Note: Descriptions are shown in the official language in which they were submitted.
1~836~8
CROSS-REFERENCES TO RELATED APPLICATION AND PAT~NTS
In Canadian ~pplication Serial No. 329,809, filed
June 14, 1979, and owned by the present assignee, is disclosed
a variable inductance ballast apparatus ~or an HID lamp which
comprises a laminated E-I core having non-magnetic gaps
intermediate the E-conformed and I-conformed members. A main
winding is carried on the leg of the E-conformed member to
provide two closed magnetic paths, and a control winding is
wrapped about another of the legs and encir¢les only one of
the magnetic paths. When the control winding is closed, the
resulting counter MMF decreases the inductance apparatus by
a predetermined amount. Such a variable inductance ballast
is particularly adapted for use with a control circuit as
described herein.
In U.S. Patent No. 4,147,962, issued April 3, 1979
to Joseph C. Engel, and owned by the present assignee, is
disclosed an illumination system which automatically dims
the lamps after a fixed time period of operation at rated
power input.
In U.S. Patent Mo. 4,147,961, issued April 3, 1979
to Robert T. Elms, and owned by the present assignee, is
disclosed an illumination!system which operates lamps with
a high degree of illumination during the early part of
the night and automatically dims the lamps during the later
part of the night when a lower degree of illumination can be
tolerated. The relative period of time the lamps are operated
at the higher and lower levels of illumination is automatically
adjusted accordi~g to the day-night seasonal variations~
,~ . .
. ~
-2-
- - .. - . .
108;~65~3
BACKGROUND OF THE INVENTION
This invention relates to ballast circuits for HID
lamps and, more particularly 9 to a ballast circuit which
very accurately regulates the wattage of HID lamps, and
particularly high-pressure sodium lamps, during prolonged
operation thereof and which also limits the line current
drawn by the lamp during starting to less that the line
current drawn by the lamp during normal operation.
U.S. Patent No. 3,873,910 dated March 25, 1975
10 to Willis, Jr., discloses a variable inductor which includes ;~ -
a main winding and a control winding positioned on opposite
sides of a gapped shunt. The control winding is adapted
to be closed by a gate-actuated AC switch, and upon closing,
the inductance of the variable inductor is decreased by a
predetermined amount? thereby controlling the power input ~ -
to the ballasted lamp.
In U~S. Patent No. 4,037,148 dated July 19, 1977
to Owens, is disclosed a ballast device especially adapted
to operate with a variable inductor as described in the afore-
mentioned U.S. Patent No. 3,873,910 to ballast a high-pressure
sodium discharge lamp wherein a non-linear amplifier is in-
corporated in circuit. For actual control, lamp ~oltage and
line voltage are sensed and these voltage signals are combined
in a programmable unijunction transistor to control the firing
time thereof, and thus the actuation of the gate-controlled
-3- -
,
48,021
AC switch.
U.S~ Patent No. 3,886,405 dated May 27, 1975 to
Kubo discloses sensing a variety of parameters in order to
effect lamp control, including sensing both lamp voltage and
line voltage to vary the impedance in circult with the lamp
and thus regulate lamp power consumption. In the case line
voltage is sensed, the sensed voltage is applied to a uni- ;
~unction transistor to control the firing time thereo~, as
in the afore-mentioned No. 4,037,148.
In U.S. Patent No. 3,590,316 dated June 29, 1971, : ~:
to Engel and Elms, the applicants herein, is disclosed a
transistorized wattmeter which is used to control a variable ; ~
impedance in order to control lamp wattage. The wattage is `` '
measured electronically and is converted into a current
signal which is used to charge a ramp-type capacitor which
in turn controls the firing oP a gate-controlled AC switch
when a predetermined voltage is achieved across the capa-
citor. ;i
Lamp starter circuits for high-pressure sodium
20 lamps are well known such as described in U.S. Patent No.
4,072,878 dated February 7, 1978 to J. C. Engel and G. F.
Saletta.
SUMMARY OF THE INVENTION ~ I
There is provided an operating circuit for con- ;
trolling at about a predetermined nominal rated value the
wattage drawn by an HID lamp during normal operation thereof
and for limiting the line current drawn by the lamp during
starting thereof to less than the line current drawn by the
lamp during normal operation thereof. The lamp has the
3o usual terminals and a nominal rated operating voltage and
-4-
` ~
~3~S8 1l8,02l `
current. The circuit comprises the following elements:
Input terminals are adapted to be connected to an
AC line voltage source having a predetermined nominal rating
and output terminals are adapted to be connected to the lamp
terminals, with a conventional power factor capacitor of
predetermined rating desirably connected in circuit there-
with.
