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Title:
ANALOG PULSE WIDTH MODULATION TEMPERATURE CONTROL
Document Type and Number:
WIPO Patent Application WO/2019/126349
Kind Code:
A1
Abstract:
A method of regulating temperature of an electrical heating appliance using a temperature control system is disclosed. The method includes generating a triangle waveform using the temperature control system. The method also includes receiving a temperature setting at the temperature control system. The method also includes comparing the temperature setting and the triangle waveform using the temperature control system. The method also includes outputting a pulse-width modulation square wave at the temperature control system based on the comparing. The method also includes selectively powering a heating unit using the temperature control system based on the pulse-width modulation output square wave.

Inventors:
CLEPPE, Benjamin Miles (6735 Frank Lloyd Wright Ave. #200, Middleton, Wisconsin, 53462, US)
VODVARKA, Brian Lloyd (3365 11th Avenue, Grand Marsh, Wisconsin, 53936, US)
KUMAR, Rajesh (3527 Salreno Ct, Apt. 2Middleton, Wisconsin, 53562, US)
Application Number:
US2018/066541
Publication Date:
June 27, 2019
Filing Date:
December 19, 2018
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
SPECTRUM BRANDS, INC. (3001 Deming Way, Middleton, Wisconsin, 53562, US)
International Classes:
H05B1/02; G05D23/20
Foreign References:
US20040149744A12004-08-05
US6031404A2000-02-29
US20160045069A12016-02-18
US5376775A1994-12-27
KR19980015518A1998-05-25
Attorney, Agent or Firm:
BINDER, Mark, W. et al. (Kagan Binder, PLLCSuite 200, Maple Island Building,221 Main Street Nort, Stillwater Minnesota, 55082, US)
Download PDF:
Claims:
WHAT IS CLAIMED IS:

1. A method of regulating temperature of an electrical heating appliance using a temperature control system, comprising: generating a triangle waveform using the temperature control system; receiving a temperature setting at the temperature control system; comparing the temperature setting and the triangle waveform using the temperature control system; outputting a pulse-width modulation square wave at the temperature control system based on the comparing; and selectively powering a heating unit using the temperature control system based on the pulse-width modulation output square wave.

2. The method of claim 1, wherein the comparing the temperature setting and the triangle waveform each include a corresponding voltage, and wherein the temperature setting voltage and the triangle waveform voltage are superimposed such that it can be determined over time if and when the temperature setting voltage is less than, equal to, or greater than the triangle waveform voltage, and wherein the pulse- width modulation square wave is output based on the determining.

3. The method of claim 2, wherein at times when the triangle waveform voltage is greater than the temperature setting voltage, the output pulse-width modulation square wave indicates that the heating unit is to be selectively operated to be turned on, and at times when the triangle waveform voltage is less than the temperature setting voltage, the output pulse- width modulation square wave indicates that the heating unit is selectively operated to be powered off.

4. The method of claim 2, wherein selectively operating the heating unit includes selectively powering on and off the heating unit in accordance with the pulse-wave modulation square wave such that the heating appliance reaches an equilibrium level.

5. The method of claim 1, wherein the temperature setting is received at the temperature control system from a potentiometer connected to a negative temperature coefficient monitor circuit.

6. The method of claim 1, wherein the selectively operating the heating unit utilizes a relay operatively connected to the output pulse-width modulation square wave and to the heating unit.

7. The method of claim 1, wherein the triangle waveform is generated using at least one comparator and at least one integrator.

8. The method of claim 7, wherein the pulse-width modulation square wave is output using a second comparator that receives the triangle waveform.

9. The method of claim 1, wherein the temperature control system comprises only analog circuitry and components.

10. An electric heating appliance, comprising: a power supply circuit; a heating unit connected to the power supply circuit; a temperature control system, comprising: a triangle wave generator, comprising: a first comparator connected to the power supply circuit, and a first integrator configured to receive an output from the first comparator; a temperature monitor having an output based on a detected temperature; a second comparator connected to the triangle wave generator and configured to receive the output from the temperature monitor, wherein the second comparator is configured to output a square wave; and a relay configured to receive the square wave output from the second comparator, and configured to output a pulse-width modulation heating signal to the heating unit based on the received square wave.

11. The electric heating appliance of claim 10, wherein the power supply circuit is configured to output at least two different voltages.

12. The electric heating appliance of claim 10, further comprising a potential divider connected between outputs of the first comparator and the first integrator.

13. The electric heating appliance of claim 10, wherein the temperature monitor is connected to a plate interlock of the heating appliance, and wherein when a grill plate is removed from the appliance, the heating unit does not operate.

14. The electric heating appliance of claim 10, wherein the temperature monitor is a negative temperature coefficient monitor.

15. The electric heating appliance of claim 14, wherein the negative temperature coefficient monitor forms a protection circuit that monitors a negative temperature coefficient connection, and wherein in an event where the negative temperature coefficient monitor connection becomes disconnected, a supply voltage can be removed from various components to prevent overheating of the appliance.

16. The electric heating appliance of claim 15, wherein the negative temperature coefficient monitor comprises an unbiased PNP transistor configured to have a default position of on.

17. The electric heating appliance of claim 10, wherein the heating appliance is selected from the group consisting of: a toaster oven, an open grate grill, an indoor/outdoor grill, a sandwich grill, a hair straightener, an iron, a toaster, or a beverage maker.

