Title: Fluorescent lamp ballast control circuit
Abstract: A fluorescent lamp ballast control circuit includes a ballast controller IC for driving a fluorescent lamp in a half-bridged topology and a control circuit. The control circuit receives an input signal and provides an output signal to the ballast controller IC. The control circuit further receives a feedback signal indicative of the fluorescent lamp current. The control circuit output signal is based on the input signal and the feedback signal. The fluorescent lamp ballast control circuit is used in combination with a fluorescent lamp ballast.
Patent Number: 6,998,796 Issued on 02/14/2006 to Sears
| Inventors:
|
Sears; Storm S. (Dayton, NV)
|
| Assignee:
|
Bruce Industries, Inc. (Dayton, NV)
|
| Appl. No.:
|
640533 |
| Filed:
|
August 13, 2003 |
| Current U.S. Class: |
315/308; 315/DIG.4 |
| Current Intern'l Class: |
H05B 37/02 (20060101) |
| Field of Search: |
315/291,299,307-308,DIG.4,DIG.5
|
References Cited [Referenced By]
U.S. Patent Documents
Other References
Data Sheet No. PD60194, "Dimming Ballast Control IC," International Rectifier,
2001, Oct. 10, 2001.
|
Primary Examiner: Tran; Thuy Vinh
Attorney, Agent or Firm: Brooks Kushman P.C.
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATION
This application claims the benefit of U.S. provisional application Ser. No.
60/404,022, filed Aug. 16, 2002.
Claims
What is claimed is:
1. A fluorescent lamp ballast control circuit comprising:
a ballast controller IC for driving a fluorescent lamp in a half-bridge topology,
the ballast controller IC having a dim control input; and
a control circuit receiving an input signal and providing an output signal to
the ballast controller IC dim control input, the control circuit further receiving
a feedback signal indicative of a fluorescent lamp current, wherein the control
circuit output signal is based on the control circuit input signal and the feedback
signal to set and keep the lamp current at a desired setting based on the control
circuit input signal;
wherein the control circuit output signal is based in part on a feed forward
of the control circuit input signal and based in part on an error determined by
comparing the control circuit input signal to the feedback signal.
2. A fluorescent lamp ballast control circuit comprising:
a ballast controller IC for driving a fluorescent lamp in a half-bridge topology;
and
a control circuit receiving an input signal and providing an output signal to
the ballast controller IC, the control circuit further receiving a feedback signal
indicative of a fluorescent lamp current, wherein the control circuit output signal
is based on the input signal and the feedback signal;
wherein the control circuit output signal is based in part on a feed forward
of the input signal and based in part on an error determined by comparing the input
signal to the feedback signal;
wherein the output signal is based on a weighted sum of the feed forward and
the error.
3. The fluorescent lamp ballast control circuit of claim 2 wherein the weighted
sum is composed of a greater weighting of the feed forward and a lesser weighting
of the error.
4. The fluorescent lamp ballast control circuit of claim 3 wherein the output
signal is about 80% based on the feed forward and is about 20% based on the error.
5. In combination with a fluorescent lamp ballast, the improvement comprising:
a ballast control circuit including a ballast controller IC for driving a fluorescent
lamp in a half-bridge topology, the ballast controller IC having a dim control
input and a control circuit receiving an input signal and providing an output signal
to the ballast controller IC dim control input, the control circuit further receiving
a feedback signal indicative of a fluorescent lamp current, wherein the control
circuit output signal is based on the control circuit input signal and the feedback
signal to set and keep the lamp current at a desired setting based on the control
circuit input signal;
wherein the control circuit output signal is based in part on a feed forward
of the control circuit input signal and based in part on an error determined by
comparing the control circuit input signal to the feedback signal.
6. In combination with a fluorescent lamp ballast, the improvement comprising:
a ballast control circuit including a ballast controller IC for driving a fluorescent
lamp in a half-bridge topology, and a control circuit receiving an input signal
and providing an output signal to the ballast controller IC, the control circuit
further receiving a feedback signal indicative of a fluorescent lamp current, wherein
the control circuit output signal is based on the input signal and the feedback
signal;
wherein the control circuit output signal is based in part on a feed forward
of the input signal and based in part on an error determined by comparing the input
signal to the feedback signal;
wherein the output signal is based on a weighted sum of the feed forward and
the error.
7. The combination of claim 6 wherein the weighted sum is composed of a greater
weighting of the feed forward and a lesser weighting of the error.
8. The combination of claim 7 wherein the output signal is about 80% based on
the feed forward and is about 20% based on the error.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to fluorescent lamp ballast control circuits.
2. Background Art
The use of fluorescent lamps has become widespread. The typical fluorescent lamp
is composed of a glass tube containing an inert gas and a small amount of mercury.
Phosphor coats the inside of the glass tube, and each end of the glass tube includes
an electrode. In operation, a ballast provides current to the electrodes. A traditional
ballast is a special transformer that uses electromagnetic principles to generate
operating and starting voltages for fluorescent lamps. An electronic ballast uses
electronics to achieve the same result. In operation, electrons migrate across
the length of the tube, and excite the mercury atoms which are in a gaseous state.
The arc releases photons in the ultraviolet band. The photons excite the phosphors
that coat the inside of the glass tube, and the phosphors emit visible light.
