Abstract: A magnetron (M) serving as the microwave source in a microwave oven is driven by a Switch Mode Power Supply (SMPS). The resonance circuit of the Power Supply contains a transformer (Tr), the secondary side of which is connected to the magnetron via a voltage multiplier consisting of a rectifier and voltage doubler circuit (C3, C4, D3, D4). In order to obtain a feedback signal which is proportional to the power fed to the magnetron thereby to regulate this power, a current transformer (ST) is connected in series with one of the diodes (D3) in the rectifier and voltage doubler circuit. The output signal of the current transformer is compared in a control circuit (K) with a reference signal and the result of the comparison is used to control the switch frequency and thereby the magnetron power.

Abstract: A microwave oven with a timer device driven by a ripple voltage related to the mains frequency. The ripple voltage appears at a circuit point in the microwave oven power supply only during the time when microwave energy is being fed into the oven cavity.

Abstract: A microwave oven includes an oven cavity, into which HF power is fed from a microwave source, e.g. a magnetron energized by a power supply device. The power supply device with its components and the microwave source are cooled with the aid of a fan. The power supply device, the microwave source (12) and the fan (11) are combined into a so-called power module, which includes a substantially closed envelope (10) having an air inlet (15) and an air outlet (16), an input for the AC supply voltage and an output for HF power (30). The microwave source is mounted as a projecting part of the envelope at the air inlet or the air outlet of the power module. This makes it possible to adapt the power module to a great number of microwave oven constructions. The power module may be mounted at the top or bottom of the oven cavity or at the side of same. Feeding microwave energy into the oven cavity is possible both at the top and bottom thereof.

Abstract: A power supply circuit for a high-frequency source (M) in a microwave oven includes a switched-mode-power-supply unit having a resonant circuit which contains a coil (L2) and a controllable switch (D1). The switching of the controllable switch is controlled by a control circuit (K) via a driving stage (S). The power supply circuit is cooled by a fan (F). The required DC voltages for supplying the driving stage, control circuit and fan are obtained by means of an auxiliary winding (W1, W2) on the coil (L2) and a rectifier (D3, D4). This results in a saving in both space and costs. At the same time, automatic supervision of the different functional units of the power supply circuit is obtained.