U.S. patent number 3,700,962 [Application Number 05/086,720] was granted by the patent office on 1972-10-24 for control circuit for mercury arc lamps.
This patent grant is currently assigned to Emerson Electric Co.. Invention is credited to Robert D. Munson.
United States Patent |
3,700,962 |
Munson |
October 24, 1972 |
CONTROL CIRCUIT FOR MERCURY ARC LAMPS
Abstract
A starting and regulating circuit for mercury arc lamps
comprising a voltage doubler network in which a pair of capacitors
parallel connected across and a.c. power supply are alternately
charged during alternate half cycles through signal controlled
solid stage switching and rectifying means to provide a starting
potential for the lamp, are then alternately discharged through the
lamp and a series inductor and alternately act to limit current
flow through the lamp; in which conduction of the switching means
is delayed each half cycle until supply voltage has substantially
increased; and in which conduction of the switching means is
variably delayed in accordance with variations in an operating
condition of the lamp to maintain a predetermined operating
condition.
Inventors: |
Munson; Robert D. (Jennings,
MO) |
Assignee: |
Emerson Electric Co. (St.
Louis, MO)
|
Family
ID: |
22200447 |
Appl.
No.: |
05/086,720 |
Filed: |
November 4, 1970 |
Current U.S.
Class: |
315/241P;
315/DIG.5; 315/243; 315/241R; 315/283 |
Current CPC
Class: |
H05B
41/042 (20130101); Y10S 315/05 (20130101) |
Current International
Class: |
H05B
41/04 (20060101); H05B 41/00 (20060101); H05b
037/00 () |
Field of
Search: |
;307/110
;315/DIG.5,241,242,243,244,283 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Kominski; John
Assistant Examiner: Dahl; Lawrence J.
Claims
I claim:
1. In a starting and ballast circuit for mercury arc lamps, a
source of a.c. power, an inductor, an arc lamp, a pair of
capacitors, parallel circuit branches connecting said capacitors in
parallel across said power source, rectifying means in each of said
circuit branches in series relationship with said capacitors and
arranged in opposite polarity, and circuit connections connecting
said lamp and said inductor in series relationship between said
parallel circuits and to points thereon between said capacitors and
said rectifying means, whereby the sum of the charges on said
capacitors is impressed across said lamp to start discharge
therethrough and whereby said capacitors thereafter alternately
discharge through said lamp and series inductor and limit the
current flow through the lamp and whereby said inductor reduces
current peaks and provides a more continuous current flow through
said lamp.
2. A circuit as claimed in claim 1 which further includes voltage
responsive switching means connected in series relationship with
both of said parallel circuit branches and operative to delay
charging of said capacitors each half cycle until the supply
voltage has increased each half cycle to a predetermined value,
thereby to increase the effective power supplied to the lamp and to
reduce the required capacitance.
3. A circuit as claimed in claim 2 which further includes a second
inductor connected in series relationship with said voltage
responsive switching means and with both of said circuit branches
across said power supply and operative to reduce peak capacitor
charging currents and increase the total inductance.
4. A circuit as claimed in claim 2 in which said voltage responsive
switching means comprises a controlled bi-directional, solid state
switching device including a gating circuit therefor responsive to
a predetermined supply voltage to effect conduction thereof.
5. In a starting and regulating circuit for vapor arc lamps, a
source of a. c. power, an inductor, an arc lamp, a pair of
capacitors, parallel circuit branches connecting said capacitors in
parallel across said power source, rectifying means in each of said
circuit branches in series relationship with said capacitors and
arranged in opposed polarity, circuit connections connecting said
lamp and said inductor in series relationship across said parallel
circuit branches at points thereon between said capacitors and said
rectifying means, whereby the sum of the charges on said capacitors
is impressed across said lamp to start discharge therethrough and
whereby said capacitors thereafter alternately discharge through
said lamp and inductor and limit the current flow through the lamp,
and switching means connected in series with both circuit branches
controlling conduction therethrough, said switching means being
responsive to variations in an operative condition of said lamp to
variably delay the charging and discharging of said capacitors each
half cycle of the power supply thereby to vary the inductive
reactance of said inductor and consequently the effective power
supplied to the lamp.
