Technical Field of Invention
The present invention concerns a power-supply device for electric discharge lamps, for
example, a power-supply device for electric discharge lamps that turns on a high-luminance
high-pressure mercury vapor lamp that is used as a light source for projectors.
Background Technology
Metal halide lamps and high-pressure mercury vapor lamps have been used as a high-luminance
light source.
In recent years, high-pressure mercury vapor lamps in which the mercury vapor pressure has
been raised to obtain desired luminance have been effective as light sources for projectors
used in luminous flux control devices such as liquid crystals. The amount of mercury sealed
in lamps has tended to increase.
Incidentally, the problem arises of a lamp extinguishing over the course of several seconds to
dozens of seconds even after successful initiation by an igniter when a lamp is turned on as
the amount of mercury sealed in lamps increases.
The inventors conducted empirical observations under various conditions and discovered that
mercury condenses on the cathode and sticks during the cooling period when a lamp is
extinguished.
This phenomenon can be briefly explained by stating that electrons are readily released from
liquid mercury, as is well known, with the result being that arc release becomes possible at
extremely low operation voltage of 15 volts to 20 volts, for example, when liquid mercury is
present on a cathode.
If discharge should commence while liquid mercury sticks to a cathode, arc discharge would
appear first, and mercury on a cathode would rapidly evaporate. At that time, as mercury on
the cathode first evaporates at those sections opposing the cathode, the discharge site
gradually would shift toward the base of the cathode. Once mercury has completely
evaporated from the cathode, including the base of the cathode, said arc discharge at low
operation voltage terminates and it shifts to glow discharge.
The impedance between electrodes is low during arc discharge, but since it rises during glow
discharge, comparatively high operation voltage must be supplied to maintain glow discharge.
However, if the voltage output from a power supply device cannot accommodate the
operation voltage that rapidly rises, the lamp extinguishes at the moment of shift to glow
discharge.
Accordingly, the temperature at the cathode tip would rise if glow discharge can be
maintained without extinguishing, and a supply of thermions would eventually become
possible, at which point the discharge would shift to arc discharge and maintenance of a
steady lighting state by the discharge lamp would become possible.
This problem of lamp extinguishing did not materialize much in the past because of the low
amount of mercury used. Accordingly, any liquid mercury on a cathode during the period of
igniter actuation could scatter and powerful glow discharge could be maintained due to the
high voltage generated by the igniter after the end of arc discharge at low operation voltage.
Accordingly, maintenance of glow discharge by continuous actuation of the igniter even after
liquid mercury on a cathode had scattered has been considered as well, but such a method
would not be practical because the electrode would be depleted and the light tube would
blacken.
One means of resolving the problem of mercury sticking to electrodes of high pressure
mercury vapor lamps was proposed in Japanese Kokai Publication Hei-10-116590.
In this means, the cathode cooling rate after the lamp extinguishes is retarded in the course of
gradual lamp cooling by raising the heat capacity of the cathode or in the vicinity thereof. By
so doing, mercury condensation commences from the cathode or the inner surface of the light
bulb, and the condensation/sticking of mercury to the cathode is prevented. Thus, even if
much liquid mercury should remain in the cathode when the lamp is relit, discharge could
easily shift to glow discharge so long as liquid mercury does not stick to the cathode.
However, the prevention of condensation/sticking of mercury on the cathode becomes
difficult when the amount of mercury inclusion is increased in the method of raising the heat
capacity in the vicinity of the cathode proposed in said gazette, and the sticking of mercury on
the cathode cannot be prevented at all, especially if the lamp is set vertically so that the
cathode is below and the anode is above. Specifically, the termination of arc discharge at low
operation voltage becomes impossible in this method while the igniter is operating, and the
operation voltage required for glow discharge after mercury has been completely depleted
from the cathode increasingly rises because of the inclusion of large amounts of mercury.
This raises the probability of the lamp extinguishing.
In this connection, said vertical lamp arrangement is useful in that it permits the location of
devitrification, which can happen within a lamp inclusion body, to be limited to harmless
sites depending on where the light is output, and installation so that the cathode is below and
the anode is above is useful in that it prevents flickering, which is important depending on the
conditions of lamp usage.
In light of said various problems, the matter resolved by the present invention involves the
provision of a power-supply device for electric discharge lamps in which the extinguishing of
a high pressure mercury vapor lamp with a comparatively high amount of mercury inclusion
can be completely prevented when mercury is completely evaporated from the cathode.
Disclosure of Invention
The present invention uses the following means for resolving said problems.
