Abnormal Protection
KA7543
Vab
30kΩ
7
+
3pF
-
2V
Abnormal protection
SQ
RQ
To output
Protection reset
From no lamp
+
-
0.7V
Vct
Figure 7. Abnormal Protection Circuit
The abnormal protection is similar to the over current protection, but it is a protection that detects abnormal connection of
lamps. The abnormal protection circuit works when the Vab pin voltage is higher than 2V. The abnormal protection is latched
using a flip-flop and the protection is reset when the ballast system restarts.
Lamp Selector Stage
Vfb 6
Cc
-
Gm
Vr +
5kΩ
1/2
ir
is-id
Selecter -
+
3V
30kΩ
-
8 Vld
5pF
+
1V
No-lamp pretection
Figure 8. Lamp Selector Stage
If the Vld pin voltage is between 1V and 3V, it means that there is one lamp connected and if the Vld pin voltage is over 3V, it
is two lamps condition. The feedback reference voltage of the two lamps condition is twice that of one lamp condition.
9