U.S. patent application number 10/268470 was filed with the patent office on 2003-02-13 for optimal fm for hf operation of high intensity discharge (hid) lamps.
This patent application is currently assigned to KONINKLIJKE PHILIPS ELECTRONICS, N.V.. Invention is credited to Bruning, Gert W..
Application Number | 20030030388 10/268470 |
Document ID | / |
Family ID | 24944123 |
Filed Date | 2003-02-13 |
United States Patent
Application |
20030030388 |
Kind Code |
A1 |
Bruning, Gert W. |
February 13, 2003 |
Optimal FM for HF operation of high intensity discharge (HID)
lamps
Abstract
A low cost method for operating a high intensity discharge (HID)
lamp including a ballast circuit. The method includes generating DC
in an AC-to-DC converter, capturing any AC ripple of the DC with a
buffer capacitor to generate a control signal, generating a high
frequency lamp power signal from DC utilizing an HF inverter
circuit and modulating the high frequency power signal utilizing
the control signal to generate a frequency swept lamp power signal
to drive the lamp while avoiding acoustic resonance.
Inventors: |
Bruning, Gert W.; (Sleepy
Hollow, NY) |
Correspondence
Address: |
Corporate Patent Counsel
Philips Electronics North America Coporation
580 White Plains Road
Tarrytown
NY
10591
US
|
Assignee: |
KONINKLIJKE PHILIPS ELECTRONICS,
N.V.
|
Family ID: |
24944123 |
Appl. No.: |
10/268470 |
Filed: |
October 10, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10268470 |
Oct 10, 2002 |
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09732584 |
Dec 8, 2000 |
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6483252 |
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Current U.S.
Class: |
315/291 ;
315/209R |
Current CPC
Class: |
H05B 41/2928 20130101;
Y02B 20/00 20130101; Y02B 20/208 20130101 |
Class at
Publication: |
315/291 ;
315/209.00R |
International
Class: |
H05B 037/02; G05F
001/00 |
Claims
What is claimed is:
1. A ballast circuit for stable operation of a high intensity
discharge (HID) lamp, comprising: an AC-to-DC converter for
converting power from an AC source to DC, the AC-to-DC converter
including a buffer capacitor for capturing AC ripple riding on the
DC; a high frequency inverter and ballasting element (HFIBE)
coupled to the AC-to-DC converter and to the HID lamp, the HFIBE
including means for generating a lamp driving signal from the DC
power drive said HID lamp; a driver circuit coupled to the HFIBE
circuit, the driver circuit including a voltage controlled
oscillator (VCO) for generating a driving signal for driving the
HFIBE; and a frequency control circuit coupled to the buffer
capacitor, the HFIBE and the driver circuit, wherein the buffer
capacitor provides a control signal to the driver circuit, and
wherein the VCO in the driver circuit responds to the control
signal by controlling the HFIBE to output frequency swept square
wave signal to power said HID lamp without driving said lamp into
an acoustic resonant state.
2. The ballast circuit set forth in claim 1, further comprising a
power correction circuit between the AC-to-DC converter and the
HFIBE.
3. The ballast circuit set forth in claim 1, wherein the frequency
control circuit is an RC circuit.
4. The ballast circuit as set forth in claim 1, wherein the
frequency control circuit is constructed as part of an integrated
circuit.
5. The ballast circuit as set forth in claim 3, wherein the
frequency control circuit senses the voltage on the buffer
capacitor and generates a current which varies in frequency with
variance of the voltage in the buffer capacitor.
6. The ballast circuit set forth in claim 3, wherein the frequency
control circuit includes a buffer capacitor of approximately 22
nanofarads.
7. The ballast circuit set forth in claim 1, wherein said lamp is a
metal halide lamp.
8. The ballast circuit of claim 1, wherein the average lamp power
signal generated in the HFIBE includes a frequency of around 80 kHz
and a power rating of approximately 39 Watts.
9. The ballast circuit of claim 8, wherein the swept frequency
signal out from the HFIBE to the lamp runs from about 75 to about
85 kHz.
10. The ballast circuit of claim 1, where the frequency control
circuit includes a capacitor and a first resistor connected in
parallel, the parallel combination connected serially to a second
resistor.
11. The ballast circuit of claim 10, where the capacitor is around
22 nanofarads and the first and second resistors are about 158
kOhms and 169 kOhms, respectively.
