GB2305311A - Self oscillating drive circuit for an electrodeless discharge lamp - Google Patents
Self oscillating drive circuit for an electrodeless discharge lamp Download PDFInfo
- Publication number
- GB2305311A GB2305311A GB9519041A GB9519041A GB2305311A GB 2305311 A GB2305311 A GB 2305311A GB 9519041 A GB9519041 A GB 9519041A GB 9519041 A GB9519041 A GB 9519041A GB 2305311 A GB2305311 A GB 2305311A
- Authority
- GB
- United Kingdom
- Prior art keywords
- coupled
- circuit
- oscillator circuit
- capacitor
- coil
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
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Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B41/00—Circuit arrangements or apparatus for igniting or operating discharge lamps
- H05B41/14—Circuit arrangements
- H05B41/26—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc
- H05B41/28—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters
- H05B41/2806—Circuit arrangements in which the lamp is fed by power derived from dc by means of a converter, e.g. by high-voltage dc using static converters with semiconductor devices and specially adapted for lamps without electrodes in the vessel, e.g. surface discharge lamps, electrodeless discharge lamps
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/5383—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a self-oscillating arrangement
- H02M7/53832—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a self-oscillating arrangement in a push-pull arrangement
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B20/00—Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
- Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Circuit Arrangements For Discharge Lamps (AREA)
Abstract
An electrodeless lamp drive coil 16 and a capacitor 14 form a series resonant circuit which is connected to an output node 10 between series connected FETs 4,6, the current in the drive coil 16 being sensed by a feedback capacitor 34 connected via a feedback resistor 32 to the gate of one of the FETs 4,6 so that the circuit is self oscillating at a frequency (eg. 2.8MHz) determined by the series resonant circuit 14,16. The relative positions of capacitors 14,34 may be interchanged, and the capacitor of the series resonant circuit may alternatively be formed by two equal value capacitors (14 a ,14 b , Fig.3) connected between one end of the coil 16 and respective rails of a DC supply. The FETs 4,6 may both be n-type with gates coupled by close coupled windings 28,30 on a transformer TX so that the FETs 4,6 turn on alternately. The two FETs 4,6 may alternatively be of opposite conductivity types (Fig.4), with their gates connected directly to one another and to one end of the feedback resistor 32, thereby forming a self starting circuit in which both the transformer TX and a starting circuit 18,20,22 are eliminated; such a circuit may be very compact and manufactured using surface mount technology as it has no magnetic components, other than the drive coil 16.
Description
IMPROVEMENTS IN OR RELATING TO ELECTRODELESS DISCHARGE LAMPS
The present invention relates to an oscillator circuit for igniting and supplying an electrodeless discharge lamp.
One form of electrodeless discharge lamp includes a glass re-entrant, formed in the base of the lamp envelope, for accommodating a coil. A relatively high radio frequency voltage/current is applied to the coil to start the lamp. After starting, the plasma within the lamp envelope acts as a load and reduces the apparent Q factor of the coil, causing the drive circuit to operate the lamp, after starting, with a lower voltage across the coil.
Drive circuits for such lamps usually comprise DC-AC converter circuits which are self oscillating. Such circuits are known from, for example, GB 2080652 and EP 0222441. These disclosures describe a self resonant circuit which is driven by two transistors in 'totem pole configuration', with the coil used to energise the lamp forming part of a parallel resonant circuit. The parallel coupled self resonant circuit does not present a high impedance laod to the driving transistors at high frequencies. Thus, an additional coil is required, coupled in series with the parallel resonant circuit to prevent overload and self destruction of the drive transistors. The additional coil, being a magnetic component, is of relatively high cost and, as it must handle a substantial amount of power, is relatively bulky.The circuits described in GB 2080652B and EP 0222441 are, therefore, relatively expensive to manufacture and are not of compact size.
US Patent 4631449 describes a crystal controlled oscillator circuit to drive a pair of series coupled power transistors.
The comnon output of the power transistors is coupled via a filter network to a lamp coil forming part of a series resonant circuit. The series coupled power transistors, with secondary windings of a transformer arranged in the gate circuits, function as a half bridge amplifier for amplifying radio frequency power provided by the crystal controlled oscillator across the primary winding of the transformer. When the input drive voltage is sufficient, regenerative feedback of the lamp current from the lamp coil to a further winding on the transformer causes the half bridge amplifier to run as a power oscillator. The output frequency is a function of the relative magnitude and phase of the signal fed back from the lamp coil with respect to the output from the crystal oscillator. The crystal oscillator is used, therefore* to control the start up and free running oscillation of the circuit.As will be appreciated, the arrangement of US 4631449 is relatively complex and includes several inductive components, including a transformer having three secondary windings. The circuit is, therefore, relatively expensive to manufacture and difficult to fabricate of compact size.
