locking the second control signal to the off state.

8. The protection circuit according to claim 7, wherein, The first switching circuit is connected to a power control relay, wherein the power control relay is connected to a power source.

9. The protection circuit according to claim 7, wherein, The second switching circuit is connected to the power control relay.

10. The protection circuit according to claim 8, wherein, The power control relay is configured to disable the power supply when one or both of the first and second switching circuits operate to de-energize the power control relay.

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