U.S. patent application number 10/096308 was filed with the patent office on 2003-09-18 for compact single-stage electronic ballast circuit for emergency lighting applications.
This patent application is currently assigned to FEGO PRECISION INDUSTRIAL CO., LTD.. Invention is credited to Chang, Chin-Hsiung, Chen, Yu-Kai, Wu, Tsai-Fu, Wu, Yung-Chun.
Application Number | 20030173907 10/096308 |
Document ID | / |
Family ID | 28039002 |
Filed Date | 2003-09-18 |
United States Patent
Application |
20030173907 |
Kind Code |
A1 |
Chen, Yu-Kai ; et
al. |
September 18, 2003 |
COMPACT SINGLE-STAGE ELECTRONIC BALLAST CIRCUIT FOR EMERGENCY
LIGHTING APPLICATIONS
Abstract
A compact single-stage electronic ballast circuit for emergency
lighting applications, integrating the functions of a flyback
charger, a flyback discharger and a half-bridge series resonant
parallel loaded electronic ballast into a single-stage electronic
ballast. The present invention only employs two active switches so
as to achieve an electronic ballast for emergency lighting
applications when the electricity is out. Furthermore, the present
invention reduces the fabrication cost by simplifying the circuit
configuration and reducing the number of employed active switching
elements.
Inventors: |
Chen, Yu-Kai; (Taipei,
TW) ; Wu, Tsai-Fu; (Chiai, TW) ; Wu,
Yung-Chun; (Kaohsiung, TW) ; Chang, Chin-Hsiung;
(Taichung, TW) |
Correspondence
Address: |
TROXELL LAW OFFICE PLLC
SUITE 1404
5205 LEESBURG PIKE
FALLS CHURCH
VA
22041
US
|
Assignee: |
FEGO PRECISION INDUSTRIAL CO.,
LTD.
|
Family ID: |
28039002 |
Appl. No.: |
10/096308 |
Filed: |
March 13, 2002 |
Current U.S.
Class: |
315/291 |
Current CPC
Class: |
H05B 45/38 20200101;
H02J 9/065 20130101; H05B 41/2827 20130101; H05B 41/2853
20130101 |
Class at
Publication: |
315/291 |
International
Class: |
H05B 037/02 |
Claims
What is claimed is:
1. A compact single-stage electronic ballast circuit for emergency
lighting applications, comprising: an input power supply, providing
the compact single-stage electronic ballast circuit with power
required; a storage voltage source, connected to the input power
supply, so as to store the power; a first capacitor, connected to
the storage voltage source in parallel, so as to store the power
during the switching operation of the compact single-stage
electronic ballast circuit; a second capacitor, connected to the
first capacitor in series, so as to store the power during the
switching operation of the compact single-stage electronic ballast
circuit; a first active switch, connected to the first capacitor in
series, so as to perform the switching operation in the compact
single-stage electronic ballast circuit; a second active switch,
connected to the second capacitor in series, so as to perform the
switching operation in the compact single-stage electronic ballast
circuit; a load resonant circuit, wherein one end is connected to
the node between the first capacitor and the second capacitor, and
the other end is connected to one terminal of the second active
switch so as to provide the lamp load with resonance; and an
inductor-based power storage element, connected in series between
the first active switch and the second active switch, wherein the
center of the inductor-based power storage element is connected to
the node between the first capacitor and the second capacitor, so
as to store the power during the switching operation of the compact
single-stage electronic ballast circuit; wherein, the operation of
the first active switch and the second active switch enables the
single-stage electronic ballast circuit to integrate the features
of a charger, a discharger and an electronic ballast; and the
storage voltage source is charged to perform the operation of the
electronic ballast circuit when the input power supply normally
works, while the storage voltage source is discharged to provide
power to perform the operation of the electronic ballast circuit
when the input power supply cannot provide power.
2. The compact single-stage electronic ballast circuit for
emergency lighting applications as recited in claim 1, wherein a
flyback charger is formed when the input power supply normally
works.
3. The compact single-stage electronic ballast circuit for
emergency lighting applications as recited in claim 1, wherein a
half-bridge series resonant parallel loaded electronic ballast is
formed when the input power supply normally works.
