[0001] The present invention relates to a control circuit for a fluorescent lamp, and more
particularly to a control circuit capable of increasing a current of the fluorescent
lamp within a specific time period, allowing to reach a normal brightness of the fluorescent
lamp rapidly in a relatively short time.
[0002] Fluorescent lamps currently available in the market utilize mercury to emit ultraviolet
light. Generally, mercury exists in a liquid form or in an amalgam form (bead-shaped
mercury alloy). Amalgam is significantly advantageous over liquid mercury, but amalgam
is able to excite for the emission of ultraviolet light only when it is heated. As
a result, an amalgam fluorescent lamp needs a period of time to reach a rated output
light flux, and after the fluorescent lamp is lit, it is the heat energy in the vicinity
of the amalgam that determines how much the bead-shaped amalgam evaporates. It is
common that the fluorescent lamp is relatively dim at the beginning of the ignition
of the fluorescent lamp, and reaches to a normal brightness after the elapse of a
period of time. This inevitably causes an inconvenience when people use fluorescent
lamps.
[0003] A fluorescent lamp usually controls its ignition and lightening by a control circuit
which comprises a ballast control unit and an oscillator unit. Generally, the control
circuit could ignite the fluorescent lamp with a specific preheating time or without
a preheating time. In these cases, the control circuit starts with a relatively high
initial oscillation frequency, and thereafter, the oscillation frequency will be decreased
at a relatively fast speed during which the fluorescent lamp is ignited. Thus, the
fluorescent lamp needs to take a period of time to reach a normal brightness after
it is ignited, such that the fluorescent lamp is always "darkish" at the beginning
of the ignition of the lamp. Therefore, there exists a need for a control circuit
for adjusting the oscillation frequency of the oscillator unit to allow a fluorescent
lamp to reach rapidly a normal brightness when the lamp is switched on.
[0004] An aim of the present invention is to provide a control circuit for a fluorescent
lamp, which is able to increase promptly a current of the fluorescent lamp within
a very short time period to boost heat energy generated by amalgam and thus an evaporation
rate of amalgam, such that a normal brightness of the fluorescent lamp could be rapidly
reached in a relatively short time.
[0005] Accordingly, the present invention provides a control circuit for a fluorescent lamp
comprising a ballast control unit and an oscillator unit, the control circuit further
comprises a signal detection unit, a switch unit and a frequency converter; the signal
detection unit outputs a signal to the switch unit after receiving a light up signal
from the ballast control unit, the switch unit outputs a signal to the frequency converter,
and the frequency converter outputs a signal to the oscillator unit and converts an
oscillation frequency of the oscillator unit.
[0006] Preferably, the signal detection unit comprises a diode, a resistor and a first capacitor;
the resistor and the first capacitor are connected in parallel together, and then
connected with a negative terminal of the diode having a positive terminal connected
with the ballast control unit; the switch unit is a NMOS transistor having its gate
terminal connected with the negative terminal of the diode and having its source terminal
earthed; the frequency converter comprises a second capacitor and a third capacitor
which are connected in series together, and in parallel between drain and source terminals
of the NMOS transistor, and the oscillator unit is connected with a point where the
second capacitor and the third capacitor are connected.
[0007] Preferably, the oscillator unit further comprises a current comparator, and the signal
detection unit comprises a diode and a first capacitor; the diode has a positive terminal
connected with the ballast control unit, and a negative terminal connected with the
first capacitor which has another terminal earthed; the switch unit is a NMOS transistor
having its gate terminal connected with the negative terminal of the diode and having
its source terminal earthed, while a drain terminal of the NMOS transistor is connected
with a negative terminal of the current comparator via a resistor; the frequency converter
comprises a second capacitor having its one terminal earthed and another terminal
connected with the oscillator unit.
[0008] According to the control circuit of the invention, the signal detection unit receives
a light up signal to trigger the switching of the switch unit so as to enable the
frequency converter to convert an oscillation frequency of the oscillator unit of
the fluorescent lamp, such that a filament current of the fluorescent lamp could be
increased to boost the light flux rate of the fluorescent lamp. Thus, a normal brightness
of the fluorescent lamp could be rapidly reached in a relatively short time.
[0009] The present invention will be described in more detail, by way of example, with reference
to the drawings, in which:
Figure 1 is a block diagram of a control circuit for a fluorescent lamp of the present
invention;
Figure 2 is a first schematic diagram of a control circuit for a fluorescent lamp
of the present invention; and
Figure 3 is a second schematic diagram of control circuit for a fluorescent lamp of
the present invention.
[0010] Referring to Fig. 1, a control circuit for a fluorescent lamp of the present invention
is illustrated, which comprises a ballast control unit 1, an oscillator unit 2, a
signal detection unit 3, a switch unit 4, and a frequency converter 5. The signal
detection unit 3 outputs a signal to the switch unit 4 after receiving a light up
signal from the ballast control unit 1, the switch unit 4 outputs a signal to the
frequency converter 5, and the frequency converter 5 outputs a signal to the oscillator
unit 2 and converts an oscillation frequency of the oscillator unit 2.
