Electric lamp and discharge devices: systems – Pulsating or a.c. supply – With power factor control device
Reexamination Certificate
2002-05-17
2004-03-09
Ho, Tan (Department: 2821)
Electric lamp and discharge devices: systems
Pulsating or a.c. supply
With power factor control device
C315S291000, C315S307000
Reexamination Certificate
active
06703794
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a power factor correction device. In particular, the invention relates to a power factor correction device including electronic ballast function, which adds a control circuit to produce the electronic ballast action to reduce harmonic interference, save power and space, and increase system reliability.
2. Description of the Related Art
Electronic ballast power factor refers to an efficient power percentage of an input current actually used in an electronic ballast circuit. In general, an electronic ballast circuit driven by the high-frequency voltage to light a lamp has a higher light output, i.e., to save more power. Hence, the electronic ballast circuit is in widespread use, e.g., various projectors, to replace the conventional ballast circuit and starter. Typically, a projector's lamp lighting circuit separates a power factor correction converter and an electronic ballast circuit as shown in FIG.
1
.
FIG. 2
is a circuit diagram of a conventional ballast system. In
FIG. 2
, the system includes a rectifier
21
, a power factor correction (PFC) circuit
22
, an energy storing capacitor C
3
, an electronic ballast circuit
24
, an ignitor
25
and a lamp. The rectifier
21
includes a full-bridge rectifier comprised of diodes BD
1
-BD
4
to produce a DC output, for example, converting 110 VAC into 150 VDC or 220 VAC into 300 VDC, and a filter capacitor C
1
to filter the DC output in order to avoid noise interference coming from rectifier
21
. The PFC circuit
22
mainly includes a transformer T
1
, start resistors R
1
, R
2
, a T
1
-waveform sensing resistor R
3
, an integrating filter capacitor C
2
, a block diode D
1
, a metal-oxide-semiconductor field-effect transistor (MOSFET) switch Q
1
and a controller CTRL
1
. The output of the rectifier
21
is coupled to an end of the start resistor R
1
and an end of a first inductor TL
1
of the transformer T
1
. Another end of the start resistor R
1
is coupled to an end of the start resistor R
2
. Another end of the first inductor TL
1
is coupled to the source of the switch Q
1
and a forward-biased diode D
2
. Another end of the start resistor R
2
is coupled to the input of the controller CTRL
1
, the grounding integrating filter capacitor C
2
, and the reverse end of the block diode D
1
(node A). The forward end of the block diode (node B) is coupled to an end of the resistor R
3
and an end of a second inductor TL
2
of the transformer T
1
. Another end of the second inductor TL
2
is to the ground. Another end of the sensing resistor R
3
is coupled to the input of the controller CTRL
1
. The output of the controller CTRL
1
is coupled to the gate of the switch Q
1
through a resistor R
4
. The drain of the switch Q
1
is coupled to the input of the controller CTRL
1
and a grounding resistor R
5
. In such a configuration, the circuit
22
uses the controller CTRL
1
to receive the output voltage sensing from the transformer T
1
by the resistor R
3
and a feedback signal FB from the drain of the switch Q
1
. The feedback signal FB is used to modify the output voltage from the two inductors of the transformer T
1
to selectively change the ON duty ratio and/or the frequency of the switch Q
1
so as to output a correct power factor. The block diode D
1
blocks the reserve current from the capacitor C
2
discharge to avoid affecting the sensing value of the sensing resistor R
3
. Hence, the controller cannot output the correct power factor. Similarly, the diode D
2
has the same block function as the grounding capacitor C
3
storing the DC output from the PFC circuit
22
. The load condition will influence the output phase coherence of the current and voltage, for example, in a projector with an incandescent lamp only able to have the same output phase on the voltage and current and the 100% output power factor. However, in practical, load is more complicated, such as, for example, when a high voltage mercury lamp is used, a capacitor (C
3
) to store the power and an electronic Ballast to keep the power factor output in a steady state, for example, over 0.95, are a must. Typically, as shown in
FIG. 2
, the circuit
24
includes an MOSFET switch Q
2
, a shunt LC resonant circuit, a block diode D
3
and a controller CTRL
2
. The source of the switch Q
2
connects to the free end of the capacitor C
3
, the gate to an input signal from the controller CTRL
2
through the resistor R
6
, the drain to the reverse end of the diode D
3
and an end of the inductor L
1
in the shunt LC circuit. The inductor L
1
connects to an end of an external lamp LAMP and the free-end of the grounding capacitor C
4
in the shunt LC circuit. The forward end of the diode D
3
connects the ground and an end of the resistor R
7
. Another end of the resistor R
7
connects to the controller CTRL
2
to produce a feedback signal BFB. Another end of the resistor R
7
also connects to an end of the ignitor
25
including a transformer T
2
to ignite and a controller CTRL
3
to control the transformer T
2
. Another end of the ignitor
25
connects another end of the lamp LAMP. The controller CTRL
2
outputs a control signal to adjust the Q
2
output frequency based on the feedback signal BFB, so as to control the output power from the LC resonant circuit having the DC—DC conversion function to the lamp LAMP. The diode D
3
having the same function as mentioned the diode D
1
above can avoid the feedback signal affected by the reversed current and voltage from the drain of the switch Q
2
. Further, the reversed current and voltage influence the voltage supply to the lamp LAMP, so as to affect the lighting (projecting) stability of the lamp (i.e., Flicker Index (FI) for light). For example, the lamp's FI over 0.01 can cause vibration on the projecting frame. To solve this problem, the PFC circuit
22
typically keeps the output voltage of the rectifier
21
around 380 VDC and decreases the output voltage to about 85 VDC by the LC resonant circuit in the ballast circuit
24
to provide the lamp LAMP the required voltage. However, this makes the circuitry complicated so as to waste power, space and cost.
SUMMARY OF THE INVENTION
Accordingly, an object of the invention is to provide a power factor correction device including electronic ballast function, which adds a control circuit to produce the electronic ballast action to reduce harmonic interference, save power and room, and increase system reliability.
The invention provides a power factor correction device including electronic ballast function. The device includes a lamp; an ignitor, connected in series with the lamp, to start the illumination; a voltage and current controller, connected in parallel with the cascade lamp and ignitor, to receive the voltage across the lamp and output a feedback signal according to the received voltage; and a power factor correction (PFC) circuit, connected in parallel with the voltage and current controller, to adjust an output power according to the feedback signal to protect the circuit and increase the stability.
REFERENCES:
patent: 6172466 (2001-01-01), Ki et al.
patent: 6181079 (2001-01-01), Chang et al.
patent: 6300723 (2001-10-01), Wang et al.
patent: 6359394 (2002-03-01), Stein
Benq Corporation
Ho Tan
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