Traditionally microwave ovens have traditionally used magnetrons to develop the microwave energy required for microwave ovens. The devices date back to the earliest days of radar in the 1940s when thermionic valve / vacuum tube technology reigned supreme.

Until recently the magnetron has been a much more cost effective route to provide the RF energy required. However the devices are crude by today’s standards and not allow much control of the microwave energy apart from on-off control. Also the output level falls with time and they make the microwave ovens much larger and heavier than they need to be. The image shows a comparison between an old magnetron and a solid-state device.

Now Freescale is launching RF devices for microwave ovens. Solid-state microwave oven RF power technology delivers efficient controllable RF energy. Also the performance does not degrade over time and in this way solid state microwave ovens will provide users with a longer lasting and economically feasible alternative to the legacy magnetron-based microwave systems.

There are further advantages to the use of semiconductors for developing the RF power. They can be made to be much smaller, and as they do not need such large transformers and require the same level of metalwork. Additionally the new semiconductor microwave ovens are far more efficient.

The new devices are part of a new portfolio of high-power, high-efficiency RF heating products. The new heating devices family includes the MHT1003N which is a 250 W transistor with 58 percent power added efficiency for 2.45 GHz microwave oven applications. Also in the family is the MHT1002N which is a 350 W transistor with 63 percent power added efficiency for 915 MHz microwave applications.

Available in over-molded plastic packages, the MHT1003N and MHT1002N provide excellent performance and address the cost challenges of the microwave appliance industry.

All the new devices are designed to withstand harsh operating conditions, as they will need to withstand high levels of VSWR when little or no load is presented. They will also need to operate in the conditions where microwave ovens are found, often in high temperature areas such as kitchens where little ventilation may be present.

The introduction of the new devices offers many possibilities for microwave ovens. It is possible to control where and when the RF energy is directed, and this opens the possibility for advanced options in microwave ovens where it will be possible to provide more precise cooking, greater consistency in quality of cooking, selective heating, and versatile and complex cooking combinations.

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