U.S. patent number 3,894,265 [Application Number 05/441,429] was granted by the patent office on 1975-07-08 for high intensity lamp dimming circuit.
This patent grant is currently assigned to Esquire, Inc.. Invention is credited to Kenneth P. Holmes, Carl R. Snyder.
United States Patent |
3,894,265 |
Holmes , et al. |
July 8, 1975 |
**Please see images for:
( Certificate of Correction ) ** |
High intensity lamp dimming circuit
Abstract
A high intensity lamp dimming circuit in which the lamp or lamps
are placed in series with a pair of reactive elements, one of which
is at least partially bypassed when the voltage across the element
and the current through it are of the same polarity. The relative
time of the bypass determines the amplitude of the lamp current and
hence its brightness. A control network, isolated from the power
lines to which the lamp network is connected, controls the timing
of the bypass. This control network preferably uses a programmable
unijunction transistor and operates on a low-level dc setting. The
control circuit design permits ready connection to single phase and
three phase power systems alike.
Inventors: |
Holmes; Kenneth P. (Houston,
TX), Snyder; Carl R. (Alief, TX) |
Assignee: |
Esquire, Inc. (New York,
NY)
|
Family
ID: |
23752836 |
Appl.
No.: |
05/441,429 |
Filed: |
February 11, 1974 |
Current U.S.
Class: |
315/194; 315/137;
315/195; 315/289; 315/DIG.4; 315/144; 315/199; 315/283 |
Current CPC
Class: |
H05B
41/40 (20130101); Y10S 315/04 (20130101) |
Current International
Class: |
H05B
41/40 (20060101); H05B 41/38 (20060101); H05b
041/38 () |
Field of
Search: |
;315/137,141,144,145,194,195,199,254,258,283,289,297,DIG.4,DIG.7 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lawrence; James W.
Assistant Examiner: LaRoche; E. R.
Claims
What is claimed is:
1. In combination with a high intensity gas discharge lamp, a
dimmer circuit for controlling the brightness thereof,
comprising:
ballast means connected to the lamp and connectable to an ac power
distribution line;
said ballast means including a reactor portion,
gated bypass means for providing at least partial bypass of current
around said reactor portion of said ballast means;
isolation means connected to said gated bypass means; and
controllable gas source voltage means operably connected through
said isolation means to said gated bypass means for controllably
rendering said gated bypass means conductive, and thereby bypassing
said reactor portion of said ballast means.
2. A dimmer circuit as set forth in claim 1, wherein said isolation
means includes a transformer.
3. A dimmer circuit as set forth in claim 1, wherein said
controllable gate source voltage means operates at a voltage
reduced from the voltage carried by said ac power distribution
line.
4. A dimmer as set forth in claim 1, wherein said ballast means
includes a first ballast element in series with said lamp and
wherein said reactor portion is a second ballast element in series
with said lamp.
5. A dimmer as set forth in claim 1, wherein said gated bypass
means includes a triac and said isolation means includes a
transformer, the gate connection of said triac being connected to
said transformer through at least two inverse parallel diodes to
prevent the inductive voltage buildup from said transformer from
falsely firing said triac.
6. A dimmer as described in claim 1, wherein said controllable gate
source voltage means includes
switch means operable when a predetermined voltage threshold value
thereof is exceeded; and
variable source voltage means connected to said switch means for
producing an amplitude controllable voltage substantially in phase
with the line voltage, the time the amplitude of the controllable
voltage reaching the threshold value of said switch means
determining the gating on of said bypass means.
7. A dimmer as described in claim 1, wherein said controllable gate
source voltage means includes
switch means operable when an applied voltage raises above a
predetermined value, the occurrence of said value being set to
occur before the voltage across the reactor portion changes
polarity with respect to the line current.
8. A dimmer as described in claim 1, wherein said controllable said
source voltage means includes
first switch means operable when a predetermined voltage threshold
value thereof is exceeded;
variable source voltage means connected to said switch means for
producing an amplitude controllable voltage substantially in phase
with the line voltage, the time the amplitude of the controllable
voltage reaching the threshold value of said switch means
determining the gating on of said bypass means; and
second switch means operably connected to said variable source
voltage means and closeably operable when the amplitude of the
controllable voltage raises above a predetermined value, the
occurrence of said value occurring before the voltage across the
reactor portion changes polarity with respect to the line
current.
9. A dimmer as described in claim 1, and including a series
resistor and capacitor in parallel with said reactor portion of
said ballast means.
10. A dimmer as set forth in claim 1, wherein said gate source
voltage means includes
sensing means for detecting the polarity of the current through and
the voltage across said reactor portion;
control means connected for producing a signal during at least part
of each half cycle of said ac power distribution line frequency;
and
means connected to said sensing means and said control means to
produce a gate source voltage when there is a signal from said
control means and which renders said bypass means non-conductive
when the voltage across said reactor portion is no longer in the
same polarity with the current therethrough.
11. A dimmer as set forth in claim 10, wherein said sensing means
includes a voltage sensing means for sensing the voltage across
said reactor portion and a current sensing means for sensing the
current through said reactor portion.
12. A dimmer as set forth in claim 10, wherein said control means
is normally on and said means for producing the gate source voltage
is an inhibiting means.