The first means provides a power-supply device for electric discharge lamps that lights high
pressure mercury vapor lamps in which a cathode and anode are disposed in a discharge space
enclosed by an inclusion body and in which noble gas as well as 0.15 mg or more of mercury
per 1 mm3 of said discharge space are sealed, wherein a switchable connection from the
connection state of a simulated arc discharge resistor virtually equal to the arc discharge
resistance during arc discharge of said high-pressure mercury vapor lamp to the connection
state of simulated glow discharge resistors that have virtually 1/7 of the glow discharge
resistance during glow discharge of said high-pressure mercury vapor lamp is completed at
the output terminal of the power-supply device for electric discharge lamps in question, said
simulated arc discharge resistor is connected to the power-supply device for electric discharge
lamps in question, and the simulated glow discharge current in the transient state of switch
from the state of flow of simulated arc discharge current to said simulated glow discharge
resistor continues to be under 30% of said simulated arc discharge current for less than 10 µs
and the duration until the current recovers to at least 70% of said simulated arc discharge
current is less than 100 µs.
The second means provides said power-supply device for electric discharge lamps of the first
means that has a function of controlling the lamp current so that the lamp power reaches a
predetermined rated power, and a function of controlling the lamp current so that the lamp
current does not exceed a predetermined maximum current, wherein the function of
controlling the lamp current so that the lamp current does not exceed said maximum current
takes priority over said function of controlling the lamp current so that the lamp power
reaches said rated power, and a control function is provided so that the duration of control so
as to restore the current to at least 70% of said simulated arc discharge current is more than
50 ms upon switching to said simulated glow discharge resistor and so that this duration will
tolerate said rated power to be exceeded.
The third means provides a power-supply device for electric discharge lamps that lights high
pressure mercury vapor lamps in which a cathode and anode are disposed in a discharge space
enclosed by an inclusion body and in which noble gas, 0.15 mg or more of mercury per 1
mm
3 of said discharge space and 1 x 10
-7 moles of halogen per 1 mm
3 of said discharge space
are sealed in said discharge space, wherein a switchable connection from the connection state
of a simulated arc discharge resistor virtually equal to the arc discharge resistance during arc
discharge of said high-pressure mercury vapor lamps to the connection state of simulated
glow discharge resistors that are virtually equal to the glow discharge resistance during glow
discharge of said high-pressure mercury vapor lamp is completed at the output terminal of the
power-supply device for electric discharge lamps in question. Vag' represents the output
voltage of the power-supply device for electric discharge lamps and Iag' represents the
simulated glow discharge current upon switching to said simulated glow discharge resistor
from the state of flow of simulated arc discharge current by connecting said simulated arc
discharge resistor to the power-supply device for electric discharge lamps in question. The
device in which the cathode surface area is represented by Sc (mm
2) has the following
characteristics.
(1) The simulated glow discharge current in the steady state is Iag' ≽ 0.14 x Sc (A) (2) The output voltage in the steady state is Vag' ≽ 180 (V) (3) The time required for the output voltage Vag' to reach 90% of the voltage in the steady
state is time τ ≦ 170 (µs).
The fourth means provides said power-supply device for electric discharge lamps of any one
of said means 1 to 3 that is provided with a variable output direct current power source that
inputs direct current voltage and then applies variably-controlled output voltage to said high-pressure
mercury vapor lamps via a smoothing capacitor, wherein the capacitance of said
smoothing capacitor is increased during transition to arc discharge following the end of glow
discharge.
Brief Description of Drawings
Figure 1 is a diagram that shows the periodic changes in the discharge current during
transition from initial arc discharge of a high-pressure mercury vapor lamp to glow discharge
and from glow discharge to arc discharge.
Figure 2 is a diagram that shows a test circuit to identify the power-supply device for electric
discharge lamps used in the high-pressure mercury vapor lamps in the first implementation
mode.
Figure 3 is a diagram that shows simulated lamp current I' and simulated lamp voltage V' in
the test circuit shown in Figure 2 of a power-supply device for electric discharge lamps that
satisfies prescribed conditions and does not extinguish.
Figure 4 is a diagram that shows simulated lamp current I' and simulated lamp voltage V' in
the test circuit shown in Figure 2 of a power-supply device for electric discharge lamps that
satisfies prescribed conditions and extinguishes.
Figure 5 is a diagram that shows one example of the structure of a power-supply device for
electric discharge lamps in a first and second implementation mode.
Figure 6 is a diagram that shows one example of the structure of power-supply device control
circuit 24 shown in Figure 5.
Figure 7 is a diagram that shows the characteristics of lamp current Ia and lamp voltage Va of
a high-pressure mercury vapor lamp.
Figure 8 is a diagram that shows the periodic course of lamp current Ia, lamp voltage Va and
lamp power Pa of a high-pressure mercury vapor lamp.
Figure 9 is a diagram that shows the characteristics of simulated lamp current Ia', simulated
lamp voltage Va' of a high-pressure mercury vapor lamp pursuant to the second
implementation mode.
Figure 10 is a diagram that shows the periodic course of simulated lamp current Ia', lamp
voltage Va', lamp power Pa' of a high-pressure mercury vapor lamp pursuant to the second
implementation mode.