18. An electric heating appliance, comprising: a power supply circuit; a heating unit connected to the power supply circuit; a first comparator connected to the power supply circuit; a first integrator connected to an output of the first comparator; a temperature monitor having an output based on a detected temperature; a second comparator connected to an output of the first integrator and the temperature monitor; and a relay connected to an output of the second comparator and configured to output a heating signal to the heating unit.

19. The electric heating appliance of claim 18, wherein the first integrator is configured to output a triangle wave.

20. The electric heating appliance of claim 18, wherein the second comparator is configured to output a pulse-wave modulation square wave.

Description:
ANALOG PULSE WIDTH MODULATION TEMPERATURE CONTROL

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to and the benefit of U.S. Provisional Patent Application No. 62/607,960, filed December 20, 2017, the entire contents of which is incorporated herein by reference in its entirety.

BACKGROUND

[0002] The field of the disclosure relates generally to methods and systems of controlling a heating unit for use in a heating appliance.

[0003] Heating appliances commonly use mechanical snap-action thermostats or digital circuitry to control temperature. Snap-action thermostats offer some temperature control, but there is room for improvement. Digital circuitry, such as temperature control application- specific integrated circuits (ASICs) can accomplish adequate temperature control, but have other drawbacks, such as complexity and cost.

[0004] Snap-action temperature control methods operate by powering on a heating unit, e.g., including a resistive heating element, and mechanically sensing when a temperature has reached a certain maximum threshold temperature level, where the snap-action temperature control turns the heating unit off completely until it falls to a certain minimum temperature and the process is repeated. Over time, this leads to an appliance heating unit temperature profile with large oscillations and relatively uneven temperature due to long and possibly unpredictable heating-cooling cycles, as well as overshoot of a target temperature upon start up. Alternatively, digital circuitry, which can employ proportional-integral-derivative (PID) control can be implemented with a negative temperature coefficient (NTC) thermistor for thermal feedback and a microcontroller improves thermal performance, but is costly relative to a snap-action thermostat. Therefore, a cost-effective and simple way of effectively controlling temperature of a heating unit within an appliance is desired.

SUMMARY

[0005] In various aspects, methods and structures of using analog pulse-width modulation (PWM) for temperature control are disclosed. According to various embodiments, analog PWM temperature control utilizes analog electronic circuitry to control the temperature of the heated appliance, such as a grill, toaster oven, or a hair straightener. Implementation of PWM temperature control significantly improves thermal performance using analog circuitry components. Improvements include reductions in oscillation amplitude of the appliance temperature (temperature swings when in steady-state operation) when compared to oscillation amplitudes produced by snap-action thermostats. Additionally, temperature evenness within the appliance is improved significantly.

[0006] According to a first aspect, a method of regulating temperature of an electrical heating appliance using a temperature control system is disclosed. According to the first aspect, the method includes generating a triangle waveform using the temperature control system. The method also includes receiving a temperature setting at the temperature control system. The method also includes comparing the temperature setting and the triangle waveform using the temperature control system. The method also includes outputting a pulse- width modulation square wave at the temperature control system based on the comparing.

The method also includes selectively powering a heating unit using the temperature control system based on the pulse-width modulation output square wave.

[0007] According to a second aspect, an electric heating appliance is disclosed. According to the second aspect, the electric heating appliance includes a power supply circuit. The electric heating appliance also includes a heating unit connected to the power supply circuit. The electric heating appliance also includes a temperature control system. According to the second aspect, the temperature control system includes a triangle wave generator. The triangle wave generator includes a first comparator connected to the power supply circuit and a first integrator configured to receive an output from the first comparator. The temperature control system also includes a temperature monitor having an output based on a detected temperature. The temperature control system also includes a second comparator connected to the triangle wave generator and configured to receive the output from the temperature monitor, where the second comparator is configured to output a square wave. The temperature control system also includes a relay configured to receive the square wave output from the second comparator, and configured to output a pulse-width modulation heating signal to the heating unit based on the received square wave.

[0008] According to a third aspect of the present disclosure, another electric heating appliance is disclosed. According to the third aspect, the electric heating appliance includes a power supply circuit. The electric heating appliance also includes a heating unit connected to the power supply circuit. The electric heating appliance also includes a first comparator connected to the power supply circuit. The electric heating appliance also includes a first integrator connected to an output of the first comparator. The electric heating appliance also includes a temperature monitor having an output based on a detected temperature. The electric heating appliance also includes a second comparator connected to an output of the first integrator and the temperature monitor. The electric heating appliance also includes a relay connected to an output of the second comparator and configured to output a heating signal to the heating unit.

DRAWINGS

[0009] FIG. 1 is a flowchart of a process, in accordance with an embodiment of the present invention.

[0010] FIG. 2 is a negative temperature coefficient voltage divider circuit, in accordance with various embodiments.

[0011] FIG. 3 is a schematic diagram of an operational amplifier showing inputs and outputs, according to various embodiments.

[0012] FIG. 4 is a pulse width modulation voltage plot for a low temperature reading of an appliance, where a heating unit is activated, according to various embodiments.

[0013] FIG. 5 is a pulse width modulation voltage plot for a high temperature reading of an appliance, where a heating unit is not activated, according to various embodiments.

[0014] FIG. 6 is a pulse width modulation voltage plot for a moderate temperature reading of an appliance, where a heating unit is selectively activated, according to various embodiments.

[0015] FIG. 7 is a schematic diagram of an appliance power supply circuit for use with various embodiments.

[0016] FIG. 8 is a schematic circuit representation of a pulse width modulation temperature control system for an appliance, according to an embodiment of the present disclosure.