13. A dimmer as set forth in claim 10, wherein said control means
is normally off and said means for producing the gate source
voltage is an enabling means.
14. A dimmer as set forth in claim 1, wherein said gate source
voltage means includes means for deriving a voltage in phase with
the voltage supplied by said ac power distribution line, and means
for amplitude regulation connected thereto for preventing said
gated bypass means from being conductive when the voltage across
said reactor portion is no longer in the same polarity with the
current therethrough.
15. A dimmer as set forth in claim 14 wherein said amplitude
regulation is provided by a pair of cathode-to-cathode connected
zener diodes for shifting the amplitude of the voltage in phase
with the power distribution voltage so that it decreases below a
predetermined level no matter than the time the voltage across said
reactor reverses in polarity.
16. A dimmer as set forth in claim 14, wherein said amplitude
regulation is provided by a detector sensing the zero crossing of
the voltage of said ac power distribution line, a one-shot
multivibrator activated by said detector, and a semiconductor
switch connected to disenable said gate source voltage means when
the voltage across said reactor portion is no longer in the same
polarity with the current therethrough.
17. A dimmer as set forth in clailm 14, wherein said amplitude
regulation is provided by a detector sensing the peak of the
voltage of said ac power distribution line, a one-shot
multivibrator activated by said detector, and a semiconductor
switch connected to disenable said gate source voltage means when
the voltage across said reactor portion is no longer in polarity
with the current therethrough.
18. A dimmer as described in claim 1, wherein said isolation means
includes a first transformer for reducing the voltage from the
voltage carried by said ac power distribution line, and wherein
said controllable gate source voltage means includes
a second transformer connected across the ac power distribution
line to provide a reduced ac voltage;
a full wave bridge rectifier for rectifying the reduced voltage to
dc voltage;
a pair of cathode-to-cathode connected zener diodes for shifting
the amplitude of the reduced ac voltage in phase with the power
distribution voltage so that it goes to zero no later than the time
the voltage across said reactor goes to zero;
a triac connected in series with said zener diodes conducting when
the gate voltage applied thereto exceeds the reduced voltage from
said first transformer and the zener diode voltage; and
programmable unijunction transistor means connected to said
rectifier and to said triac for determining the amplitude and
timing of the gate voltage applied to said triac.
19. A dimmer as described in claim 18, wherein said programmable
unijunction transistor means includes
a unijunction transistor; the cathode of which is connected to said
triac;
first variable resistor means operably connected to the dc
terminals of said rectifier for controlling the voltage applied to
the anode of said unijunction transistor,
said first variable resistor means including
a resistance divider connected to said rectifier,
a diode connected to the output of said divider, and
a time constant network; and
second variable resistor means operably connected to the dc
terminals of said rectifier for controlling the voltage level on
the gate of said unijunction transistor.
20. The dimmer as described in claim 18, wherein said programmable
unijunction transistor means includes reset means for rendering
said unijunction transistor conductive when the anode-to-gate
voltage does not cause conduction and for rendering said
unijunction transistor non-conductive following polarity reversals
of said ac power distribution line voltage.
21. A dimmer as described in claim 20, wherein said reset means
includes
a capacitor connected to the gate of said unijunction transistor
and to said full wave bridge rectifier; and
a diode connected to said anode of said unijunction transistor and
to said full wave bridge rectifier.
22. In combination with at least three high intensity gas discharge
lamps, a dimmer circuit for controlling the brightnesses thereof,
comprising
a separate ballast means connected respectively to each of the
lamps and connectable to an ac power distribution system,
each of said ballast means including a reactor portion,
separate gated bypass means for respectively providing bypass
current around said reactor portion of each of said plurality of
ballast means;
separate isolation means connected to each of said gated bypass
means; and
commonly controllable gate source voltage means operably connected
through said isolation means to each of said gated bypass means for
controllably rendering said gated bypass means conductive, and
thereby bypassing said reactor portion of each of said ballasts
through a time range when the current through said reactor portions
and the voltages thereacross are respectively of the same
polarity.
23. A dimmer circuit as set forth in claim 22, wherein said
separate ballast means are connected respectively to different
phases of said ac power distribution system.
24. A dimmer circuit as set forth in claim 22, wherein said
separate ballast means are connected to the same phase of said ac
power distribution system.
25. A dimmer as described in claim 22, and including a series
resistor and capacitor in parallel with said respective reactor
portions of said separate ballast means.
26. The dimmer circuit as described in claim 22, wherein each of
said isolation means includes a first transformer for reducing the
voltage from the voltage carried by said ac power distribution
line, and wherein said controllable gate source voltage means
includes
a second transformer connected across each phase of the ac power
distribution line to provide a reduced ac voltage for each
phase;
a separate full wave bridge rectifier for rectifying each of the
reduced voltages to dc voltage;
a separate pair of cathode-to-cathode connected zener diodes for
shifting the amplitude of each reduced ac voltage in phase with the
power distribution voltage so that it goes to zero no later than
the time the voltage across said respective reactor goes to
zero;
a triac connected in series with each pair of said zener diodes
conducting when the gate voltage applied thereto exceeds reduced
voltage from said first transformer and the zener diode voltage;
and
programmable unijunction transistor means connected to each of said
bridge rectifiers and to said triac for determining the timing and
amplitude of the gate voltage applied to said respective
triacs.
