Electric lamp and discharge devices: systems – Condenser in the supply circuit – Inductance in the condenser circuit
Reexamination Certificate
2001-11-06
2003-11-25
Wong, Don (Department: 2821)
Electric lamp and discharge devices: systems
Condenser in the supply circuit
Inductance in the condenser circuit
C315S283000, C315S307000, C315S291000
Reexamination Certificate
active
06653800
ABSTRACT:
BACKGROUND OF INVENTION
The present invention relates generally to a ballast circuit for fluorescent lamps. More particularly, this invention relates to a self-oscillating electronic ballast circuit with cathode protection during normal operation and ballast protection during no-lamp and cathode failure conditions.
FIG. 1
shows a ballast circuit
100
with a series-resonant parallel-loaded electronic ballast having an inherent open-cathode protection function. The open-cathode protection function is provided by placing a resonant capacitor
112
between the two cathodes
114
,
116
of the fluorescent lamp
118
. If the fluorescent lamp
118
is removed from the ballast circuit
100
, or if one or two of the cathodes
114
,
116
fail (i.e., cathode current path opens), the resonant inductor
120
is disconnected from the resonant capacitor
112
. With the resonant circuit disconnected, the self-oscillating electronic ballast is disabled. Upon replacing the lamp
118
, the ballast circuit
100
will resume its normal operation. However, the resonant current that flows through the resonant capacitor
112
during normal operation also flows through each of the cathodes
114
,
116
. The continuous resonant current can cause overheating of the cathodes
114
,
116
, reduces the life of the cathodes
114
,
116
, and reduces the lumens per watt (LPW) of the lamp
118
.
FIG. 2
shows another ballast circuit
200
with a series-resonant parallel-loaded electronic ballast with reduced cathode current and a corresponding reduction in power dissipation by the cathodes during normal operation. The ballast circuit
200
achieves reduced cathode current by splitting the resonant capacitance between two capacitors (i.e., capacitor
212
and capacitor
214
). Capacitor
212
is between the two cathodes
216
,
218
of the fluorescent lamp
220
, like in FIG.
1
. However, capacitor
214
is in parallel with the two cathodes
216
,
218
. In this arrangement, the current that flows through cathodes
216
,
218
during normal operation of the lamp
220
is reduced. Likewise, the corresponding power dissipated by the cathodes
216
,
218
during normal operation is reduced. However, under a no-lamp condition the resonant circuit formed by capacitor
214
and resonant inductor
222
is still intact and continues to conduct current. Furthermore, with the lamp
220
removed, the resonant circuit will have a higher voltage and higher current than with the lamp
220
installed. This could result in damage to the ballast under the no-lamp condition.
SUMMARY OF INVENTION
In one aspect of the present invention a ballast circuit for driving a fluorescent lamp is provided. The ballast circuit comprises: a self-oscillating circuit; and a series resonant circuit.
In another aspect of the present invention a ballast circuit for driving a fluorescent lamp is provided. The ballast circuit comprises: a self-oscillating circuit; a resonant inductor; a resonant capacitor; a first diode; and a second diode.
In another aspect of the present invention a series resonant circuit for a ballast circuit, wherein the ballast circuit is adapted for driving a fluorescent lamp is provided. The series resonant circuit comprises: a resonant inductor; a resonant capacitor; a first diode; and a second diode.
REFERENCES:
patent: 5187411 (1993-02-01), Boyd et al.
patent: 5355055 (1994-10-01), Tary
patent: 5436529 (1995-07-01), Bobel
patent: 5932974 (1999-08-01), Wood
Fay Sharpe Fagan Minnich & McKee LLP
General Electric Company
Tran Thuy Vinh
Wong Don
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