A MAGNETRON POWERED LAMP
The present invention relates to a lamp, incorporating a magnetron powered
light source.
In European Patent No EP1307899, granted in our name there is claimed a
light source a waveguide configured to be connected to an energy source and for
receiving electromagnetic energy, and a bulb coupled to the waveguide and
containing a gas-fill that emits light when receiving the electromagnetic energy from
the waveguide, characterised in that:
(a) the waveguide comprises a body consisting essentially of a dielectric material
having a dielectric constant greater than 2, a loss tangent less than 0.01 , and a DC
breakdown threshold greater than 200 kilovolts/inch, linch being 2.54cm,
(b) the wave guide is of a size and shape capable of supporting at least one electric
field maximum within the wave guide body at at least one operating frequency
within the range of 0.5 to 30GHz,
(c) a cavity depends from a first side of the waveguide,
(d) the bulb is positioned in the cavity at a location where there is an electric field
maximum during operation, the gas-fill forming a light emitting plasma when
receiving microwave energy from the resonating waveguide body, and
(e) a microwave feed positioned within the waveguide body is adapted to receive
microwave energy from the energy source and is in intimate contact with the
waveguide body.
In our International Application No PCT/GB20 10/00091 1, applied for on 6th
May 2010, ("Our 1st Light Source and Starter Application") we have described and
claimed a light source to be powered by microwave energy, the source having:
• a solid plasma crucible of material which is lucent for exit of light therefrom,
the plasma crucible having a closed void in the plasma crucible,
• a Faraday cage surrounding the plasma crucible, the cage being at least
partially light transmitting for light exit from the plasma crucible, whilst being
microwave enclosing,
• a fill in the closed void of material excitable by microwave energy to form a
light emitting plasma therein, and
• an antenna arranged within the plasma crucible for transmitting plasmainducing
microwave energy to the fill, the antenna having:
• a connection extending outside the plasma crucible for coupling to a
source of microwave energy;
the light source also including:
• a controllable source of microwaves coupled to the antenna connection;
• a starter for starting a plasma in the fill in the closed void,
• a detector for detecting starting of the plasma and
• a control circuit for powering the source at low power initially and
simultaneously with the starter and switching off the starter and increasing
power of the microwave source after detection of starting of the plasma.
In Our 1 t Light Source and Starter Application and in the present application,
we use the following definitions:
• "microwave" is not intended to refer to a precise frequency range. We use
"microwave" to mean the three order of magnitude range from around 300MHz to
around 300GHz;
• "lucent" means that the material, of which an item described as lucent is
comprised, is transparent or translucent;
• "plasma crucible" means a closed body enclosing a plasma, the latter being in the
void when the void's fill is excited by microwave energy from the antenna;
• "Faraday cage" means an electrically conductive enclosure of electromagnetic
radiation, which is at least substantially impermeable to electromagnetic waves at
the operating, i.e. microwave, frequencies.
EPl 307899 and Our 1st Light Source and Starter Application have in common
that they are in respect of:
A microwave plasma light source having:
• a Faraday cage delimiting a waveguide;
• a body of solid-dielectric material at least substantially embodying the
waveguide within the Faraday cage;
• a closed void in the waveguide containing microwave excitable material; and
• provision for introducing plasma exciting microwaves into the waveguide;
• the arrangement being such that on introduction of microwaves of a
determined frequency a plasma is established in the void and light is emitted.
Such a light source is referred to herein as a "Microwave Plasma Light Source" or
MPLS.
We also refer below to the Microwave Plasma Light Source of Our 1st Light
Source and Starter Application as a Light Emitting Resonator or LER.
In our International Application No PCT/GB201 1/000920, filed on 17 h June
201 1 ("Our Magnetron Power Supply Application"), we have described and claimed a
power supply for a magnetron comprising:
• a DC voltage source;
• a converter for raising the output voltage of the DC voltage source, the
converter having:
• a capacitative-inductive resonant circuit,
• a switching circuit adapted to drive the resonant circuit at a variable frequency
above the resonant frequency of the resonant circuit, the variable frequency
being controlled by a control signal input to provide an alternating voltage,
• a transformer connected to the resonant circuit for raising the alternating
voltage,
• a rectifier for rectifying the raised alternating voltage to a raised DC voltage
for application to the magnetron;
• means for measuring the current from the DC voltage source passing through
the converter;
• a microprocessor programmed to produce a control signal indicative of a
desired output power of the magnetron; and
• an integrated circuit arranged in a feed back loop and adapted to apply a
control signal to the converter switching circuit in accordance with a
comparison of a signal from the current measuring means with the signal
from the microprocessor for controlling the power of the magnetron to the
desired power.