A current controlling means is included in circuit
intermediate the input terminals and the output terminals,
lO and the current controlling means has a first operating mode ;
ln which a current less than the lamp nominal operatlng
current is passed to the output terminals and through the
lamp as connected thereacross. The current controlling
means also has a second operating mode in which a current
greater than the lamp nominal operating current is passed to ~ -
the output terminals and through the lamp as connected
thereacross. The ratio of the magnltude of the current
passed to the output terminals in the second mode to the
magnitude of current passed to the output terminals in the
first mode ls less than 2
A switch is aperable to switch the current con-
trolling means between the two operating modes thereof
during each half cycle o~ the AC line voltage and the switch
comprises a gate-controlled AC switch together with a ramp ;
capacitor of predetermined ratlng in circuit with the gate
of the AC switch and operable to ef~ect the gating of the
switch when a predetermined voltage slgnal is developed
across the ramp capacitor. ~`
A line voltage sensing means measures the magni-
tude of the AC line voltage and generates a first current
-5-
.
- "
48,021 ~
~;~83~S~
signal, the magnikude o~ which is indicative of the devia-
tion of line voltage from nominal, with the first current
signal feeding into the ramp capacitor durinK each halP
cycle of AC line voltage.
A lamp voltage sensing means measures the voltage
drop across the lamp both during startup when the voltage ~ ;
drop thereacross is relatively small and also during normal
lamp operation and there is generated a second current
signal, the magnitude of which is indicative of the devia-
tion of operating lamp voltage from nominal, with the second
current signal also feeding into the ramp capacitor during
each half cycle of AC line voltage.
Means are provided to discharge the ramp capacitor
to a predetermined potential at a predetermined time in each
half cycle of the AC line voltage and the ramp capacitor is
thereafter charged in the same half cycle, with the time in-
terval, in each half cycle of the AC line voltage which is
required to develop the AC switch gatlng signal being deter-
mined by the cumulative charge delivered to the capacitor by
the first current signal and the second current signal.
During startup of the lamp, the second current
signal which corresponds to lamp voltage has a minimal value
due to the low voltage drop across the lamp and this pro-
vides at most only a slow voltage variation in the charge on
the ramp capacitor which maintains the current controlling
means in the first operating mode for at least a substantial
portion of each half cycle of the AC line voltage. After
the lamp is normally operating with approximately nominal
voltage drop thereacross, the predetermined capacitance of
the ramp capacitor coupled with the cumulative charge de-
--6--
48,021
6S8
livered thereto by the first current signal and the second
current signal coupled with the relatively small ratio of
current passed by the current controlling means in the
second mode to current passed by the current controlling
means in the first mode providing a stable and accurate -
control of wattage drawn by the normally operating lamp.
BRIEF DESCRIPTION OF THE DRAWINGS
For a better understanding of the invention,
reference may be had to the preferred embodiment, exemplary
of the invention, shown in the accompanying drawings, in
which:
Flgure 1 is a connection diagra~m for the present
operatlng ballast circult;
Figure 2 is a simplified diagrammatic sketch of
the preferred variable inductor used as a part of the pre- `
sent apparatus;
Figure 3 is a circuit diagram of a portion of the
control device with integrated circuit chips shown therein
in block form; and
Figure 4 is a detailed circuit diagram for the
integrated circuit chip which completes the control device.
DESCRIPTION OF_THE PREFERRED EMBODIMENTS
With re~erence to the schematic circuit shown in
Figure 1, this comprises an operating circuit 10 for con-
trolling at about a predetermined nominal rated value the
wattage drawn by a high-intensity-discharge lamp means 12
during normal operation thereof and for limiting the line
current drawn by the lamp means during starting thereof to
less than the line current drawn by said lamp means during
normal operation thereof. The lamp 12 has terminals 14 and
:' :
., . ~, ... ..