[0011] Preferably, as shown in Fig. 2, the signal detection unit comprises a diode D1, a
resistor R1 and a first capacitor Ctimer. The resistor R1 and the first capacitor
Ctimer are connected in parallel, and then connected to a negative terminal of the
diode D1 which has a positive terminal connected with the ballast control unit. The
switch unit is a NMOS transistor having its gate terminal connected with the negative
terminal of the diode D1 and having its source terminal earthed. The frequency converter
comprises a second capacitor Cf and a third capacitor Cqst connected in series together,
and in parallel between drain and source terminals of the NMOS transistor. The oscillator
unit is connected to a point where the second capacitor Cf and the third capacitor
Cqst are connected.
[0012] The control circuit shown in Fig. 2 can be actuated by a digital signal or a preheating
time signal from the ballast control unit. When a high level signal is detected by
the diode D1, the diode D1 is turned on and the timer capacitor Ctimer is charged
up with a voltage for driving the turning-on of the NMOS transistor which serves as
a switch in the circuit. When the NMOS transistor is turned on, the second capacitor
Cf parallels with the third capacitor Cqst to determine a frequency at which the fluorescent
lamp can reach rapidly the normal brightness, and the third capacitor Cqst determines
a frequency at which the fluorescent lamp ignites normally. After the elapse of the
period of time for reaching the normal brightness (time signal is zero), the NMOS
transistor is turned off and the oscillator unit is connected only with the second
capacitor Cf where the circuit operates at a normal working frequency.
[0013] Preferably, as shown in Fig. 3, the oscillator unit further comprises a current comparator,
and the signal detection unit comprises a diode D2 and a capacitor C1. The diode D2
has a positive terminal connected with the ballast control unit, and a negative terminal
connected with the capacitor C1 which has another terminal earthed. The switch unit
is a NMOS transistor having its gate terminal connected with the negative terminal
of the diode D2 and having its source terminal earthed. The NMOS transistor further
has its drain terminal connected with a negative terminal of the current comparator
via a resistor R3. The frequency converter comprises a capacitor Cquickstart having
one terminal earthed and another terminal connected with the oscillator unit.
[0014] The control circuit shown in Fig. 3 can be actuated by a digital signal or a preheating
time signal from the ballast control unit. When a high level signal is detected by
the diode D2, the diode D2 is turned on and the timing capacitor C1 is charged up
with a voltage for driving the turning-on of the NMOS transistor which serves as a
switch in the circuit. When the NMOS transistor is turned on, the negative input terminal
of the current comparator becomes a short-circuit , and a biased current is generated
at the positive terminal of the current comparator because this positive terminal
is subject to the action of a voltage Vset1 or a dimming circuit voltage signal Vdim.
When the current level at the negative input terminal of the current comparator is
zero, the circuit would work at its minimum working frequency where the frequency
of the circuit is determined by the capacitor Cquickstart. When the period of time
for rapidly reaching the normal brightness comes to end (time signal is zero), the
NMOS transistor is turned off, and the voltage at the negative input terminal of the
current comparator (corresponding to the voltage across the terminals of the Rlamp)
would be adjusted to the voltage level at the positive input terminal of the current
comparator, such that the circuit operates at its normal working frequency (at a normal
current level) or at the frequency corresponding to the dimming level of the dimming
fluorescent lamp.
[0015] While the invention has been described with reference to above preferred embodiments,
it will be understood by those skilled in the art that various changes, additions
or deletions may be made and equivalents may be substituted for elements thereof without
departing from the scope of the invention and its claims, and all such alteration
and/or modification shall fall into the scope of the present invention.
1. A control circuit for a fluorescent lamp comprising a ballast control unit (1) and
an oscillator unit (2), characterized in that: the control circuit further comprises a signal detection unit (3), a switch unit
(4) and a frequency converter (5); the signal detection unit (3) being arranged to
output a signal to the switch unit (4) after receiving a light up signal from the
ballast control unit (1), the switch unit (4) outputting a signal to the frequency
converter (5) and the frequency converter (5) outputting a signal to the oscillator
unit (2) and converting an oscillation frequency of the oscillator unit (2).
2. A control circuit for a fluorescent lamp according to claim 1, wherein the signal
detection unit (3) comprises a diode (D1), a resistor (R1) and a first capacitor (Ctimer);
the resistor (R1) and the first capacitor (Ctimer) are connected in parallel together
and then connected with a negative terminal of the diode (D1), the diode (D1) having
a positive terminal connected with the ballast control unit (1); the switch unit (4)
is a NMOS transistor having its gate terminal connected with the negative terminal
of the diode (D1) and having its source terminal earthed; the frequency converter
(5) comprises a second capacitor (Cf) and a third capacitor (Cqst) which are connected
in series together and in parallel between drain and source terminals of the NMOS
transistor, and the oscillator unit (2) is connected with a point where the second
capacitor (Cf) and the third capacitor (Cqst) are connected.
3. A control circuit for a fluorescent lamp according to claim 1, wherein the oscillator
unit (2) further comprises a current comparator, and the signal detection unit (3)
comprises a diode (D2) and a first capacitor (C1); the diode (D2) has a positive terminal
connected with the ballast control unit (1), and a negative terminal connected with
the first capacitor (C1) which has another terminal earthed; the switch unit (4) is
a NMOS transistor having its gate terminal connected with the negative terminal of
the diode (D2) and having its source terminal earthed, while a drain terminal of the
NMOS transistor is connected with a negative terminal of the current comparator via
a resistor (R3); the frequency converter comprises a second capacitor (Cquickstart)
having one terminal earthed and another terminal connected with the oscillator unit
(2).