Microwave oven power supply circuit
阅读：423发布：2023-08-14
专利汇可以提供Microwave oven power supply circuit专利检索，专利查询，专利分析的服务。并且A microwave oven power supply includes a synchronous switch and a phase control circuit. The switch is electrically connected in series with the supply lines which, until actuated, maintains normally open the path for current flow to the transformers and other electrical components found within the oven power supply. An On-Off switch and interlocks are in series with the power line and an electrical circuit completed through the phase control circuit inhibits the operation of the power circuit until it is desired to commence cooking operations. The phase control circuit determines the proper phase of the applied line voltage for which the synchronous switch should be initiated. By design, this phase control circuit is matched to the transformer characteristics and senses the magnitude of the applied line voltage so that initial conduction of the synchronous switch falls within a preselected range which has been determined to minimize transient voltage spikes and/or in-rush current transients. In this way, the initiation of current flow in the high voltage transformer and filament transformer and other oven elements is delayed until the sinusoidal voltages of the power line are in the phase relationship that I have determined to be proper.，下面是Microwave oven power supply circuit专利的具体信息内容。
1. In a microwave oven, the combination comprising: a pair of lines for connection to a source of alternating voltage to provide an alternating voltage; a magnetron for generating microwave energy; a transformer, said transformer having an iron core, a primary winding mounted on said core, and at least one high voltage secondary winding mounted on said core; diode rectifying means coupled to said high voltage secondary winding anD said magnetron for applying direct voltages to said magnetron; said magnetron, transformer, rectifying means combination resulting in a large transient voltage spike across said magnetron and a large in-rush current to said magnetron when the alternating line voltage is applied across said primary winding at a first predetermined phase angle of said alternating voltage and wherein said transient voltage and inrush current is minimized substantially when said alternating line voltage is applied across said primary winding at a second predetermined phase angle of said alternating voltage; solid state semiconductor switch means having a pair of main terminals and a trigger input terminal, said switch having the characteristic of being electrically nonconductive between its main terminals until triggered by an input at said trigger input terminal and thereupon becoming substantially instantaneously electrically conductive between said main terminals independently of any further inputs until the current flow through its main terminals reverses in direction or ceases and thereupon substantially instantaneously becoming nonconductive until triggered again at its input terminal; first electrical switch means for opening and closing an electrical circuit; circuit means connecting said first switch means, said primary winding and the main terminals of said semi-conductor switch electrically in series circuit across said pair of lines, whereby current cannot flow through said primary winding until said switch means closes and said semiconductor switch is in its conductive state; control circuit means coupled to said trigger input terminal of said semiconductor switch means, said control circuit means including: synchronizong circuit means responsive to said alternating voltage for providing an output synchronized with said second predetermined phase angle of said alternating voltage, latch circuit means coupled to said synchronizing means and to said semiconductor switch means responsive to said output of said synchronizing means for triggering said semiconductor switch means into its conductive state and thereafter for maintaining said semiconductor switch means in its current conducting state during subsequent half cycles of said alternating voltage; and selectively adjustable timer means coupled to said control means for inhibiting operation of said control means at the expiration of a preselected interval of time to cause said semiconductor switch to revert to its electrically nonconductive state; whereby said semiconductor switch means permits current in said series circuit to commence only at a predetermined phase angle of alternating voltage and continues to permit current flow during each succeeding half cycle of alternating voltage over the inverval of time selected with said timer means.
2. The invention as defined in claim 1 wherein said synchronizing means further includes: means responsive to the level of said alternating voltage for adjusting said predetermined phase angle to different values as a function of the level of said alternating voltage.
3. The invention as defined in claim 1 wherein said synchronizing means comprises: an input coupled to said alternating voltage; unijunction transistor means having a first base electrode, a second base electrode, and an emitter electrode; first bias circuit means coupled between said first base electrode and said input; output circuit means coupled to said second base electrode responsive to current flow through said unijunction transistor for providing an output; first circuit means coupled to said input for establishing at an output a single polarity voltage of a predetermined level only during alternate ones of the half cycles of said alternating voltage; an RC circuit comprising a resistance, R, and a capacitance, C, said RC circuit having a time constant, T, equal to 1/RC, and said time constant is less than T1, wheRe T1 equals the time period of one-half cycle of said alternating voltage; means connecting said RC circuit to said output of said first circuit means to permit said capacitor C to charge up to a predetermined voltage level over a predetermined period of time within each half cycle of said alternating voltage; means coupling said capacitor, C, to said emitter electrode for applying said voltage on said capacitor to said emitter; silicon controlled rectifier means having an anode, cathode and trigger terminal; means connecting said silicon controlled rectifier anode to said input; circuit means connecting the output of said unijunction transistor to said trigger terminal for triggering said silicon controlled rectifier into its current conducting state; whereby said silicon controlled rectifier provides an output at a predetermined time initiated only once within each alternate positive half-cycle of alternating voltage applied to said input which corresponds in time to a predetermined phase angle of said alternating voltage.