48 021
~83~S8
a nominal rated operating voltage and current. As a speci-
fic example, the lamp is a high-pressure sodium lamp having
a nominal rating of 250 watts, a nominal rated voltage of
100 volts, and a nominal current of 3.0 amperes. The cir-
cuit 10 comprises input terminals 16 adapted to be connected
to an AC line voltage source 17 having a predetermined
nominal rating such as 240 VAC., and output ter~inals 18 are
adapted to be connected to the lamp terminals. A po~er-
factor capacitor means 20 rated at 330 VAC, 2~.2 ~f deslr-
ably is connected in circuit therewith although the capaci-
tor 20 can be omitted, if desired.
A current controlling means 22~is connected in
circuit intermediate the input terminals 16 and the output
terminals 18, and the current controlling means has a first
operating mode in which a current less than the lamp nominal
operating current is passed to the output terminals and
through the lamp as connected thereacross, and the current
controlling means also has a second operating mode in which
a current greater than the lamp nominal operating current is
passed to the output terminals and through the lamp as
connected thereacross. In accordance with the present
invention, the ratio of the magnitude of current passed to
the output terminals and through the lamp in the second mode
to the magnitude of current passed to the output terminals
and the lamp in the first mode is less than 2:1, for reasons
explained hereinafter. A preferred current control~ing
means is shown in Figure 2 and this constitutes a variable
reactor 22 as described in detail in the aforementioned
Canadian application Serial No. 329,~09, filed June 1
1979. The current control
-8-
j
:, . . . .. .
~ 8 l~8,021
ling means thu~ compris~s a -~riab~e reactor where:~n t~le
connections II and ~I are ~or the .r~aln winding 24~ the
connections ~V and ~ are ~or the contr~l winding 26 3 and the
connections II and lII are for the starting winding 28. As
a specific example, the gaps 30 are each 889 mlcrons and the
gap 32 is 4.064 mm. The connectlon points II-VI are shown
in each of Figures 1, 2 and 3. ~ith the control winding
open, ~or a 240 volt line, the reactor 22 will pass a cur-
rent of 2.6 amperes to the connected lamp and with the
control winding shorted, the reactor will p2SS a current of
4.6 amperes to the connected lamp.
In Figure 3 is shown a circuit diagram of the basic
control unit, with the integrated circults or IC chips shown ::
therein in block ~orm, with numbered pins shown on ~Cl. For
purposes of a description, the circuit will be broken down
into the various functions which are performed3 with each
portion identified by an appropriate letter designation.
POWER SUPPLY - .A
The power supply comprises two half wave diode
rectifiers in order to produce a plus and a minus power
supply. The current islgenerated through R308 and directed
through the diode D3 for the positive power and through the
diode D4 for the negative power supply. C4 and C5 filter
these rectified currents to produce the DC voltages, with
resistors R309 and R311 and Zeners Zl and Z2 providing the
voltage regulation.
: LINE ~OLTAGE SENSI~G - ~ :
R3Q4 and R305 provide a Yoltage div~der and the
divided v~ltage is peaX rectlfied by D2 and ~iltered b~ C3
and ~31q to provide a current which is proportional to line
_g_
.. . . .. ..... . .
4~,021
~836~3
volta~e~ less a re~erence Yoltage? ~hich current ls fed into
the integrated clrcuit chip a~ Pin 1.
LI ~ ~OLT~CT~ Z~ R~SET - C
~30~, R3~2, R32/
Component~a~ ~&~ are an R-C phase
shifting net~ork. This produces a very slight phase shift in
order to provide a voltage which slightly leads the line volt-
age for purposes of reset. Essentially the resistors and cap-
acitors of this circuit portion merely provide a slight RC
phase shift, with the voltage input being applied to the
integrated circuit at pin 4.
BIAS AND REFERENCE CURRENTS - D
The resistor R313 provides both bias ancl reference
currents to the IC chip. The current through R313 also con-
stitutes what amounts to a re~erence current which ls used
for control.
~NER~IY STORAGE FOR ~ATE PULSE
AND HALF CYCLE TIMlNG - E
Pin 5 on the IC chip is charged negatively with
respect to ground to approximately the negative power supply
level. When it is desired to gate the AC switch, Q3019 all of
the energy ~stored in C6 is discharged through pin 6 to the
gate termlnal "g" of triac Q301. This discharge occurs in
~ rP 0 ~ cly
less than ppr~ximatoly 10 mircroseconds. R303 and C2 which
parallel Q301 provide for positlve operation of the triac.
