AN1010
Application Notes
Ballast
14 W - 22 W
5 µF
400 V
MT2
47 k
220 k
120 V ac
Line
Q401E4
MT1
Input
G
0.047 µF
50 V
1N4004
HT-32
Lamp
Optional
15 W - 20 W
Charging
Network
Figure AN1010.2
120 V ac Triac/Diac Circuit
Figure AN1010.3 illustrates a circuit using a sidac (a simpler thy-
ristor) phase control network to ignite a 120 V ac fluorescent
lamp. As in the triac/diac circuit, the 5 µF ac capacitor is charged
and added to the peak line voltage, developing greater than
200 V peak or 400 V peak to peak. Since the sidac is a voltage
breakover (VBO) activated device with no gate, a charging net-
work is essential in this circuit to charge the capacitor above the
peak of the line in order to break over (turn on) the sidac with a
BO of 220 V to 250 V.
As the sidac turns on each half cycle, the filaments are pre-
heated and in less than 1.5 seconds the lamp is lit. Once the
lamp is lit, the voltage across it clamps to approximately 60 V
peak (for a 15 W to 20 W lamp), and the sidac ceases to function
until the lamp is required to be ignited again.
V
Ballast
14 W - 22W
5 µF
400 V
47 k
120 V ac
Line
K2400E
Sidac
Input
1N4004
Lamp
15 W - 20W
Optional
Charging
Network
Figure AN1010.3
120 V ac Sidac Circuit
The circuits illustrated in Figure AN1010.2 and Figure AN1010.3
use 15 W to 20 W lamps. The same basic circuits can be applied
to higher wattage lamps. However, with higher wattage lamps the
voltage developed to fire (light) the lamp will need to be some-
what higher. For instance, a 40 W lamp is critical on line input
voltage to ignite, and after it is lit the voltage across the lamp will
clamp to approximately 130 V peak. For a given type of lamp, the
current must be limited to constant current regardless of the watt-
age of the lamp.
Figure AN1010.4 shows a circuit for igniting a fluorescent lamp
with 240 V line voltage input using triac and diac networks.
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AN1010 - 2
©2002 Teccor Electronics
Thyristor Product Catalog
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