Figure 11 is a diagram that shows the test circuit for identifying the power-supply device for
electric discharge lamps used in the high-pressure mercury vapor lamps pursuant to the third
implementation mode.
Figure 12 is a diagram that shows the characteristics of simulated lamp power Ia', simulated
lamp voltage Va' in the test circuit shown in Figure 11 of the power-supply device for electric
discharge lamps that satisfies prescribed conditions and does not extinguish.
Figure 13 is a diagram that shows the structure of the power-supply device for electric
discharge lamps pursuant to the fourth implementation mode.
Figure 14 is a diagram that shows the periodic details of lamp voltage Va of a high-pressure
mercury vapor lamp pursuant to the fourth implementation mode.
Best Mode For Implementation Of The Present Invention
The first implementation mode of the present invention is explained using Figures 1 to 6.
Figure 1 is a diagram that shows the periodic changes in the discharge current during
transition from initial arc discharge of a high-pressure mercury vapor lamp to glow discharge
and from glow discharge to arc discharge.
The principle of preventing extinguishing of the lamp pursuant to the present invention is
explained first using the diagrams.
When discharge of a high-pressure mercury vapor lamp with a comparatively high amount of
sealed mercury commences while liquid mercury is stuck on the cathode, arc discharge
appears and mercury rapidly evaporates from the cathode. At time tg shown in the diagram,
arc discharge ends at low operation voltage, at which point the mercury on the cathode has
been completely depleted and discharge transits to glow discharge. However, lamp current Ia
rapidly decreases since the impedance between electrodes rapidly rises at time tg and the
lamp extinguishes at that point.
The inventors were able to create a power supply device that does not extinguish as a result of
various improvements to the power supply device.
The results of studies using the test circuit discussed below revealed that prescribed
conditions must be satisfied to prevent extinguishing by the power supply device.
The test circuit is explained first. Figure 2 is a diagram that shows a test circuit to identify the
power-supply device for electric discharge lamps used in high-pressure mercury vapor lamps
that have a comparatively high amount of mercury sealed within, 0.15 mg or more per 1 mm3
volume of the discharge space of a high-pressure mercury vapor lamp.
Said high-pressure mercury vapor lamps used in this implementation mode have arc
discharge resistance during arc discharge of 5Ω and glow discharge resistance during glow
discharge of 300Ω.
In the diagram, reference number 2 denotes a power-supply device for electric discharge
lamps that is the object of evaluation to evaluate whether or not lamp extinguishing can be
effectively prevented. Reference numbers 59, 60 denote resistors of 5Ω and 38Ω resistance,
respectively, that are connected in series to the output terminal of power-supply device 2 for
electric discharge lamps. Reference number 57 denotes a FET that shorts and opens resistor
60. Reference number 58 denotes a gate drive circuit that switches FET 57.
Here, resistor 59 is set to resistance roughly equal to the 5Ω arc discharge resistance during
said arc discharge so that the current flowing through resistor 59 is roughly equal to the
current flowing during arc discharge when liquid mercury is present on the cathode of an
actual high-pressure mercury vapor lamp, and resistor 59 + resistor 60 are set to resistance
equal to about 1/7 of the 300Ω glow discharge resistance during glow discharge of said high-pressure
mercury vapor lamp. The resistance of resistor 59 + resistor 60 is set at about 1/7 of
the glow discharge resistance in order to distinctly discriminate if the power-supply device for
electric discharge lamps that is the object of evaluation has satisfied the prescribed
conditions.
In the operation of this test circuit, arc discharge when liquid mercury is present on the
cathode of a high-pressure mercury vapor lamp is simulated when only resistor 59 is
connected with FET 57 ON. Next, gate drive circuit 58 is actuated, FET 57 is rapidly turned
OFF and the state transits to serial connection of resistor 59 and resistor 60. As a result,
mercury on the cathode is completely depleted and transition to glow discharge is simulated.
By observing the response of these two states, it becomes possible to assess whether or not
the performance of an actual power-supply device for electric discharge lamps satisfies the
conditions recommended in the present invention.
The conditions that should be satisfied when a power supply device that does not extinguish
is tested using this test circuit are explained next.
The conditions are explained using Figure 1. Whether or not duration Td exists during which
simulated glow lamp current during rapid increase of impedance of a high-pressure mercury
vapor lamp is under 30% of the simulated lamp current Iao' immediately preceding rapid
increase, the continuous duration TD would be under 10 µs. Furthermore, the conditions
would be controlled so that the duration Tr would be under 100 µs before the simulated glow
lamp current during rapid increase of impedance of a high-pressure mercury vapor lamp
recovers to at least 70% of the simulated lamp current Iao' immediately preceding rapid
increase. The empirical discovery was made that lamp extinguishing can be prevented when
a power supply device satisfies these conditions. Furthermore, the fact was clarified that
lamp extinguishing could be prevented when lighting it under such conditions even in the
worst cases in which a lamp is set vertically with the cathode below and the anode above.