[0017] FIG. 9 is a schematic circuit representation of a pulse width modulation temperature control system for an appliance including a negative temperature coefficient monitor circuit, according to an embodiment of the present disclosure.

[0018] FIGS. 10A-10C show graphical data comparing an indoor/outdoor grill with pulse width modulation temperature control of the present invention with a similar grill controlled using existing snap-action temperature control. [0019] FIGS. 11A-11C show graphical data comparing an open grate grill with pulse width modulation temperature control of the present invention with a similar grill controlled using existing snap-action temperature control.

[0020] FIGS. 12A-12C show graphical data comparing a toaster oven with pulse width modulation temperature control of the present invention with a similar toaster oven controlled using existing snap-action temperature control.

[0021] FIGS. 13A-13C show graphical data comparing an electric hair straightener with pulse width modulation temperature control of the present invention with a similar hair straightener controlled using existing digital temperature control.

[0022] Corresponding reference characters indicate corresponding parts throughout the several views of the drawings.

DETAILED DESCRIPTION

[0023] Disclosed are methods and structures of using analog pulse-width modulation (PWM) for temperature control. As used herein, analog PWM temperature control utilizes analog electronic circuitry to control the temperature of the heated appliance, such as a grill, a toaster oven, a coffee maker, an iron, a hair straightener, among many other appliances and devices that use a resistive heating element. Implementation of analog PWM temperature control significantly improves thermal performance using analog circuitry components as compared to existing options, such as snap-action thermostats. Improvements include reductions in oscillation amplitude of the appliance temperature (temperature swings when in steady-state operation) when compared to oscillation amplitudes produced by existing snap- action thermostats. Additionally, temperature evenness within the appliance is improved significantly. By generating a triangle wave and using operational amplifiers (op-amps) to compare the triangle wave with a read voltage and/or a reference voltage, analog circuit components can use an output PWM wave to effectively regulate/power on a heating unit and the temperature of an appliance as a thermostat.

[0024] With reference now to FIG. 1, a method of using analog PWM temperature control is disclosed in flowchart 100. Initially, a triangle waveform is generated at operation 110 using analog circuitry, such as op-amps. Additionally, a temperature setting or reading is received at operation 112, e.g., from a user. The temperature setting or reading operation 112 can be received from a potentiometer set by a user according to a target temperature, according to various embodiments. After the triangle waveform is generated at operation 110, and the temperature setting is received at operation 112, the temperature setting and the triangle waveform are compared at operation 114, e.g., using another op-amp component. Based on the comparing, a PWM square wave is output at operation 116. Then, a heating unit (or appliance) is selectively operated (e.g., using a relay) according to modulated pulse widths according to the output square wave at operation 118.

[0025] In greater detail and with reference now to FIG. 2, embodiments of PWM analog circuitry can include a voltage divider circuit 200 that includes a negative temperature

i

coefficient (NTC) thermistor (or monitor). The NTC thermistor can be used within an appliance for temperature feedback in an analog PWM temperature control system as described herein. Generally speaking, the electrical resistance of the NTC will decrease as its temperature increases. As shown, the NTC can be operatively placed in the voltage divider circuit 200. Therefore, as the temperature of the appliance increases, the read voltage of the voltage divider circuit 200 also increases.

[0026] The voltage divider circuit also includes a potentiometer POT, and a power source, such as a 12V power source from power supply circuit 700 of FIG. 7. In other embodiments, the power source can be other suitable voltages. The resistance of POT can be changed to change the temperature set point of the appliance, e.g., by a user. POT is an example of a user input device, which can include continuous potentiometers, potentiometers with detents, and/or mechanical buttons with one or more logic chips, among other types. A continuous potentiometer can allow for a continuously variable temperature input from the user, between an“off’ setting and a maximum temperature. A potentiometer with detents can allow the user to select from discrete temperature settings. Mechanical buttons with logic chips can allow the user to select a cooking/heating mode while still keeping the circuit analog. Various combinations of the above and other input devices are contemplated, herein. Using the voltage divider circuit 200, a read voltage (V read ) can be output to be used in embodiments, herein.

[0027] With reference now to FIG. 3, an op-amp 300 is shown. Op-amp 300 can be used to compare a reference voltage to the read voltage output from, for example, voltage divider circuit 200. Inputs and outputs of op-amp 300 are shown, including V read , an inverting input, V ref , a non- inverting input, a 12V connection, a ground connection, and a V out output connection. In essence, an input at a non-inverting input of an op-amp causes an output voltage that changes in the same direction as the input voltage. Likewise, an inverting input of an op-amp causes an output voltage that changes in the opposite direction as the input voltage at the inverting input. When the reference voltage is greater than the read voltage, the output is high (12V in this case). When the reference voltage is less than the read voltage, the output is low (0V in this case). The output voltage can be used to actuate a relay that cycles the heating unit power on and off. When the reference voltage (V ref ) is greater than the read voltage (V read ), the output voltage (V out ) is high, and the heating unit(s) will be powered on using, for example, a relay or a triode for alternating current (TRIAC). When the reference voltage is less than the read voltage, the output voltage is low, and the heating unit(s) will be powered off. In various other embodiments, the op-amp 300 can instead connect to a 5 V power supply circuit output, among other options.

[0028] Op-amps disclosed herein may not show a connection to a 5V or a 12V source in some embodiments. In embodiments where no voltage source is shown, the op-amps can be connected to various 5V/12V sources, neutral connections, and/or ground connections. Various op-amps described herein can be characterized as being integrators or comparators depending on input connections being inverting or non-inverting, for instance.