12. The ballast circuit of claim 1, wherein the AC-to-DC converter
includes a full-wave rectifier.
13. The ballast control circuit of claim 1, wherein the AC-to-DC
converter includes an EMI protect circuit.
14. A high intensity discharge lamp for stable operation including
a very low cost (VLC) ballast circuit which captures a
sawtooth-like AC ripple signal in a buffer capacitor to produce a
control signal for frequency modulating an average lamp power
signal used to drive the lamp outside a state of acoustic
resonance, the ballast circuit comprising: an AC-to-DC converter
for connection to an AC power source, the AC-to-DC converter
including said buffer capacitor; a high frequency inverter and
ballasting element coupled to the AC-to-DC converter and buffer
capacitor for generating a square wave signal to drive said HID
lamp; and a coupling circuit for coupling a control signal
generated by the buffer capacitor into a driver; wherein a VCO
within the driver responds to the control signal to generate a
swept FM signal causing the HF inverter and ballasting element to
drive the HID lamp such that it is maintained in a stable
state.
15. A low cost method for operating a high intensity discharge
(HID) lamp comprising a ballast circuit, the method comprising the
steps of: generating DC in an AC/DC converter; capturing any AC
ripple of the DC with a buffer capacitor to generate a control
signal; generating a high frequency lamp power signal from DC
utilizing an HF inverter circuit; and modulating the high frequency
power signal utilizing the control signal to generate a frequency
swept lamp power signal to drive said lamp while avoiding acoustic
resonance.
16. The method set forth in claim 15, wherein the frequency
modulated signal has a range from about 75 to about 85 kHz to
operate the HID lamp without going into acoustic resonance.
17. The method set forth in claim 15, wherein the control signal
has a frequency range of around 10 to 1000 Hz.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates generally to high intensity discharge
(HID) lamps and ballasts, and more particularly to a very low cost
(VLC) ballast which avoids the need for a separate ramp generator
circuit to generate a ramp signal to modulate the average lamp
power and achieve desired FM modulation for lamp stability.
[0003] 2. Description of Related Art
[0004] Operation of high intensity discharge (HID) lamps, e.g.,
metal halide lamps, by electronic ballast results in a phenomena
(problem) referred to as acoustic resonance. Acoustic resonance
causes the arc within the lamp to girate, flicker, and even
extinguish when a ballast circuit operates the HID lamp at
frequencies greater than a few kilohertz. High frequency operation
in HID lamps is most desirable but for the acoustic resonance
problem.
[0005] The arc tubes employed in HID lamps are hollow tubes of
alumina, quartz or hard glass shaped in various sizes with cupped
or conical ends filled with gas at several different pressures,
depending on the operating state of the lamp. The pressure
increases within the lamp as the lamp heats up. What are referred
to as "organ pipe" (acoustic) resonances can occur at different
lamp operating frequencies depending on the size, shape, and
pressure within the arc tube. Operation at or near a resonance
point (that is, at a particular high frequency) will result in
acoustic resonance, i.e., arc flicker, arc stretch, arc elongation
and spiraling, and even extinguishing the arc and causing arc tube
breakage.
[0006] Various attempts are known to overcome the effect of
acoustic resonances at high frequency. For example, U.S. Pat. No.
4,373,146, to Bonazoli, et al., discloses a method and circuit for
operating a high intensity discharge (HID) lamp in a mode which
minimizes or avoids acoustic resonance inside the arc tube. To do
so, Bonazoli frequency modulates a carrier waveform in the
kilohertz range to provide a variable frequency AC output. By
varying the frequency of the ac signal, the lamp is not driven at
any particular frequency for a substantial length of time, e.g., on
the order of milliseconds. This FM output is provided across the
electrodes of an HID lamp to drive the lamp while minimizing or
avoiding acoustic resonance.
[0007] The Bonazoli circuit, however, is not low cost. The Bonazoli
circuit is reproduced in prior art FIG. 1. The Bonazoli circuit
includes a DC source 2 with an output connected to an inverter 6,
the inverter DC input coupled to the output of the DC source 2. A
carrier waveform (square wave) generator 8 in the kHz range is
included which has an output coupled into inverter 6, as well as
ramp generator means 20 (a conventional ramp generating circuit)
for frequency modulating the carrier waveform to provide the
inverter 6 with a variable frequency signal. A starter means 4 for
coupling the AC signal across the lamp electrodes 12, 14 is also
included. The Bonazoli square wave generator 8 operates at a
voltage-controlled frequency of at least 20 kHz modulated by the
sawtooth signal generated by the ramp generator.