The tlming of the discharge of C6 is accomplished
by C7 which is charged through pin 3 by IC chip current
sources, and ~hen the charge on C7 reaches approximately 7
volts~ the AC switch Q301 is triggered. C7 thus constitutes
the ramp charging capacitor which provides the very large
phase shifts in the triggering of ~he AC switch ~h~ch the
-10- ~,
- . . .. .. . , ,. : . ,
48,021 ,
~336~8
present ballast provides.
LAMP VOLTA~E SENSING - F
The voltage drop across R317 is related to peak
lamp voltage and this is peak-detected through D6-R316 and ~ -~
stored in C10. The voltage is then converted to a current
through R315 and divided through pins 12 and 15. Pin 12 is -';
effective during lamp startup and works through the chip
(ICl) to minimize the time that the AC switch Q301 is on ~; ; -
during lamp warmup, and after the lamp ls normally operating
the current input to pin 15 is primarily effective to con-
trol the operation of the AC switch through the chip ICl. ;
LA~P STARTER - G
The lamp pulse starting means (block G) has an
output or starting winding 28 comprising a few turns of the
main winding 24 to constitute an autotransformer therewith.
As a specific example, the main winding has 400 turns and
the starting winding 28 has forty turns. A starting capaci-
tor means Cll is adapted to charge upon inltial connection
of the operating circuit to the AC source or line and then
to discharge through the starting winding 28 when a prede-
termined voltage level of 180 volts is achieved. The result-
ing autotransformer function generates a high voltage start-
ing pulse such as 1800 volts in the main winding 24 and
across the lamp 12 to initiate the discharge therein. After
the lamp 12 is operating, the starting capacitor Cll is
never charged to the level at which it will discharge,
thereby rendering the starting clrcuit inoperative.
More specifically, when the capacitor voltage
exceeds the Zener voltage o~ Z3, SCR Q302 is trlggered which
causes a high voltage pulse to appear across the lamp because
48,021
~L~83~
of the autotransformer relationship of the main inductor 24,
28 (Figures 1 and 2). This breaks down the discharge path
to start the lamp 12 and once the lamp ls operating, the
lamp voltage drop never exceeds the Zener breakdown voltage
of Z3 so that the lamp starter mechanism is thereafter
essentially removed from the circuit.
AC SWITCH VOLTAGE SENSING - H
This is a voltage divider-resistor arrangement
provided by resistors R306 and R307 whose function ls to
reduce the AC switch voltage sufficiently to ensure that no
damage will occur to the IC chip.
CLOCK MECHANISM - I
R320 and C8 provide the RC timing and the chip ICl
provides clock pulses to the binary counter of the clock
mechanism, shown as a chip IC2. Such a chip is commercially
available from R.C.A. under the designation CD4020AF. Other
similar chips can be substituted therefor. When the binary
counter counts up to 214 pulses, the clock mechanism gen
erates a signal which is fed back into the chip ICl in order
to cause a dimming of the lamp. When llne power ls removed,
such as by a momentary failure, or the opening of the photo-
control switch on a standard luminaire, R314 and C9 act to
reset the counter back to zero so that full power cycle
operation for the lamp is again initiated and continues for
another four hours. This prevents random startup of the
lamp and controls the functioning of the timer. The use of
the binary counter as a lamp dimmer does not form a part of
the present invention and such structures are described in
the aforementioned U. S. Patent 1~,1471962 and UO .~. Patent
No~ 49147,961.
-12-
48~021
~3~i8
For a specific i~entification of each of the cir-
cuit components as shown in Figure 3, reference should be ; ,
made to the ~ollowlng component chart identified as Table I,
TABLE I
Comp. Value % Tbl. pe Mfg. (or e~uiv~
R301 lM 1/2W 5 Carbon Comp. Ohmite
R302 lOOK 1/4W 5 SEB Deposited Carbon
R303 lK lW 5 Carbon Comp. "
R304 240K 1/2W 5 Carbon Comp. "
R305 25K Pot. 1/2W20 375 Cermet ~rimmerC.T.S.