6. A starting and regulating circuit as claimed in claim 5 in which
said switching means is responsive to variations in the light
intensity of said lamp to variably delay the charging and
discharging of said capacitors each half cycle of the power
supply.
7. A staring and regulating circuit as claimed in claim 5 in which
said switching means is responsive to variations in the average
current flow through said lamp to variably delay the charging and
discharging of said capacitors each half cycle of the power
supply.
8. In a starting and regulating circuit for the operation of vapor
arc lamps, an a. c. power source, first and second inductors, an
arc lamp, a pair of capacitors, parallel circuit branches
connecting said capacitors in parallel across said power supply, a
normally non-conductive, silicon controlled rectifier in each of
said circuit branches, each connected in series with a capacitor
and arranged in opposed polarity, circuit connections connecting
said lamp and said first inductor in series between said circuit
branches and to points thereon between said SCR's and said
capacitors, gating means operative to apply a firing signal to each
of said SCR's at a predetermined time during their conductive half
cycle, whereby the sum of the charges on said capacitors is
impressed across said lamp to start discharge therethrough and
whereby said capacitors thereafter alternately discharge through
said lamp and series inductor and limit current flow through the
lamp, and circuit connections connecting said second inductor
across said power source in series with both of said circuit
branches.
9. A starting and control circuit as set forth in claim 8 in which
said gating means comprises a resistor and a capacitor series
connected across said power source, a transformer secondary winding
connected between the control electrode of each of said SCR's and
the cathode side thereof, a transformer primary winding common to
both of said secondary windings and a bi-directional, voltage
breakdown, triggering switch, said primary winding and said
triggering switch being series connected in parallel with said
capacitor and in series with said resistor.
10. A starting and regulating circuit as claimed in claim 9 which
further includes a photoconductive element series connected with
said resistor and capacitor and being responsive to variations in
the light intensity of said lamp to vary the firing time of said
SCR's.
11. A starting and regulating circuit as claimed in claim 10 which
further includes a filament lamp connected in series relationship
with said lamp across said circuit branches and adapted to be
heated by current passing through said lamp, and in which said
photoconductive element is responsive to variations in the radiant
energy of said filament to vary the firing time of said SCR's.
12. In a starting and regulating circuit for the operation of vapor
arc lamps, an a. c. power source, first and second inductors, an
arc lamp, a pair of capacitors, a pair of parallel circuit branches
connecting said capacitors in parallel across said power source, a
solid state diode in each of said branches, each in series
relationship with a capacitor and said diodes being arranged in
opposed polarity, circuit connections connecting said first
inductor and said lamp in series relationship between said circuit
branches and to points thereon between said capacitors and said
diodes, a normally non-conductive, controlled, bi-directional,
solid state switching device, circuit connections connecting said
solid state switching device and said second inductor in series
across said power source and in series relationship with both of
said circuit branches, and gating means operative to apply firing
signals to said bi-directional switching device during alternate
half cycles of the power supply to effect conduction thereof at a
predetermined time during each half cycle.
13. A starting and control circuit as set forth in claim 12 in
which said bi-directional, solid state switching device is a Triac,
and in which said gating means comprises a resistor and a capacitor
series connected across said Triac, and a bi-directional, voltage
responsive, triggering switch connected between the control
electrode of said Triac and said R-C timing circuit at a point
thereon between said resistor and said capacitor.
Description
This invention relates generally to circuits for the operation of
mercury arc lamps which include means to apply the required
starting voltage to the lamp and ballast means to limit the current
flow therethrough. It further relates to means in circuits of this
kind to manually vary the effective power supplied to the lamp
thereby to effect a selected operating condition of the lamp, and
to means responsive to variations in an operating condition of the
lamp, as caused by variations in the supply voltage or lamp aging,
to automatically vary the effective power supplied to the lamp as
required to maintain the selected operating condition of the
lamp.