It is an object of the present invention to provide an oscillator circuit for an electrodeless lamp which is relatively simple in configuration, is reliable in self oscillation, and which includes a minimum of magnetic components, thereby enabling relative low cost manufacture and compact size of circuitry to be achieved.
Accordingly, there is provided an oscillator circuit for an electrodeless discharge lamp, the oscillator circuit comprising first and further semiconductor switching elements each including a control electrode and coupled in series to provide an output node therebetween, and a feedback circuit, coupled to the output node, comprising a series resonant circuit including a capacitor coupled in series with a coil for causing a discharge in the lamp the feedback circuit further comprising, for enabling self oscillation of the oscillator circuit, a feedback resistor arranged between the series resonant circuit and a control electrode of a switching element, and a feedback capacitor coupled. to the feedback resistor, for sensing current flowing in the coil.
Alternatively, the capacitor of the series resonant circuit comprises two capacitors each coupled between one end of the coil and a respective supply rail for the oscillator circuit, and the resistor is coupled between the other end of the coil and a control electrode of a switching element.
Additionally, the control electrodes are coupled to respective windings of a transformer, the winding coupled to one of the switching elements being of opposite phase to the winding coupled to the other of the switching elements for inhibiting contemporaneous operation of the first and further switching elements.
The oscillator may also include a starter circuit including a starter resistor serially coupled with a starter capacitor between supply rails for the oscillator circuit and a diac coupled between the starter resistor and starter capacitor and a control electrode of a switching element.
Alternatively, the first and further switching elements are of opposite conductivity types and the control electrode of the first swtiching element is coupled to the control electrode of the further switching element for enabling self starting of the oscillator circuit.
It is a further object of the invention to provide an electrodeless lamp including an oscillator circuit having any or all of the above features.
Figure 1 is a schematic representation of an oscillator circuit according to the present invention;
Figure 2 is a circuit diagram of one embodiment of an oscillator circuit according to the present invention;
Figure 3 is a circuit diagram of an alternative embodiment of an oscillator circuit in accordance with the present invention; and
Figure 4 is a circuit diagram of a further embodiment of an oscillator circuit according to the present invention.
The basis of an oscillator circuit 2 in accordance with the present invention for driving an electrodeless lamp is shown in
Figure 1. The circuit 2 includes semiconductor switching elements, in the form of field effect transistors T1 and T2, including respective control electrodes 4,6, arranged as a totem pole pair, i.e. coupled in series, between DC supply rails 8,10. An output node 12 is thereby provided between transistors
T1 and T2 and the output signal produced at this node is used to drive a capacitor 14 and coil 16 coupled in series to provide a series resonant circuit. The coil 16 is, in effect, the driving coil placed within the re-entrant cavity in an electrodeless lamp. Oscillators for driving electrodeless lamps, if not carefully designed, are temperamental to start and to maintain self oscillation.Appropriate feedback, correctly phased at the frequency of operation, is required and, for the circuit of Figure 1 in which transistors T1 and T2 are both of n-conductivity type, appropriate starting circuitry must be employed to start oscillation.
Figure 2 shows an embodiment of the invention including appropriate feedback control and a starter circuit. The starter circuit comprises a starter 18 coupled in series with a starter capacitor 20 across the supply rails 8,10. A diac 22 is coupled between the junction of resistor 18 and capacitor 20 and the control electrode 6 of transistor T2. Zener diodes 24,26 are also provided to prevent excessive and damaging voltages appearing at the control electrodes 4,6 of transistor T1 and
T2. A closely coupled transformer TX is provided, having windings 28 and 30 coupled, respectively, to the control electrodes 4,6 of transistors T1 and T2. As can be seen from the heavy dots in Figures 2 and 3, the windings 28 and 30 are of opposite phase for reasons which will become clear from the description below.
The feedback circuit comprises a feedback resistor 32 coupled in series between the coil 16 and control electrode 6, and a feedback capacitor 34 coupled between the coil 16 and supply rail 10. A voltage supply decoupling capacitor 36 is also provided to reduce conducted radio frequency interference from the ciruit 2.
When a DC supply voltage is connected to the oscillator circuit 2, the capacitor 20 charges via resistor 18. Once capacitor 20 is charged sufficiently, the diac 22 provides a pulse to the control electrode 6 of transistor T2 of sufficient magnitude to kick start the oscillator. The windings 28 and 30 of transformer TX ensure that the waveforms between the control and source electrodes of transistors T1 and T2 are of equal magnitude but of opposite phase. The semiconductor devices which are used, typically, for transisitors T1 and
T2 switch when the control electrode voltage is at about 3 volts.The windings 28 and 30 of transformer TX ensure that the control electrode voltages of transistors T1 and T2 both pass through zero at the same time, providing a short period during each cycle when both transistors are switched OFF, thereby ensuring that the transistors are never ON at the same instant in time, which could cause a short circuit of the supply voltage.