27. The dimmer circuit as described in claim 26, wherein each of
said programmable unijunction transistor means includes
a unijunction transistor, the cathode of which is connected to said
triac;
first variable resistor means operably connected to the dc
terminals of said rectifier for controlling the voltage applied to
the anode of said unijunction transistor, said first variable
resistor means including
a resistance divider connected to said rectifier,
a diode connected to the output of said divider, and
a time constant network; and
second variable resistor means operably connected to the dc
terminals of said rectifier for controlling the voltage level on
the gate of said unijunction transistor.
28. The dimmer as described in claim 26, wherein said programmable
unijunction transistor means includes reset means for rendering
said unijunction transistor conductive when the anode-to-gate
voltage does not cause conduction and for rendering said
unijunction transistor non-conductive following polarity reversals
of said ac power distribution line voltage.
29. A dimmer as described in claim 28, wherein each of said reset
means includes
a capacitor connected to the gate of said unijunction transistor
and to said full wave bridge rectifier; and
a diode connected to said anode of said unijunction transistor and
to said full wave bridge rectifier.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to lamp dimming circuits for high intensity
discharge lamps, such as mercury vapor lamps, having two electrode
terminals and no heater, and more specifically, to improved control
circuits which are isolated from the lamp circuits for convenience
of making multiple connections, both single phase and three phase,
and for safety.
2. Description of the Prior Art
Mercury vapor and other metallic-additive high intensity discharge
(H.I.D.) lamps have found wide-spread acceptance in lighting large
areas, such as warehouses, gymnasiums, and the like, primarily
because of their relatively high efficiency and low maintenance
when compared to incandescent lighting systems. There has been
general approval of such systems for large area illumination in
spite of the fact that therer has been no wide-spread satisfactory
method of reducing the illumination during periods when full
illumination has not been desired. When it is desired to reduce
illumination in an area normally lit by a high intensity discharge
lamp system, it has been necessary either to completely turn off
some of the lamps in the system or to switch to an auxiliary
incandescent or fluorescent lamp system.
Switching off some lamps and not others gives unsatisfactory
full-range control and increases the complexities of the system by
requiring additional wiring, switching equipment, etc. Having to
provide an auxiliary system likewise greatly increases the
complexities of the overall lighting system. In addition to
additional wiring and switches, additional fixtures, lamps and even
power handling equipment is required when an auxiliary system is
employed.
Only recently has a system been developed which could incorporate a
dimming control system directly into a high intensity discharge
lamp network. This system is revealed in copending patent
application Ser. No. 353,793, filed Apr. 23, 1973, now U.S. Pat.
No. 3,816,794, and entitled "High Intensity Gas Discharge Lamp
Dimmer System", a continuation of patent application Ser. No.
238,800, filed Mar. 28, 1972, now abandoned, assigned to the same
assignee as the present application. Before this system was
marketed, it was widely supposed that when power consumption was
reduced in a high intensity discharge lamp, electrode sputtering
would result, which would cause damage to the environment within
the lamp. Such damage would greatly reduce the life of the lamps
and also cause undesirable flickering. Second, the existing dimming
circuits for incandescent and fluorescent lamps caused the
extinguishment of a high intensity discharge lamp. This is because
such circuits actually turn off the lamps with which they operate
for short periods of time during each operating cycle. Although
this mode of operation was acceptable for incandescent and
fluorescent lamp operation, it was not acceptable for operation
with high intensity discharge lamps. Such a lamp, once turned off,
requires a relatively long cooling period after extinguishment
before it can be restarted.
It was discovered, however, that by employing a dimmer circuit that
did not cause off time during half cycles in lamp current, but
which was controllable for changing its rms value without having
dwell time at zero, that a practical high intensity discharge lamp
system could be dimmed. The reduction of current through a high
intensity discharge lamp could be effective in providing dimming
without damage to the lamp by bypassing current around an
accompanying ballast element and hence achieving reduction of lamp
current for part of a half cycle, provided such operation did not
operate to cause bypass current flow at such times when the
accompanying ballast element voltage and current are of opposite
polarity.
Because phasing of ballast voltage and current was so important,
the control circuit and the lamp circuit were operated from the
same power connections. This was the case even though it is common
in other types of control circuits to have one power circuit for
the lamp fixtures and another for the control and switching
components. When the control and lamp fixtures in the prior art
system were connected separately to a line source, overloads could
often occur and fuses would blow. Not only was this a nuisance, but
every light fixture had to have a protective fuse or circuit
breaker of its own. Further, the control circuit for a three phase
circuit was considerably different from a single phase circuit.
Therefore, one circuit had to be fabricated for a single phase
application and another quite different circuit had to be
fabricated for a three phase application, rather than having one
basic circuit which permitted modification or simple additional
components to be connected, as required, in the field at the time
of installation into either a single phase or a three phase power
circuit.
It is therefore a feature of this invention to provide improved
apparatus as part of a dimming circuit for a high intensity
discharge lamp which includes provisions for separate power
connections to the lamp and for the control and switching circuit,
thereby effectively isolating these components from each other.
