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6.1
Appendix 1:
Capacitor
Coupled Low
Voltage Supply
-V
PK
Ballast Demonstrator User Guide
The ballast demonstrator shows that the Atmel microcontroller and supporting IXYS
devices can control and regulate one or more fluorescent lamps with precision and effi-
ciency, therefore providing the lamp controller manufacturer with maximum flexibility
with their design. Universal input and power factor control adds to the flexibility of the
design with a minimal addition of more expensive active components.
Additionally, the programmability of the microcontroller offers the lamp manufacturer the
flexibility to add or modify design features to enhance their market position. The ballast
demonstrator, with its many features, does not address all the possibilities available to
the lamp controller designer.
Small currents for the low voltage supply can be obtained from the AC line at low loss by
means of capacitor coupling as shown in the figures below. To estimate the required
size of the coupling capacitor, use the following relationships for current, charge, voltage
and capacitance.
1.dQ/dt = I
DC
Figure 6-1. Negative Line Half Cycle
C1
- V
+
C1
AC
Ich1
"Negative" line half -cycle:
C1 charges to Vpk - V
V
D
V
D
with polarity shown.
D
Section 6
Conclusion
Vo
C2
I
DC
-23
7629A–AVR–04/06
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