Electronic control for a microwave oven

A microwave oven comprising a microwave source and a power unit including a high voltage transformer for supplying a high voltage to the microwave source, said high voltage transformer being supplied with a mains voltage via a switch device and a control unit in order to connect the mains voltage, when starting the oven, at a moment substantially coinciding with a mains voltage maximum,

• said switch device comprising a relay being supplied at switch-on with a control voltage from said control unit and the relay contacts of which are closed at switch-on with a delay corresponding to the switch-on time of the relay,
• feedback means operatively connected to said switch device, said feedback means supplying a feed back signal to the control unit indicating changing states when the relay contacts change from an open to a closed position, a reference signal indicating the mains voltage phase also being supplied to the control unit,
• said control unit operatively connected to said switch device and said feedback means and comprising a microprocessor device being programmed to perform the following steps during switch-on of the relay;
• assume a value t.sub.dc for the relay switch-on time
• calculate the moment T.sub.on of a mains voltage maximum from said reference signal
• switch on the relay by supplying the control voltage at the moment T.sub.on -T.sub.dc
• sense the feedback signal within a interval around T.sub.on
• when the relay contacts are closed within said interval, maintain the relay switched on alternatively, when the relay contacts are open within said interval, perform relay switch-off by interrupting the control voltage supply, assume a new value of t.sub.dc and repeating the programmed steps until the relay contacts are closed within the interval.