When the lamp current is cut off or reduced, the discharge plasma decreases and is dissipated
before long, but since dissipation of discharge plasma can be avoided if the lamp current
recovers to the prescribed size before the discharge plasma is dissipated, there must be no
duration TD during which the simulated glow lamp current during rapid increase of
impedance of a high-pressure mercury vapor lamp is under 30% of the simulated lamp current
Iao' immediately preceding rapid increase to ensure that the lamp does not extinguish during
transition to glow discharge, or if duration TD does exist, it must continuously be less than 10
µs.
Even if there are a plurality of durations TD during which the simulated glow lamp current
during rapid increase of impedance of a high-pressure mercury vapor lamp is under 30% of
the simulated lamp current Iao' immediately preceding rapid increase of the impedance, so
long as each duration is under 10 µs, their sum may exceed that figure without any problem.
Of course, the absence of duration TD during which it is under 30% would be ideal, but said
concern could be attained with a reserve if duration TD is under 8 µs, and a duration under 5
µs would be still more desirable.
Furthermore, by controlling duration Tr so that it is under 100 µs before the simulated glow
lamp current during rapid increase of impedance of a high-pressure mercury vapor lamp
recovers to at least 70% of the simulated lamp current Iao' immediately preceding rapid
increase, thermion release can be rapidly activated to complete a rapid shift to arc discharge
following a shift to glow discharge.
Furthermore, it is preferable to have a short duration Tr until the simulated glow lamp current
during rapid increase of impedance of a high-pressure mercury vapor lamp recovers to at least
70% of the simulated lamp current Iao' immediately preceding rapid increase, and said issue
could be attained with a reserve if it is under 80 µs, and a duration under 60 µs would be still
more desirable. In addition, the issue could be attained with a reserve if the extent of
recovery of the lamp current were to at least 85% of the simulated lamp current Iao'
immediately preceding rapid increase of the impedance of a high-pressure mercury vapor
lamp.
The power-supply device for electric discharge lamps in the invention of this claim must be
specified using a test circuit because the individual elements comprising a power-supply
device for electric discharge lamps may be adjusted or modified to prevent extinguishing of a
high-pressure mercury vapor lamp, and it is important whether or not the ultimately-modified
power-supply device for electric discharge lamps satisfies said prescribed conditions.
Figure 3 is a diagram that shows simulated lamp current Ia' and simulated lamp voltage Va' in
the test circuit shown in Figure 2 of a power-supply device for electric discharge lamps that
satisfies prescribed conditions and does not extinguish. Here, Figure 3(a) and Figure 3(b)
show the same phenomena, but the periodic scale differs.
Figure 4 is a diagram that shows the relation between simulated lamp current Ia' and
simulated lamp voltage Va' in the test circuit shown in Figure 2 of a power-supply device for
electric discharge lamps that satisfies prescribed conditions and extinguishes. Here, Figure
4(a) and Figure 4(b) show the same phenomena, but the periodic scale differs.
The oscilloscope was subjected to smoothing processing to facilitate contrast of Figures 3 and
4 with Figures 8 and 10 discussed below.
As stated above, by testing the power-supply device for electric discharge lamps that is the
object of evaluation using the test circuit shown in Figure 2, a power-supply device for
electric discharge lamps that does not extinguish the lamp could be discovered through
various modifications based on the test results shown in Figures 3 to 4.
In this implementation mode, the arc discharge resistance during arc discharge of an actual
high-pressure mercury vapor lamp is assumed to be Ra while the glow discharge resistance
during glow discharge is assumed to be Rb. Lamp extinguishing could be effectively
prevented by using a power-supply device for said high-pressure mercury vapor lamps that
satisfies two conditions. The first is that the duration during which the simulated glow
discharge current in the transient state of switch from the state of flow of simulated lamp
current Iao' to resistors (59 + 60) is under 30% of simulated lamp current Iao' is continuously
less than 10 µs as a result of connecting resistor 59 to the power-supply device for electric
discharge lamps that is the object of evaluation when connection to the output terminal of the
power-supply device for electric discharge lamps that is the object of evaluation has been
switched from connection of resistor 59 that is virtually equal to arc discharge resistance Ra
to resistors (59 + 60) that have virtually 1/7 of glow discharge resistance Rb. The second is
that the duration would be under 100 µs before the current recovers to at least 70% of the
simulated lamp current Iao'.
The power-supply device for electric discharge lamps in the implementation mode of the
present invention is explained next using Figures 5 and 6.
