MC4111L / MAG 690
Technical Training
5 - POWER SUPPLY TO POWER CIRCUIT
The transformer primary winding is energized
by parallel-mounted relay and triac.
The triac is made conductive when the voltage
is maximum, in order to have minimum current
(owing to the phase shift related to the
transformer winding choke coil).
So, it enables the magnetron to be energized
at a predetermined moment, unlike the relay,
which has a none precise switching time
(6 to 20 ms).
On the board, a "mains synchro." synchronises the microprocessor clock with the rising curve of the
voltage.
When pressing "START", the triac is controlled on the maximum voltage.
As the triac cannot withstand the power for a very long time, the relay will supply the primary winding of the
transformer for the rest of the time.
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