Microwave oven having generator power supply

A microwave oven and a method of operating the same is provided herein. The method includes the steps of: sensing that a door of the microwave is in an open state; interrupting a power input to a generator power supply unit comprising a first converter, a first energy reserve, a second energy reserve located downstream from the first energy reserve, and a second converter located between the first and second energy reserves; detecting an input voltage; and disabling the second converter if the detected input voltage is less than a threshold voltage that is proportional to the detected input voltage, wherein disabling the second converter triggers the second energy reserve to discharge, and wherein the time necessary to discharge the second energy reserve is free of influence from the first energy reserve and is independent of the detected input voltage.

BACKGROUND

The present disclosure generally relates to a cooking apparatus, and more particularly, to a microwave oven having a generator power supply unit with a discharge function.

A conventional microwave oven cooks food by a process of dielectric heating in which a high-frequency alternating electromagnetic field is distributed throughout an enclosed cavity. A sub-band of the radio frequency spectrum, microwave frequencies at or around 2.45 GHz cause dielectric heating primarily by absorption of energy in water.

To generate microwave frequency radiation in a conventional microwave, a voltage applied to a high-voltage transformer results in a high-voltage power that is applied to a magnetron that generates microwave frequency radiation. The microwaves are then transmitted to an enclosed cavity containing the food through a waveguide. Cooking food in an enclosed cavity with a single, non-coherent source like a magnetron can result in non-uniform heating of the food. To more evenly heat food, microwave ovens include, among other things, mechanical solutions such as a microwave stirrer and a turntable for rotating the food. A common magnetron-based microwave source is not narrowband and not tunable (i.e. emits microwaves at a frequency that is changing over time and not selectable). As an alternative to such a common magnetron-based microwave source, solid-state sources can be included in microwave ovens which are tunable and coherent.

SUMMARY

According to one aspect of the present disclosure, a microwave oven is provided having a door movable between an open state and a closed state and a microwave generator for generating microwaves. A generator power supply unit is provided having the following components ordered from upstream to downstream: a first converter for converting a power input to a power output; a first energy reserve electrically coupled to the first converter for receiving the power output; a second converter electrically coupled to the first energy reserve for converting the power output to a low voltage power output; and a second energy reserve electrically coupled to the second converter for receiving the low voltage power output and supplying the low voltage power output to the microwave generator. A detection circuit is configured to detect an input voltage and disable the second converter based on the door being in the open state, wherein disabling the second converter triggers the second energy reserve to discharge, and wherein the time necessary to discharge the second energy reserve is free of influence from the first energy reserve.

According to another aspect of the present disclosure, a microwave oven is provided and includes a door movable between an open state and a closed state and a microwave generator for generating microwaves. A generator power supply unit is provided having the following components ordered from upstream to downstream: a first converter for converting a power input to a power output; a first energy reserve electrically coupled to the first converter for receiving the power output; a second converter electrically coupled to the first energy reserve for converting the power output to a low voltage power output; and a second energy reserve located downstream from the first energy reserve and electrically coupled to the second converter for receiving the low voltage power output and supplying the low voltage power output to the microwave generator. A detection circuit is configured to detect an input voltage and disable the second converter based on the door being in the open state, wherein disabling the second converter triggers the second energy reserve to discharge, and wherein the time necessary to discharge the second energy reserve is independent of the detected input voltage.

According to yet another aspect of the present disclosure, a method of operating a microwave oven to reduce microwave leakage is provided. The method includes the steps of: sensing that a door of the microwave is in an open state; interrupting a power input to a generator power supply unit comprising a first converter, a first energy reserve, a second energy reserve located downstream from the first energy reserve, and a second converter located between the first and second energy reserves; detecting an input voltage; and disabling the second converter if the detected input voltage is less than a threshold voltage that is proportional to the detected input voltage, wherein disabling the second converter triggers the second energy reserve to discharge, and wherein the time necessary to discharge the second energy reserve is free of influence from the first energy reserve and is independent of the detected input voltage.

DETAILED DESCRIPTION

The present disclosure may be implemented in any environment using a radio frequency (RF) generator or amplifier capable of generating a field of electromagnetic radiation (e-field) in the radio frequency spectrum regardless of the application of the e-field and regardless of the frequency or frequency range of the e-field. For purposes of this description, any e-field generating device, for example, a microwave generator or infrared signal generator, will be generally referred to as an RF generator, or similar language, and any e-field applying device, such as a waveguide, an antenna, or anode/cathode coupling or pair, will be generally referred to as an RF applicator. These descriptions are meant to make clear that one or more frequencies or frequency ranges of e-field may be included in the embodiments described herein. While this description is primarily directed toward a microwave oven providing an e-field capable of heating and or cooking food (collectively, “cooking”), it is also applicable to alternative uses of e-field generation such as drying fabrics, for example.