Figure 5 is a diagram that shows one example of the structure of a power-supply device for
electric discharge lamps. In the figure, reference number 17 denotes a DC power source that
provides voltage from DC power source 17 to step-down chopper 16. Step-down chopper 16
primarily comprises switch device 11, gate drive circuit 12, diode 13, inductor 14 and
smoothing capacitor 15. DC power source 17 is not illustrated, but a device that converts a
commercial AC power source into direct current using rectifier diodes, diode bridges and
smoothing capacitors, a power source module that has a function of inhibiting harmonic
current or a battery can be used.
Reference number I denotes a high-pressure mercury vapor discharge lamp having discharge
space 6 within lamp inclusion body 3 in which is sealed a comparatively large amount of
mercury and in which cathode 4 and anode 5 are disposed opposing each other. Reference
number 18 denotes a voltage detector constructed using differential voltage resistors that
detects applied voltage Va that is applied to high-pressure mercury vapor discharge lamp 1,
and reference number 19 denotes a current detector constructed using shunt resistors and CT,
etc., that detects current Ia flowing to high-pressure mercury vapor discharge lamp 1.
Reference number 7 denotes an igniter inserted between step-down chopper 16 and high-pressure
mercury vapor discharge lamp 1 to create discharge breakdown of sealed gas
between cathode 4 and anode 5 when high-pressure mercury vapor discharge lamp 1
commences lighting. Igniter 7 basically is constructed by transformer 8 that has a large
primary-to-secondary winding ratio to generate a high-voltage pulse series of several kV to
several dozen kV. Reference number 9 denotes a coil that is inserted between step-down
chopper 16 and discharge lamp 1. Reference number 24 denotes a power-supply device
control circuit that provides gate drive signal 23 to gate drive circuit 10 of igniter 7 and that
inputs lamp voltage signal 20 that was detected by voltage detector 18 as well as lamp
current signal 21 that was detected by current detector 19. Gate drive signal 22 is supplied to
gate drive circuit 12 of switch device 11 based on lamp voltage signal 20 and lamp current
signal 21 so as to control switching of switch device 11.
The diagram shows an example in which power-supply device control circuit 24 supplies gate
drive signal 23 to gate drive circuit 10, but there are cases in which gate drive signal 23 would
be rendered unnecessary depending on the form of igniter 7.
Figure 6 is a diagram that shows one example of the structure of power-supply device control
circuit 24 shown in Figure 5.
Lamp current signal 21 and lamp voltage signal 20 that were detected in the diagram are
assumed to have positive polarity, and are optionally input to the power-supply device control
circuit 24 in question via buffer 25 and buffer 38, respectively.
Lamp current signal 21 is input to error integrator 31 comprising operational amplifier 27 and
substrate 30 via resistor 26. On the other hand, output from maximum current signal
generator 29 assumed to have negative polarity is input to operational amplifier 27 via
resistor 28. The difference between the current set by maximum current signal generator 29
and lamp current signal 21 is integrated by capacitor 30 and output from error integrator 31.
The output from error integrator 31 is output to overcurrent signal 36 via inverter 35
comprising resistor 32, resistor 33, operational amplifier 34.
On the other hand, lamp current signal 21 is combined with lamp voltage signal 20 by
operator 39 to create power signal 40 which is input via resistor 41 to error integrator 46
comprising operational amplifier 42 and capacitor 45. In addition, the output from rated
power signal generator 44 assumed to have negative polarity is input to operational amplifier
42 via resistor 43, and the difference in power between power signal 40 from error integrator
46 and the power determined by rated power signal generator 44 is integrated by capacitor 45
and then output.
The output from error integrator 46 is output as overcurrent signal 51 via inverter 50
comprising resistor 47, resistor 48, and operational amplifier 49.
Overcurrent signal 36 and overcurrent signal 51 are pulled down by resistor 53 via diode 37
and diode 52, respectively, with the result that the higher signal of either overcurrent signal
36 or overcurrent signal 51 is output to resistor 53 as step-down chopper control signal 54.
Overcurrent signal 36 becomes the higher signal when lamp current signal 21 is greater than a
power value determined by maximum current signal generator 29, while overcurrent signal 51
becomes the higher signal when power signal 40 is greater than a power value determined by
rated power signal generator 44. Accordingly, overcurrent signal 36 and the larger of the
overcurrent signals appears preferentially in resistor 53. Step-down chopper control signal 54
compares the output signals of saw-tooth wave generator 55 by comparator 56. A high level
signal when step-down chopper control signal 54 is smaller than the output signal of saw-tooth
wave generator 55 or a low level signal when step-down chopper control signal 54 is
greater than the output signal of saw-tooth wave generator 55 is output to gate drive circuit 12
of switch device 11 as gate drive signal 22.
If logic of gate drive circuit 12 is designed so that switch device 11 turns ON when gate drive
signal 22 is at a high level, feedback control is instituted so that lamp current signal 21 would
match the current determined by maximum current signal generator 29 when overcurrent
signal 36 is the higher of overcurrent signal 36 or overcurrent signal 51, or conversely so that
power signal 40 would match the power determined by rated power signal generator 44 when
overcurrent signal 51 is the higher since the duration during which gate drive signal 22 is at
the high level becomes shorter as step-down chopper control signal 54 rises.