It has been found that a voltage doubler network having the
required capacitance and switching means to effect the alternate
charging of a pair of capacitors and the alternate discharging
thereof through a lamp throughout each full half cycle of an a.c.
power supply provides a suitable starting and ballast circuit for
the operation of some mercury arc and other types of gas-filled
lamps. The addition, however, of suitable inductance in series with
the lamp reduces current peaks and effects a more continuous flow
of current through the lamp. This provision has been found to be
essential to the operation of other types of lamps.
It is well known that variations in supply voltage and lamp aging
effect objectionable variations in the light output of mercury arc
lamps and that means operative to maintain a more constant light
output under these varying conditions is highly desirable.
Accordingly, it is an object of this invention to provide a
generally new and improved ballast and regulating circuit for
mercury arc and other types of gaseous lamps in which the effective
power supplied to the lamp is maintained substantially constant
under conditions of varying supply voltage.
A further object is to provide a ballast and regulating circuit for
mercury arc and other types of gaseous lamps in which the effective
power supplied to a lamp is automatically varied to maintain a more
constant light output under conditions of varying supply line
voltage or lamp aging.
A further object is to provide a generally new and improved ballast
and control circuit for mercury arc and other types of gaseous
lamps in which the effective power supplied to the lamp may be
varied manually.
A further object is to provide an economical ballast for mercury
arc and other types of gaseous lamps comprising a voltage doubler
network having oppositely charged capacitors, in which a
considerable reduction in the usually required capacitance to
maintain rated output of the lamp is achieved by provision of
switching means operative to delay charging and discharging of the
capacitors until the supply voltage has increased each half cycle
to some predetermined value.
Further objects and advantages will appear from the following
description when read in connection with the accompanying
drawing.
In the drawing:
FIG. 1 is a schematic illustration of a regulating ballast for
mercury arc lamps constructed in accordance with the present
invention;
FIG. 2 is a schematic illustration of a modified form of the
regulating ballast shown in FIG. 1.
FIGURE 1
Referring to FIG. 1 of the drawing, capacitors C.sub.1 and C.sub.2
with respective diodes D.sub.1 and D.sub.2 are connected in
parallel across a.c. power source terminals T.sub.1 and T.sub.2
through bi-directional solid state switching means, such as a Triac
Q.sub.1, the conduction angle of which is controlled. The diodes
D.sub.1 and D.sub.2 are arranged in opposed polarity with respect
to each of the supply terminals so that, during one half cycle of
the power supply when Q.sub.1 is conducting in one direction, one
of the capacitors may be charged to line voltage, and during the
succeeding half cycle when Q.sub.1 is conducting oppositely, the
other capacitor may be charged to line voltage while the charge on
the one capacitor is maintained by a blocking diode. The described
network will function, therefore, as a voltage doubler ballast with
a potential of substantially twice that of line voltage appearing
across junction points 10 and 12 to start a lamp 14.
A mercury arc lamp 14 and an inductor L.sub.1 are series connected
across junctions 10 and 12. The system also includes a second
inductor L.sub.2 connected in series with Triac Q.sub.1 during both
half cycles and in series with capacitors C.sub.1 and C.sub.2
during alternate half cycles. Control of the firing angle and
therefore the conduction angle of Triac Q.sub.1 is accomplished by
a gate control network comprising a fixed resistor R.sub.1, a
photoconductive element 16, a variable resistor 18, and a capacitor
C.sub.3, all series connected across the Triac Q.sub.1.
Bi-directional, breakdown switching means, such as a Diac Q.sub.2,
is connected between the control electrode of Triac Q.sub.1 and a
point 18 between the capacitor C.sub.3 and variable resistor
R.sub.2. Diac Q.sub.2 is a solid state, bi-directional, voltage
breakdown switch which blocks current flow in both directions until
a predetermined threshold voltage is applied thereacross. When the
threshold potential is applied, Diac Q.sub.2 conducts in either
direction according to the polarity of the applied potential and
thereby fires the Triac Q.sub.1.
