Electric lamp and discharge devices: systems – Condenser in the supply circuit – Inductance in the condenser circuit
Reexamination Certificate
2001-03-20
2002-01-15
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Condenser in the supply circuit
Inductance in the condenser circuit
C315S094000, C315S105000, C315S224000, C315S291000, C315SDIG004, C315SDIG005
Reexamination Certificate
active
06339299
ABSTRACT:
FIELD OF THE INVENTION
The present in vent ion relates to a preheating circuit for detecting the filament temperature of fluorescent lamps, and more particularly to a circuit indirectly detecting a filament temperature to ensure that filaments operate at a thermionic emission temperature.
BACKGROUND OF THE INVENTION
Properly preheating filaments becomes considerably necessary to avoid deteriorating the lamp life. Igniting a lamp at a low filament temperature requires a relatively high ignition voltage, causing bombardment and resulting in extremely sputtering on filaments. On the other hand, overheating the filaments will cause their coating material over evaporating and thermal shock. Both of the two improper preheating conditions engender sputtering and shorting the life of the lamp. Lamp filaments must reach their emission temperature at starting stage to minimize electrode sputtering. The preheating ratio (&ggr;=R
h
/R
c
) of the hot resistance (R
h
) of the electrodes to their cold resistance (R
c
) is an index in knowing a n approximate emission temperature, and the electrodes with such a ratio means that it reaches a temperature high enough for thermionic emission.
FIGS.
1
(
a
)~(
c
) show three typical preheating circuits for fluorescent lamps. Please refer to FIG.
1
(
a
). The preheating circuit is implemented by using the characteristic that the resistance of the positive temperature coefficient (PTC) of the resistor R
1
is increased with increasing temperature to preheat the filaments. When the resistance of the resistor R
1
is low at a low temperature, most of the preheating current flows through the capacitor C
1
and the resistor R
1
. At this time, the circuit operates at a preheating frequency to preheat the filaments. When the resistance of the resistor R
1
increases with the increasing temperature, more current flows from the capacitor C
1
to the capacitor C
2
. The disadvantage of the preheating circuit is that the filaments are hard to operate at a thermionic emission temperature because the preheating time depends on the variation of the positive temperature coefficient resistance.
Referring to FIG.
1
(
b
), the resistors R
3
and R
4
in series form a voltage divider. The voltage V
1
in the voltage divider turns on the switching element Q
2
and the switching element Q
2
is in parallel with the capacitor C
4
. Therefore, the voltage across the lamp is low. When the current flows through the resistor R
2
to charge the capacitor C
3
until the capacitor voltage of the capacitor C
3
reaches the breakdown voltage of the diode D
1
, the switching element Q
1
is turned on and the switching element Q
2
is forced to be turned off. The capacitance of the capacitor C
3
is adjusted to determine the charging time of the capacitor C
3
to control the preheating time so as to let the filament temperature is high enough. Therefore the preheating time is determined by the amount of the charges on the capacitor C
3
. If the initial voltage of the capacitor C
3
is high, the charging time for reaching the breakdown voltage of the diode D
1
is shorter. On the other hand, the initial voltage of the capacitor C
3
is zero, the charging time for reaching the breakdown voltage of the diode D
1
is the longest. Therefore, the phenomenon of overheating the filaments or igniting a lamp at a low filament temperature also exists because the preheating time depends on the amount of the charges on the capacitor C
3
but does not depend on the filament temperature.
As shown in FIG.
1
(
c
), the charging time of the RC circuit is used to control the preheating time. When the voltage of the capacitor C
5
is not charged to the breakdown voltage of the diode D
2
, the circuit operates in higher frequency and the lamp voltage is not high enough to ignite the lamp. And the resonant current is used to preheat the filament. The drawback is same as described in FIG.
1
(
b
). The phenomenon of overheating the filaments or igniting a lamp at a low filament temperature also exists because the preheating time depends on the amount of the charges on the capacitor C
5
but does not depend on the filament temperature.
Otherwise, U.S. Pat. No. 5,920,155 discloses an electronic ballast for discharge lamps which sets a filament current and a voltage across a discharge lamp at their suitable operational levels according to respective operational states of the discharge lamps, and which also provides a sufficient dimming function even when the lamp is of a slim type. However, it is not mentioned how to dynamically adjust the preheating time. Therefore, the filaments are not sure to operate at a thermionic emission temperature. Thus, the preheating circuit needs to be improved to overcome the above problem.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to propose a preheating circuit for a fluorescent lamp. The preheating circuit includes a filament detecting circuit for indirectly detecting a filament resistance in a fluorescent lamp by measuring a filament voltage and a filament current, a pulse generation circuit for providing pulses of one of a first frequency and a second frequency determined by the detected filament resistance and a specific filament resistance, and a filament resonance circuit operating the fluorescent lamp at an operating frequency determined by the pulse generation circuit so that the filament resonance circuit operates at the first frequency to preheat the fluorescent lamp when the detected filament resistance is smaller than the specific resistance and the filament resonance circuit operates at the second frequency to operate the fluorescent lamp when the detected filament resistance is one of a first value being larger than and a second value being equal to that of the specific resistance.
According to an aspect of the present invention, the first frequency is a preheating frequency &ohgr;
s(ph)
.
Preferably, the second frequency is a switching frequency &ohgr;
s(fl)
at full load.
Preferably, the specific resistance is a hot filament resistance R
h
which is an index to preheat the fluorescent lamp when the detected filament resistance R
f
is smaller than the hot filament resistance R
h
.
Preferably, the hot filament resistance R
h
is &ggr; times a cold filament resistance R
C
where &ggr; is a preheating ratio and &ggr;>1.
Preferably, the filament detecting circuit includes a first series circuit of a secondary winding of a transformer and a first diode electrically connected in parallel to a first smoothing capacitor and a first resistor for generating a first DC output voltage, a second series circuit of a filament resistor and a second diode connected in parallel to a second smoothing capacitor and a second resistor for generating a second DC output voltage, and a comparator having an inverting input electrically connected in parallel to the first smoothing capacitor, and a noninverting input electrically connected in parallel to the second smoothing capacitor for providing a switching signal to the pulse generation circuit for generating the operating frequency.
Preferably, the first DC output voltage is in proportion to a secondary voltage V′
Lr
of the secondary winding of the transformer and the second DC output voltage is in proportion to a filament voltage V
R
f
across the filament resistor.
Preferably, the secondary voltage V′
Lr
equals to &ggr;R
c
*V
Lr
/&ohgr;
s(ph)
L
r
where V
Lr
is a primary voltage of the primary winding of the transformer, and L
r
is an inductance of the primary winding of the transformer.
Preferably, the filament voltage V
Rf
equals to R
f
*V
Lr
/&ohgr;
s(Ph)
L
r
.
Preferably, the filament resonance circuit operates at the preheating frequency &ohgr;
s(ph)
to preheat the fluorescent lamp when the detected filament resistance R
f
is smaller than the hot filament resistance R
h
while the filament resonance circuit operates at the switching frequency &ohgr;
s(fl)
to operate the fluorescent lamp when the detected filament resistance R
f
is one of a first value bei
Wu Tsai-Fu
Wu Yong-Jing
Klivans Norman R.
National Science Council
Philogene Haissa
Skjerven Morrill & MacPherson LLP
LandOfFree
Preheating circuit for detecting the filament temperature of... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Preheating circuit for detecting the filament temperature of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Preheating circuit for detecting the filament temperature of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2831543