FIG.1schematically illustrates an RF device in the form of a microwave oven10including a cabinet12defining a cavity14for electromagnetically heating and/or cooking food, or foodstuff, in the cavity14. The microwave oven10also includes a door16movably mounted to the cabinet12, an RF shielding layer, for example, wire mesh18, removably or fixedly attached to the cabinet12and the door16. The door16is movable between an opened state and a closed state to selectively provide access to the cavity14, for instance, to allow for inserting food items to be cooked or for removing food items previously cooked. When closed, the door16and corresponding segment of the wire mesh18are configured to align with the cabinet12to effectively prevent access to, and/or effectively seal, the cavity14. The cavity14is further sealed due to the configuration of the wire mesh18, which operates to prevent e-field leakage into, or out of, the cabinet12and cavity14.

The microwave oven10further includes a microwave generator shown as an RF generator24having at least one RF amplifier, shown as a first solid state RF amplifier26and a second solid state RF amplifier28. The microwave oven10further includes at least one RF applicator, shown as a first RF applicator30and a second RF applicator32, each of which is configured to apply an e-field34to the cavity14. The microwave oven10also includes a generator power supply unit36, an interruption circuit37, a power source38(e.g., mains power), and a controller40. While the cavity14is shown to include the RF generator24and the first and second RF applicators30,32located in opposing corners of the cavity14, other embodiments contemplate alternative placements of the RF generator24and the first and second RF applicators30,32, including a configuration where the RF generator24and the first and second RF applicators30,32are located outside of the cavity14. In one specific embodiment, the first and second RF applicators30,32are waveguides that feed an e-field into the cavity14. Furthermore, while the generator power supply unit36, interruption circuit37, power source38, and controller40are generally shown outside of the cabinet12, they are collectively contemplated to be included as components of the oven10, and various placements of the aforementioned components are contemplated, which may include placement within the cavity14, cabinet12, and/or wire mesh18.

As shown, the first solid state RF amplifier26may be electrically coupled with the first RF applicator30and the second solid state RF amplifier28may be electrically coupled with the second RF applicator32. The RF generator24may also be electrically coupled with the generator power supply unit36, which may further be electrically coupled to the power source38via the interruption circuit37. The interruption circuit37is configured to electrically couple the power source38to the generator power supply unit36when the door16is in a closed state and electrically decouple the power source38to the generator power supply unit36when the door16is in an open state. Accordingly, the interruption circuit37may be electrically coupled to a door switch, shown as door switch41, which is configured to provide a signal indicative of a state of the door16to the interruption circuit37. The controller40is shown communicatively coupled (illustrated as dotted lines) to the RF generator24and the generator power supply unit36. In operation, the controller40may provide communication signals to one or more of the foregoing components for controlling the operation thereof.

The RF generator24is configured to receive a power input from the generator power supply unit36and may generate one, two, three, four, or any number of RF signals, as needed by the particular oven application. The RF generator24is further configured to deliver each respective signal to a corresponding RF amplifier26,28. In the depicted embodiment, the RF generator24is capable of generating two RF signals, each of which is delivered to the corresponding first and second solid state RF amplifiers26,28such that each of the first and second solid state RF amplifiers26,28amplifies an independent RF signal. Thus, it is contemplated that each RF signal may correspond to at least one of the first and second RF amplifiers26,28. As a non-limiting example, it is contemplated that one RF signal may correspond to one RF amplifier, two RF signals may correspond to two respective RF amplifiers, three RF signals may correspond to three respective RF amplifiers, four RF signals may correspond to four respective RF amplifiers, and so on and so forth. In contrast, it is also contemplated that one RF signal may correspond to, for example, two, three, or four RF amplifiers, such that each RF amplifier amplifies the same RF signal. Accordingly, it should be appreciated that any number of combinations and/or permutations of any number of RF signals and/or RF amplifiers as described are contemplated.

Each of the first and second RF amplifiers26,28may be correspondingly configured to deliver the amplified signal to the one or more RF applicators30,32, which are configured to direct the amplified RF signal, shown as an e-field34, into the cavity14. The generator power supply unit36may be additionally configured to operatively convert power received from the power source38to an alternative power output. For example, the generator power supply unit36may be configured to convert an alternating current (AC) power input to a high current, low voltage direct current (DC) power output. However, it should be appreciated that alternative power conversions are contemplated, and the example provided is merely one non-limiting example of a power conversion. Additionally, the controller40may be any appropriate device that is capable of receiving input signals, generating, processing, and/or determining commands, and providing the commands and/or command signals based on said commands, as one or more outputs. For example, the controller40may include one or more programmable logic devices, application specific integrated circuits, digital signal processors, and/or microcontrollers.