[0008] During operation, a ramp period could be in a range of 1 to
10 milliseconds (100-1000 Hz.) with a flyback of about microsecond.
The application of the ramp voltage to the square wave generator
causes the carrier waveform to be swept from 20 to 30 kHz. And as
mentioned above, such a mode of operation, because of the
constantly changing high frequency, avoids resonance. A problem
with the Bonazoli circuit resides in the fact that Bonazoli and
like apparatus and methods for dealing with the problem of acoustic
resonance within HID lamps is that such a circuit must incur the
cost of a ramp generator circuit to provide a ramp signal to
modulate the carrier waveform (FM) to drive the lamp.
OBJECTS AND SUMMARY OF THE INVENTION
[0009] It is therefore an object of the present invention to
provide a simple and eloquent circuit for driving an HID lamp,
e.g., a metal halide lamp, with a frequency modulated square wave
which avoids the shortcomings of the ballast circuits of the prior
art.
[0010] It is another object of the invention to provide, in a VLC
ballast where FM is used for feedforward control to conform to line
regulation, a simple R-C circuit is utilized to couple the low
frequency (100-120 Hz.) ripple derived from a buffer capacitor into
the frequency control portion of the ballast circuit (e.g., to vary
the frequency of a signal output by a VCO). Utilizing the inherent
AC ripple signal avoids the need for a separate and additional ramp
generator circuit to generate a ramp signal to frequency modulate
the average lamp power signal. The invention is particularly useful
in lamps having a long aspect ratio, that is, at least one (1) and
preferably greater than three (3).
[0011] To that end, a first embodiment of the present invention is
a very low cost (VLC) ballast for driving HID lamps. The VLC
ballast comprises an AC to DC converter block which includes a
buffer capacitor (C.sub.BUF) for receiving AC from a main source of
AC power and converting it to DC. The output of the AC to DC
converter provides to an HF inverter and ballasting element. The AC
signal component captured by the buffer capacitor is filtered by a
frequency control circuit constructed and provided to a high
voltage driver to modulate the carrier waveform provided by the HF
inverter and ballasting element to drive the lamp. The frequency
control circuit includes a capacitor in parallel with a first
resistor, the parallel combination in series with a second
resistor. The resulting sawtooth-like signal derived from C.sub.BUF
(as shown in FIG. 4A) is summed with the carrier signal thereby
modulating same. Since the AC is either 50 or 60 Hz, the sawtooth
will have a frequency of about 100 or 120 Hz. If the carrier
waveform is around 80 kHz, for example, the driver will modulate
the 80 kHz carrier with the filtered "sawtooth" signal, to vary the
frequency of the lamp driving signal from around 75 to around 85
kHz.
[0012] The reader must note that the frequency range of HID lamps
is conditioned upon power outage of the HID. For example, the HID
lamp of the first embodiment is about 39 Watts. In a case of a 70
Watt lamp, the range would vary from 45-55 kHz, and a lamp putting
out about 150 Watts would sweep from about 18 to about 26 kHz. The
AC component of the buffer capacitor is used to modulate the
average lamp power to achieve the desired FM modulation for stable
operation of the lamp, that is, unnoticeable acoustic
resonance.
[0013] The present invention also includes a very low cost method
for operating a high intensity discharge (HID) lamp. The method
includes receiving AC and converting it to DC in an AC-to-DC
converter. The DC is then provided to an HF inverter and ballasting
circuit, wherein a carrier signal for driving an HID lamp is
generated. A ripple from atop the DC generated in the AC-to-DC
converter is captured by a buffer capacitor and provided as an
input to a driver to drive the HF inverter and ballasting circuit.
The sawtooth or ripple modulates the carrier frequency (lamp
average power) which is provided across the HID lamp electrodes
such that a swept frequency signal is generated. Hence, the lamp is
driven by a frequency modulated signal which minimizes the effects
of acoustic resonance on the HID lamp.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0014] FIG. 1 is a circuit diagram of a prior art circuit for
driving an HID ballast which includes a sawtooth wave
generator;
[0015] FIG. 2A is a schematic block diagram of a circuit for
optimally generating FM for HF operation of HID lamps of the
present invention;
[0016] FIG. 2B is a more detailed schematic block diagram of the
circuit for optimally generating FM for HF operation of HID lamps
of FIG. 2A;
[0017] FIG. 2C is a more detailed schematic block diagram of a
circuit for optimally generating FM for HF operation of HID lamps
of FIG. 2B;
[0018] FIG. 3 is a detailed circuit diagram of a specific
embodiment of the circuit for optimally generating FM for HF
operation of HID lamps of FIG. 2A; and
[0019] FIGS. 4A and 4B depict the variation of the voltage across
the buffer capacitor over time, and the frequency variation of the
current in the lamp over time, respectively.
