5. Resonance output circuit
To make the life-span of fluorescent light bulb longer, supply the filament pre-heat current.
Line current is running through filament C
6
RT
1
filament C
5
PT
1
.
Resistance value is increased at PT
1
by running of PTC pre-heat current.
When impedance of PT
1
is Higher than impedance of C
7
, the current runs toward C
7
and so, discharge voltage
is permitted to both ends of lamp. And finally, discharge occurs at lamp as a result of resonance of L and C.
After LAMP is ON, the resonance current runs through lamp RT
2
C
5
PT
1
.
6. Guard circuit
On abnormal operation of LAMP or abnormal operation of switching circuit, toward D
7
, more than 0.7 V of
voltage is held at GATE of SCR and so, SCR operates to block power.
When abnormal voltage or over-voltage is held at power part, FUSE at the primary power circuit is gone to
block the power.
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