R306 lM 1/2W 5 Carbon Comp. Ohmite
R307 lM 1/4W 5 SBB Deposited Carbon "
R308 56K 2W 5 Carbon Comp. "
R309 2K 1/4W 5 S~B Deposited Carbon "
R310 lOOK 1/4W 5 " " " " `
R311 2K 1/4W 5 " " " "
R312 750 1/4W 5 " " " "
R313 120K 1/4W 5 " " " "
R314 lM 1/4W 5 " " " " ;
R315 750K 1/4W 5 " " " "
R316 lK 1/4W 5 " " " "
R317 1.2K 1/4W 5 " " " "
R318 lK 1/4W 5 " " " "
R319 lOK 8W 5 200 Wire Wound "
R320 IM 1/4W 5 SBB Deposited Carbon "
R321 lM 1/2W ! 5 Carbon Comp. "
Cl .01 MFD 50V MW50 Polyester Paktron
C2 .068 MFD 600V PS Iubular Sangamo
C3 1.0 MFD 35V 196D Solid Iantalum "
C4 10 MFD 15V " "
C5 10 MFD 15V
C6 .047 MFD 5~V MW50 Polyester Paktron
C7 .01 MFD sav
C8 3.3 MFD 15V " " ~7
C9 1.0 MFD 35V
C10 1.0 MFD 35V " " "
Cll 0.15 MFD 40~V PKM TubularCornell Dubilier
C12 470 P~. 500V Ceramic " "
-13- ;`^`
3~3 48~021
TABLE I - Cont'd.
~ Value % Tol. Type l!~g. (or equiv.)
D2 IN457 Texas Instrument
D3 '
D4 " " "
D5 IN469 ~- "
D6 "
D7 IN457 " "
Zl 10 VoltsIN961 " "
Z2 8.2 VoltsIN959
Z3 180 VoltsIN991 " "
Ql Q6010 Teccor -
Q2 C106B "
IC2 CD4020AF R.C.A.
GENERAL IC CHIP DESCRIPTION
The complete circuit diagram for the custom chlp
ICl is shown in Figure 4. All of the resistors which are
numbered in the 200 range are included purely for purposes
of chip interconnections and serve no other circuit f'unc-
tions. Reslstors whlch do serve circult f'unctions are ~;~
numbered from Rl to R34.
BIAS CURRENT SECTION - J
Bias current is in~ected into pin lO through R313
(Flgure 3) and develops a voltage at the base of Q7 whlch
constltutes a blas level for a multiplicity of transistors.
This bias level is one base-emitter ~unction drop (Q8) plus
the voltage drop across R9. This current source essentially
serves all NPN transistors. The current from Q7 is fed to
Q105 and develops the current sources for all PNP transis-
tors.
TIMED PULSE GENERATOR - K
C8 charges through R320 (see Figure 3) untll C8
-14-
!
~ ' '
48~021 ~,
~ 33'~'5;8
reaches the breakdown of Q3, at which point Q2 conducts to
turn on Ql, which regeneratively turns on Q4 and Q103. Thls
discharges C8 (see Figure 3) which pulls R4 toward the level
of the negative power supply. When C8 is discharged to a
level of about 2 volts, Q4 and Q103 regeneratively turn off.
During the time C8 is being discharged, Q1 and Q4 are turned
on and Ql produces a low signal at pin 13 which provides the
clock input pulse. When Ql and Q4 turn off, Q101 pulls the
pin 13 toward the positive power supply. The pulses are
then timed by R320 and C8 to about 2 seconds. Thus the
function of the timed pulse generator essentially relates to
energlzing the clock circuit, which need not be used and
need not be included in the circuit if lamp dimming is not
to be provided.
TRIAC TRIGGERING - L
The energy storage capacitor (C6 in Figure 33 is
tied to pin 5 and this is at the negative voltage level as
previously described. Pin 6 is tied to the gate of the
triac Q301 and when a trigger condition occurs, current is
pulled through Q31 to the bases of QllO and Q22, causing
QllO, Q22, Q23, and Q24 to regeneratively turn on. This
produces a very low impedance between pin 6 and pin 5 and
discharges C6 to the control terminal or gate of triac Q301
(Figure 3). Q27 which is tied to pin 5 is used to charge C6
from the negative power supply.
GATE DRIVE INHIBIT CIRCUIT - M
It is desirable to withhold any gate drive until
the AC switch is in a nonconducting state and this circuit
achieves that function. The voltage at pin 9 is provided by
the voltage divider R306, R307 as previously descrlbed.