4. The compact single-stage electronic ballast circuit for
emergency lighting applications as recited in claim 1, wherein a
flyback discharger is formed when the electricity provided stops to
provide power.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention generally relates to a compact
single-stage electronic ballast circuit for emergency lighting
applications, and more particularly, to a compact single-stage
electronic ballast circuit, having the features of battery
charging, discharging and lamp ballasting so as to reduce the
fabrication cost by simplifying the circuit configuration and
reducing the number of employed active switching elements.
[0003] 2. Description of the Prior Art
[0004] The use of a multi-stage power converter suffers from
increased volume and weight. Such a multi-stage power converter
employs a considerable amount of elements, which results in high
fabrication cost. Furthermore, the overall power conversion
efficiency may also decrease due to multi-stage conversion. These
drawbacks are unacceptable since the modern-day standards require
high efficiency, low cost, small volume and lightness. Therefore,
efforts have been made to provide single-stage converters with
multiple functions so as to overcome the foregoing problems.
[0005] With the rapid development in power conversion technology,
the safety regulations have become strict. A state-of-the-art
electrical power conversion system is required to possess various
functions. An UPS (uninterruptible power supply), for example,
employs a charger and a discharger to assist the storage and/or the
release of power and a converter to convert direct-current (DC)
voltages into alternate-current (AC) voltage so as to provide
required power during the electricity interruption. Furthermore, an
electronic ballast or a DC power converter with the function of
active power factor correction is used an additional stage of power
converter to perform unit power factor.
[0006] Accordingly, a single-stage system integrating a plurality
of power converters to reduce the fabrication cost has become a
tendency.
[0007] To date, electronic ballasts for emergency lighting
applications are exemplified as below.
[0008] Please refer to FIG. 1A, which is a commonly used circuit
configuration in the prior art. When the electricity is provided
normally, the switch S.sub.1 is turned on. The power passes through
the half-bridge series-resonant parallel-loaded electronic ballast
to light up the lamp. Also, the electricity passes through the
flyback charger to charge the battery. Furthermore, the switch
S.sub.2 is turned off, preventing the battery from discharging. On
the contrary, when the electricity is provided abnormally, the
battery voltage V.sub.B is increased by the flyback discharger to a
voltage level under normal electricity, thus lighting up the lamp
by the electronic ballast.
[0009] FIG. 1B shows a modification of the circuit in FIG. 1A, in
which the charger and the discharger are integrated and
bi-directional switches M.sub.3 and M.sub.4 are used to implement
bi-directional charging/discharging. When a charger is concerned, a
flyback circuit is formed of M.sub.3 and D.sub.4 to charge the
battery; and when a discharger is considered, a flyback circuit is
formed of M.sub.4 and D.sub.3 to increase the battery voltage to a
voltage level under normal electricity. It is obvious from the
above discussion that, under proper control, the active switches
M.sub.3 and M.sub.4 can be used to implement bi-directional
charging/discharging.
[0010] Even though the prior arts disclosed in FIG. 1A and FIG. 1B
can achieve electronic ballasts for emergency lighting
applications, these circuit configurations suffer from a large
number of elements and high fabrication cost. Therefore, the
present invention provides an integrated single-stage converter
circuit as shown in FIG. 2, in which only two active switches
M.sub.S1 and M.sub.S2 are required. The single-stage converter
circuit according to the present invention can, with reduced cost
and volume, achieve the same functions as the prior arts disclosed
in FIG. 1A and FIG. 1B. Furthermore, the active switches M.sub.S1
and M.sub.S2 have high efficiency due to a zero voltage switching
(ZVS) turn-on feature.
SUMMARY OF THE INVENTION
[0011] Therefore, the present invention has been made to solve such
problems in view of the forgoing status and to further provide an
electronic ballast that functions as a multi-conversion to store
power in the battery by a charger when electricity is provided
normally and to achieve emergency lighting by a discharger when
electricity is interrupted.
[0012] The present invention integrates a charger, a discharger and
an electronic ballast as a single-stage circuit so as to simplify
the circuit configuration and to reduce the cost. In addition, the
related reports only emphasize on a lamp lighting system of
high-voltage power source without high-frequency voltage
conversion. In the present invention, a 12-volt battery is employed
to light up the lamp. However, the DC voltage for an electronic
ballast is 156 V (the rectified and filtered value of the provided
electricity 110 V.sub.rms). Therefore, a transformer for increasing
low voltage to high voltage is required. To date, researches of a
single-stage converter with such a transformer for emergency
lighting applications have never been found in publications such as
patent applications and journal papers.