It is another feature of this invention to provide an improved
dimming circuit for a high intensity discharge lamp which includes
provisions for operating in a single phase or a three phase power
distribution system with little modification.
It is still another feature of this invention to provide improved
apparatus as part of a dimming circuit for a high intensity
discharge lamp including a programmable unijunction transistor as
part of a control network, such use increasing the flexibility of
control and reducing the cost of components when compared with
prior art control networks.
SUMMARY OF THE INVENTION
A preferred embodiment of the present invention comprises, in
combination with a single high intensity discharge lamp, circuitry
operating with two ballast elements connected in series with the
lamps and a control circuit for operating a bypass to one of the
elements.
Preferably, this bypass includes a gated triac, the voltage for its
gate being derived from a transformer that isolates the power
distribution circuit for the lamp from a controllable gate source
voltage used for determining the conduction time of the triac.
The gate source voltage is controlled by a signal derived from a
voltage in phase with the ac power distribution line, such as from
a transformer-full-wave-bridge-and-zener-diode-regulator connection
to the like. A programmable unijunction transistor (PUT) connected
to the regulated voltage is also connected to be gated on by a
voltage derived from a time constant network. The output of the PUT
is applied to the gate of a triac, in the output line from the
control circuit. The gate source voltage out of the control circuit
is clipped by two cathode-connected zener diodes so that the gated
bypass triac in the bypass network is conductive only when the
voltage across the bypass to the reactor element is in polarity
with the current therethrough.
A variable resistor and diode connection may be connected to each
of three bridge rectifiers in a three phase power distribution
system and also connected to each of three programmable unijunction
transistors in three separate control networks for operating in
three separate high intensity discharge lamp networks, one network
drawing its power from each of the phases. The simple connection
does not require additional fuses for each control network or for
each lamp network and does not interfere with the isolation
qualities of the control network from the power distribution line
for each of the lamp networks, thereby making the single phase
system and the three phase system virtually identical.
BRIEF DESCRIPTION OF THE DRAWINGS
So that the manner in which the above-recited features, advantages
and objects of the invention, as well as others which will become
apparent, are attained and can be understood in detail, more
particular description of the invention briefly summarized above
may be had by reference to the embodiments thereof which are
illustrated in the appended drawings, which drawings form a part of
this specification. It is noted, however, that the appended
drawings illustrate only typical embodiments of the invention and
are therefore not to be considered limiting of its scope, for the
invention may admit to other equally effective embodiments.
In The Drawings:
FIG. 1 is a schematic diagram of a preferred embodiment of dimming
apparatus in accordance with the present invention.
FIG. 2 is a waveform diagram showing the amplitude and phase
relationship existing in the lamp voltage and the range of bright
and dim currents in the circuit shown in FIG. 1.
FIG. 2a is a waveform diagram illustrating relative currents to
achieve full and dim conditions.
FIG. 2b is a waveform diagram illustrating summing of currents to
achieve an intermediate current value between full and dim.
FIG. 3 is a waveform diagram showing the amplitude and phase
relationship existing in various important voltages and currents in
the circuit shown in FIG. 1.
FIG. 4 is a partial schematic diagram showing the connection of
multiple control electronics in a single control system in
accordance with the present invention.
FIG. 5 is a block diagram of an alternate embodiment for limiting
the timing of the control circuit of the present invention.
FIG. 6 is a block diagram of another alternate embodiment for
limiting the timing of the control circuit of the present
invention.
FIG. 7 is a block diagram of an alternate embodiment for limiting
the timing of the bypass circuit of the present invention.
FIG. 8 is a partial schematic diagram of an alternate control
circuit of the present invention.
FIG. 9 is a partial block diagram of an alternate arrangement of
the triac module in the present invention.
FIG. 10 is a partial block diagram of another alternate arrangement
of the triac module in the present invention.
FIG. 11 is a partial block diagram of an alternate arrangement of
the triac module in the present invention, the arrangement also
employing a high reactance autotransformer.
FIG. 12 is a partial block diagram of another allternate
arrangement of the triac module in the present invention, the
arrangement also employing a high reactance autotransformer.
FIG. 13 is a partial block diagram of an alternate arrangement of
the triac module in the present invention, the arrangement also
employing an autotransformer.
FIG. 14 is a partial block diagram of another alternate arrangement
of the triac module in the present invention, the arrangement also
employing an autotransformer.
DESCRIPTION OF PREFERRED EMBODIMENT
Now referring to the drawings and first to FIG. 1, high intensity
discharge lamp 10 is connected in series with two inductive ballast
elements 12 and 14, the entire combination being connected between
lines 16 and 18. Gated bypass means in the form of traic 20 is
connected across element 14, first main terminal 22 of the triac
being connected to line 16 and second main terminal 24 being
connected to a junction between the two elements. Gate terminal 26
is connected to shunt resistor 28, which is also connected to line
16. Resistor 30 and capacitor 32, connected in series with each
other and in parallel with element 14, are provided as a snubber
device to provide triac 20 immunity from commutating dv/dt false
turn on. Two pairs of diodes 34 and 36 and 38 and 40 connected to
gate 26 provide the gate source voltage to triac 20 from
transformer 42. These diodes are connected so that two diodes 34
and 36 face forward and two diodes 38 and 40 face backwards, with
the junction point between each pair being connected together.