-15-
~ ,
, , ~
~ ~836~8 l~8~021
When the ~urrent from the voltage divider R306 R307 is
negative and in excess of approximately 14 volts, current
flows through Q13 and Q25 in the reverse direction and
through Q26, and by virtue of the base-emltter matching,
Q112 carries a current equal to Q113 which flows into the
base of Q34, provided a gate pulse is required at that point
in time If a gate drive is not required, Q20 is turned on
and this sorts out any signals. To trigger the AC switch,
the current through Q34 is mirrored by virtue of the base-
emitter ~unctions in order to provide a signal to turn onthe triac trigger which shorts pin 6 to pin 5 to discharge
the capacitor C6 into the triac gate terminal to trigger
same. When the AC switch voltage is positive and in excess
of about 14 volts, current ~lows through Q26 ln the reverse
direction and then through Q5, then through Qlll into Q34
and the operation thereafter is as previously descrlbed
RAMP TIMING P~IASE CONTROL
FOR TRIAC TRIGGER - N
Pin 11 is at ground potential and the tlming or
ramp capacitor means C7 (Figure 3) is tled from pin 11 to
pin 3. Numerous internal current sources, as will be des-
cribed hereinafter, are tied to pin 3 to control the charg-
ing rate of the ramp capacitor C7. Q108 is a constant
current source as is Q15 with the current provided by Q15
being twice that provided by Q108. Whenever the voltage
; charge on Q7 is less than the Zener voltage drop of Q17, the
current from Q15 flows through Q18 and to ground. When the
capacitor voltage C7 equals or exceeds the Zener voltage of
Q17, the current from Q15 flows through Q17 and Q]6 to the
emitter resistor R20 tled to Q108. Under these conditions,
-16-
~ 48,021 ~
~8~i51~ -
Q108 is non-conducting. With Q108 non-conducting, Q20
receives no base drive and is non-conducting and this per-
mits the drive from the AC switch voltage to trigger the
triac at a predetermined time. When the voltage at capaci-
tor C7 is less than the Zener breakdown of Q17, however,
Q108 is conducting and this turns on Q20 which shunts the
current signal ~rom the AC switch to ground, thereby pre-
venting triggering of the triac Q301 (Figure 3). `
LINE VOLTAGE ZERO RESET - O
The input signal to pin 4 is obtained from the RC
network previously described under Figure 3 entitled "Line
Voltage Zero Reset". When thls voltage l~s in excess of
approximately 60-70 volts, current will flow through Q6 ln
reverse direction and through Q5 into the base of Q10. Q10
is thus turned on which shorts the bias current flow nor-
mally flowing into Q29 to ground, which turns Q29 of~. In
the negative direction, when the line voltage exceeds minus
60-70 volts, current flow is from ground through Q106 through
Q5 in the reverse direction and through Q6 to pin 4. Thls
causes Q106 to be turned on, again shorting the base drive
to Q29 to turn same off. Whenever the line voltage i9
within the limits o~ plus or minus 60-70 volts, no current
flow occurs in pin 4 which means that both Qlo and Q106 are
in a non-conducting state and this permits the bias current
of Q116 to flow into the base of Q29 causing it to be in a
low impedance state and this resets the capacitor C7 tied to
pin 3 to ground level.
LINE VOLTAGE SENSING - P
The voltage at the negative terminal of C3 (Figure
; 30 3) is proportional to the line voltage and the voltage
~ -17-
,~ :
~ 836~8 118,021
across R310 (Figure 3) ls equal to khe voltage across C3
mlnus the Zener voltage drop of Q12. Therefore, the current
through R310 flowlng into pln 1 is proportlonal to the line
voltage less a reference. Thls current then flows through
Qll and into pin 3, which causes the capacitor C7 to charge
at a slower rate wlth lncreaslng line voltage and at a
higher rate with decreasing line voltage.
LOW LAMP VOLTAGE (STARTING CONDITION) - Q
When the voltage at the negatlve terminal of C10
(Figure 3), whlch is proportional to lamp voltage, is less
than approximately 14 volts, all o~ the currenk flow through
R315, which is proportional to ~he volta~e across C10, flows
into pin 12. This current ~lows through Q28 into Q114 which
is mlrrored by the base-emltter ~unction matching to current
flow Q115 lnto pin 3. This in turn causes the capacitor C7
to charge at a higher rate as the lamp voltage increases.