[0013] The primary object of the present invention is to implement
an electronic ballast for emergency lighting applications by using
a minimize number of elements to reduce the size and cost.
[0014] Other and further features, advantages and benefits of this
invention will become apparent in the following description taken
in conjunction with the following drawings. It is to be understood
that the foregoing general description and following detailed
description are exemplary and explanatory but are not to be
restrictive of the invention. The accompanying drawings are
incorporated in and constitute a part of this application and,
together with the description, serve to explain the principles of
the invention in general terms. Like numerals refer to like parts
throughout the disclosure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The objects, spirits and advantages of the preferred
embodiment of the present invention will be readily understood by
the accompanying drawings and detailed descriptions, wherein:
[0016] FIG. 1A is a circuit configuration of a conventional
electronic ballast for emergency lighting applications in the prior
art;
[0017] FIG. 1B is a circuit configuration of another conventional
electronic ballast for emergency lighting applications in the prior
art;
[0018] FIG. 2 is a circuit configuration of a single-stage
electronic ballast for emergency lighting applications in
accordance with the preferred embodiment of the present
invention;
[0019] FIG. 3A is a circuit configuration having the functions of a
charger and an electronic ballast, showing that the switch M.sub.S1
is turned off and the current flows through the diode D.sub.S1, in
accordance with the preferred embodiment of the present
invention;
[0020] FIG. 3B is a circuit configuration having the functions of a
charger and an electronic ballast, showing that the switch M.sub.S1
is turned off and the switch M.sub.S2 is turned on, in accordance
with the preferred embodiment of the present invention;
[0021] FIG. 3C is a circuit configuration having the functions of a
charger and an electronic ballast, showing that the switch M.sub.S2
is turned off and the diode D.sub.S1 is turned on, in accordance
with the preferred embodiment of the present invention;
[0022] FIG. 4A is a circuit configuration having the functions of a
discharger and an electronic ballast, showing that the switch
M.sub.S1 is turned on, the switch M.sub.S2 is turned off and the
current flows through the diode D.sub.S2, in accordance with the
preferred embodiment of the present invention;
[0023] FIG. 4B is a circuit configuration having the functions of a
discharger and an electronic ballast, showing that the switch
M.sub.S1 is turned on and the switch M.sub.S2 is turned off, in
accordance with the preferred embodiment of the present
invention;
[0024] FIG. 4C is a circuit configuration having the functions of a
discharger and an electronic ballast, showing that the switch
M.sub.S1 is turned off and the diode D.sub.S2 is turned on, in
accordance with the preferred embodiment of the present invention;
and
[0025] FIG. 5 is a circuit configuration for analyzing a
series-resonant parallel-loaded in accordance with the preferred
embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0026] The present invention disclosing a compact single-stage
electronic ballast circuit for emergency lighting applications can
be exemplified by the preferred embodiment as described
hereinafter.
[0027] To start with, please refer to FIG. 2, which a circuit
configuration of a compact single-stage electronic ballast circuit
for emergency lighting applications in accordance with the
preferred embodiment of the present invention. As shown in the
figure, the compact single-stage electronic ballast for emergency
lighting applications comprises: an input power supply, composed of
diodes D.sub.1, D.sub.2, D.sub.3 and D.sub.4 to form a bridge
rectifier that converts the electricity V.sub.u to provide the
compact single-stage electronic ballast circuit with power
required; a storage voltage source V.sub.B, which is a battery for
charging/discharging to be connected to the input power supply, so
as to store and provide the power for lighting up the lamp; a first
capacitor C.sub.1, connected to the storage voltage source V.sub.B
in parallel, so as to store the power during the switching
operation of the compact single-stage electronic ballast circuit;
and a second capacitor C.sub.2, connected to the first capacitor
C.sub.1 in series, so as to store the power during the switching
operation of the compact single-stage electronic ballast
circuit.