Diodes 34, 36, 38 and 40 provide a slight forward voltage drop to
block out the residual magnetizing force from transformer 42 and to
thereby prevent false firing of triac 20. Everything between and
including transformer 42 and its accompanying load resistor 52, and
inductor 14 may be considered to be in triac module 15.
When triac 20 is conducting to form a complete bypass around
element 14, a maximum amount of current (designated "full lamp
current" in FIGS. 2 and 3) flows through lamp 10. On the other
hand, when triac 20 is not conducting, then the minimum amount of
current flows through lamp 10, as indicated by the "dim lamp
current" curve in FIGS. 2 and 3. By allowing triac 20 to conduct
for part of the cycle as shown by the dash lines in FIG. 2, then
the current through lamp 10, and hence the illumination therefrom,
may be varied between the dim lamp current and full lamp current
values. A short period of conduction by triac 20 creates a curve
101, a little longer conduction period creates a curve 103 and a
still longer period creates a curve 105. It is apparent therefore,
that merely controlling the period of conduction of triac 20 will
achieve controllable illumination of lamp 10.
Control of the conduction of triac 20 is accomplished by the
controllable gate voltage means connected to transformer 42. To
understand the operation of the control circuit, some additional
phase relationships have to be appreciated, which can best be shown
by reference to FIG. 3. The voltage across element 14 (reactor
voltage) is leading the lamp current by approximately 85.degree.
and also is leading the line voltage by approximately
30.degree..
Triac 20 should not be rendered conductive until the current
through and the voltage across element 14 are both of the same
polarity, either both positive or both negative. If traic 20 was
rendered conductive when the voltage across element 14 and the
current therethrough were not of the same polarity, a phenomenon
known as "half cycle conduction" would occur. The lamp would appear
to flash from dim to full bright each half cycle and would produce
an irritating strobing effect to the eye that would also be harmful
to the lamp.
Considering the positive polarity cycles, the current through
element 14 does not go positive until point 107. At this time, the
reactor voltage is already positive. At point 109, the reactor
voltage goes negative, although the current through inductive
elements 14 is still positive. The range 111 of time over which
gate voltage may be applied is hence determined as being the time
between points 107 and 109.
Power is applied to transformer 42 via the secondary 44 of power
transformer 46 whose primary is connected across lines 16 and 18.
One terminal of secondary 44 is connected to fuse or circuit
breaker 48. Load resistors 50 and 52 connected to the two sides of
the primary of transformer 42 are connected to ground. The power
connection from the secondary 44 of transformer 46 to the primary
of transformer 42 is through a bidirectional voltage regulating
means in the form of cathode-to-cathode zener diodes 54 and 56 and
triac 58. It is well known that alternatively zener diodes 54 and
56 may be connected anode-to-anode and operate in the same
manner.
It is well known that the gate pulse to a triac controlling an
inductive load is desirably a continuously applied gate voltage,
rather than an instantaneous pulse. Again referring to FIG. 1, it
may be seen that cathode-to-cathode zener diodes 54 and 56 are
connected in series with the main terminals of triac 58, the entire
combination being connected as previously mentioned in series with
secondary 44 of transformer 46. It is readily apparent that the
gate voltage has for its source from secondary 44 a voltage which
is in phase with the voltage across lines 16 and 18. This voltage
is labeled "gate source voltage" on FIG. 3. It is, of course, in
phase with the line voltage across lines 16 and 18.
Connected to the gate terminal of triac 58 is the cathode of
programmable unijunction transistor 60. The gate connection to PUT
60 is connected to a rectified dc voltage via variable resistor 62.
The timing of the conduction of PUT 60 is determined by the voltage
differential between the voltage applied via resistor 62 and the
voltage applied to the anode of PUT 60. Both the voltage applied to
the anode and to the gate of PUT 60 are important to its
conduction. The anode voltage must be slightly larger than the gate
voltage to cause conduction. That is, conduction is dependent on
the arithmetic difference between the voltage applied to the anode
and gate. Therefore, the setting of resistor 62 "programs" what
anode voltage is required to produce conduction. The dc voltage
applied to resistor 62 is developed by bridge rectifier 64
connected to secondary 66 of transformer 46. A zener diode 68 and
current limiting resistor 70 insures that the voltage applied to
resistor 62 never exceeds a predetermined value.
The output from bridge rectifier 64 is also connected through diode
72, fuse 73 and variable resistor 74 to a time constant control
network connected to the anode of PUT 60. This time constant
network includes capacitors 76 and 78 and resistor 80. A diode 82
is included in series with the voltage from resistor 74.
A diode 84 in the anode circuit of PUT 60 and capacitor 86 in the
gate circuit of PUT 60 insure positive reset of PUT 60 following
conduction. It should be noted that the operating adjustment for
PUT 60 is determined by variable resistor 62. The ultimate control
for determining the amount of brightness of lamp 10 is determined
by the setting of resistor 74. As PUT 60 ages, the setting of
resistor 62 can be changed, as well as permitting an easy setting
for initial conditions.