One type of electronic ballast employs a ballast control integrated circuit (IC)
to drive the fluorescent lamp. A ballast controller and half-bridge driver in one
IC are described in Data Sheet No. PD60194, "DIMMING BALLAST CONTROL IC."
SUMMARY OF THE INVENTION
This circuit is used to enhance the performance of fluorescent ballast designs
based on a half-bridge topology, employing a ballast controller IC. The addition
of a current feedback control loop to the circuit provides the following improvements
to ballast operation:
- 1. Tighter load regulation;
- 2. Improved load regulation over temperature;
- 3 Eliminates the need for trimming adjustments during ballast production;
- 4. Allows a single ballast to operate several lamp loads without changing
the resonant L and C values, or readjusting the ballast (universal ballast operation); and
- 5. Analog control loop design provides a low cost solution for step
dim or continuous dim applications.
In carrying out the present invention, a fluorescent lamp ballast control circuit
is provided. The control circuit comprises a ballast controller IC for driving
a fluorescent lamp in a half-bridge topology, and a control circuit. The control
circuit receives an input signal and provides an output signal to the ballast controller
IC. The control circuit further receives a feedback signal indicative of the fluorescent
lamp current. The control circuit output signal is based on the input signal and
the feedback signal.
At a more detailed level, the invention comprehends basing the control circuit
output signal in part on a feed forward of the input signal and in part on an error
determined by comparing the input signal to the feedback signal. Further, the output
signal may be implemented as a weighted sum of the feed forward and the error.
More specifically, in the preferred implementation, the weighted sum is composed
of a greater weighting of the feed forward and a lesser weighting of the error.
In a suitable application, the output signal is about 80% based on the feed forward
and is about 20% based on the error.
Further, in carrying out the invention, the control circuit including a
ballast controller IC for driving a fluorescent lamp in a half-bridge topology
and a control circuit are provided in combination with a fluorescent lamp ballast.
The control circuit employs various features described above.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A-1B are a schematic view of the circuit in the present invention
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
With reference to FIGS. 1A-1B, a current transformer, CT
1 is placed in
series with the lamp load to convert the lamp current to a proportional voltage.
In the example illustrated, the ballast is designed to provide a step dim response
of the lamp current with a dim current level of 50 mA and bright current level
of 200 mA. The DC voltage developed from the CT network, composed of CT
1,
D
3, R
13, R
14 and C
4, is 0.74 VDC for a lamp current
of 50 mA (dim) and 2.85 VDC for a lamp current of 200 mA (bright).
A voltage divider network, composed of R
1, D
1, R
2, R
3
and R
4, is used to adjust either a step control signal or a variable control
voltage so that the voltage is equivalent to the CT network output voltage. This
command voltage is buffered by U
2D.
The bulk of the command voltage, approximately 80%, is passed directly to the
dim control input of the ballast controller IC. In this fashion, the ballast controller
IC will respond rapidly to either step or variable command voltages and then, will
be gradually adjusted to the desired current set point by an additional error voltage
signal, representing the remaining 20% of the control signal. The error voltage
is proportional to the deviation in lamp current from the desired set point.
The buffered command voltage is amplified by U
2A, an inverting op amp
configuration and converted from a range of 0.74 to 2.85 VDC, to a range of -1
to -4 VDC. Op amp U
2A is configured with resistors R
5, R
6
and capacitors C
1, C
2. This voltage is passed through an inverting,
unity gain summing amplifier, U
2C, to the ballast controller IC. In the
example illustrated, a IR21592 ballast controller IC has been employed, which responds
to a dim control voltage in the range of 0.5 to 5 VDC. The minimum and maximum
values of the controller IC have been adjusted so that with a 1 volt dim control
signal, the ballast will attempt to regulate lamp current at 50 mA (dim) and with
a 4 volt dim control signal, the ballast will attempt to regulate lamp current
at 200 mA (bright).
The buffered command voltage is also applied as a reference to comparator U
2B.
As the voltage from the CT network, applied to the other lead of the comparator,
either exceeds or falls below the reference established by the command voltage,
the comparator output will either switch to the high or low rail. During normal
operation, the output of the comparator is switching continuously back and forth
between the high and low rail, as the lamp current varies away from the commanded
lamp current. The varying comparator output is reduced in amplitude by a voltage
divider consisting of R
11 and R
12 and is filtered to a DC error voltage
by capacitor C
3. The error voltage is then summed together with the bulk
of the command voltage by summing amplifier U
2C. Op amp U
2C is configured
with input resistors R
7, R
8, and feedback resistor R
9. The
output of op amp U
2C is connected through R
10, D
2 and C
5
to the ballast controller IC. The use of a bipolar supply allows the error voltage
to either subtract or add to the command voltage as required to keep the lamp current
at the required setting.
The ballast controller IC drives the lamp using a half-bridge topology. FIG.
1B illustrates a suitable half-bridge topology composed of R
15, R
16,
R
17, R
18, R
19, C
6, C
7, Q
1, Q
2,
and L
1. In operation, the ballast controller IC drives the lamp based on
the control circuit output signal applied to the dim control input.
While embodiments of the invention have been illustrated and described, it
is not intended that these embodiments illustrate and describe all possible forms
of the invention. Rather, the words used in the specification are words of description
rather than limitation, and it is understood that various changes may be made without
departing from the spirit and scope of the invention.
*