This power supply (i.e. the one of Our Magnetron Power Supply Application)
is an improvement on an earlier power supply utilising a differently arranged
operational amplifier and a differently arranged microprocessor.
Again in this application, we use the further additional definition:
"Magnetron, Switched Converter Power Circuit" or MSCPC means the following
components of the power supply:
• the converter adapted to be driven by a DC voltage source and produce an
alternating current output, the converter having:
• the resonant circuit including an inductance and a capacitance ("LC
circuit") exhibiting a resonant frequency and
• the switching circuit adapted to switch the inductance and the capacitance
to generate a switched alternating current having a frequency greater than
that of the resonance of the LC circuit;
• the output transformer for increasing the voltage of the output alternating
current; and
• the rectifier and smoothing circuit connected to the secondary circuit of the
output transformer for supplying increased voltage to the magnetron;
The object of the present invention is to provide an improved lamp utilising a
MSCPC and a starter improved from that disclosed in Our 1 t Light Source and Starter
Application.
According to the invention there is provided a magnetron powered lamp, the
lamp comprising:
• a Microwave Plasma Light Source;
• a magnetron arranged to power the MPLS;
• a Magnetron, Switched Converter Power Circuit arranged to power the
magnetron;
• a microprocessor arranged to control the MSCPC;
• a starter for starting a plasma in the fill in the closed void of the MPLS, the
starter comprising:
• a starter electrode arranged to apply starter voltage to the closed void,
• a starter circuit including:
• a capacitor,
• means for selectively charging the capacitor from a switched point in
the MSCPC,
• means for discharging the capacitor,
• a transformer having:
• a primary winding arranged to receive discharge current from the
capacitor and
• a secondary winding arranged to generate the starter voltage, the
secondary winding being connected to the starter electrode for
application of starter voltage to the closed void and
• a detector for detecting starting of the plasma;
wherein:
• the microprocessor is arranged to select charging of the capacitor for starting
of the plasma until the detector detect that the plasma has started.
Whilst it is envisaged that the selective charging means could be an electronic
switch normally isolating the discharging means from the switched point of the power
circuit, in the preferred embodiment, the selective charging means is a electronic
switch normally grounding the discharging means. In either instance, the state of the
switch is changed for starter operation.
Also in the preferred embodiment, the means for discharging the capacitor is a
gas discharge unit. Alternatively trigger diode could be employed.
Further in the preferred embodiment, the microprocessor controls the MSCPC
via an integrated circuit arranged in a feed back loop and adapted to apply a control
signal to the converter switching circuit in accordance with a comparison of a signal
from means for measuring MSCPC with a signal from the microprocessor for
controlling the power of the magnetron to a desired power.
To help understanding of the invention, a specific embodiment thereof will
now be described by way of example and with reference to the accompanying
drawings, in which:
Figure 1 is a block diagram of a magnetron powered lamp of the invention;
Figure 2 is a more detailed circuit diagram of a Magnetron, Switched
Converter Power Circuit similar to that described in Our Magnetron Power Supply
Application and incorporating a starter of this invention; and
Figure 3 is a scrap view of a variation of the diagram of Figure 1.
Referring to Figure 1, the LER lamp is shown diagrammatically as having a
quartz crucible 1 with a central closed void 2 containing material 3 excitable by
microwaves as a plasma. The crucible is enclosed in a Faraday cage 4 defining a
waveguide, in which microwaves resonate in operation of the lamp. An antenna 5,
having a coaxial connection 6 extending from a matching circuit wave guide 7, passes
into the crucible adjacent to the fill. Remote from the crucible a magnetron 8 is
arranged to transmit microwaves into the wave guide for onwards transmission to the
crucible.
Extending close to the end of the void is a starter electrode 11 and adjacent to
this is mounted a photodiode 2 for detecting whether the plasma has been lit and is
emitting light.
A power supply 21 for the magnetron 8 is connected to a voltage source 22
and a microprocessor 23. As shown in Figure 2, the power supply comprises a quasiresonant
converter 101 having MOSFET field effect switching transistors T1,T2.
These are switched by an integrated circuit IC1 . An inductance LI and primary coil
of a transformer TRl are connected in series to the common point C of the transistors
and capacitors C3,C4 connected beyond the primary coil back to the remote contact of
the transistors. The inductances and the capacitors have a resonant frequency, above
which the converter is operated, whereby it appears to be primarily an inductive
circuit as regards the down-stream magnetron circuit. This comprises four half bridge
diodes D3,D4,D5,D6 and smoothing capacitors C5,C6, connected to the secondary
winding of the transformer and providing DC current to the magnetron 8. The
windings ratio of the transformer is 10:1, whereby voltage of the order of 4000 volts
is applied to the magnetron, the augmented mains DC voltage on line 05 being 400
volts (at least in Europe).