In operation, programmable unijunction PUT 60 is turned on by the
voltage difference between the voltage on the anode of PUT 60
(voltage on capacitor 78) and the voltage on the movable contact of
resistor 62. On each cycle of ac voltage applied to the bridge,
there is a rise to a dc level at the output of this bridge for
application to the gate of PUT 60 through resistor 62. In a more
sluggish fashion, a voltage determined by the setting of resistor
74 will be applied to the anode of PUT 60. When the differential in
these two voltages is reduced at the gate and anode of PUT 60 to
the point of causing conduction, a gate voltage is supplied to
triac 58. Triac 58 conducts when the secondary voltage of 44
applied thereto exceeds the zener diode voltage of diodes 54 and
56. When diodes 54 and 56 conduct, there is a complete circuit in
secondary winding 44 of transformer 46. This permits voltage to be
supplied to transformer 42 for operation in accordance with the
diagram shown in FIGS. 2 and 3.
Yet another method of achieving the desired timing of PUT 60 to
achieve firing within gate range 111, even without zener diodes 54
and 56, may be accomplished by selecting the components of resistor
74, resistor 75, which is connected between resistor 74 and ground,
resistor 80, capacitor 78, the voltage determined by zener diode
68, and the setting of the voltage on the gate of PUT 60 by the
setting of the movable arm on resistor 62. The setting is
determined by placing variable resistance 74 at its lowest or dim
setting.
Referring now to FIG. 2a, there is shown a waveform illustrating
summing of currents taken at points I.sub.1 (through reactor 14)
and I.sub.2 (through triac 20) in FIG. 1. If triac 20 is not gated
on, no I.sub.2 current flows and the only current flow through the
lamp (I.sub.T) is I.sub.1. This is reflected as the "dim state". On
the other hand, if triac 20 is gated on during the entire time,
then the entire current is bypassed around reactor 14 and through
triac 20. Hence, I.sub.1 becomes essentially zero and I.sub.T
equals I.sub.2, as shown by the full on state curve.
If triac 20 is gated on to an angle .theta. following the
occurrence when current through the lamp becomes positive, a triac
current I.sub.2 will be generated which is added to reactor current
I.sub.1, as shown in FIGS. 2 and 2b. At the same time, current
I.sub.1 that had been rising assumes essentially a steady state
I.sub.1a, until the time that triac 20 is no longer conducting.
Hence, current I.sub.T relative to time is equal to I.sub.1 before
the triac is fired, then equal to I.sub.2 plus I.sub.1a while the
triac is conductive, and then is equal to I.sub.1 again after triac
20 commutates.
As shown in FIG. 3, it is necessary that the gate voltage is
prevented from continuing past the gate cutoff point. Although the
gate voltage may be readily controlled by zener clipping as
indicated above and as illustrated in FIG. 3, it is deemed within
the scope of the present invention to provide other appropriate
circuit means for controlling the gate voltage to prevent voltage
past the gate cutoff point from energizing the triac.
Further, in FIG. 3, it is assumed that the ballasting is such that
the line voltage, and hence the reactor voltage, leads the lamp
current. Should there be a lagging situation so that the phase
relationships are the other way, gating means may be provided so
that the gate range would still be only while the reactor voltage
and lamp current are of the same polarity. Generically, this gating
scheme is also within the scope of the present invention.
Once conduction of triac 20 is started, the gate source voltage
must return to zero before the reactor voltage reverses polarity.
This is accomplished in the circuit shown in FIG. 1 by the zener
diodes cutting off when the gate source voltage applied thereto
falls below a predetermined value, as shown in FIG. 3.
The turn off point of the zener diodes does not vary. It is
apparent, however, that the shutting off of the zener diodes and
hence the gate source voltage to triac 20 does not instantaneously
render triac 20 nonconductive. The inductance of elements 12 and 14
causes current to continue through triac 20 until the reactor
current crosses zero and the triac commutates. The current through
lamp 10, after such commutation, is only current through reactor 14
as illustrated in FIGS. 2, 2a, 2b and 3.
Two switches are provided, either of which may be used to replace
the variable control of the circuit to a full bright or full dim
operation, if desired. Switch 90 is connected between diode 82 and
resistor 74. This switch is a three-position switch. When it is on
its center connection, connection is made to the variable contact
of resistor 74 and operation is as previously described for
variable control operation. When placed to the HIGH position,
contact is made to the top of resistor 74 and the greatest amount
of voltage is applied. The LOW position of the switch disconnects
voltage from diode 82.
In operation, the highest setting of resistor 74, causes the anode
voltage applied to PUT 60 to reach the level of firing the PUT in
the shortest period of time. That is, the critical anode-to-gate
voltage difference occurs at the earliest time possible within gate
range 111, namely, at point 107. This assures gate voltage to triac
20 the maximum amount of time and hence full lamp current to lamp
10, as explained above. Absence of voltage, or low voltage
operation, achieves the opposite effect.
Alternatively, switch 92 may be used to achieve high (full
brightness) or low (dim) operation. In the LOW Position of switch
92, there is a disconnect of transformer 46 from transformer 42.