DETAILED DESCRIPTION OF THE INVENTION
[0020] The present invention uses an AC ripple to frequency
modulate (FM) a lamp power signal, the FM signal used to drive a
high intensity discharge (HID) lamp without problems associated
with acoustic resonance. The AC ripple is derived from an AC-to-DC
converter included to provide DC power to the ballast in order to
generate a square wave carrier signal. The present invention
presents a low cost method and circuit for solving the problem that
HID lamp ballast designers have long struggled with, that is, to
realize a cheap and efficient method for operating the lamps at
high frequency while avoiding acoustic resonance.
[0021] In particular, the invention presents a low cost ballast
circuit which derives a sawtooth-like signal to modulate the
average power driving the lamp from the Ac ripple riding the DC.
That is, by tapping into the AC ripple riding on the DC put out by
the AC-to-DC converter, the ripple or sawtooth-like signal for
modulating the AC carrier generated to drive the lamp is available
without the need for a conventional sawtooth generating circuit.
The resulting benefit resides in the lowered cost for the ballast
circuit because it does not require the separate sawtooth
generator.
[0022] FIG. 2A shows a first embodiment of the invention comprising
a ballast circuit for generating optimal FM for HF operation of HID
lamps, e.g., 39 Watts. In FIG. 2A, an AC-to-DC block B1 is shown
connected across a buffer capacitor, C.sub.BUF, e.g., 22
nanofarads, to HF inverter and ballasting element B2. The HF
inverter and ballasting element B2 receives DC from B1 and converts
it to a square wave carrier signal to drive HID lamp L1. Driver D1
drives the HF inverter and ballasting element B2. The ripple
voltage captured by the buffer capacitor is directed to a frequency
control section FC1 to allow a portion of the ripple to be fed into
the driver D1. Within driver D1, the AC ripple signal is utilized
to frequency modulate the carrier frequency of the square wave
signal. The frequency changes of the square wave output signal
varies inverse proportionally to the change in voltage with time of
the voltage on the buffer capacitor (as shown in FIG. 4).
[0023] FIG. 2B shows the FIG. 2A embodiment where the AC-to-DC
block B1 and frequency control section FC1 are further defined.
More particularly, AC-to-DC block B1 includes an AC/DC converter
AD1 coupled to a power factor correction (PFC) circuit, PFC. The
PFC circuit provides DC to the HF inverter and ballasting element
B2, and to buffer capacitor C.sub.BUF. C.sub.BUF takes the ripple
riding on the DC generated within the AC/DC converter AD1 and
provides it to the frequency control circuit FC1.
[0024] In the present embodiment, the frequency control circuit is
an RC circuit comprising a capacitor C.sub.FM (22 nanofarads in the
first embodiment) in parallel with a first resistor R1 (around 158
kOhm in the first embodiment), the parallel combination in series
with a second resistor R2 (around 169 k Ohms in the first
embodiment). The PFC circuit provides a signal to Driver D1 to
compel it to frequency modulate the square wave signal (average
lamp power) generated in the HF inverter and ballasting element B2
to drive lamp L1. In other words, the ripple on the DC is provided
to the driver to vary the frequency of the average lamp power. For
example, assuming an average lamp power signal operating at about
80 kHz (average for an approximately 39 Watt HID lamp, that is, the
frequency is inversely related to power), i.e., the square wave
generated by the HF inverter and ballasting element B2. With 60 Hz
AC, the ripple is around 120 Hz and modulates the 80 kHz signal
from about 75 to about 85 kHz.
[0025] FIG. 2C depicts the embodiment of the invention shown in
FIGS. 2A and 2B, where the AC/DC converter AD1 of AC-to-DC block B1
is further defined to include an EMI protect circuit B1-1 and a
full-wave rectifier circuit B1-2. A more detailed description of
the construction of an embodiment of both may be found below,
operation of which is known to those skilled in the art.