[0028] In FIG. 2, the circuit configuration also comprises: a first
active switch M.sub.S1, connected to the first capacitor C.sub.1 in
series, so as to perform the switching operation in the compact
single-stage electronic ballast circuit; a second active switch
M.sub.S2, connected to the second capacitor C.sub.2 in series, so
as to perform the switching operation in the compact single-stage
electronic ballast circuit; a load resonant circuit, comprising a
inductor L.sub.r, a capacitor C.sub.r and a lamp-load equivalent
resistance R.sub.lamp connected in series, wherein one end is
connected to the node between the first capacitor C.sub.1 and the
second capacitor C.sub.2, and the other end is connected to one
terminal (the source) of the second active switch M.sub.S2 so as to
provide the lamp load with resonance; and an inductor-based power
storage element T.sub.1, connected in series between the first
active switch M.sub.S1 and the second active switch M.sub.S2,
wherein the center of the inductor-based power storage element
T.sub.1 is connected to the node between the first capacitor
C.sub.1 and the second capacitor C.sub.2, so as to store the power
during the switching operation of the compact single-stage
electronic ballast circuit. In addition, the body diodes in the
first active switch M.sub.S1 and the second active switch M.sub.S2
are diodes D.sub.S1 and D.sub.S2, respectively.
[0029] In the present invention, the first active switch M.sub.S1
and the second active switch M.sub.S2 are controlled to enable the
compact single-stage electronic ballast circuit to integrate the
features of a charger, a discharger and an electronic ballast. When
the input power supply operates normally, the storage voltage
source V.sub.B is charged and the electronic ballast circuit lights
up the lamp. When the input power supply fails to operate normally,
the storage voltage source V.sub.B is discharged to provide the
electronic ballast circuit with power.
[0030] In the compact single-stage electronic ballast circuit for
emergency lighting applications in accordance with the present
invention, when the input power supply operates normally, a flyback
charger is formed to charge the storage voltage source V.sub.B, and
the half-bridge series resonant parallel loaded electronic ballast
circuit is operated to drive the lamp. On the contrary, when the
input power supply stops to provide electricity, a flyback
discharger is formed to release power to enable the electronic
ballast circuit to drive the lamp.
[0031] The operation modes of the compact single-stage electronic
ballast circuit according to the present invention are described
hereinafter.
[0032] A. Analysis of the bi-directional charger/discharger:
[0033] When the compact single-stage electronic ballast circuit for
emergency lighting applications is used as a charger, as shown in
FIG. 3A, it can be regarded as a flyback charger that receives the
electricity form the power supply and them charges the battery. In
the drawing, M.sub.S2 is an active switch and M.sub.S1 is regarded
as a passive switch. The resonant inductor L.sub.r, the resonant
capacitor C.sub.1 and lamp resistor R.sub.lamp are shown with
dotted lines, which form a flyback charger with a battery as a
load. Assume that all the transistors and diodes are ideal elements
and the circuit operates in continuous conduction mode (CCM). When
the power switch M.sub.S2 is turned on (while M.sub.S1 is turned
off), the current i.sub.L1 gets larger and the inductor L.sub.p
stores the power, as shown in FIG. 3B. When the driving signal of
M.sub.S2 is interrupted, M.sub.S2 is turned off and the body-diode
D.sub.S1 (which is connected to M.sub.S1 in parallel) is turned on,
as shown in FIG. 3C. Meanwhile, the inductor current i.sub.L1 gets
smaller and the inductor L.sub.S releases power to the battery. As
it goes on and on, the provided electricity may be converted by a
power converter to charge the battery. Furthermore, we can obtain
the relation between the voltage of provided electricity V.sub.dc
and the storage voltage source V.sub.B, which is expressed as: 1 V
B V dc = D 1 - D .times. N 1 N 2 ( 1 )
[0034] wherein D denotes the duty ratio of the power switch
M.sub.S2.
[0035] When the electricity is provided abnormally, the
single-stage electronic ballast can be regarded as a discharger, as
shown in FIG. 4A. when the battery operates in a discharging mode,
M.sub.S2 acts as a passive switch and M.sub.S1 acts as an active
switch. When the power switch M.sub.S1 is turned on (M.sub.S2 is
turned off), the equivalent circuit is as shown in FIG. 4B and the
battery releases power to be stored by the inductor L.sub.S. When
the driving signal of the power switch M.sub.S1 is interrupted, the
body-diode D.sub.S2 (which is connected to M.sub.S2 in parallel) is
turned on and the equivalent circuit is as shown in FIG. 4C.