This means that no gate voltage is provided triac 20 and hence dim
current is always supplied to lamp 10. In the HIGH position of
switch 92, a center-tap connection is made from secondary 44 of
transformer 46 to transformer 42. This supplies all the gate
voltage necessary to keep triac conducting the maximum amount of
time and therefore supplies full lamp current to lamp 10. Only part
of transformer secondary 44 is used since switch 92 provides
operation without having to supply power also to the variable
control circuit.
Reset operation of PUT 60 involves capacitor 86, capacitor 78,
which is somewhat smaller than capacitor 86, diode 84 and triac 58.
As already mentioned, when the exponential voltage rise on the
anode of PUT 60 reaches a value that is a predetermined difference
to the voltage applied to the gate of PUT 60, PUT 60 conducts.
Assuming that the anode voltage never reaches the critical level
with respect to the steady state dc level on the gate for
conduction, PUT 60 will conduct nevertheless at point 109 shown in
FIG. 3 because the voltage on the gate of PUT 60 reduces until the
critical predetermined voltage differemce between gate and anode
exists. In other words, there is a forced firing of PUT 60. The
firing of PUT 60 is caused by capacitor 86 discharging through the
path comprising resistor 70, the resistor in the center of bridge
64, capacitor 78 and through the anode-to-gate path of PUT 60.
When PUT 60 turns on, capacitor 78 discharges through the PUT and
triggers triac 58. If the secondary voltage of 44 exceeds the zener
threshold voltage of zener diodes 54 and 56, then the gate source
voltage from this control circuit is produced, as previously
described. In any event, because capacitor 86 is bigger than
capacitor 78, eventually diode 84 conducts to cause a slight
reverse build-up on capacitor 78. Since triac 58 commutates, the
cathode of PUT 60 becomes zero, and hence there is an
anode-to-cathode reverse bias which turns off the PUT. Moreover,
when the line again begins to buildup, the gate voltage of PUT 60
rises to further ensure that gate current stops until the rising
voltage on the anode again establishes conduction conditions.
Now referring to FIG. 4, a partial diagram is shown of a three
phase connection utilizing the improved dimmer control circuit of
the invention. Three lines 16, 18 and 19 provide the three phase
power distribution to the circuit. In conventional fashion they are
connected to three power transformers 46a, 46b and 46c. Each
transformer has connected across its secondary a bridge rectifier
circuit 64a, 64b and 64c, in the same manner as shown in FIG. 1.
Connected to the output of each of these bridge rectifiers is a
diode 72a, 72b and 72c, respectively, each connected to fuse 73.
Fuse 73 may be viewed as the same fuse 73 shown in FIG. 1. Only one
such fuse 73 is required for the three phase connection shown in
FIG. 4. Fuse 73 is connected to variable resistor 74 which is
connected to ground via a fixed resistor 75. The output from the
variable resistor is connected to diode 82, which is also part of
the common circuit of each of the three phases. The output from
diode 82 is supplied to the time control networks in the respective
phases. For example, in the first phase, the connection is made to
capacitor 76a and 78a and resistor 80a. In the second phase
network, connection is made to capacitor 76b and 78b and resistor
80b, and in the third phase, connection is made to capacitor 76c
and 78c and resistor 80c. The remainder of the components in each
of the phases is the same for the single phase circuit shown in
FIG. 1.
In operation, setting of dimmer control 74 effects the lamp
connected in each of the phases in the same manner as described
above with respect to FIG. 1. Note that separate fuses are not
required for each of the phases.
In addition to the three phase connection which is shown in FIG. 4,
it is also possible to connect multiple single phase connections
all through the same variable dimmer control 74 in the same manner.
In this instance the diagram would be the same as shown in FIG. 4
except the three power transformers 46a, 46b and 46c would be
connected across the same power distribution line.
Further, although a three-phase delta connection is illustrated in
FIG. 4, the circuit may be connected to various other three-phase
power connections, such as a wye connection.
Now turning to FIGS. 5-7, alternate embodiments of controlling the
operation of the FIG. 1 basic circuit is shown. To more fully
appreciate the timing reuired in controlling the circuit, reference
is made again to the waveform shown in FIG. 3. Gate cutoff point
109 is adjusted to be approximately 30.degree. ahead of the
cross-over point for the line voltage. In other words, gate cutoff
point 109 occurs 150.degree. after the line voltage. In the basic
circuit, PUT 60 is prevented from firing at a time after the
reactor voltage (across inductor 14) and the current therethrough
(lamp current) are of opposite polarity by the clipping action of
zener diodes 54 and 56.
Assuming the absence of zener diodes 54 and 56, an alternate method
of achieving PUT 60 from firing later than 150.degree. after the
line voltage reverses polarity is shown in FIG. 5. In this
embodiment the voltage across the line (voltage from line 16 to 18)
is sensed by zero-crossing detector 94 to produce an output at the
time the line voltage reverses polarity. The output from
zero-crossing detector 94 is applied to one-shot multivibrator 96,
which produces a pulse of a predetermined duration. This pulse may
be set not to exceed 150.degree. of the cycle of the line voltage,
since this line frequency, and hence cycle duration, is well known.
This adjustment may be made variable, if desired.