As a result, during lamp warmup, when the lamp voltage ls
very low, C7 charges at a very slow rate thereby triggering
the triac Q301 (Flgure 3) at a much later tlme ln each half
cycle which minimlzes lamp current durlng warmup. The
overall effect is to limit the line current drawn by the
lamp during the starting thereof to less than the line
current drawn by the lamp during normal operation thereof
and this is desirable from an installation and lamp perfor-
mance standpoint.
HIGH LAMP VOLTAGE SENSING - R
.
After the lamp is normally operating, when the
voltage at the negative terminal of C10 (Flgure 3) exceeds
about 14 volts, any further increased current flows through
R315 (Figure 3) into pin 15 and the current flowing into pin
-18-
1~8,,021 '
1~3~S~3 ~
15 is proportional to the lamp voltage minus the reference
voltage of Q14 which is acting as a Zener reference. This
current ls conducted through Q13 to the emitter Or Q107 and
this subtracts from the normal emitter current of Q107 with ~`
the following result: As pin 15 current increases, the
current through Q107 flowing into capacitor C7 (Flgure 3)
through pin 15 causes C7 to charge at a slower rate, whlch ~
of course has the effect of decreasing the average current -
drawn by the operating lamp. ~.
Summarizing the foregoing operation, the rarnp
capacitor means, C7, is in circuit with the gate of the AC
switch means (Q301) and is operable to effect gating of the
swltch means when a predetermined voltage signal is devel-
oped across the ramp capacitor. The line voltage is sensed
and there is generated a first current slgnal, the magnitude
of which is indicative of the deviation of line voltage from
nominal, with the first current signal feeding into the ramp
capacitor during each half cycle of the AC line voltage. A
lamp voltage sensing means measures the voltage drop across
the lamp~ both during lamp startup when the voltage drop
thereacross is relatively small and also during normal lamp
operation, and there is generated a second current signal, -
the magnitude of which is indicative of the deviation of
operating lamp voltage from nominal, and the second current
signal also feeds into the ramp capacitor C7 during each
half cycle of the AC line voltage.
As described hereinbefore, the line voltage zero
reset portion of the circuit resets the ramp capacitor C7 to
a predetermined potential at a predetermined time in each
half cycle o~ the AC line voltage, and the ramp capacitor is
-19-
~3~58 48,021
thereafter charged in the same half cycle, with the time
interval in each half cycle in the AC line voltage which is
required to develop an AC switch gating signal being deter-
mined by the cumulative charge delivered to the ramp capaci-
tor C7 by the first current signal which ls indicative of
line voltage and the second current signal which is indica-
tive of lamp voltage. Of course, during startup of the
lamp, the second current signal which is indicative of lamp ~:
voltage has only a minimum value due to the low voltage drop
across the lamp, which provides at most only a 810w voltage
variation in the charge on the ramp capacitor which main-
tains the triac Q301 open and which in turns maintains the
inductor 22 ln the first or high reactance mode for at least
the substantial portion of each hal~ cycle of the AC line
voltage. After the lamp is normally operating with approxi-
mately nominal voltage drop thereacross, however, the prede~
termined capacitance of the ramp capacitor C7 coupled with
the cumulative charge delivered thereto by the first current
signal and the second current slgnal, indicative of line
voltage and lamp voltage, coupled with a relatively small
ratio of current passed by the variable inductor in its two
operating modes provides for a stable and accurate control
of wattage drawn by the normally operating lamp, wlth the
current inputs to the ramp capacitor providing a very
sensitive and accurate control which can be varied over a
substantial portion of each half cycle of energizing poten- .
tial.
Remaining sections of the chip ICl~ which is ~:
custom designed, deal with lamp dimming such as might be
used by stage lighting and form no part of the present
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r
,. . . ..
~ I '. . . ` ., ' , ~ "
~836~8 48,021
invention. This will be briefly described hereinafter,
however, so that the description will be complete.
LAMP DIMMING CIRCUIT WHICH FORMS
NO PART OF PRESENT INVENTION - S
The squaring circuit (S) operates as ~ollows: With
a positive current flow into pln 1, Q118 conducts into Q41
and Q42 and Q41, Q42, Q43 and Q47 constitute a logarlthmic
multlpllcation circuit wherein Q47 is the constant current
source. Q43 therefore produces a current which is propor-
tional to the input current squared divided by a constantcurrent. The resultlng network, that ls, that the resistor-
transistor Q44, Ql16, Q45 network is to produce a constant
current ln Q47. The current through Q43 iB then conducted
through Q40 and ls ~iltered by a capacitor (not shown) tied
to pin 2 and the resistor 30. A current through Q40 then
flows directly into the timing capacitor C7 which of course
controls the triac Q301 and thus the dimming of the lamp.