[0029] Turning now to FIGS. 4-6, a triangular reference voltage waveform can be created using analog circuitry, such as op-amps (shown in greater detail with reference to FIGS. 8 and 9). The maximum and minimum values of the triangular voltage waveform can be optimized parameters to maximize thermal performance of the appliance. As shown, various read voltages (V read ) at the heating unit are visually plotted with respect to an example reference voltage (V ref ) triangle wave having an amplitude of 6V from maximum to minimum. The reference voltage triangle wave is unchanged at various temperature settings and readings of FIGS. 4-6, but is used to effect a PWM square heating wave in cases where the read voltage is at a level below the peaks (maximum) voltage of the reference voltage. Furthermore, the read voltage is at a level above the trough (minimum) voltage of the reference voltage, where PWM is preferably employed to control a heating unit at a substantially stable equilibrium level, which can be a substantially steady state temperature. FIGS. 4-6 demonstrate how a read voltage (V read ), a reference voltage (V ref ), and a square wave output voltage (V out ) can together lead to analog PWM temperature control, as described herein. [0030] In a case where an appliance has just begun heating and its temperature is determined to be relatively low as shown by the position of the read voltage (V read ), plot 400 of FIG. 4 displays the condition where the heating unit is continuously on. Since the temperature is relatively low, so is the read voltage (V read ) of the NTC voltage divider circuit 200. The read voltage (V read ) is less than the minimum triangle wave reference voltage (V ref ), so the appliance remains powered on at least until read voltage conditions change, e.g., during heating. Therefore, as shown, the output voltage (V out ) is high.

[0031] FIG. 5 displays a plot 500 showing a condition where the appliance heats past a point where the read voltage is greater than the maximum voltage of the generated input triangular reference voltage waveform. In this condition, the output voltage (V out ) is low, so the heating unit(s) are not on and the appliance is allowed to cool at least temporarily. During cooling, once the read voltage (V read ) falls back below the maximum voltage of the reference voltage (V ref ) triangular waveform, temperature regulation can begin using steady-state analog PWM temperature control, as described with respect to FIG. 6.

[0032] With reference now to plot 600 of FIG. 6, as the example appliance or heating unit heats up, the read voltage (V read ) increases until it eventually lies between the minimum and the maximum voltages of the reference voltage (V ref ) triangle wave. During this condition, the output voltage (V out ) square wave cycles between high and low as the triangle wave reference voltage oscillates. This is in contrast to FIG. 4 and FIG. 5, where the output voltage (V out ) was always either high or low, respectively. This cycles the power of the appliance according to analog PWM. At higher temperatures, the read voltage increases and falls between the maximum and minimum voltages of the triangular reference voltage waveform. When the reference voltage is greater than the read voltage, the output voltage is high and the appliance is powered on. When the reference voltage is less than the read voltage, the output voltage is low and the appliance or heating unit is powered off. As the temperature of the appliance rises from the heating unit being powered on, so does the read voltage (V read ), and the heating unit(s) spend a lower proportion of the time powered on. As a result, the appliance can eventually reach an equilibrium level, a substantially steady state where the temperature neither increases nor decreases drastically. Of note, as shown, the power of the appliance and heating unit is not varied while on, but instead the techniques described herein operate to regulate when the power is switched on or off using analog PWM temperature control schemes. [0033] FIG. 7 shows an example power supply circuit 700 for use with various analog PWM temperature control embodiments. Other power supply configurations and structures are also contemplated as well as various methods of supplying power to various circuit components.

[0034] Power supply circuit 700 includes various components, as shown. A source of alternating current at VI can be 120V root-mean-square at 60 Hz. VI can represent a standard 120V wall plug in a household or a business. It is contemplated that the source of alternating current can also be of a 240V wall plug as found in certain locations. VI can be electrically connected to a voltage split, and to resistor R8 at a negative terminal of VI, R8 having a resistance of 100 Ohms (W), and a 250mA fuse U3 on a positive terminal of VI.

Also connected to the voltage split, as shown, is capacitor C2 and a 1 mega-Ohm (MW) resistor R7, which can be connected in series to fuse U3 to serve as a voltage drop.

Preferably, various voltages used in embodiments herein can include 12V 710 and 5V 712 outputs, direct current, with a positive polarity, for example. Outputs 710 and/or 712 can have a negative polarity output in other embodiments.

[0035] Resistor R8 and split R7/C2 are then connected to a bridge rectifier 714 formed by diodes D2-D5 in order to produce desired direct current for powering an example appliance. The bridge rectifier 714 can include Zener diodes D2 and D4, as well as standard diodes D3 and D5. In addition, a linear voltage regulator U2 (e.g., an LM7805CT) can be used at least in part to supply both a 12V (+12V) output 710 via connection 716 and a 5 V (+5V) output 712 via connection 718. As shown, the linear voltage regulator U2 can also include a connection 720 for connection to a ground. An LED (LED1) can also be included, e.g., to demonstrate that the power supply circuit 700 is activated and/or functioning. A resistor R15 can be connected in series with LED1, as shown. Various other capacitors (e.g., C3, C4, and/or C5) and other components, as shown, can preferably be employed in power supply circuit 700. As shown, capacitor C3 can be a filter capacitor configured to filter out ripple from rectified alternating current. Capacitors C4 and C5 can be configured to act as transient filters to the linear voltage regulator U2, which can connect high frequency transient power to ground.