The output from one-shot multivibrator 96 is applied to a
transistor switch 98 which shunts the anode of PUT 60 to ground at
the end of the pulse from the multivibrator. The connection makes
it impossible for PUT 60 to conduct after the switch is closed by
the multivibrator. On the following zero-crossing of the line
voltage, the multivibrator is again pulsed to produce a similar
switching action. As may be seen, this switching occurs every
half-cycle.
FIG. 6 shows a circuit which is identical to FIG. 5, except that
this embodiment includes peak detector 100, rather than
zero-crossing detector 94. That is, the detector is activated on
the change of slope of line voltage and produces an output from
one-shot multivibrator within a period of 60.degree. following peak
detection. Again, this pulse duration may be predeterined to be
something less than 60.degree., if desired. It may be seen that
peak detection takes place 90.degree. after zero-crossing
detection, and therefore, the 60.degree. pulse from the
multivibrator is equivalent to the 150.degree. pulse which was
described in the FIG. 5 embodiment.
Now referring to FIG. 7, another method of ensuring proper firing
of triac 20 in triac module 15 is shown. A current sensing element
in the form of a resistor 120, sensing coil or other is placed in
series with inductor 14. A connection is made across inductor 14
for sensing the voltage. The current sensing element and the
voltage connection are connected to current and voltage sensing
means 122, which may be separate current sensor 124 and voltage
sensor 126, respectively. Outputs indicative of the presence of a
specified polarity of the current through and the voltage across
induction 14 are applied to inhibit circuit 128. Inhibit circuit
128 is also connected to control circuit 104, which may include all
of the electronics in the control circuit of FIG. 1, except
preferably zener diodes 54 and 56.
When there is an output gate signal from control circuit 104
applied to inhibit circuit 128 and also an output from the current
and voltage sensors, there is a gate source signal for causing
triac 20 in triac module 15 to conduct. The firing of triac 20
produces the operation which has previously been described with
respect to inductors 12 and 14 and lamp 10.
Although circuit 128 has been described as an inhibit circuit, it
is well-known in the art how to achieve operation as described
above by incorporating an enable circuit as circuit 128.
Now referring to FIG. 8, a partial schematic diagram of an
alternate control circuit is shown. In this circuit, all components
are identical to the circuit shown in FIG. 1. However, it is
assumed that diode 82 is connected to a variable dc source 112.
Since PUT 60 operates on a voltage difference, the level of the
voltage supplied from source 112 ultimately controls the conduction
of PUT 60 and hence the brightness of lamp 10. An example of source
112 is a dc control circuit employing a photocell which monitors
the ambient light. When the amient light indicates a need for more
brightness from lamp 10, the photocell causes an amplifier in the
dc control circuit to increase the voltage level to diode 82,
which, in turn, causes earlier conduction of PUT 60, as explained
above. Hence, there is more brightness provided from lamp 10.
Reset elements 84 and 86 are illustrated in FIG. 8. However, it
should be noted that other reset means may be employed, so long as
the reset means is synchronized to the line. Suitable reset means
connected between the anode of PUT 60 and ground are shown in FIGS.
5 and 6. In addition, separate source means, rather than
transformer winding 66 and full-wave rectifier 64, synchronized to
the ac power distribution line and acting in part as reset means
for PUT 60, may be employed.
FIGS. 9-10 illustrate alternate connections for the circuit of FIG.
1. It may be recalled that triac module 15 has four connections:
two terminals to transformer 42 and accompanying load resistor 52
and two power terminals to permit connection in series with lamp 10
and inductive ballast element 12 across lines 16 and 18. FIG. 1
shows one such connection, where inductor 14 is connected to the
high line. Alternatively, inductor 14 of module 15 may be connected
between inductor 12 and lamp 10, as in FIG. 9, or connected to the
low line, as in FIG. 10.
FIGS. 11-14 show various autotransformer connections. FIG. 11
illustrates a high reactance autotransformer 17 connected to lines
16 and 18, inductive element 14 internal to triac module 15 being
connected between the halves of autotransformer 17. The secondary
of this autotransformer is loosely coupled to the primary, as
indicated. The impedance of this secondary is designed to have in a
high reactance autotransformer circuit many of the operational
characteristics as inductor 12 in the FIG. 1 circuit.
FIG. 12 illustrates another connection of triac module 15 in a
circuit employing high reactance autotransformer 17. In this
embodiment, triac module 15 and lamp 10 are connected in series and
the autotransformer coils are connected together. If desired, the
lamp and triac module may be reversed.
Conventional autotransformer 19 is connected in two example
alternate arrangements of lamp 10, inductive element 12 and triac
module 15 in FIGS. 13 and 14. Any other arrangement previously
discussed may be employed, if desired.
While particular embodiments of this invention have been shown and
discussed, it will be understood that the invention is not limited
thereto, since many modifications may be made and will become
apparent to those skilled in the art.
For example, although FIG. 1 illustrates transformer means as the
isolation means between the control circuit and the triac module,
other isolation means may be employed, such as magnetic isolation
means, optical isolation means or sound (transducer) isolation
means. In a circuit employing optical isolation, a photo emitter
may be used in a network for developing the gate source voltage and
a photo detector may be used as the control isolation device driven
thereby.
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