Phase-Chopping Control - Principle Of Operation; Service And Maintenance; Figure 4-4: Phase-Chopping Control - Miele S 247i Technical Manual

S 2xx, S 3xx & S 4xx Canister Vacuums
4.4.4

Phase-Chopping Control - Principle of Operation

Figure 4-4: Phase-Chopping Control

α
C1
D1
D2
R1
R
L
X
View of half-wave:
The triac D2 blocks (chops) the sinusoidal wave at the zero crossover point.
The triac now has high impedance. The capacitor is charged via the circuit R1-
C1-R .
L
When U
C
discharged in a pulse via the gate of D2.
This pulse switches the triac D2, making it conductive.
At the next zero crossover point, the triac D2 blocks the sinusoidal wave and
the process repeats itself.
Figure 4-4 shows the chopping of the half-wave. The phase angle, α, is
directly proportional to the potentiometer setting R1 which thus controls the
average motor power.
5.0

Service and Maintenance

General information:
Service and repair work should only be carried out by qualified persons in
accordance with local and national safety regulations.
The appliance should be disconnected from the power supply before starting
Phase angle
Capacitor
Trigger diode, here a diac
Bi-directional thyristor, here a triac
Potentiometer for setting the phase angle α
Load, here the motor
Triac, conductive
reaches the switching level for the diac D1, the capacitor C1 is
27
Technical Information