During operation of the microwave oven10, food items to be cooked are placed into the cavity14via the open door16, and then the door16is closed. The controller40operates to control the microwave oven10such that the power source38provides a power input to the generator power supply unit36, which is controlled to convert the power input from the power source38to a sufficient power output delivered to the RF generator24. One example of the generator power supply unit36may include, for instance, converting an AC power input to a low voltage (DC) output. In response, the RF generator24may generate a radio frequency electromagnetic radiation (e-field) signal, which may be significantly or trivially amplified by each respective first and second RF amplifier26,28, and delivered from each first and second RF amplifier26,28to the respective first and second RF applicators30,32for application of the electromagnetic radiation to the cavity14.

FIG.2schematically illustrates the power source38, the interruption circuit37, the generator power supply unit36, and the RF generator24in further detail. In the depicted embodiment, the generator power supply unit36includes, as components, a bridge rectifier44, at least one converter shown as a first converter46and a second converter48, and at least one energy reserve shown as a first energy reserve50and a second energy reserve52. For purposes of understanding, the aforementioned components are shown ordered in a linear arrangement to more clearly illustrate the direction of power transfer, beginning at the power source38, then moving across the components from an upstream to downstream direction (i.e., from left to right inFIG.2), and ultimately ending at the RF generator24. As shown, the components of the generator power supply unit36are positioned on a voltage line56and a ground line58, both of which also serving to electrically connect the power source38, the generator power supply unit36, and the RF generator24. While a detection circuit54is illustrated as being a component of the generator power supply unit36, it should be appreciated that the detection circuit54may be separately provided in other embodiments. With respect to any of the embodiments described herein, operation of the detection circuit54may be based on a state of the door16.

In the depicted embodiment, the interruption circuit37electrically couples the power source38to the generator power supply unit36while in a closed state, and electrically decouples the power source38to the generator supply36while in an open state. The power input provided by the power source38to the generator power supply unit36may correspond to an AC power input. As shown, the interruption circuit37is electrically connected to the bridge rectifier44, which rectifies the power input. In the depicted embodiment, the bridge rectifier achieves full-wave rectification of the AC power input. The bridge rectifier44is also electrically coupled to the first converter46for converting the power input to a power output. In the depicted embodiment, the first converter46is configured as an AC to DC converter so as to convert the AC power input to a DC power output. The first converter46is electrically coupled to the first energy reserve50, which receives the power output, i.e., the DC power output, and may include a bulk capacitor60that becomes energized from the DC power output supplied thereto from the first converter46. The second converter48is electrically coupled to the first energy reserve50for converting the DC power output to a low voltage DC power output. The second energy reserve52is located downstream from the first energy reserve50and is electrically coupled to the second converter48for receiving the low voltage DC power output and supplying the low voltage DC power output to the RF generator24.

In the depicted embodiment, the second converter48includes a first DC to DC converter62and a second DC converter64, each configured to convert the DC power output to the low voltage DC power output and individually supply the low voltage DC power output to a corresponding one of a first output capacitor66and a second output capacitor68of the second energy reserve52. In turn, the first and second output capacitors66,68individually supply the low voltage DC power output to a corresponding one of the first solid state RF amplifier26and the second solid state RF amplifier28. In embodiments having additional RF amplifiers, a corresponding number of DC to DC converters and output capacitors may be similarly configured for individual power delivery.

With continued reference toFIG.2, the detection circuit54is configured to detect an input voltage and disable the second converter48based on the door16being in the open state. In the depicted embodiment, detection circuit54detects the input voltage upstream from the first converter46. For example, the input voltage may correspond to a rectified peak AC input voltage detected between the output of the bridge rectifier44and the input of the first converter46at a first point70on voltage line56and a second point72on ground line58. For purposes of disclosure, the voltage line56and the ground line58will be collectively referred to herein as “the main line”. As shown, the detection circuit54includes a comparator74for comparing the detected rectified peak AC input voltage to a threshold voltage that is proportional to the detected rectified peak AC input voltage. If the detected rectified peak AC input voltage is greater than the threshold voltage, the detection circuit54functions on standby, or in other words, does not disable the second converter48. Such a scenario may occur, for example, when the door16is in a closed state and the microwave oven10is executing a cooking operation. In such an instance, the power source38is electrically coupled to the generator power supply unit36via the interruption circuit37. As a result, the detected rectified peak AC input voltage is generally greater than the threshold voltage.