SQUARE ROOTING CIRCUIT - T
- :
This also ls a part of the dlmming circuit and
20 when positive current flows lnto pin 12, lt ls conducted ;
through Q117 and Q36 by the mirror clrcult of Q48 and Q39 to
circult ground. Thus the current through Q36 is proportional
to the current enterlng pin 12. The current through Q35 i9
a constant current produced by Q102. Q35, Q36, Q37, and Q38
~orm a logarithmic multiplier with the feature that the
current through Q37 is equal to current through Q38, which
i~ equal to the square root of the current through Q36 times
the constant current in Q35. Thus the output current is
proportional to the square root o~ the input current. The ;~
current through Q37 flows into Q114 and is mirrored into
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~.
. . .
~ 3~S~ 48,021.
Q115 to pin 3 to charge the capacitor C7. In the foregoing
circuit, the lamp voltage is squared to develop a signal in
order to charge the timing capacitor to phase control the
lamp. Squaring the lamp voltage to develop a signal pro-
vides a better control of the lamp brightness. In the
square rooting circuit, the functional effect is to provide
what essentially is a linear relationship between control
voltage and light output. Thus the present dimming circuit
enables two types o~ control to be achieved, namely, a
linear light relationship which is valuable for use with
cameras and an apparent light relationship which can be used
in stage llghting for human response.
GENERAL DESIGN CONSIDERATIONS
As a general comment, lt is desirable to minimize
the size of the lamp ballast inductor from an expense stand-
point and to provide an inductor with as little voltage drop ~`
across it as possible, commensurate with reasonable regula-
tion. With a large change in inductance in the inductor,
lamp starting currents tend to be excessive and to minimize
lamp starting currents, it is highly desirable to limit the
change~ in inductance to a relatively small ratio, i.e.,
less than 2:1. This in turn requires a very large phase
shift control, especially where high pressure sodium lamps
are involved, to adequately control the power into the lamp
throughout its life where increases in lamp voltages with
life can normally be anticipated. The present circuit
achieves these obJectives.
To complete the description of the custom chip
ICl, shown in Flgure 4, precise values for all components
3 thereof are set forth in the following Table II.
-- . . , . . , ............... .. , ....................... :
, .; ~ : ,
~8365~ 48j021 ~
TABLE II
Component Value
Rl 3.15K
R2 450
R3 2.7K
R4 1035K
R5 3.6K
R6 450 Q ;~
R7 3.6K
R8 gooilL ~;
R9 1.8K
R10 450JQ
Rll 3.6K
R13 3.6K `i
R14 3.6K
R15 1.3K
R16 3.6K
R17 1.8K
R18 4.95K
Rl9 3.6K
R20 4~05K
R21 450 Q
R22 7.9K
R23 1.8K
R24 6.75K ;
R25 10.4K
R26 , 900f~
R27 3.6K
R28 3.15K
3 R29 1.35K
R30 3OK (Pinch)
R31 13OK ~Pinch)
R32 130K (Pinch)
R33 30K (Pinch)
R34 1.35K
C200 (connection resistors)
R201 1.35K
R202 1.8K
R203 ~OO~L
23-
j
: ; , . ;
., : : . ~ .,: . . . -, . . .
~8365~ 48,021
TA~L~ Cont'd.
Componenk ~lue
R204 ' 3.6
R205 900
R206 450 n
R207 200 n
~208 400n ~`,
R20~ 2.7K ,~j
R210 1.8K
R211 1.35K
R212 200Q .;~:
R213 200Q '
R214 1.35K
R215 3.6K :
R216 4soQ
R217 5.4K
R218 1.8K ; : ~:
R219 400
R220 3.6K
R221 700n :-
R(C and 201-221) resistors are included
in chip to facilitate fabrication and not for
circuit operation.
Schottky diodes are rated at 100 micro :. -
amps forward current, 20V blocking.
All transistors rated at 20V collector-
emitter breakdown.
Large NPN (Q5, Q24) rated at 200 ma; other
NPN ~1-50 series) rated at 20 ma; PNP (100 series)
rated at 2 ma. ! : :
,~
~ ' '
' ' '
' ,' ,:;
~`"'
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! :
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