To the common point C of the transistors is connected a coupling capacitor
CI 1 which provides input to a starter circuit 24. A transistor switch 25 is in series
with the capacitor CI 1 and a diode Dl. When the switch is off no current flows in
Dl 1. When the switch is made, Dl 1 conducts during alternate halves of cycles
present at C. A second diode D12 also conducts and allows current to pass through
discharge capacitor CI . This progressively charges until the voltage across it
reaches the breakdown voltage of a gas discharge tube GTD. Whereupon the
capacitor discharges through the primary winding of transformer TR2. The secondary
winding has many more turns and a starter voltage is induced in the starter electrode
11. This is isolated from the Faraday cage 4 and terminates adjacent the crucible,
close to the void 2.
Every time the discharge capacitor discharges, the void is pulsed. The
magnetron is being driven - the starter being able to operate only as a result of the
converter operating. Once a plasma in the void establishes, this is detected by a
photodiode 12 adjacent the starter electrode 1. Presence of plasma is signalled to the
microprocessor which opens the transistor switch 25.
For completeness, a current measurement resistor Rl, an operational amplifier
EA1 and associated components are shown for operation of the converter in
accordance with Our Magnetron Power Supply Application. A further transistor
switch 26 is also shown. With this the microprocessor can immediately close down
the power supply, either under human control or automatically, for instance in the
event of the magnetron current exceeding a limit such as when its magnets degrade.
In practical operation, with the lamp not on, the voltage source (not shown
above) and the microprocessor are switched on. The microprocessor is instructed to
power up the lamp in accordance with one or more protocols. The microprocessor
controls the power supply to apply a low power to the magnetron and the starter to
apply a starter pulse stream of a determined duration to the starter. If the plasma does
not start, the pulse stream is repeated after a delay. The process is repeated until the
plasma lights. Should this fails the operator is alerted. Once the plasma has lit, power
to the magnetron is increased to a desired level, commensurate with desired light
output from the plasma crucible.
Turning to the variant of Figure 3, the arrangement of the discharge capacitor
CI 1 and the gas discharge tube GTD is interchanged. They operate in an analogous
way to that in which they operate in Figure 2. The variant also includes a voltage
doubler stage comprising diodes D14, D15 and capacitors CI4, CI 5. With this
arrangement, including an appropriate value GDT, doubled primary voltage is applied
to the transformer TR2.
CLAIMS:
1. A magnetron powered lamp comprising:
• a Microwave Plasma Light Source;
• a magnetron arranged to power the MPLS;
• a Magnetron, Switched Converter Power Circuit arranged to power the
magnetron;
• a microprocessor arranged to control the MSCPC;
• a starter for starting a plasma in the fill in the closed void of the MPLS, the
starter comprising:
• a starter electrode arranged to apply starter voltage to the closed void,
• a starter circuit including:
• a capacitor,
• means for selectively charging the capacitor from a switched point in
the MSCPC,
• means for discharging the capacitor,
• a transformer having:
• a primary winding arranged to receive discharge current from the
capacitor and
• a secondary winding arranged to generate the starter voltage, the
secondary winding being connected to the starter electrode for
application of starter voltage to the closed void and
• a detector for detecting starting of the plasma;
wherein:
• the microprocessor is arranged to select charging of the capacitor for starting
of the plasma until the detector detect that the plasma has started.
2. A magnetron powered lamp as claimed in claim 1, wherein the selective charging
means is an electronic switch normally isolating the discharging means from the
switched point of the power circuit.
3. A magnetron powered lamp as claimed in claim 1, wherein the selective charging
means is a electronic switch normally grounding the discharging means.
4. A magnetron powered lamp as claimed in claim 1, claim 2 or claim 3, wherein the
electronic switch is a transistor and the means for discharging the capacitor is a gas
discharge unit.
5. A magnetron powered lamp as claimed in claim 1, claim 2 or claim 3, wherein the
electronic switch is a transistor and the means for discharging the capacitor is a trigger
diode.
6. A magnetron powered lamp as claimed in any preceding claim, wherein the
microprocessor controls the MSCPC via an integrated circuit arranged in a feed back
loop and adapted to apply a control signal to the converter switching circuit in
accordance with a comparison of a signal from means for measuring MSCPC with a
signal from the microprocessor for controlling the power of the magnetron to a
desired power.