4. The invention as defined in claim 3 wherein said first bias circuit means comprises: filter circuit means coupled to said input for providing a second alternating voltage having a phase angle advanced by a predetermined number of degrees relative to the phase angle of said applied alternating voltage and of a substantially lower voltage level relative to the level of said alternating voltage; and rectifier means coupled to said first base electrode of said unijunction transistor means for applying a pulsed direct voltage to said first base electrode of said unijunction transistor; whereby said unijunction transistor switches into its electrically conductive state only at a time during which the phase angle of said alternating voltage is other than zero.
5. The invention as defined in claim 4 wherein said rectifier means comprises further: a first diode for rectifying said second alternating voltage, a Zener diode for reducing said rectified voltage from said first diode and applied to said first base electrode by a predetermined substantially constant voltage level, which constant voltage level is within the range of one-half to one-fifth of the voltage output from said first diode, whereby any change in voltage level at said input results in a change in bias voltage at said second base electrode to vary the phase angle of said alternating voltage at which said unijunction transistor becomes current conducting.
6. The invention as defined in claim 5 wherein said control means includes a latching circuit for maintaining an output signal subsequent to initial energization, said latch circuit comprising: second silicon controlled rectifier means having a trigger input terminal; output means connected to said trigger input terminal of said solid state semiconductor switch means; means for connecting said silicon controlled rectifier to said alternating voltage; means for coupling the output of said first silicon controlled rectifier of said synchronizong means to said trigger input terminal of said second silicon controlled rectifier; feedback circuit means, said feedback circuit means connected between said silicon controlled rectifier output and said trigger input terminal; whereby said second silicon controlled rectifier switches from its non-conductive to its electrically conductive state in response to a signal from said synchronizing means and maintains said conductive state.
7. The invention as defined in claim 6 further comprising interlock switch means responsive to movement of said door from the closed position for opening an electrical circuit, said second switch being connected electrically in series with said second silicon controlled rectifier, whereby said latch circuit is de-energized upon opening of said oven door.
8. The invention as defined in claim 7 further comprising mechanical operator means coupled between said door and said fiRst and second switch means for preventing opening or closing of said first switch means until subsequent to opening or closing of said second switch means.
9. The invention as defined in claim 6 wherein said selectively adjustable timer means includes switch means operable to close a circuit upon the lapse of a predetermined cooking time interval, said switch means connected across said second silicon controlled rectifier for shunting said second silicon controlled rectifier upon the expiration of said predetermined interval of time, whereby said second silicon controlled rectifier restores to its electrically nonconductive state and further output from said second silicon controlled rectifier to said semiconductor switch means is inhibited.
10. The invention as defined in claim 6 wherein said timer means is coupled to said second silicon controlled rectifier for terminating operation of said second silicon controlled rectifier subsequent to the expiration of a predetermined interval of time.
11. The invention as defined in claim 9 wherein said timer means comprises: a positive polarity terminal and negative polarity terminal; a timing capacitor; means responsive to the voltage across said terminals for providing a constant current to said capacitor and for charging said capacitor at a constant rate of current flow whereby a corresponding voltage is built up across said capacitor over a period of time; unijunction transistor means, said unijunction transistor means having a first base electrode, second base electrode, and emitter electrode; first resistor means coupling said second base electrode to said negative polarity terminal; means coupling said timing capacitor to said emitter electrode; second electrical resistance means having first and second terminals and a selectively adjustable tap terminal, said first and second terminals coupled to said positive and negative polarity terminals, respectively, and said tap terminal being coupled to said first base electrode for establishing a direct voltage at said first base electrode; whereby said unijunction transistor means switches from an electrically nonconductive state to an electrically conductive state when the voltage built up on said capacitor means attains a predetermined ratio to the voltage established at said first base electrode to generate an output voltage across said second resistor means at the expiration of a predetermined time interval subsequent to the application of a voltage across said positive and negative polarity terminals.
12. The invention as defined in claim 9 wherein said timer operated switch means comprises a third silicon controlled rectifier connected in circuit across said second silicon controlled rectifier to provide a shunt current path around said second silicon controlled rectifier.
13. The invention as defined in claim 11 further comprising door switch means responsive to the oven door being in the closed position for completing a circuit for applying a voltage across said positive and negative polarity terminals.