As a result, power-supply device 2 for electric discharge lamps with the function of
controlling lamp current Ia so that lamp power Pa would become predetermined rated power
Pas, and with the function of controlling lamp current la so that lamp current Ia would not
exceed predetermined maximum current Ias can be realized in which the function of
controlling lamp current Ia so that said maximum current Ias would not be exceeded takes
priority over the function of controlling lamp current Ia so that lamp power Pa would become
said rated power Pas.
For example, resistor 26 could be set at a low resistance value and/or capacitor 30 could be
set at a small electrostatic capacitance value while the response of error integrator 31 in order
to control maximum current Ias could be set at a high speed to implement the invention in
this implementation mode. If adequate results are not attained by these steps alone, the
inductance on the secondary side of transformer 8 of igniter 7 could be increased, coil 9 could
be added or both could be completed. Of course, the operating frequency of step-down
chopper 16, specifically, the oscillation frequency of saw-tooth wave generator 55, must be
high enough to support the high speed control required for maximum current Ias. Reducing
the electrostatic capacitance of smoothing capacitor 15 in a range such that ripples of step-down
chopper 16 does not become excessive would be useful.
Figure 5 and Figure 6 are presented to explain the basic structure of the power-supply device
for electric discharge lamps pursuant to the present invention, but additional components or
additional circuits such as protective circuits or noise filters may be added to ensure safe
circuit operation or safe unit operation as required in the actual implementation, or means
such as circuit simplification may also be necessary. In particular, inverters 35 and 50 were
added to simplify the explanation, but these may be omitted.
A second implementation mode of the invention of this claim is explained using Figures 5 to
10.
This implementation mode concerns a power-supply device for electric discharge lamps with
functions added to more reliably prevent extinguishing of the power-supply device for electric
discharge lamps obtained in the first implementation mode.
Lamp current Ia is controlled so that lamp power Pa becomes predetermined rated power Pas
even if the lamp voltage Va should fluctuate accompanying change of the impedance between
electrodes in the power-supply device for mercury vapor lamps shown in Figure 7. At that
time, very great lamp current Ia must flow to attain rated power Pas if lamp voltage Va is very
low, but lamp current Ia is controlled so that lamp current Ia does not exceed predetermined
maximum current Ias to prevent breakdown of the circuit elements installed in the actual
power supply device. This function takes priority over controlling lamp current Ia so that
lamp power Pa would become predetermined rated power Pas. Furthermore, the same
diagram shows that maximum voltage Vas is determined, but this is a restriction to ensure
that the required maximum limitation voltage is not exceeded to ensure safety during no-load
switching. Based on said results, the voltage current characteristics of general power-supply
devices for electric discharge lamps basically form the hyperbola H shown in Figure 7.
Figure 8 (a), (b), (c) are diagrams showing the periodic courses of lamp current Ia, lamp
voltage Va and lamp power Pa during this period.
When a high-pressure mercury vapor lamp with a comparatively large amount of mercury
sealed within is lit by a common power-supply device for electric discharge lamps, the arc
discharge when liquid mercury is present on the cathode immediately after lighting would be
at point A in Figure 7 since the impedance between electrodes is low enough. This is a state
in which said lamp current Ia is controlled so as not to exceed predetermined maximum
current Ias. Rated power is not reached in this state. Next, mercury is completely evaporated
from the cathode and the state transits to glow discharge. The impedance between electrodes
rises and lamp voltage Va rapidly increases. Accordingly, the state transits from point A to
point B along the voltage-current characteristic curve H in Figure 7, but lamp current Ia is
greater than lamp current Iao immediately before the rapid increase in impedance of the high-pressure
mercury vapor lamp, as shown in Figure 8 (a), and falls, presenting the possibility of
the lamp extinguishing.
Thus, to avoid such a state, it passes through the range above voltage-current characteristic
curve H rather than along the voltage-current characteristic curve H shown in Figure 7,
specifically, through the excess power range. The conditions pertaining to the method of
passage through the excess power range can be determined using the test circuit shown in
Figure 2 just as before, specifically, a test circuit that switches between resistance roughly
equal to the lamp impedance during arc discharge and resistance equal to roughly 1/7 of the
lamp impedance during glow discharge.
Figure 9 is a diagram showing the intended voltage current characteristics in the invention
pursuant to this implementation mode.
When transiting from point A to point B, as shown by the voltage-current characteristics in
this diagram, the state persists for a prescribed period in range U in which the current is at
least 70% of simulated lamp current Iao' at point A rather than transiting along voltage-current
characteristic curve H, followed by transit to point B.