[0036] FIG. 8 is a schematic circuit representation of a PWM temperature control system 800, according to an embodiment of the present disclosure. [0037] PWM temperature control system can be connected to power supply circuit 700 of FIG. 7 in various placed to be used to power various components, such as triangle wave generation components 812, NTC 814, temperature setting LED 818, and heating unit 820. Also shown is an NTC temperature setting unit 816, which may not be connected directly to power supply circuit 700. The 12V output 710 of power supply circuit 700 can be connected to relay K1 of heater unit 820 at 824 for use in appliance heating using a heating unit, as described herein.

[0038] Regarding the triangle wave generation components, a 5 V output 712 of the power supply circuit 700 can be connected to various components of the system 800, including 822 A, 822B, 822C, and 822D. The 5 V output 712 is connected to an inverting input of a comparator op-amp U1 A via 822A and also connected to a non- inverting input of an integrator op-amp U1B by a feedback connection, as shown. The 5 V supply 822A can be supplied through a resistor R6, and the signal can be grounded through another resistor R10, as shown. In other embodiments, the 5V supply 822A (among others) can be other suitable voltages. Comparator op-amp U1A can also include a second, power input 5V voltage at 822B, as shown.

[0039] As discussed above, the triangle wave generation components 812 include two op- amps connected in series, including a comparator U1A and an integrator U1B. The comparator U1 A has an output, which is connected to the non-inverting input as a feedback loop connection. The output, which can include a square wave signal, is also connected to an inverting input connection of integrator U1B. Similar to comparator U1A, and although not shown, the integrator op-amp U1B can also include a power input at 5V, similar to 5V input 822B of comparator op-amp Ul A, and the integrator U1B can be powered from the power supply circuit 700 and can be grounded. As shown, an output of integrator U1B is connected to ground through a resistor R9, and also is connected to the inverting input of itself by way of feedback capacitor Cl, and also to the non-inverting input of comparator U1A through resistor Rl. Feedback capacitor Cl can give a delay of an output triangle wave, e.g., changing the frequency of the triangle wave. Cl in combination with resistor R6 can set or select a triangle wave frequency or other characteristic.

[0040] Based on application and configuration, and parameters, the combination of capacitor Cl and resistor R6 can be selected and configured to give a desired triangle wave frequency. In some applications (e.g., some appliances) a desire may exist for a low frequency triangle wave. In other applications, a desire may exist for a medium or high frequency triangle wave. A triangle wave frequency can be selected based on thermal load, thermal constants of a device, and/or a desired relay life. In some embodiments, a relay can have a longer lifespan if subjected to fewer cycles. In some cases a larger thermal mass to be heated in an appliance can be suited to slower wave cycles. In some cases, a toaster oven appliance may have relatively shorter cycles as the toaster oven may lack a substantial (thermal storage, heat conductive, etc.) plate to be heated during operation. The frequency of the output (V ref ) triangle wave can affect the operation of the analog PWM temperature control.

[0041] A triangle waveform or signal can then be transmitted to temperature zone 810 circuit components, and specifically to a comparator U1C at a positive switch input. An NTC temperature setting can be set or received at the NTC temperature setting unit 816, which can include, e.g., a potentiometer R13, as shown. Temperature zone 810 can also include an NTC unit 814 for detecting a temperature in an appliance. NTC unit 814 can be connected to the power supply circuit 700 5V signal 822C and can include a gain feedback resistor R5. A temperature setting from NTC temperature setting unit 816 and a temperature read setting of the appliance from NTC unit 814 can together (e.g., as [V read ] of FIGS. 4-6) be received at comparator op-amp U1C at an inverting input. Using a voltage divider circuit similar to circuit 200 of FIG. 2, a V read can be a composite of a temperature reading of an appliance combined with a potentiometer setting. Although not shown, comparator U1C can also be connected to 5V power from power supply circuit 700 and can be grounded (and/or connected to one or more neutral connections).

[0042] As comparator U1C receives both the triangle wave signal (e.g., [V ref ] of FIGS. 4-6) from the triangle wave generation components 812, and the setting/reading (e.g., [V read ] of FIGS. 4-6) signal from the NTC temperature setting 816 and NTC 814 components, comparator U1C then outputs an analog PWM temperature control signal (e.g., [V out ] of FIGS. 4-6), for example to a relay within heater 820. As described with respect to FIGS. 4-6 in particular, the setting voltage signal and the reading voltage signals in combination with the generated triangle wave lead to an analog PWM temperature control of the appliance. The heater unit can include a relay K1 powered through NPN transistor Ql, with a transistor base connected through a resistor R11, emitter connected to ground, and a collector connected to relay Kl. Relay K1 is then connected to and powered by 12V power received at 824 from power supply circuit 700. As described herein, relay Kl can also be replaced with a TRIAC, among other heater control units and structures. Examples of relay Kl can include

EMR011A12 or JSM1-12V-5, among others.

[0043] Also shown connected to comparator U1C is a temperature setting LED unit 818. LED temperature setting unit 818 can be omitted in some embodiments without affecting the function of appliance temperature control. However, some users may find various lights on an appliance as indicator of status and/or temperature as beneficial.

[0044] The circuit structure of LED unit 818 includes another op-amp U1D, which has an output connected to resistor R17 in line with LED2. A signal from comparator op-amp U1C can be received at a resistor R16 and a diode Dl. A capacitor C6 can also be connected to R16 and DL R16 and Dl then pass a signal to a negative switching input of op-amp U1D, which can selectively cause LED2 to be powered on, depending on signal and temperature. A positive switching input of op-amp U1D is connected to a capacitor C7, and resistors R12 and R14, as shown. Op-amp U1D can also be connected to 5V power 822D received from power supply circuit 700 and can be grounded.