In contrast, if the detected rectified peak AC input voltage is less than the threshold voltage, the detection circuit54bypasses the bridge rectifier44, the first converter46, and the first energy reserve50and disables the second converter48(e.g., each of the first and second DC to DC converters62,64) by transmitting a switch-off signal76thereto. In one implementation, the foregoing threshold condition is satisfied shortly after the door16is opened while a cooking application is underway. More specifically, when the door16is opened, the interruption circuit37electrically decouples the power source38from the generator power supply unit36, thereby ceasing the supply of power input to the generator power supply unit36from the power source38. As a result, the detected rectified peak AC input voltage will satisfy the threshold condition after a period of time, typically no more than 10 milliseconds. In operation, disabling the second converter48triggers the second energy reserve52(e.g., each of the first and second output capacitors66,68) to quickly discharge in an effort to minimize the amount of microwave leakage due to the door16being opened while a cooking process is underway. Advantageously, since the detection circuit54bypasses components located downstream of the second converter48, the time necessary to discharge the second energy reserve52is free of influence from said components, namely the first energy reserve50(e.g., bulk capacitor60). In other words, in embodiments where the detection circuit54is not included, the time necessary to discharge the second energy reserve52would be dependent on the time necessary to discharge the first energy reserve50, thereby increasing the amount of microwave leakage while the door16is opened. As an added advantage, the inclusion of the detection circuit54enables the first energy reserve50to remain charged while the discharging of the second energy reserve52is underway. With respect to the depicted embodiment, the threshold voltage may be maintained at a predetermined value greater than zero so as to avoid a deactivation of the switch-off signal76.

Referring toFIGS.3and4, graphs are shown illustrating a detection time at which the threshold condition (i.e., the detected rectified peak AC input voltage is less than the threshold voltage) is satisfied following an electrical decoupling of the power source38and the generator power supply unit36. InFIG.3, the top graph illustrates a maximum peak AC input voltage78of approximately 264 Vrmsand the bottom graph illustrates a corresponding detected rectified peak AC input voltage80and voltage threshold82. InFIG.4, the top graph illustrates a minimum peak AC input voltage84of approximately 177 Vrmsand the bottom graph illustrates a corresponding detected rectified peak AC input voltage86and voltage threshold88. It should be appreciated that the maximum and minimum peak AC input voltages are provided as non-limiting examples and may correspond to other values, if desired. With reference to bothFIGS.3and4, the power source38is decoupled from the generator power supply unit36at time T1, thereby ceasing the supply of the maximum and minimum peak AC input voltages78,84, respectively. At time T2, the threshold condition is satisfied, thereby prompting the detection circuit54to transmit the switch-off signal76to the second converter48in order to trigger the discharge of the second energy reserve52. As can be seen inFIGS.3and4, the detection time, i.e., the time between T1and T2, at which the threshold condition is satisfied is the same regardless of the input voltage supplied by the power source38. Accordingly, by extension, the time necessary to discharge the second energy reserve52is independent of the input voltage (i.e., the voltage associated with the input power supplied by the power source38) and the detected input voltage (i.e., the voltage detected on the main line).

Referring toFIG.5, a flow diagram is shown illustrating a method90of operating a microwave oven during a door opening event. The method90may be implemented using the microwave oven10and associated components described previously with reference toFIGS.1-4. In describing the method90, it is assumed that a cooking process is underway and the door16of the microwave oven10is initially in the closed state. Additionally, it is assumed a user later opens the door16prior to the completion of the cooking process. With these assumptions in mind, the method includes, at step94, interrupting a power input to the generator power supply unit36, as set forth at step94. As described herein, this may be achieved by electrically decoupling the power source38from the generator power supply unit36via the interruption circuit37when the door16is moved to an open state. In turn, the detection circuit54is operated to detect an input voltage at step96. As described herein, the detected voltage may correspond to a detected rectified peak AC input voltage. If the detected input voltage satisfies a threshold condition (decision block98), the detection circuit54disables the second converter48at step100via the switch-off signal76. Otherwise, the detection circuit54continues to detect the input voltage until the threshold condition is satisfied. As described herein, disabling the second converter48triggers the second energy reserve52to discharge. By virtue of the detection circuit54bypassing the first energy reserve50, the time necessary to discharge the second energy reserve52is free of influence from the first energy reserve50and is independent of the detected input voltage, thus minimizing the exposure to microwave leakage. The second converter48may remain disabled until the door16is returned to a closed state, at which point the switch-off signal is deactivated, as set forth at step102.

It is also to be understood that variations and modifications can be made on the aforementioned microwave oven10without departing from the concepts provided herein, and further it is to be understood that such concepts are intended to be covered by the following claims unless these claims by their language expressly state otherwise.