Figure 10 (a), (b), (c) are diagrams showing the periodic courses of simulated lamp current
Ia', simulated lamp voltage Va' and simulated lamp power Pa' during this period.
The issue of the present invention could be more reliably attained by adding a function to the
power-supply device for electric discharge lamps pursuant to this implementation mode
wherein the duration of residence in range U in which the current is at least 70% of simulated
lamp current Iao' at point A exceeds 50 ms.
Thermion release must be rapidly activated to maintain discharge, but prolonging duration Tu
to control the current so as to recover to at least 70% of simulated lamp current Iao'
immediately preceding the rapid increase in impedance of the high-pressure mercury vapor
lamp would be useful in preventing lamp extinguishing. A duration above 70 ms would be
preferable in that it would permit the issue of the present invention to be attained with a
reserve, and a duration above 100 ms would be still better.
Since excess power operation takes place in range U in which the current is at least 70% of
simulated lamp current Iao' at point A, this may be implemented by adding the function of
controlling simulated lamp current Ia' so that the power supply device reaches the original
predetermined rated power Pas only while it resides in range U in which the current is at least
70% of simulated lamp current Iao' at point A. Since this excess power operation is
inappropriate for safe operation of lamps and power supply devices, long-term continuation
beyond the necessary duration should be avoided. In fact, a duration of 300 ms would be
adequate.
Concretely, the power-supply device for electric discharge lamps shown in Figures 5 and 6 to
implement the invention in this implementation mode would be designed so that duration Tu
of control so that the current recovers to at least 70% of simulated lamp current Iao'
immediately preceding rapid increase in the impedance of high-pressure mercury vapor
discharge lamp 1 exceeds 50 ms when the impedance of high-pressure mercury vapor
discharge lamp 1 rapidly increases in the operational state in which the simulated lamp
current Ia' is controlled so as not to exceed maximum current Ias. For example, it would be
designed so that resistor 41 has great resistance and/or capacitor 45 has great electrostatic
capacitance, and the response of error integrator 46 would be designed to reach a lower speed
in order to control rated power Pas.
A third implementation mode of the invention pursuant to the invention of this claim is
explained next using Figures 11 and 12.
Figure 11 is a diagram showing a test circuit for detecting a power-supply device for electric
discharge lamps in which the lamp does not extinguish. Such a device is used in high-pressure
mercury vapor lamps with a comparatively large amount of mercury sealed within so
that 0.15 mg or more of mercury per 1 mm3 volume of discharge space and 1 x 10-7 moles of
halogen per 1 mm3 of said discharge space are sealed within.
The inventors in the present invention discovered that lamp extinguishing could be effectively
prevented by this power-supply device for electric discharge lamps when the device satisfies
the conditions presented below through this test circuit.
The high-pressure mercury vapor lamp used in this implementation mode is explained on the
assumption that arc discharge resistance Ra during arc discharge of 5Ω and glow discharge
resistance Rb during glow discharge of 300Ω are used, just as in the first implementation
mode.
In this diagram, reference numbers 70 and 71 denote resistors of 5Ω and 300Ω resistance that
are connected in series to the output terminal of power-supply device 2 for electric discharge
lamps. The other structures are identical with those in the structure shown in Figure 2
designated by the same notation and are omitted.
Here, resistor 70 is set to a value equal to arc discharge resistance Ra during arc discharge so
that roughly the same current as the current flowing during arc discharge when liquid mercury
is present on the cathode of an actual high-pressure mercury vapor lamp flows through
resistor 70, and resistor 70 + resistor 71 are set to a value equal to glow discharge resistance
Rb so that roughly the same current as the current flowing during glow discharge of a high-pressure
mercury vapor lamp flows through resistors 70, 71.
Figure 12 is a diagram showing the periodic change in simulated lamp current Ia' and
simulated lamp voltage Va' when the state is switched from connection only of resistor 70 to
serial connection of resistor 70 and resistor 71.
In this implementation mode, the discovery was made that extinguishing could be prevented
even when power-supply device for
electric discharge lamps 2 uses said high-pressure
mercury vapor lamps if the individual conditions presented below are satisfied while
simulated arc current flows through
resistor 70 when only resistor 70 is connected to the
output terminal of power-
supply device 2 for electric discharge lamps that is the object of
evaluation wherein the cathode surface area is Sc (mm
2)
(1) The simulated glow discharge current Iag' in the steady state following switching from
resistor 70 to resistor 70 + resistor 71 is Iag' ≽ 0.14 x Sc (A) (2) The output voltage of the power-supply device for electric discharge lamps in the steady
state following switching from resistor 70 to resistor 70 + resistor 71 is Vag' ≽ 180 (V) (3) The time required for the output voltage Vag' in the steady state to reach 90% of the
voltage in the steady state following switching from resistor 70 to resistor 70 + resistor 71 is
time τ ≦ 170 (µs).