The signal produced at the output node 10 by conduction of transistors T1 and T2, which is essentially a square wave, drives the series resonant circuit of capacitor 14 and coil 16.
In operation, the series resonant circuit has a relatively low 'Q' factor as the plasma created in the electrodeless lamp envelope gives the coil 16 a relatively large resistive component. The current flowing through coil 16 is sensed in a lossless way by feedback capacitor 34. A voltage is developed at the node between capacitor 34 and coil 16 which is fed back by feedback resistor 32 to the control electrode 6 of transistor T2 As will be appreciated, to provide self oscillation of the circuit 2, a 3600 phase shift is required in the feedback loop. The resistive component of coil 16 caused by the plasma in the lamp envelope gives rise to, typically, a phase advance 0 of about 45 within the feedback loop.Hence, without appropriate phase compensation in the feedback loop, the oscillator circuit, once kick started, would not continue in self oscillation. The feedback capacitor 34 in combination with the feedback resistor 32, assisted partially by the inherent capacitance at the control electrode input of transistor T2, act as an appropriate phase shifting network to enable self oscillation of the circuit to be maintained at a frequency determined by the capacitor 14 and coil 16. It will be realised that the coil 16 can be arranged before the capacitor 14 in the series resonant circuit. The capacitor 14 can then be configured by two equal value components, one of which connects to the feedback capacitor 34 and the other of which connects to the supply rail 8.Such an arrangement reduces any conducted radio frequency interference from the circuit 2 but the current fed into the feedback capacitor is halved, reducing the energy available to drive the control electrodes 4,6 of transistors
T1 and2.
The embodiment of Figure 3 may also be used to reduce conducted radio frequency interference. It can be seen from
Figure 3 that the feedback resistor is now coupled to the control electrode 4 of transistor T1 with the feedback capacitor coupled to the output node 10. The capacitor 14 of the series resonant circuit is split into two equal components 14a and 14b, each coupled from the coil 16 to a respective supply rail 8,10. This arrangement reduces any conducted radio frequency interference whilst enabling the full energy available at the output node 10 of transistor T1 and T2 to be fed back to drive the transistors, with the oppositely phased windings 28,30 of the transformer TX ensuring that transistors T1 and
T2 are never both biased into conduction at the same instant in time.
Referring now to Figure 4, where like reference numerals have been used to designate like components of the oscillator circuit 2, the transistor T2 now comprises a p-type device instead of an n-type transistor, as per figures 1 to 3. As a result, the control electrodes 4 and 6 of transistors T1 and
T2 require the same waveshape (in contrast to one being the inverse of the other) to maintain oscillation. The gate electrodes can, therefore, be coupled together directly, thereby obviating the need for transformer TX with associated windings 28,30. The circuit shown in Figure 4 is self starting and, therefore, the starter circuit of resistor 18, capacitor 20 and diac 22 can also be omitted. Although shown with a series resonant capacitor comprised of two equal components 14a and 14b, a single capacitor may equally be used, coupled as per the embodiment of Figure 2.It will be appreciated from Figure 4 that the oscillator circuit 2 can be fabricated of a very compact size, as it has no magnetic components other than the coil 16 actually used to excite the lamp, and is well suited to manufacture using surface mount technology.
With appropriate component values and size of coil 16, an oscillator circuit according to the present invention has been shown to provide visually instantaneous starting of an electrodeless lamp with reliable continued operation at a frequency of 2.8MH . However, other frequencies may also be
z achieved by appropriate component values in the series resonant circuit.
Although the present invention has been described with respect to specific embodiments, it should be realised that modifications may be effected whilst remaining within the scope of the invention. For example, transistors T1 and T2 incorporating built-in input overload protection diodes may be used, obviating the need for the diodes 24 and 26 shown in
Figure 2.
Claims (7)
1. An oscillator circuit for an electrodeless discharge lamp,
the oscillator circuit comprising first and further
semiconductor switching elements each including a control
electrode and coupled in series to provide an output node
therebetween, and a feedback circuit, coupled to the output
node, comprising a series resonant circuit including a capacitor
coupled in series with a coil for causing a discharge in the
lamp the feedback circuit further comprising, for enabling self
oscillation of the oscillator circuit, a feedback resistor
arranged between the series resonant circuit and a control
electrode of a switching element, and a feedback capacitor
coupled to the feedback resistor, for sensing current flowing
in the coil.
2. An oscillator circuit according to claim 1 wherein the
capacitor comprises two capacitors each coupled between one end
of the coil and a respective supply rail for the oscillator
circuit, and the resistor is coupled between the other end of
the coil and a control electrode of a switching element.