[0045] In order to indicate temperature/heating progress or status, an example appliance can include a display including a strip of LEDs (e.g., controlled by temperature setting LED unit 818) or other lights that can be selectively lighted or changed color. Although shown schematically with only a single LED (LED2), more LEDs or other lights can be employed to display a larger range or more detailed temperature or operation status. For example, five LEDs can be arranged vertically, with a lowest LED, a highest LED, and for example, three LEDs between, for a total of five LEDs. The lowest LED can indicate whether an appliance is on or off by being lit or not lit. In some embodiments, a second LED being lit can indicate a temperature of 200° F (93.3° C), a third LED being lit can indicate a temperature of 300° F (148.9° C), a fourth LED being lit can indicate a temperature of 400° F (204.4° C), and the highest LED being lit can indicate a temperature of 500° F (260° C), which can represent a highest temperature in some embodiments. Other variations in number of function of LEDs are also contemplated, herein.

[0046] In a case where multiple LEDs are employed, the various LEDs can be controlled, e.g., using a dot bar generator (not shown). The example dot bar generator can be an integrated circuit chip that powers LEDs based on the NTC temperature of the appliance. Alternatively, an added circuit can be used to light the LEDs using a second quad op-amp integrated circuit chip to create a comparator circuit for each LED temperature level. NTC feedback can be fed into each comparator/op-amp.

[0047] In some cases, it may be desirable for an appliance to have more than one heat setting or zone. For example, a user may desire to cook meat at one temperature, and vegetables at a different, second temperature. As shown in FIG. 8, the triangle wave generation components 812 are connected to a single temperature zone 810. Dual (or three or more) temperature zones can also be introduced. Embodiments include circuit components configured to independently control multiple heater units (e.g., 820) giving the user separate, independent temperature zones. In other embodiments, a single heater unit 820 and/or temperature zone components 810 could be instead connected to multiple triangle wave generation components 812, among other variations and configurations. For example, the triangle wave generation components 812 and power supply circuits 700 can be shared between temperature zones 810. However, in the case of dual temperature zones, the components and connections of temperature zone 810 can be duplicated, including duplicating the heater unit 820, a temperature setting LED unit 818, an NTC temperature setting unit 816, an NTC unit 814, and a comparator op-amp U1C, as shown. In so duplicating the various components, each temperature zone 810 can have independent NTC feedback, (e.g., potentiometer) input, and heater output. This can allow for a single appliance having multiple zones, for example, multiple zones on a heating surface of a grill that are selectively heated to different temperatures, etc.

[0048] FIG. 9 is a schematic circuit representation of an alternative PWM temperature control system 900, according to an embodiment of the present disclosure. System 900 can be similar to system 800 of FIG. 8, and system 900 includes an NTC monitor circuit 910.

Generally, NTC monitor circuit can be employed so that if an NTC (appliance temperature sensor) is removed or not installed, the NTC monitor circuit 910 would turn off the op-amps and no output (V out ) will be delivered to the heaters, relay heaters, or heating units, as used herein. System 900 can be connected to a power supply, such as power supply circuit 700 of FIG. 7, which can include one or more of a 5 V supply output 710 and a 12V supply output 712, which can connect to various components of, for example, systems 800 or 900.

[0049] In some embodiments, the NTC monitor circuit 910 can also be connected to a plate interlock for a grill (or an equivalent interlock for other appliances contemplated herein). The plate interlock (not shown) can also be introduced so that if a grill plate is removed from the appliance or not properly in place, the heater does not operate. The monitor circuit can include a mechanical switch, that, when opened can be used to detect removal of a grill plate (or other component). Alternatively, an infrared radiation (IR) LED and encoder can be used to detect removal of the grill plate (or other suitable heating related component).

[0050] As described, above in particular with respect to FIG. 8, there are various ways to generate a triangle waveform and square wave using analog differential amplifiers such as op-amps. It should be noted that various embodiments of the present disclosure include examples that use exclusively or substantially all analog circuitry, in various other embodiments some or all of the components of the various embodiments can alternatively use some or all digital components.

[0051] In the shown system 900, an op-amp U3 is wired as an integrator, and is driven from an output of another op-amp, U2. U2 can be employed as a square wave generator. As shown, U2 is wired as a differential voltage comparator, driven from the output of U3 via potential divider R2 (lOOKQ)-R5 (47KW), which is connected between the outputs of U2 and U3. As shown, the square wave output of U2 switches alternately between a positive (or negative) 5 and 0 volts, e.g., based on the 5 V output 710 of power supply circuit 700, which can connect to various components of system 900 at one or more of 5 V connections 912A, 912B, 912C, 912D, 912E, 912F, 912G, 912H, and/or 9121. System 900 can also receive a 12V signal at connection 914, as shown. The 12V signal received at connection 914 can be received from power supply circuit 700 12V output 710.

[0052] In one example, the output of integrator U3 is positive and the output of comparator U2 has just switched to positive saturation. In this case, a current (i) of +V sat /Rl flows into Rl, which can cause the output of comparator U2 to start to swing down linearly at a rate of i/Cl volts per second. This output can then be fed to the non-inverting input of U2 comparator via an R2-R5 divider, as shown.

[0053] Consequently, the output of integrator U3 falls linearly until the R2-R5 junction voltage falls to zero or below V ref , at which point integrator U3 can enter a regenerative switching phase, in which its output abruptly switches. This reverses the inputs of integrator U3 and comparator U2 so the integrator U3 output starts to rise linearly, until it reaches a positive value at which the R2-R5 junction voltage reaches the reference value, initiating another switching action. The whole process can then repeat.

[0054] Examples of preferable op-amps to be used can include LM324 Quad in some embodiments, but different op-amps can be used as well. For example, integrator U3 can alternatively operate as a comparator and U2 can operate as an integrator. When power (e.g., 5V power 712 or 12V power 710 from power supply circuit 700) is given to the circuit of system 900, and in particular 5V input connection 912A and 9121, the comparator U2 drives its output“high.” This signal is driven to the integrator U3 through the resistor R6. The capacitor Cl then starts to charge gradually with R6-C1 time constant. While the capacitor Cl is charging, the output of the integrator U3 is also taken to its low state at the same rate. When the positive input of the comparator U2, through the voltage divider that that 47KW and 100KW resistors can perform, can be driven low enough, then it changes state, and the integrator U3 starts operating vice-versa.

[0055] The frequency of oscillation (FOSC) can be determined based on the RC standard.

A half cycle period is preferably the result of the R x C. A full cycle is twice this amount. Therefore, the FOSC can be preferably defined as 1/(2 x R6 x Cl).

[0056] The output of integrator U3 can then be fed to the non-inverting input of a voltage comparator Ul. The inverting input of Ul can be fed from the NTC monitor circuit 910, as is described in greater detail with respect to FIG. 8. In summary, the described configuration can operate as a standard voltage comparator with the triangle wave being the reference voltage and the NTC being the temperature feedback voltage.

[0057] As discussed, an NTC exhibits a negative resistance with increasing temperature. A RT1 (NTC) thermistor along with resistor R9 can performs as a voltage divider that supplies the inverting input. As the temperature increases, the voltage level at the inverting input of Ul begins to increase in accordance with the voltage divider consisting of the NTC RT1 and resistor R9. R9 can be employed to reduce the likelihood than NTC resistance would approach zero.

[0058] At a time when a non-inverting input voltage at op-amp Ul is less than the inverting input voltage, the op-amp Ul outputs a voltage, this op-amp Ul output voltage can then be fed to the base of transistor Ql. The output voltage can turn on transistor Ql, which can in turn activate a relay turning on the heaters/heating units/heating elements of various heating appliances. In other embodiments, the relay could also be a TRIAC, which could be used to turn on the heaters.

[0059] A comparator U4 can also be used to turn an LED on/off based on whether or not the required temperature has been reached, the LED will light indicating temperature has been reached. Dl along with R10 and C2 cause a slight delay, which preferably keeps the LED (LED1) from flickering due to the temperature being very close to the set point.

[0060] NTC monitor circuit 910 can include a transistor Q2 and associated circuitry, as shown. Transistor Q2 can be an unbiased PNP transistor, with a default“on” position. The NTC monitor circuit 910, as described above, can form a protection circuit that monitors a connection to the NTC. In the event a part of the NTC monitor circuit 910 becomes disconnected, whether from removal or a bad connection (e.g., broken wire, removed plate, etc.) the 5 V supply voltage (e.g., from 5 V output 712 of FIG. 7) can be removed from the various op-amps, which in turn will prevent the heaters from turning on and can prevent thermal runaway or overheating. Resistors Rl 1 and R15 are preferably sized to keep the bias voltage from turning on Q2 while RT1 is in place. Once RT1 is removed, then Q2, being a PNP transistor, turns on and shuts down the op-amps.

[0061] FIGS. 10A-10C show graphical data comparing an indoor/outdoor grill with pulse width modulation temperature control of the present invention (e.g., an indoor/outdoor grill with analog PWM) at FIG. 10B, 1012 with a similar indoor/outdoor grill controlled using existing snap-action (the same indoor/outdoor grill, but unmodified) temperature control at FIG. 10A, 1010.

[0062] According to one simulation, the example indoor/outdoor grill can be a George Foreman grill with the model number GFO201R. The indoor/outdoor grill was tested using the present invention according to various quantifiable parameters. As shown, these grill parameters used in the shown embodiment included a 500W set point, a 12V scale with a 2V minimum and an 8V maximum, and a 0.25 Hz triangle reference waveform. Other parameters can be used and can also yield beneficial results.

[0063] For comparison, various data for the unmodified indoor/outdoor grill and the same indoor/outdoor grill with analog PWM temperature control according to the present invention are displayed at data chart 1014 of FIG. 10C. As shown, the indoor/outdoor grill unmodified power is shown at 1011 of FIG. 10 A, and the indoor/outdoor grill with AP WM power is shown at 1013 of FIG. 10B. As shown, the power 1013 of the grill using the APWM has a higher frequency of on/off than the power 1011 of the unmodified grill, which in

embodiments leads to a smoother and steadier state temperature of the grill.

[0064] According to FIG. 10B, the indoor/outdoor grill (e.g., GFO201R) unit was modified so that an NTC was used for temperature feedback at 1012. The NTC was placed in a voltage divider circuit like the one shown as voltage divider 200 of FIG. 2. The voltage drop across the potentiometer was used as the read voltage. As shown in FIGS. 10B, a testing or modeling program (e.g., Lab VIEW) was used to read the voltage, simulated a reference voltage, actuate a relay to power the grill on and off, and the record temperature and power data. With a 0.25 Hz triangular wave reference voltage with a peak voltage of 8V and a minimum voltage of 2V, the thermal profile and thermal performance displayed in FIG. 10B were observed. This testing shows that analog PWM temperature control has benefits when used in heated appliances as a high-performance alternative to temperature control using a mechanical snap-action thermostat as shown in FIG. 10A.

[0065] FIGS. 11 A-l 1C show graphical data comparing an open grate grill with pulse width modulation temperature control of the present invention with a similar grill controlled using existing snap-action temperature control.

[0066] According to one simulation, and similar to the procedures and testing of FIGS. 10A-10C, an example open grate grill (e.g., a Steinbrenner open grate grill) using the present invention was tested using various parameters, such as an optimized triangle wave, e.g., produced by triangle wave generation components such as 812 of FIG. 8. At FIG. 11A, data for an unmodified open grate grill, with a snap-action thermostat, is displayed at chart 1110. At FIG. 11B, data for a similar open grate grill, equipped with the analog PWM temperature control is displayed at chart 1112. The power level of the open grate grill for the unmodified, GFO thermostat is shown at 1111 of FIG. 11 A, and the power level of the open grate grill with APWM is shown at 1113. As shown, the power 1113 of the grill using the APWM has a higher frequency of on/off than the power 1111 of the unmodified grill, which in embodiments leads to a smoother and steadier state temperature of the grill.

[0067] Various data for comparison is also shown at data chart 1114, which shows beneficial performance improvements. The parameters used in the shown embodiment included a 500W set point, a 5V scale with a 1.67V minimum and a 3.33V maximum, and a 0.25 Hz triangle reference waveform. As shown, the open grate grill also yields benefits when equipped with the analog PWM temperature control of the present invention.

[0068] FIGS. 12A-12C show graphical data comparing a toaster oven with pulse width modulation temperature control of the present invention with a similar grill controlled using existing snap-action temperature control.

[0069] According to one simulation, and similar to the procedures and testing of FIGS. 10A-10C and FIGS. 11A-11C, an example toaster oven (e.g., a BLACK+DECKER TO3210 toaster oven) using the present invention was tested using example parameters at 1212 of FIG. 12B and compared to a similar toaster oven using an existing snap-action thermostat at

1210 of FIG. 12 A. Data for an unmodified toaster oven, with a snap-action thermostat, is displayed at chart 1210 of FIG. 12 A. Data for a similar toaster oven, equipped with the analog PWM temperature control is displayed at chart 1212 of FIG. 12B. AT FIG. 12C, various data for comparison is also shown at data chart 1214, which shows beneficial performance improvements. The parameters used included a 2KW set point, a 12V scale with a 0V minimum and an 8V maximum, and a 0.25 Hz triangle reference waveform. As shown, the toaster oven also yields benefits when equipped with the analog PWM temperature control of the present invention. The power level of the unmodified toaster oven is shown at

1211 of FIG. 12 A, and the power level of the same toaster oven with APWM is shown at 1213. As shown, the power 1213 of the toaster oven using the APWM has a higher frequency of on/off than the power 1211 of the unmodified toaster oven, which in embodiments leads to a smoother and steadier state temperature of the toaster oven.

[0070] FIG. 13A-13C show graphical data comparing an electric hair straightener with pulse width modulation temperature control of the present invention with a similar grill controlled using existing digital temperature control.

[0071] According to one simulation, and similar to the procedures and testing of FIG. 10A- 10C, 11 A-l 1C, and 12A-12C, but a hair straightener using a digital temperature control circuit is compared to a similar hair straightener with PWM, instead of comparing a hair straightener that uses a snap-action thermostat. An example hair straightener (e.g., a Remington Pro S7330) using the present invention was tested using example parameters as shown at 1310 and 1312 of FIGS. 13A and 13B, respectively. [0072] Data for a hair straightener with digital temperature control is displayed at chart 1310 of FIG. 13 A. Data for a similar hair straightener, equipped instead with the analog PWM temperature control is displayed at chart 1312. Various data for comparison is also shown at data chart 1314, which shows comparable performance between the digital temperature control and the analog PWM temperature control. The parameters used included a 3KW set point, a 12V scale with a 4V minimum and a 6.5V maximum, and a 1 Hz triangle reference waveform. The power level of the hair straightener with digital temperature control is shown at 1311 of FIG. 13 A, and the power level of the hair straightener with APWM is shown at 1313.

[0073] The hair straightener equipped with the analog PWM temperature control also yields similar results as the digital temperature control equipped hair straightener. As shown, the power 1313 of the hair straightener using the APWM has a comparable frequency of on/off as compared to the power 1311 of the hair straightener with digital control, which in embodiments leads to comparably smooth and steady state temperature of the hair straightener, but without the use of digital temperature control. This can lead to lower cost of manufacture, simpler construction, and greater flexibility in parts sourcing, among others, in addition to offering favorable temperature control for the hair straightener.

[0074] When introducing elements of the present disclosure or the preferred

embodiments(s) thereof, the articles "a," "an," "the," and "said" are intended to mean that there are one or more of the elements. The terms "comprising," "including," and "having" are intended to be inclusive and mean that there may be additional elements other than the listed elements.

[0075] As various changes could be made in the above apparatus and methods without departing from the scope of the disclosure, it is intended that all matter contained in the above description and shown in the accompanying figures shall be interpreted as illustrative and not in a limiting sense.