This cathode surface area is the surface area of the entire electrode having a cathode effect
that is exposed in the discharge space.
The reason that the capacity to provide simulated glow discharge current Iag' in the steady
state should increase proportionally to the cathode surface area Sc is that discharge takes
place over the entire cathode surface in glow discharge, in contrast to arc discharge. If the
capacity to provide current whose size is proportional to the cathode surface area is lacking,
the electrode surface could not be heated enough to permit transition to arc discharge due to
thermion release. A capacity to provide simulated glow discharge current of lag' ≽ 0.016 x
Sc would be more desirable.
The reason that the capacity is required to provide more than 180 V as simulated glow
voltage Vag' in the steady state is that voltage exceeding 180 V would be required for glow
discharge, almost independently of the gas pressure or the separation between the cathode and
anode, if the amount of halogen that is sealed exceeds 1 x 10-7 moles per 1 mm3 of discharge
space in electric discharge lamps in which are sealed noble gases such as mercury or argon
and halogens such as bromine.
The ability to provide Vag' ≽ 200 V as output voltage Vag' would be more desirable.
The reason that time τ required for output voltage Vag' to reach 90% of the voltage in the
steady state should be under 170 µs is that glow discharge could not be maintained and
discharge would be discontinued if the time were longer. By the time the voltage had
subsequently risen adequately, the electrode would already have cooled, resulting in a high
probability of the lamp extinguishing. Time τ ≦ 100 µs would be more desirable.
Experiments of the inventors revealed that the extinguishing rate falls completely to 0% if
Iag' ≈ 0.4A in a lamp using a cathode whose surface area is about 25 mm2 at Vag' ≈ 200 V, τ
≈ 100 µs.
Even if the performance should fall to Vag' ≈ 180 V, τ ≈ 170 µs, Iag' ≈ 0.35A, the
extinguishing rate would be under 1%, which is practical enough.
The fourth implementation mode of the invention of this claim is explained next using
Figures 13 and 14.
Figure 13 is a diagram that shows the structure of the power-supply device for electric
discharge lamps pursuant to this implementation mode.
In this diagram, reference number 72 denotes a smoothing capacitor 72 that is mounted to
permit parallel connection with smoothing capacitor 15, 73 denotes a FET that switches
insertion/removal of smoothing capacitor 72, and 74 denotes a gate drive circuit that switches
FET 73. The other structures are identical with those in the structure shown in Figure 5
designated by the same notation and are omitted.
Figure 14 is a diagram that shows the periodic details of lamp voltage of a high-pressure
mercury vapor lamp pursuant to this implementation mode when a high-pressure mercury
vapor lamps is first lit.
After the period of great impedance during lamp glow discharge has elapsed in this
implementation mode, as shown in Figure 13, smoothing capacitor 15 and FET 73 in parallel
turn ON and the capacitance of the smoothing capacitor is increased by inserting smoothing
capacitor 72.
Reducing the electrostatic capacitance of smoothing capacitor 15 to a range such that ripples
of smoothing capacitor 15 do not become excessive was explained to be useful in explaining
the power-supply device for electric discharge lamps shown previously in Figure 5, but by
maintaining a small capacitance of the smoothing capacitor until the transition to thermal arc
discharge, lamp damage could be prevented through suppression of the charge released to the
lamp from a smoothing capacitor in sudden transition to arc discharge during glow discharge.
On the other hand, ripples readily develop if the smoothing capacitor is small, and that
creates acoustic resonance which leads to lamp flickering and extinguishing.
In light of said problems, the invention of this implementation mode prevents lamp flicking
and extinguishing due to said acoustic resonance by turning on FET 73 after the transition to
thermal arc discharge following elapse of a period of high impedance during glow discharge,
whereupon smoothing capacitor 15 and smoothing capacitor 16 are connected in parallel to
increase the capacitance of the smoothing capacitor, as shown in Figure 14.
In the invention stated in Claim 1, lamp extinguishing when mercury has completely
evaporated from the cathode at the start of lighting can be prevented when using high-pressure
mercury vapor lamps with a comparatively large amount of mercury sealed within.
In the invention started in Claim 2, lamp extinguishing can be prevented more reliably by
augmenting the effects of the invention stated in Claim 1.
In the invention stated in Claim 3, lamp extinguishing when mercury on the cathode has
completely evaporated at the start of lamp lighting can be prevented when using high-pressure
mercury vapor lamps with a comparatively large amount of mercury sealed within.
In the invention stated in Claim 4, lamp flickering and extinguishing due to acoustic
resonance after transition to thermal arc discharge following the elapse of a period of high
lamp impedance can be prevented in addition to the effects of the inventions stated in Claims
1 to 3.
Industrial Field of Invention
The present invention can be used in a power-supply device for electric discharge lamps to
light high-luminance high-pressure mercury vapor lamps that are used as the light source in
projectors, for example.