When T.sub.1 is positive C.sub.3 is charged to the threshold of
Q.sub.2 at a time during that half cycle of the power supply
determined by the resistance of series connected R.sub.2, photocell
16 and R.sub.1, and upon conduction of Q.sub.2, a positive firing
signal is applied to the gate of Triac Q.sub.1. When T.sub.2 is
positive C.sub.3 is again charged to the threshold potential of
Q.sub.2 at a time determined by series connected R.sub.2, photocell
16 and R.sub.1, and when Q.sub.2 conducts, a firing signal is again
applied to the gate of Triac Q.sub.1. The variable resistor R.sub.2
provides means for manually adjusting the circuit so that it will
supply a measure of effective power to the lamp 14 which will
effect a predetermined operating condition thereof at a given
supply voltage. The photoconductive element is arranged to respond
to variations in the light output of lamp 14, its resistance to
electrical current flow varying inversely with the light output of
the lamp so that more rapid charging of capacitor C.sub.3 and
therefore earlier firing of Q.sub.1 occurs as the light output of
the lamp increases.
OPERATION OF FIGURE 1
In starting, when power supply terminal T.sub.1 is positive and
Triac Q.sub.1 is conducting, capacitor C.sub.1 will be charged
through Triac Q.sub.1, inductor L.sub.2, and diode D.sub.1. During
the succeeding half cycle when supply terminal T.sub.2 is positive,
C.sub.2 will charge through diode D.sub.2, inductor L.sub.2, and
Triac Q.sub.1, and when sufficient potential occurs across
junctions 10 and 12 to effect ionization and conduction through the
lamp, capacitor C.sub.1 will discharge through inductor L.sub.1,
the lamp, and diode D.sub.2. When conduction through the lamp
occurs charging of C.sub.2 will continue and C.sub.1 will also
charge in the opposite direction through L.sub.2 and Q.sub.1 during
this half cycle.
During the next succeeding half cycle, when T.sub.1 is again
positive and with the vapor in the lamp ionized, C.sub.1 will again
discharge through inductor L.sub.1 and lamp 14, and capacitor
C.sub.2 will discharge through inductor L.sub.2 and Triac Q.sub.1
in the same direction with respect to lamp 14. Also, during this
half cycle, C.sub.2 will also charge in the opposite direction
through lamp 14, inductor L.sub.1, and diode D.sub.1. It will be
seen that either C.sub.1 or C.sub.2 limits the current through the
lamp and that L.sub.1 and L.sub.2 act to reduce peak lamp current
and prolong its flow.
Under conditions of operation of a voltage doubler ballast in which
the switching means is rendered conductive immediately following
the zero voltage point each half cycle of the power supply, so that
the capacitors charge during substantially 180.degree. each half
cycle, the effective power supplied to the lamp for a given power
supply voltage will be a minimum and the capacitance required will
be a maximum. It has been found, however, that the effective power
supplied to the lamp through a voltage doubler ballast circuit
increases as the conduction angle of the switching means each half
cycle is reduced by delaying the firing angle thereof until the
supply voltage has increased substantially.
When the firing of Triac Q.sub.1 is delayed each half cycle until
supply voltage has increased substantially, the abrupt application
of higher voltage to L.sub.1 and L.sub.2 increases self-inductance
therein and the value of capacitors C.sub.1 and C.sub.2 as power
factor corrective means increases. Also, when the firing of Triac
Q.sub.1 is so delayed so as to reduce its conduction angle, the
circuit can be considered to be operating at a higher frequency,
therefore requiring less capacitance.
I have found that when the firing of Triac Q.sub.1 is delayed
45.degree. or more following zero voltage each half cycle, the
capacitance of C.sub.1 and C.sub.2 may be reduced to one half the
value required for a given supply voltage when the circuit is
operated through substantitally 180.degree. each half cycle. This
reduction in required capacitance permits a considerable reduction
in the cost of producing a non-regulating voltage doubler type
ballast. Also, this reduction in size, and therefore cost, of
capacitors C.sub.1 and C.sub.2 permits the manufacture of a
regulating voltage doubler type ballast at substantially the cost
of one which is non-regulating, with the greater capacitance
required for conduction throughout substantially the entire
cycle.