14. In a microwave oven the combination comprising: a cooking cavity for exposing food to microwave energy, said cavity having an opening to provide access thereto; a movable door for closing said opening; a magnetron for generating microwave energy; means for coupling microwave energy from said magnetron into said cooking cavity; a pair of lines for connection to a source of alternating voltage; a transformer, said transformer having an iron core, a primary winding mounted on said core, and a high voltage secondary winding mounted on said core to provide a high alternating voltage from said secondary winding during alternating current flow in said primary wiring; rectifier means, including at least one diode, coupled between said high voltage secondary winding and said magnetron responsive to alternating voltage from said secondary winding for applying direct voltages to said magneTron; said magnetron, transformer, rectifying means combination resulting in a large transient voltage spike across said magnetron and a large in-rush current to said magnetron when the alternating line voltage is applied across said primary winding at a first predetermined phase angle of said alternating voltage and wherein said transient voltage and in-rush current is minimized substantially when said alternating line voltage is applied across said primary winding at a second predetermined phase angle of said alternating voltage; first switch means coupled to said movable door, said switch means having contacts movable between an open and closed circuit position for closing a circuit through said contacts only when said door is in the closed position; semiconductor switch means having a control terminal and having an electrically nonconductive state and an electrically conductive state and capable of switching between said nonconductive and said conductive state substantially instantaneously and responsive to a signal at said control terminal for switching into the conductive state and responsive to an effective zero current flow and an absence of a signal at said control terminal for switching back to its nonconductive state; first series electrical circuit means connecting said first switch means, said primary winding and said semiconductor switch means electrically in series circuit across said lines; control circuit means coupled to said semiconductor switch means responsive to alternating voltage at a predetermined location in said series circuit for providing a signal to said control terminal of said semiconductor switch means to cause said semiconductor switch means to switch from its nonconductive state into its electrically conductive state only at said second predetermined phase angle, theta , of said alternating voltage and for thereafter maintaining said semiconductor switch means in said electrically conductive state; and selectively adjustable timer means for inhibiting said control means at the expiration of a predetermined interval of time so as to permit said semiconductor switch means to restore to its electrically nonconductive state.
15. The invention as defined in claim 14 further comprising: second switch means, said second mechanical switch means being coupled to said oven door for operation to a first position only when said movable door is in its closed position; and said second switch means being electrically coupled between said first series circuit and said control circuit means for inhibiting said control circuit means when said switch is not in said first position.
16. The invention as defined in claim 15 further comprising: means for sequencing said second switch means together with said first switch means for operating said second mechanical switch means prior to operating said first mechanical switch means.
17. In a microwave oven the combination comprising: a cooking cavity for exposing food to microwave energy, said cavity having an opening to provide access thereto; a movable door for closing said opening; a magnetron for generating microwave energy; means for coupling microwave energy from said magnetron into said cooking cavity; a pair of lines for connection to a source of alternating voltage; a transformer, said transformer having an iron core, a primary winding mounted on said core, and a high voltage secondary winding mounted on said core to provide a high alternating voltage from said secondary winding during alternating current flow in said primary wiring; rectifier means, including at least one diode, coupled between said high voltage secondary winding and said magnetron responsive to alternating voltage from said secondary winding for applying direct voltages to said magnetron; said magnetron, transformer, rectifying means combination resulting in a large transient voltage spike across said magnetron and a large in-rush current to said magnetron when the alternating line voltage is applied across said primary winding at a first predetermined phase angle of said alternating voltage and wherein said transient voltage and in-rush current is minimized substantially when said alternating line voltage is applied across said primary winding at a second predetermined phase angle of said alternating voltage; first switch means coupled to said movable door, said switch means having contacts movable between an open and closed circuit position for closing a circuit through said contacts only when said door is in the closed position; semiconductor switch means having a control terminal and having an electrically nonconductive state and an electrically conductive state and capable of switching between said nonconductive and said conductive state substantially instantaneously and responsive to a signal at said control terminal for switching into the conductive state and responsive to an effective zero current flow and an absence of a signal at said control terminal for switching back to its nonconductive state; first series electrical circuit means connecting said first switch means, said primary winding and said semiconductor switch means electrically in series circuit across said lines; control circuit means coupled to said semiconductor switch means responsive to alternating voltage at a predetermined location in said series circuit for providing a signal to said control terminal of said semi-conductor switch means to cause said semiconductor switch means to switch from its nonconductive state into its electrically conductive state only at a predetermined phase angle, theta , of said alternating voltage and for thereafter maintaining said semiconductor switch means in said electrically conductive state; means for adjusting said phase angle, theta , to different values as a function of the level of said alternating voltage; and selectively adjustable timer means for inhibiting said control means at the expiration of a predetermined interval of time so as to permit said semiconductor switch means to restore to its electrically nonconductive state.
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