Microwave Circuit
9-5
MAGNETRON CIRCUIT
Overview of a microwave circuit
The microwave circuit consists of a magnetron
and a voltage doubler circuit. The voltage doubler
consists of a special step–up transformer, a
capacitor, a diode. In addition to the power
circuitry in the magnetron the oven utilizes a
filament transformer to pre-heat the magnetron
filament before applying the high voltage to the
anode. As for safety a monitor circuit is used to
make the magnetron circuit fail in the failsafe
mode.
Monitor Circuit Description:
In addition to the HV circuit, it is imperative to
understand how the monitor circuit operates.
The Monitor Circuit is a failsafe circuit that is
designed to protect the operator if both the
Primary and Secondary Interlock Switches fail to
operate normally.
The Monitor Circuit consists of the Primary
Interlock Switch, Secondary Interlock Switch,
Monitor Safety Switch, Monitor Relay and the trip
coil on the 35A circuit breaker. When the Cook
Door closes during normal operation, the Monitor
and Secondary/ Primary Switches close in this
order. When all switches are closed, the
microwave system is allowed to operate. If
during normal operation, either Interlock Switch
opens, such as when the Cook Door opens, the
Control system will turn OFF the Microwaves;
however, if the Monitor Switch opens before both
the Primary and Secondary Interlock switches,
i.e., abnormal operation, the Monitor switch will
de-energize the Monitor Relay. When this
occurs, a dead short is placed across L1 and L2.
The short then trips the trip coil on the circuit
breaker, which permanently interrupts power to
the Microwave system until both the Primary and
Secondary Interlocks are repaired. See Figure
below for a schematic of the monitor circuit. .
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