Some additional inductance is required when the firing angle of
Triac Q.sub.1 is delayed any considerable amount. The inductor
L.sub.2 supplements inductor L.sub.1 in reducing current peaks
through the lamp and in continuing current flow therethrough. By
positioning that portion L.sub.2 of the total inductance so as to
be alternately in series with C.sub.1 and C.sub.2, the peak
capacitor charging currents are also limited.
FIGURE 2.
Referring to FIG. 2, the Triac Q.sub.1 and diodes D.sub.1 and
D.sub.2 of FIG. 1 are replaced by a pair of silicon controlled
rectifiers Q.sub.3 and Q.sub.4 arranged in opposite polarity with
each of terminals T.sub.1 and T.sub.2. Additionally, a means 20 to
indicate current flow through mercury arc lamp 14, comprising a
small incandecent lamp 22 and a parallel connected resistor 24, is
provided.
A firing signal is applied to each of the SCR's during each
conducting half cycle thereof through respective transformer
secondary windings 26 and 28 connected between their control
electrodes and the cathode sides thereof. A transformer primary
winding 30 common to both secondary windings 26 and 28 alternately
induces a positive firing pulse in the secondary windings 26 and
28. Primary winding 30 is connected across the supply terminals
T.sub.1 and T.sub.2 in series with Diac Q.sub.2, variable resistor
R.sub.2, photoconductive element 16, fixed resistor R.sub.1 and
inductor L.sub.2 and in parallel with capacitor C.sub.3.
OPERATION OF FIGURE 2.
When silicon controlled rectifiers Q.sub.3 and Q.sub.4 are
alternately conducting during alternate half cycles of the power
supply, the capacitors C.sub.1 and C.sub.2 are alternately charged
and discharged through lamp 14, as in FIG. 1. The firing angle of
the SCR's is determined by the time required to charge capacitor
C.sub.3 to the threshold voltage of Diac Q.sub.2 through the
resistors R.sub.1 and R.sub.2 and photocell 16. When Diac Q.sub.2
conducts in one direction during one half cycle, an energy pulse
flows through primary winding 30 in a corresponding direction and
therefore through one of the secondary windings 26 or 28 in a
direction to apply a positive signal to the gate of one of the
SCR's. During the alternate half cycle when Q.sub.2 is caused to
conduct oppositely, a positive firing signal is applied to the
other SCR.
When the current flow through lamp 14 varies due to any reason,
such as supply voltage variation, from that predetermined to effect
a predetermined optimum operating condition of the lamp, the light
output of incandescent lamp 22 will vary directly with the current
flowing through lamp 14. The relative resistance of resistor 24 and
the filament of lamp 22 is preferably such that a considerable
portion of the radiation from the filament is in the red and
infra-red frequency band to which an inexpensive, reliable, cadmium
sulphide, photoconductive element 16 is responsive. The inductors
L.sub.1 and L.sub.2 function similarly to their counterparts in
FIG. 1 to limit current peaks through the lamp and capacitor
charging current.
Experiments were conducted with a ballast and regulating circuit
constructed in accordance with FIG. 1 of the drawing. In these
experiments it was found that when the supply voltage was adjusted
to provide 360 watts at lamp 14 and with Triac Q.sub.1 conducting
substantially a full 180.degree., the lamp power could readily be
increased to 440 watts by decreasing the conduction angle of
Q.sub.1, that is, by retarding the firing thereof until the supply
voltage has increased substantially each half cycle. It was also
found that the circuit could be readily adjusted to provide 400
watt lamp power with 20 per cent variation in input voltage.
Further, in this circuit having a 10 millihenry inductor L.sub.1, a
13.8 millihenry inductor L.sub.2, and a capacitance of 43
microfarads, it was found that rated lamp power in a 400-watt
mercury arc lamp could be maintained under conditions in which the
supply voltage was varied from 110 to 165 volts a.c.
* * * * *