Abstract: An arrangement provides for the electrical grounding of a temperature probe and allows its use in conjunction with a cooking appliance control circuit having a floating signal ground. An isolation transformer connects the temperature probe to the control circuit. A temperature sensing circuit includes two parallel voltage-dividing legs. One of the legs includes a primary winding of the isolation transformer, whereas the other of the legs includes a variable resistor allowing a consumer to set the predetermined temperature at which the control circuit will stop heating. Preferably the control circuit is used to control a full wave full bridge inverter connected to an AC input line by way of a bridge rectifier. The inverter is connected to a magnetron by way of a power transformer. The voltage-dividing legs are connected to receive gate pulses from the control circuit, which gate pulses also are used for controlling switches within the inverter.

Abstract: An arrangement for providing power to a cooking magnetron uses a full wave bridge inverter circuit. Four semiconductor switches, pairs of which are switched on and off by a pulse width modulation control circuit provide power to a primary winding of a power transformer. A secondary winding of the power transformer supplies the power to the magnetron. The control circuit switches two of the four transistors on and off by way of an isolated drive circuit such that the control terminals of the semiconductor switches float with respect to the other two semiconductor switches. The control circuit includes pulse width modulation circuitry which provides a control pulse having a width proportional to an input provided across a transconductance amplifier. A signal dependent upon magnetron current is used as part of a feedback loop such that a magnetron current is stabilized against variations due to line voltage changes.

Abstract: A microwave oven uses a full wave full bridge inverter for supplying energy to a cooking magnetron by way of a power transformer. The inverter is controlled by a microprocessor which acts upon a control circuit having an oscillator. Two feedback loops are provided for controlling the operation of the magnetron. A relatively slow feedback loop uses the microprocessor to adjust inverter operation in order to stabilize the magnetron power output. A relatively fast feedback loop senses current passing through a primary of a power transformer. A signal based on the sensed current is provided to a comparator and compared to a reference. If the signal from the current sensor indicates that the current has become excessive, the comparator generates a shutdown signal which will stop the generation of gating pulses to the transistor switches of the inverter.

Abstract: A microwave heating system uses a magnetron powered by a full wave full bridge inverter. The magnetron has its power output stabilized against variations which might be caused by fluctuations in the AC input line. The inverter powers the magnetron by way of a power transformer having a primary and a secondary. The current is sensed in the primary in order to change the switching frequency of the inverter. As the current in the primary will depend upon fluctuations in the AC input line voltage, sensing of the current in the primary may be used to sense variations in the voltage of the AC input line. Alternately, current in the secondary of the power transformer may be sensed and used to detect variations in the AC input line voltage. In either case, the sensed variations in AC input line voltage are used to change the inverter frequency.

Abstract: An arrangement for providing power to a cooking magnetron uses a ful wave bridge inverter circuit connected to a power transformer. The filament of the magnetron is energized by a secondary winding of the power transformer. The inverter controls the microwave output of the magnetron by duty cycle control. In order to stabilize filament power against variations due to changes in the inverter duty cycle, a saturable reactor is connected in series with the filament. The reactor has a control winding which changes the impedance of the reactor in order to compensate for variations in the power supplied by the power transformer. The control winding of the reactor may be supplied with a voltage dependent upon the magnetron current. Since the magnetron current depends on the duty cycle of the inverter, this voltage may be used to make the impedance of the reactor dependent upon the duty cycle.

Abstract: A microwave oven uses a full wave full bridge inverter for supplying energy to a cooking magnetron by way of a power transformer. The inverter is controlled by a microprocessor which acts upon a control circuit having an oscillator. The control circuit provides gating pulses which are used to switch on FET switches in the inverter. The microprocessor stops and starts the gating pulses. The microprocessor may adjust the power of magnetron by turning the control circuit on and off for variable time intervals. Alternately, the microprocessor may control the power of the magnetron by changing the switching frequency of the inverter. The microprocessor is used in a filament standby mode to monitor the current in the magnetron's filament. In the filament standby mode, the inverter is operated at a lower than normal voltage such that the magnetron is not generating microwave power, but its filament is receiving sufficient current to warm it up, the current flowing through a filament winding of a power transformer.