[0026] FIG. 3 shows a more detailed version of the first embodiment
of a ballast circuit for optimizing frequency modulation (FM) for
high frequency (HF) operation of an HID, depicted broadly in FIG.
2A, and constructed in accordance with the inventive principles
disclosed herein.
[0027] From left to right in FIG. 3, AC power (AC main) is provided
at the L, N and G terminals of the inventive ballast circuit of
this invention. The AC is first filtered by EMI protect circuit
B1-1. EMI protect circuit B1-1 includes a fuse F1 attached to a
cathode end of varistor V1 and a first end of a primary of common
mode filter choke transformer T1. An anode end of varistor V1 is
connected to a first end of a secondary of filter choke transformer
T1 and terminal N. The second end of the T1 primary is connected to
a first end of differential mode filter inductor L1. The second end
of differential mode filter inductor L1 is connected to full wave
rectifier circuit, B1-2, and the top of a differential mode
capacitor C.sub.DM. The second end of capacitor C.sub.DM is
connected to the top of a common mode capacitor C.sub.CM, a second
side of which is connected to terminal G.
[0028] Full-wave rectifier B1-2 connects to the first end of
capacitor C.sub.DM to a cathode end of diode D1 and a cathode end
of diode D3. The first end of capacitor C.sub.CM and the second end
of capacitor C.sub.DM are connected to an anode end of diode D4 and
a cathode end of diode D2. The anode ends of diodes D1 and D2 are
connected to a cathode end of diode D5 of the PFC section. An anode
end of diode D5 is connected to a cathode end of diode D6, the top
of capacitor C.sub.PF, and a capacitor C.sub.R1 of the HF inverter
and ballasting element B2. An anode end of diode D6 is connected to
a parallel combination of capacitor C.sub.FM and R1, which in turn
is connected serially with a resistor R2, to a source end of
transistor Q1 and a first end of capacitor C.sub.BUF A second end
of capacitor C.sub.BUF is connected to cathodes of diodes D3 and D4
to a first end of a resistor Rs, and directly to driver D1.
[0029] A second end of resistor R2 of the frequency control
section, a gate of transistor Q1, a drain of transistor Q1, a gate
of transistor Q2 and a drain of transistor Q2 are also connected to
D1. A second end of capacitor C.sub.R1 is connected to a first end
of inductor L2, a second end of which is connected to a parallel
combination of a first end of capacitor C.sub.R2 and a primary of a
transformer T2. A secondary of transformer T2 is connected to lamp
L1 through a capacitor C.sub.DC. A second end of capacitor C.sub.R2
and a second end of a primary of transformer T2 are connected to a
first end of a capacitor C.sub.O, to the drain and source of
transistors Q1 and Q2, respectively, and to a first end of a
capacitor C.sub.F and an input to driver D1.
[0030] During operation, AC is converted to DC by the AC-to-DC
block, and the HF inverter and ballasting element generates an
average power signal (at an average frequency) to drive the lamp.
Of course to avoid acoustic resonance, the average frequency must
be constantly varied to prevent the lamp from being driven at a
fixed frequency (e.g., high frequency) for any length of time,
which could result in acoustic resonance. Instead of utilizing a
separate circuit to generate a sawtooth-like signal to frequency
modulate the average lamp power signal, the buffer capacitor
captures the AC ripple riding on DC after conversion in the full
wave rectifier in AC-to-DC block B1, filters it and provides the
filtered version of the signal into a VCO contained within the
driver circuit. In a preferred form, the driver may embody a high
voltage driver for CFL, L6567 provided by ST Microelectronics of
Italy. The ripple signal causes the square wave signal output from
the HF inverter and ballasting element (an average power rating of
39 Watts and average frequency of around 80 kHz) to be swept in
frequency over a range from about 75 to about 85 kHz. Please note
that the embodiment depicted is for exemplary purposes only and is
not meant to limit the scope of protection claimed herein.
[0031] In addition to the ballast circuit described, the invention
may embody a method of utilizing a sawtooth-like signal derived
from inherent AC ripple riding on DC output from an AC-to-DC
converter to control frequency modulation of lamp power signal
generated to power the lamp.
[0032] Those skilled in the art will recognize that the method and
apparatus of the present invention has many applications, and that
the present invention is not limited to the representative
example(s) disclosed herein. Moreover, the scope of the present
invention covers conventionally known variations and modifications
to system or circuit components described herein, as would be known
by those skilled in the art.
* * * * *