Meanwhile, the inductor current i.sub.L1 gets smaller and the
inductor L.sub.p releases power to the capacitor C.sub.2. That is,
the battery releases power to the capacitor C.sub.2. Furthermore,
we can obtain the relation between the voltage of provided
electricity V.sub.dc and the storage voltage source V.sub.B, which
is expressed as: 2 V dc V B = D 1 - D .times. N 1 N 1 ( 2 )
[0036] wherein D denotes the duty ratio of the power switch
M.sub.S1.
[0037] From the foregoing discussion, when D is around 50%, the
voltage of provided electricity V.sub.dc is increased to
N.sub.2/N.sub.1 the battery voltage, which is high enough to drive
the lamp. Therefore, when the provided electricity is abnormal, the
system according to the present invention can still drive a
fluorescent lamp by using the power from the battery.
[0038] In order to obtain a large output power at the output, the
inductors in the circuit must be designed to be larger than those
under the boundary condition between continuous conduction mode
(CCM) and discontinuous conduction mode (DCM) when the
bi-directional flyback charger/discharger operates in continuous
conduction mode (CCM). The boundary condition indicates a zero
inductor current when the conduction cycle ends. Therefore, we
obtain the inductor L.sub.S expressed as: 3 L s > ( V 0 + V f )
( 1 - D max ) T s I sb ( 3 )
[0039] wherein V.sub.o represents the output voltage, V.sub.f the
forward voltage drop of the diode, T.sub.s the reciprocal of the
switching frequency, I.sub.sb the peak current along L.sub.s,
D.sub.max the maximum duty ratio. Furthermore, if the circuit
operates in continuous conduction mode (CCM), the control over the
operation of the whole circuit is easier, resulting in a simplified
design.
[0040] B. Analysis of the series resonant parallel loaded inverter
(SRPLI):
[0041] In FIG. 5, it is shown a circuit configuration for analyzing
a series-resonant parallel loaded inverter, wherein L.sub.r denotes
the resonant inductor, C.sub.r denotes the resonant capacitor and
R.sub.lamp is the equivalent resistance of the lamp. Furthermore,
both M.sub.S1 and M.sub.S2 are high-frequency switches and compose
a half-bridge converter. The operation principles of the circuit is
described as below:
[0042] Assume the power switch driving frequency .omega..sub.S is
larger than the resonant frequency .omega..sub.R and the voltages
across the capacitors C.sub.1 and C.sub.2 are constant. When the
power switch M.sub.S1 is turned on (M.sub.S2 is turned off), the
current i.sub.l,r flows into the resonant circuit and provides the
lamp with power. Since the operation frequency .omega..sub.S is
higher than the resonant frequency .omega..sub.R, M.sub.S1 is
turned off when the driving signal of the power switch M.sub.S1 is
interrupted. But meanwhile, there is still some current flowing
through the resonant inductor i.sub.L1. In order to keep the
current continuity on the inductor, the body-diode D.sub.S2 (which
is connected to the M.sub.S2) is turned on and forms a loop.
Meanwhile the inductor current gets smaller. When D.sub.S2 is
turned on, a driving signal is delivered to M.sub.S2. Meanwhile,
the voltage drop V.sub.DS across the power switch is almost zero,
leading to a very small loss of the M.sub.S2. Such a phenomenon is
called zero voltage switching (ZVS). When the inductor current
flows in a reversed direction through the power transistor
M.sub.S2, D.sub.S2 is turned off. Similarly, when the driving
signal of the power switch M.sub.S2 is interrupted, M.sub.S2 is
turned off. In order to keep the current continuity on the
inductor, the body-diode D.sub.S1 (which is connected to the
M.sub.S1) is turned on and forms a loop. Meanwhile the inductor
current gets smaller and zero voltage switching (ZVS) can be
obtained. Therefore, the electronic ballast has little switching
loss, resulting in a high efficiency.
[0043] According to the above discussion, the present invention
discloses a compact single-stage electronic ballast circuit for
emergency lighting applications, having the features of battery
charging, discharging and lamp ballasting so as to reduce the
fabrication cost by simplifying the circuit configuration and
reducing the number of employed active switching elements.
Therefore, the present invention has been examined to be
progressive, advantageous and applicable to the industry.
[0044] Although this invention has been disclosed and illustrated
with reference to particular embodiments, the principles involved
are susceptible for use in numerous other embodiments that will be
apparent to persons skilled in the art. This invention is,
therefore, to be limited only as indicated by the scope of the
appended claims.
* * * * *