3. An oscillator circuit according to claim 1 or claim 2
wherein the control electrodes are coupled to respective
windings of a transformer, the winding coupled to one of the
switching elements being of opposite phase to the winding
coupled to the other of the switching elements for inhibiting
contemporaneous operation of the first and further switching
elements.
4. An oscillator according to any one of the claims 1 to 3
comprising a starter circuit including a starter resistor
serially coupled with a starter capacitor between supply rails
for the oscillator circuit and a diac coupled between the
starter resistor and starter capacitor and a control electrode
of a switching element.
5. An oscillator circuit according to claims 1 or claim 2
wherein the first and further switching elements are of opposite
conductivity types and the control electrode of the first
switching element is coupled to the control electrode of the
further switching element for enabling self starting of the
oscillator circuit.
6. An oscillator circuit substantially as hereinbefore
described with reference to the accompanying drawings.
7. An electrodeless lamp comprising an oscillator circuit
according to any one of the preceding claims.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9519041A GB2305311A (en) | 1995-09-18 | 1995-09-18 | Self oscillating drive circuit for an electrodeless discharge lamp |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9519041A GB2305311A (en) | 1995-09-18 | 1995-09-18 | Self oscillating drive circuit for an electrodeless discharge lamp |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB9519041D0 GB9519041D0 (en) | 1995-11-15 |
| GB2305311A true GB2305311A (en) | 1997-04-02 |
Family
ID=10780878
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB9519041A Withdrawn GB2305311A (en) | 1995-09-18 | 1995-09-18 | Self oscillating drive circuit for an electrodeless discharge lamp |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2305311A (en) |
Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0852454A2 (en) * | 1996-12-03 | 1998-07-08 | Patent-Treuhand-Gesellschaft für elektrische Glühlampen mbH | Operating circuit for a low pressure electrodeless discharge lamp |
| WO1999041954A1 (en) * | 1998-02-10 | 1999-08-19 | Patent-Treuhand-Gesellschaft für elektrische Glühlampen mbH | Circuit for actuating at least one electrode-less discharge lamp |
| WO2001026428A1 (en) * | 1999-10-05 | 2001-04-12 | Central Research Laboratories Limited | A power supply for driving a discharge lamp |
| WO2001026429A1 (en) * | 1999-10-05 | 2001-04-12 | Central Research Laboratories Limited | A power oscillator for driving a discharge lamp |
| WO2001039555A1 (en) * | 1999-11-23 | 2001-05-31 | Fusion Lighting, Inc. | Self-tuning electrodeless lamps |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2080652A (en) * | 1980-07-21 | 1982-02-03 | Philips Nv | Oscillator for supplying an electrodeless discharge lamp |
| EP0222441A1 (en) * | 1985-11-04 | 1987-05-20 | Koninklijke Philips Electronics N.V. | DC-AC converter for igniting and supplying a discharge lamp |
-
1995
- 1995-09-18 GB GB9519041A patent/GB2305311A/en not_active Withdrawn
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2080652A (en) * | 1980-07-21 | 1982-02-03 | Philips Nv | Oscillator for supplying an electrodeless discharge lamp |
| EP0222441A1 (en) * | 1985-11-04 | 1987-05-20 | Koninklijke Philips Electronics N.V. | DC-AC converter for igniting and supplying a discharge lamp |
Cited By (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0852454A2 (en) * | 1996-12-03 | 1998-07-08 | Patent-Treuhand-Gesellschaft für elektrische Glühlampen mbH | Operating circuit for a low pressure electrodeless discharge lamp |
| EP0852454A3 (en) * | 1996-12-03 | 1999-06-30 | Patent-Treuhand-Gesellschaft für elektrische Glühlampen mbH | Operating circuit for a low pressure electrodeless discharge lamp |
| WO1999041954A1 (en) * | 1998-02-10 | 1999-08-19 | Patent-Treuhand-Gesellschaft für elektrische Glühlampen mbH | Circuit for actuating at least one electrode-less discharge lamp |
| US6181080B1 (en) | 1998-02-10 | 2001-01-30 | Patent-Treuhand-Gesellschaft Fuer Elektrische Gluehlampen Mbh | Circuit for actuating at lease one electrode-less discharge lamp |
| WO2001026428A1 (en) * | 1999-10-05 | 2001-04-12 | Central Research Laboratories Limited | A power supply for driving a discharge lamp |
| WO2001026429A1 (en) * | 1999-10-05 | 2001-04-12 | Central Research Laboratories Limited | A power oscillator for driving a discharge lamp |
| WO2001039555A1 (en) * | 1999-11-23 | 2001-05-31 | Fusion Lighting, Inc. | Self-tuning electrodeless lamps |
Also Published As
| Publication number | Publication date |
|---|---|
| GB9519041D0 (en) | 1995-11-15 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |