Note: Descriptions are shown in the official language in which they were submitted.
SELF-REGULATING, NO LOAD PROTECTED
ELECTRONIC BALLAST SYSTEM
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
This invention is directed to an electronic ballast
system for fluorescent or gas discharge tubes. In
particular, this invention relates to automatic gain
controlled ballast systems for fluorescent tubes.
This invention limits the output voltage of the electronic
ballast system and substantially reduces such when
the gas discharge tube or fluorescent tube is electrically
removed from the overall circuit. More in particular,
this invention pertains to a no load protection transformer
being series coupled to an induction circuit for preventing
the generation of voltages above a predetermined value
when the gas discharge or fluorescent tube is electri-
cally removed from the circuit. More in particular,
this invention relates to an electronic ballast system
'' ~
.~ .
:,'
- ' - '
-
:. ' :
.
9~)~3()
--2--
where a primary winding of a no load protection trans-
former forms a variable inductance which is inversely
proportional to the magnitude of power delivered to
the gas discharge or fluorescent tube.
; ~
. .
. ~ ~
,. : . .
~' . .` . ' : . . ~. '
~: :
,, ~ . ' .
.
. .. .
.
. ~
9~
--3--
PRIOR ART
Electronic ballast systems for gas discharge or
fluorescent tubes are known in the art. However, in
some prior art electronic ballast systems, removal
of the gas discharge or fluorescent tubè from the ballast
circuit causes excessive voltage outputs to the gas
discharge or fluorescent tubes. This condition can
have a deleterious effect to the operating life of
the particular tube or set of tubes utilized in a parti-
cular ballast system.
. ``'` `' ~`~ ,
'' '-
- - ' ,
: ' ~' ' `' ` '
. ~ ` .
: -
1~790'~)
.~,
SUMMARY OF THE INVENTION
A self-regulating, no load protected electronic
ballast system having a power source for actuating
at least one gas discharge tube with a regulated current
and limited voltage to maintain the gas discharge tube
input and output power at predetermined values. The
electronic ballast system includes a filter circuit
connected to the power source for ~1) maintaining a
substantially smooth direct current voltage signal,
and (2) suppressing harmonic frequencies generated
by the electronic ballast system. Additionally, the
self-regulating, no load protected electronic ballast
system includes induction circuitry coupled to the
filter circuit having a tapped primary winding providing
an auto-transformer configuration for establishing
the fre~uency of the regulated current.
BRIEF DESCRIPTION OF THE DRAWINGS
The Figure is an electrical schematic diagram
of the self-regulating, no load protected electronic
~ ballast system.
.` ' .
::`
~ .
.
,
.
`
-:
. ... , :
.
.. . .
.... - -
'
~ ' ~
1;~79~)'~3()
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the Figure, there is shown self-regu-
lating, no load protected electronic ballast system
10 having power source 12 for actuation of at least
one gas discharge tube 66. Gas discharge tube 66 may
be a standard fluorescent type system having first
and second filaments 68 and 70, respectively. Self-regu-
lating, no load protected electronic ballast system
10 is provided to maintain the output and input power
of gas discharge tube 66 at a substantially predetermin~d
value which is relatively constant during operation
and substantially constant and independent of electrical
component tolerances from one electror.ic ballast system
10 to another. -
- In overall concept, self-regulating, no load protected
electronic ballast system 10 is provided for maximization
of efficiency of light output from gas dir,charge tube
66 with respect to a power input from power source
- - . .
- 12. Additionally, self-regulating, no load protected
electronic ballast system 10 provides for a substantially
.
,: :...... , . . - :
., :: ~ . ' - -.-. -, . - ' -
: ~ :.' . , : --. , , -
. - . ~ . : . . .
: . ~ ': :' ' : .' : :: ~ .
: . -: :- : - - .-: . . .
.- : - . : . .: .
: ~ ~ ",. - - ' '' , '' - :
:
,-
: - - .
~ . ..
9()'~)
constant light output in the order of approximately
+ 3.0%, regardless of the voltage variation by virtue
of the output of gas discharge tube 66 being responsive
to a square wave form of pulsating driving current
as opposed to a square wave form of pulsating input
voltage.
As will be seen in following paragraphs, output
voltage of electronic ballast system 10 is limited
and substantially reduced when gas discharge tube 66
is electrically removed from the circuit.
Of importance, electronic ballast system 10 provides
initially for a regulation control which eliminates
the need for adjusting or pre-selecting transistors
of specific gain, in order to provide a relatively
constant light output substantially independent of
manufacturing tolerances associated with the manufacture
of contained electronic components.
.. ~ , .
.
. , ~ . - .
. . : . .
, .. ': -, - ~
~. . .
-. ; ~ .
. .
' ~'. '. .. ~ :
.
1.;~'79~)~3()
-7
The output voltage is reduced below its normal
operating voltage when the gas discharge tube 66 is
electrically removed from the circuit, either by its
failure or by its physical removal from the system.
Additionally, self-regulating, no load protected
electronic ballast system 10 provides for a frequency
control mechanism using the inductive characteristics
of inverter transformer 40 and the tank circuit formed
by the secondary winding 160 of transformer 100 and
capacitor 130 allowing for frequency stabilization
and having the advantage of permitting electronic ballast
system 10 to operate in a normal manner without bothersome
visual flickering.
- Particularly, operation of gas discharge tube
66 is maintained at a minimum level due to the higher
efficiency obtained by self-regulating, no load protected
electronic ballast system 10. Of importance to the
reliability of system 10 is the minimization of electri-
. -
.
~' ' .' ~ ' - :
- .
- :
: '
1;~7~()<3()
--8--
reliability of system 10 is the minimization of electri-
cal components coupled with the simplicity of the circuitry
associated with ballast system 10. ~his concatenation
of elements has the effect of increasing reliability
of self-regulating, no load protected electronic ballast
system 10 while simultaneously maximizing the operating
lifetime of gas discharge tube 66.
Referring now to the Figure of electronic ballast
system 10, having a power source 12 for actuating gas
discharge tube 66, such includes filter circuit 11
coupled to power source 12 for establishing a substan-
tially direct current voltage signal and suppressing
harmonic frequencies generated by electronic ballast
.. system 10.
In still further overall concept, self-regulating,
no load protected electronic ballast system 10 include~
. induction circuitry 15 which is electrically coupled
- to filter circuit 11 for establishing the magnitude
of a pulsating driving current established by switching
network 13. As will be detailed in following paragraphs,
. '~ .
, ; '' : '
. , - . :
' :. . . : - . - ' .' : ' . :
.
' . ~. ` --, ' ' ':
:.
1;~7~ 30
_9_
induction circuitry 15 includes no load protection
circuit 99 for generating a voltage across gas discharge
tube 66 responsive to the pulsating driving current,
and for maintaininy the output voltage at a predetermined
value when gas discharge tube 66 is not electrically
connected to ballast system 10. Induction circuit , '
15 is coupled to regulation control circuit 17 for
maintaining a gain value of switching network 13 to
a predetermined level. Thus, filter circuit 11 is
connected to power source 12 for (1) maintaining a
substantially smooth direct current voltage signal;
and, (2) suppressing harmonic frequencies generated
~y electronic ballast system 10.
Induction circuitry 15 also includes base drive
winding 48 for generating a switching slgnal. Switching
network 13 generates a pulsating driving current respon-
sive to the switching signals generated in base driving
winding 48.
As will be further described, no load protection
circuit 99 is coupled to filter circuit 11 and includes
:
-; :
, ~
.. , .. , ~ , . . . .
: - : : -
- ~ .
,. :
' ' ,. ' ' - ' . ' ,' .
- ' '' , , ` - ,,,` . ~ . " :: :
- -' : .
',
'. ~
: -
73()~'30
--10--
a tuned high voltage output secondary winding 160 for
generating across gas discharge tube 66 responsive
to the regulated driving current.
~ eferring further to the Figure, there is shown
power source 12 to provide an electrical power input
for self-regulating, no load protected electronic ballast
system 10. In the embodiment shown in the Figure,
power source 12 may be an AC power source of standard
voltage such as 120, 240, 270 volts, or any acceptable
standardized power voltage generated at approximately
50.0 or 60.0 Hz. In broad general concept, power source
12 may be a DC power electrical source applied internal
or external to self-regulating, no load protected electronic
ballast system 10 in a manner well-known in the art
by removal of some elemental circuitry and filtering
elements.
For the purposes of illustration, power source
12 will be in the-following paragraphs designated as
a 210-240 volt, 50.0 Hz., AC power source, and will
be used in the embodiment to be described.
~ ~, ,. ,,,, - -
.. . .
~ ' - . ,- ' ,
- ~,
~ . .
t~ 3(`)
Power for system 10 is supplied by power source
12 to switch 14 which may be a standard switch element
such as a single pole, single throw switch mechanism.
Power is applied from switch element 14 to choke 32
and harmonic filter capacitor 28. Harmonic filter
capacitor 28 is coupled in parallel relationship with
power source 12 and is designed to shunt high frequency
components which would be fed back from electronic
ballast system 10 to the power source 12. Choke element
32 is coupled in series relation with power source
12 and rectification circuit 16, which is used for
providing full-wave rectification of the power source
AC voltage.
Rectification circuit 16 may be a fuli-wave bridye
circuit well-known and standard in the art. In the
embodiment illustrated, full wave bridge circuit 16
is formed of diode elements 18, 20, 22, and 24 for
providing the necessary rectification of AC voltage~
from power source 12. Diode elements 18, 20, 22 and
24 may be one of a number of standard diode elements,
"
'
. .
.
' :
:
~" ` '
9()'~(~
-12-
and in one form o self-regulating, no load protected
electronic ballast system~10, diode elements 18, 20,
22 and 24 have a standardized designation of lN4005.
Rectification by full wave bridge circuit 16 provides
a pulsating DG voltage signal passing on output line
26 which is applied to shunt capacitor 34 of filter
network 11. Filter network 11 filters the voltages
input and output from rectification circuit 16, and
is electrically connected to bridge circuit 16 by input
line 19 and output line 26. Rectification bridge circuit
16 is coupled to return line 64 which is the return
path for the DC supply for the opposing ends of bridge
circuit 16, providing DC power input to shunt capacitor
34 of filter network 11.
. The smoothing filter portion of filter network
- . 11 includes choke element 32 and shunt capacitor 34.
Choke element 32 is coupled on a first end to power
source 12 and on a second end to rectification circuit
16 through input line 19. As is seen, shunt capacitor
34 is coupled in parallel relation with the output
~' `
.
-: .
,
~' ~' ' `
,~'` `' `.:' "
- :
:
~ , --
1;~79()'~3()
-13-
of rectification circuit 16 through output line 26.Shunt capacitor 34 is connected on a first end to recti-
fication circuit 16 output line 26 and coupled on opposing
end to DC return line 64.
In combination, shunt capacitor 34 and-choke element
~2 function to average out the 100 Hz pulsating DC
voltage supplied by full wave bridge circuit 16. Addi-
tionally, this combination substantially maintains
the current draw at an average value without creating
a power factor which is either unacceptzbly leading,
or unacceptably lagging. Deleterious lead or lag may
be found wherein a large capacitance is used, or a
~ - large inductance, as the sole filtering means for smooth-
- ing a pulsating DC voltage.
For purposes of illustration, in the event choke
element 32 were not incorporated within self-règulating,
no load protected electronic ballast system 10, shunt
capacitor 34 would draw an increase current commonly
referred to as a surge current on each cycle as capacitor
~- 34 began to charge. By incorporatio~ of choke element
:'~.
.
,
,
' ~:
~: : -
:~ '
. ,~ . . .
: ::
30~)
-1~
32, the inductance stores energy during each half-cycle
to supply current for ini~ial charging of shunt capacitor
34 which provides a substantially smooth, average current
as seen by power source 12.
In the embodiment herein provided, choke element
32 may be an inductor approximately 2.0 Henries, with
a resistance of less than 40.0 Ohms, and shunt capacitor
34 is a commonly available 100.0 microfarad, ~50.0
volt electrolytic capacitor.
Filter network 11 includes harmonic filter capacitor
28 which in combination with choke element 32 substantially
reduces harmonic frequencies generated by induction
circuit 15. The tuning of harmonic filter capacitor
28 in combination with choke element 32 has been design~d
to provide significant reductlon in amplitude of at
least the first five harmonic frequencies coupled from
the DC supply of oallast system 10. As is typical --
. . . - : ,
in filters of this nature, harmonic frequencies which
are multiples of these first five harmonic frequencies
are also reduced.
.
,
,
':
1;~790~0
-15-
In the embodiment herein provided~ harmonic filtercapacitor 28 is approximately a 1.5 microfarad, 400.0
volt Mylar type capacitor, which is coupled in parallel
relation with power source 12 and bridge circuit 16
through choke element 32.
No load protection circuitry 99 is coupled between
filter network 11 and induction circuit 15. No load
protection circuit 99 includes transformer 100, with
primary winding 125 and tuned high voltage output secondary
winding 160 as well as a pair of filament excitation
windings 140 and 150. Tuned, high voltage output secon-
dary winding 160 is coupled in parallel relation with
tuning capacitor 130 to form a tank circuit for generating
the output voltage to gas discharge tube 66. Filament
excitation windings 150 and 140 are coupled to gas
discharge tube 66 filàments 70 and 68, reQpectively.
. In the embodiment herein provided, no load pro-
tection circuit 99 is comprised of transformer 100
with the core material being a ferrite composition
having the designation of Ferroxcube 2616 with primary
winding 125 composed of 29 turns, and tuned high voltage
~ trc-de~o~rl~
. ~....:
:'~ ,: ~, ` - . :
:: `: .: . '
,. ' ., : , '~ ' ' ': ' '
: : . .: . . . - .
.: ~ -: .. . .
, -- ~ .
:~ ~ : . : . .: -
,::, . - -
,. , : , ..
.~ : . .: . -
3()~
-16-
output secondary winding having 50 turns and each of
filament excitation windi~gs 140 and 150 being composed
of a single turn each. Transformer 100 has a linear
magnetic core and does not saturate. Tuning capacitor
130 is a ten nanofarad capacitor.
Self-regulation control circuit 17 is coupled
between no load protection circuit 99 and inverter
network 15. Self-regulstion control circuit 17 includes
first capacitor 54, toroid transformer 56, and shunt
resistor 51. Shunt resistor 51 is coupled in parallel
relation with first winding 55 of toroid transformer
56. First winding 55 of toroid transformer 56 besides
being parallel coupled to shunt resistor 51 is coupled
on a first end to return line 64 and on a second end
to base coupling capacitor 54. Base coupling capacitor
54 is coupled on one end to first winding 55 of toroid
.
transformer 56 and on the opposing end to base drive
winding 48 of induction circuit 15.
Although not important to the inventive concept
as he~rein described, shunt resistor 51 may have a value
.~ :
:. ' .
.
.
- - : - -
.: ~
-~ . . ~ - . . : .
-
' '- ' '-' -- - '- ' ~ - :
-
..
1~79()~0
-17-
of approximately 200 Ohms. Toroid transformer 56 may
have a ferrite core materlal composition which is a
Ferroxcube designated 3B7-266T1~5, or 3B7-266CT125,
with first winding 55 having 12 turns of number 2~
wire, and a second winding 57 of a single turn rormed
by DC power input or filter output line 36 passing
through the axis of the toroid core. Base coupling
capacitor 54 may be a 0.22 microfarad, 100 volt Mylar
type capacitor.
The series combination of first winding 55 of
toroid transformer 56, and base coupling capacitor
54 provides for return paths for the base drive signal
of switching network 13 subsequent to self-regulating,
no load protected electronic ballast system 10 going
into an oscillation phase.
Self-regulating, no load protected electronic
ballast system 10 further includes switching network
- . - -
13 which is feedback coupled to induction circuitry
.. . , ~ .
`~ 15 for estabiishment of a pulsated current. As will
- be seen in following paragraphs, switching network
13 includes a regulation mechanism for maintaining
- . - - ..
, .. . .
::,
.
: ~ .
,:: , .
,
.. : : .
- :' ~- :
.
-
~i ,
~;~'79()'~30
-18-
the power output of gas discharge tube 66 at a pre-
determined and subsequently constant value.
Switching network 13 includes transistor 72 connected
in feedback relation to bias or trigger control winding
48 of inverter transformer 40. This coupling allows
switching of a current signal responsive to a bais
signal produced. Referring to bias control winding
48 of inverter transformer 40, current entering the
first end of bias control winding 48 passes through
winding 48 to base element 78 of transistor 72. Tran-
sistor 72 includes respectively base element 78, collector
element 74, and emitter element 76.
It is to be understood that self-regulating, no
load protected electronic ballast system 10 is designed
to provide a consistency in visual light output, as
well as power input to gas discharge tube 66 by main-
taining the current of collector element 74 substantially
constant independent of the current gain of a particular
: . .
. ' ' ' - .
.. . . .
1;~7~t()'3(~
--19--
transistor 72 used in electronic ballast system 10.
It has been determined that the light output should
not fluctuate more than + 3.0% while the current gain
of transistor 72 used in system 10 may vary in the
extreme between 10 and 60. It is to be further under-
stood that although system 10 as shown in the illus-
trated embodiment operates a single gas discharge tube
66, the principle as herein described is general in
concept and may be used in dual systems, since in such
cases, transistor current gains would not necessarily
have to be matched by pairs.
Initially, a positive voltage provided~to base
element 78 by resistcr 53 assures a small but sufficiently
initiating current flow through base element 78 for
. . . .
initiation of conduction through transistor 72. A
value of 1.0 megohms has been used successfully for
resistor 53.
:~: When transistor 72 goès intc a conductinq or "on"
state, current from power source 12 flows through choke
32, bridge circuit 16 and primary winding 125 of trans-
, former 100 to ~C output line 36. DC output line 36
;.~ . :
.
- - .
.
~ - ~
~;~'7'3()'3()
,, j ,
is coupled to primary winding 42 of inverter transformer
40 and passes through the axis of the core of toroidal
transformer 56. Such current passes through first
section 46 of primary winding 42 to tap line 25 which
is coupled to collector el ment 74 of switching transis-
tor 72.
Current flows through transistor 72 from collector
74 to emitter 76 and then from emitter element 76 through
return line 64. The increase in collector current
established by switching transistor 72 induces a voltage
in bias control winding 48 which is coupled to base
element 78 of transistor 72. Base current flows from
base element 78 to emitter element 76 in transistor
72 and from emitter element 78 to return line 64.
In completion of the circuit, the current flows
through first winding 55 of toroid transformer 56, -
and base coupling capacitor 54. The series combination
of elements as aforementioned, creates a pulse type
base drive for switching transistor 72 from an non~
state to an "off" state after a predetermined period
. .
.
`
.~' ~' ' ` ' .
,
.. .
-
- '
;'9()'3(~
-21-
of time.
The pulse which drives switching transistor 72
controls the duration of the "on" time during the fre-
quency of operation of self-regulating, no load protected
electronic ballast system 10. At the terminating point
of this pulse, transistor 72 goes to an "off" state
and the pulse differentiation through capacitor 54
supplies a negative signal to base element 78 which
is limited in value magnitude by diode 38. The energy
stored in inverter transformer 4Q is discharged from
primary winding 42 to capacitor 62 and therethrough
to return line 64.
Concurrently, as the collector current passes
through the primary winding 125'of`transformer 100,
a voltage is induced in each of transformer 100 secondary
- . - -- .
, windings. The voltage induced in filament excitation
,
windings 140 and,,150 causes a current flow through
filaments 68~ànd 70 respectively of gas discharge tube
; . ' 66.
The voltage induced in tuned high voltage output
secondary winaing 160 i coupled across tuning capacitor
~:
. ., ~ . ,
,"~ .
.
:, : - ' -
.- -
' ~ '
-~' "~, ~ " ' ' '
.~, ~ ' - ' ' ' '
1;~7~ 30
-22--
130 and gas discharge .ube 66. The voltage induced
at this point in the cycl~ is sufficient to maintain
the discharge within gas discharge tube 66 but not
sufficient to initiate the discharge itself.
Reiterating, transistor 72 is initially switched
to an "on~ state by the small current flowing from
output line 36, through resistor 53, base drive winding
48 to base 78 of transistor 72. This provides a current
flow from output line 36 through first section 46 of
primary winding 42, line 25, collector 74, emitter
76 and then to return line 64.
Due to the aforementioned, the magnetic field
in the ferrite magnetic core of transformer 40 increases
from substantially zero to a predetermined value of
magnetic induction, B, on the hysteresis cycle in a
manner such that the circuit operates in a linear region
~ . - .
- - ~ of the characteristic. The change in the magnetic
` ~ field induces a voltage in the windings surrounding
the magnetic core of transformer 40 proportional to
the number of turns of a particular winding. The windings
-
~ .
,.'~. `' ` . ~: . ,
: , . . .
: . . , -
~ ~-
1;~79()'3(~
-23-
are coupled in a manner to enhance the positive voltage
applied to the base 78 which increases the current
flow in the loop comprising collector 74, emitter 76
and alI elements in series coupling therewith, until
the current reaches a maximum value determinea by the
impedance of first section 46 and the voltage'level
on line 36.
When the current in the path of collector 74 and
emitter 76 ceases to increase, the magnetic induction
having reached the predetermined value B abruptly collapses
and induces a voltage of opposite polarity in base
drive winding 48, which terminates the flow through
collector 74 and emitter 76.
At this time, the induced voltages are large and
classically are equal to the inductance sum multiplied
by the differential of the current flowing with respect
to time. The inductance sum is the sum of the inductances
of transformer primary winding 125, first section 46,
primary winding second section ~4 and twice the mutual
inductance between sections 46 and 44 which results
~ "
'~
~ .~ - - .' -
~ ~ '
~ , ~
'3()
--24-
in a frequency of discharge equal to one over 2 times
the square root of the sum of the inductances multiplied
by the capacitance of capacitor 62.
he discharge current assumes a sinusoidal shape
dependent on the inverse of the frequency of discharge
which is the "off" time and is the time taken to discharge
the energy stored during the "on" time, namely one-half
the inductance sum multiplied by the current squared.
Once again, an abrupt fall in the magnetic induction
is provided with the direction of the current opposite
in direction to that portion of the sine wave. The
substantially instantaneous voltages and currents are
large enough to induce the starting voltages either
positive or negative in winding 160.
The magnitude of the voltage across winding 160
of transformer 100 is equal to the mutual inductance
between primary winding 125 and winding 160 multiplied
by the current flow through the winding 125 and 2
times the discharge frequency.
It is to be understood that the electromotive
forces across windings 125 and 160 of transformer 100
.
.
. .
- .
.
: ' ,. . , - ,
,: ~ ~ , . . . -.
-
~ ' : - . - ,
1;~79090
-25-
. are opposite in phase and current flowing in windings140, 150 as well as 160 a~e such that it opposes changes
in magnetic flux in primary winding 125. This has
the effect of reducing the impedance of primary winding
125 and allows a larger current to flow in the loop
inducing such. Thus.when a current flows in any secondary
winding, the current in primary winding 125 increases.
When discharge tube 66 is removed from the circuit,
there is no current flow in windings 140, 150 or 160
:
and the impedance of primary winding 125 increases
. ~
which substantially reduces the current flow in the
: circuit loop including primary winding 125, first section
46 and transistor 72.
Switching network 13 further includes switching
diode 38 which iG coupled in parallel relation to the
J,~:: . - base emitter junction of transistor 72 ana as is seen,
. the polarity of switching diod- 38 is provided to prèvent
. negative voltage from damaging transistor 72. Switching
diode 38 may ~e a commercially available lN4005 type
: and is connected such that its polarity is opposite
~'. ': ' - . ' ' '
. ` . . .
' ~'':, ': - - - ' -
' ' '' ' ' ' . ~ : ' .
:.,'~ ' , ' , ,, ' - : ' ' - '
'~ ~ . ' . . ~ , . .
,:~, . .. . ' . :.
- , ' ' - '
: ~ ' ' '
': ', . ' ' . ' ,: '
.: . ': .: .
~: ',: ': ` '' '
~'~ ' ' ~ . ` '
: . :
1;~790~0
-26-
to that formed by the base-emitter junction of transistor
` 72.
Primary winding 42 of inverter transformer 40
: is a tapped winding which is connected in an autotrans-
former configuration such that the voltage induced
in primary winding second section 44 is coupled in
series relation and adds to the voltage across primary
winding first section 46.
.~ The total voltage across primary winding 42
: ~ is coupled to capacitor 62 which is connected in series
:~ relation with primary winding 42. Obviously, as seen
, :
:~ : in the Figure, capacitor 62 is coupled on a first end
: ~ to primary winding 42 of inverter transformer 40 and
r~ i8 further coupled~on a second end to return line 64.
For purposes of the embodiment herein descr~bed, capacitor
: 62 may be a 3.5 nanofarad, 1.0 kilovolt Mylar capacitor,
` for discharge during transistor 72 "off" cyc~e of energy
' " ' stored in inverter transformer 40 during transistor
72 "on" cycle.
:~ . .,. . . . . - .
~t790~3
--27--
Primary winding 125 of no load protection transformer
lOQ, as previously descri~èd, is one element in the
series combination of elements through which the transistors
72 collector current flows. Thus, thG magnitude of
the current in each of those elements is identical
and the maximum value for that current is equal to
the DC supply voltage on output line 36 divided by
the sum of the series impedances in the current path.
:-~
The impedance of primary winding 125 of transformer
100 is a function of the impedance of the winding itself
and the impedance which is reflected from the secondary
windings. When the tuned high voltage output secondary
winding 160 is loaded, the resulting impedance of primary
winding 125 is at a minimum value. The filament excitation
windings 140 and 150 have a~negligible effect on the
refle~cted impedance, since each is composed of only
one~turn. With the impedance of primary winding 125
at its minimum value, the collector current is therefore
at its maximum, assuming the DC supply voltage on line
36 is at its desi~ned value.
jj, , .. ,, . ,.. ~. ,, , ,, . -
, i; : - , , , - ~ , .
. .:, . . .. . .
,, :~: :: - ' ' ' ' ' ' ' '
, . . . .
~ . -: , . . . .
79(19~
~ 2
.
' When the gas discharge tube 66 is no longer connected
~- to electronic ballast sys~em 10, the resulting reflected
impedance of tuned high voltage secondary winding 160
in the primary winding 125 becomes very high. The
,~ now high series imped~nce of primary winding 125 causes
.,
the collector current to be proportionally reduced.
Thus, the energy stored in transformer 100 is likewise
propGrtionately reduced and the resulting voltage across
- ~ the output terminals of winding 160 will be reduced
- .
~;~ , as well.
Primary winding 125 of no load protection trans-
, .
,~, former 100 therefore functions as a variable impedance
which is inversely proportional to the load seen on
,; ,.,~, : , ~
the secondary,winding 160 of transformer 100. Since
the impedance of primary winding 125 is substantially
all inductive, there is very little dissipation in
the form of heat in primary winding 125 to effect the
efficiency or component life of electronic baIlast
system 10.
Referring still to the Figure of self-regulating,
no load protected electronic ballast system 10, it
; . , -: . -
.. -: ~ . . . ..
9l~7909t)
is seen that when this system is in oscillation and
transistor 72 is in an 'lonu state, the collector current
which is the system driving current flows from power
source 12 through filter network 11 including rectifi-
cation circuit 16, through primary winding 125 of tranc~
former 100 via line 26 to line 36. DC power o~tput
line 36 passes through the axis of toroidal transformer
56 and is coupled to one end of primary winding 42
of inverter transformer 40.
The driving current flows through first section
46 of primary winding 42 to tap line 25 where it is
coupled to collector element 74 of switching transistor
72. Transistor 72 being in an "on" state allows current
to pass from collector element 74 to emitter element t
76 and back to the return of the power supply through
line 64. This current being of an increasing nature,
induces a voltage in bias control winding 48 which
is wound in a direction to produce a voltage on base
element 78 of transistor 72 which is positive with
' .
. ~
~'`,~`
~'
" , .. ..
~: ~ - ' - . ` -
:
,~ :
. - .
. .
.
.
, -
: : ` '
1;~'7~t~)'3~)
-30-
respect to emitter element 76 and greater than approxi-
mately 0.7 volts which is required to keep transistor
72 in an "on" state, thus, the voltage produced in
bias control winding 48 reinforces the "on" condition
of transistor 72.
The collector current increases in a subs.tantially
linear mannex until a maximum value is reached. The
maximum value is a function of the power supply voltage
and the impedance of the collector circuit. Thus,
when the collector current flows through first section
46 of primary winding 42, during the transistor "on~
state, a magnetic flux is generated within the core
of inverter transformer 40 which induces the voltage
in secondary winding 48 reinforcing the "on" condition
and provides the base drive current. The same driving
- current also flowing through primary winding 125 of
transformer 100 generates a magnetic flux within the
core of transformer 100 which induces the voltages
in all of the secondary windings of no load protection
transformer 100.
"`- ', '
,. ,, . - .
.~.- - ~ -
1;~7~)''30
-31-
The induced voltages in secondary windings 140
and lS0 provide the heate~ current for respective fila-
ments 68 and 70 of gas discharge tube 66. The voltage
induced in tuned high voltage output secondary winding
160 is coupled to tuning capacitor 130 and gas discharge
tube 66 for generation of visible light output from
gas discharge tube 66.
The induced voltage in seccnd section 44 of primary
winding 42 of inverter transformer 40 being monopolar
only charges capacitor 62 during this portion of the
cycle.
When transistor 72 is turned to an "off" state,
the collector current which was flowing through first
section 46 of inverter transformer primary winding
42 and primary winding 125 of no load protection trans-
former 100 terminates abruptly.. The rapid change in
collector current induces voltages again in aecond:-
section 44 of inverter transformer primary winding .
- , .
,, , ' ' .
,,: ;
,: ;. - . . . .
, . . - , .
: ~ :
~ ` . ~ - - - -,
.-: . : - '
: ~ ' ' ~ -' '.,
~ 3()'~
-32-
42 and secondary winding 48 as well as secondary windings
150, 140 and 160 of transformer 100. As is known from
classical theory, the polarity of the voltages induced
by the rapid collapse of the collector current is such
that transformer 40 and transformer 100 attempt to
maintain the direction of the original current in the
respective primary windings 46 and 125. Due to the
direction of current flow in windings 46 and 48 as
indicated by nomenclature dots 77, the voltage induced
in bias control winding 48 of inverter transformer
40 is of the opposite polarity as previously described
when the collector current was flowing. Thus, a nega-
tive signal on base element 78 with respect to emitter
76 is generated and transistor 72 is switched to an
: "off" condition.
: '
1;~7~()'3~)
-33-
It is of importance to maintain a relatively uniform
gain of transistors used in self-regulating, no load
protected electronic ballast system 10 such that light
output may be relatively consistent from one particular
unit to another within a range of approximately + 3.0%.
However, due to normal manufacturing techniques
known in the industry, the gain of transistors 72 may
vary between 10.0 - 50.0 or greater. Thus, a self-
regulation control is a requirement as an advantage
over having to manually adjust gain control elements
or in the alternative, to preselect devices within
a small tolerance in order to obtain an output of light
which is relatively constant from one electronic ballast
system 10 to another.
Self-regulating, no load protected electronic
ballast system 10 makes use of the concept of a variable
inductance in the form of toroidal core 27 wound with
~'
~: ' ' .
: - ' .
. .
~ J(~
1~ turns in which the base current passes. Line 36
passes through the axis the toroidal core 27 which
carries the collector current of transistor 72. The
direction in which current flows through the two windings
is such that the respective magnetic fields are addi-
tive within toroidal core 27 of toroidal transformer
56.
Therefore, the inductance which is seen in first
winding 55 of toroidal transformer 56 is a function
of both the base current and the collector current
multiplied by th~ respective turn ratios and the perme-
ability of magnetic core 27.
In actual practice, the inductance variations
of second winding 57 of toroidal transformer 56 may
be neglected since second winding 57 is formed of only
a single turn and winding 57 inductance is relatively
low as well as coupled in series with the inductance
of first section 46 of primary winding 4~. The induc-
tance of second winding 57 has been found not to be
significant when compared with the inductance of first
'3(~'3
-3~-
section 4Ç of primary winding 42 which is substantially
larger in absolute value..~
In order to insure oscillation within self-regulating,
no load protected electronic ballast system 10 of switching
transistor 72, bias control winding 48 is specifically
designed to supply sufficient voltage to turn "on"
transistor 72 of the lowest ~ain which may be expecte.
to be obtained from a manufacturer of these systems.
In this manner, it is assured that transistor 72 will
go to an "on" state and reach saturation and thus,
the base to emitter voltage will be at least 0.7 volts
required to switch transistor 72 to the saturation
state.
Regardless of the gain of transistor 72 used in
self-regulating, no load protected electronic ballast
system 10, the collector voltage and collector circuit
impedance is substantially the same and thus, the sub- ~ -
stantially same collector current will flow whether
a transistor with a gain of 10.0 or 50.0 is being utilized.
Therefore, since the base current is a function of
the collector current divided by the gain of transistor
1~'7~3()'3()
--36-
72, it is seen that the base current must change if
a transistor 7~ of differënt gain value is to be used
and function properly in self-regulating, no load protected
electronic ballast system 10. Where the base current
changes, then an electronic element in the base circuit
must change its impedance value which is the func.ion .
of self-regulating circuit 17 and primary first winding
55 of toroidal transformer 56.
In order to achieve self-regulation, the design
of toroidal transformer 56 is such that the maximum
permeability of core 27 is reached with a transistor
whose gain is at a maximum expected value. Likewise,
the inductance of first winding 55 of toroidal trans-
former 56 will therefore be at a maximum and hence
a minimum current will flow through the base circuit
for transistor 72.
.
,~ The impedance of a winding having a magnetic core
- is related to the number of turns of the winding and
- current flowing therethrough, as well as inversely
. to the length of the magnetic path in the core. The
.
1~79(~
point of operation may be adjusted by either changing
the size of the toroid or by inserting parallel resistor
51 in parallel relation with toroid ~irst winding 55
for adjustment of the corresponding exciting field.
A value of approximately 200 Ohms has been successfully
used for parallel resistor 51.
Thus, with first winding 55 of toroidal transformer
56 being at a maximum value of inductance, its impedance
is significantly larger than the impedance of base
coupling capacitor 54 such that it is the controlling
factor in limiting the current to base element 78 of
transistor 72. With transistor 72 having a maximumi -
gain value, little current is needed, and for example,
if the gain or beta of transistor 72 is 50.0, then
it is seen that the base current is 1/50th of the collector
current.
.. , ., , . , . ~ , ,
However, the voltage induced in base drive winding
48 has been designed to turn "on" a transistor of lower
; gain and therefore, there is excess energy to be dissi-
pated in the base circuit of transistor 72. The excess
. ..
-~ ~. - . :
- .
' . '
-. -
:
: '; "' ~ '
': ' . -
`-:' ' ~ . , '
1;~79(~
-38-
energy is stored in first winding 55 of toroidal trans-
former 56. This impedance of first winding 55 is pri-
marily inductive as opposed to resistive, and there
is little dissipation in the form of heat, and thus,
there is provided an efficient means of dissipating
the excess energy which is liberated when transistor
72 is in an "off" state.
In opposition, when a transistor of low gain is
used in self-regulating, no load protected electronic
ballast system 10, the base current obviously must
increase and the permeability of core 27 of toroidal
transformer 56 shifts in a downward direction to a
lower value than would be measured for a high gain
transistor and the inductance is less than was seen
with a high gain transistor. Thus, the series impedance
is reduced which allows a greater base current to flow
and compensates for the low gain transistor 72 being
used in system 10.
: - ~
~;~79()'~3()
-39-
Further, with tuned no load protection transformer
100 heing series coupled to induction circuit 15 for
preventing the generation of voltages above a predeter-
mined value when gas discharge tube 66 is electrically
removed from the circuit. The primary winding 125
of tuned no load protection transformer 100 forms ,a
variable inductance which is inversely proportional
to the magnitude of the power delivered to gas discharge
tube 66.
The variable impedance seen in primary winding
125 is a function of the impedance reflected from the
tuned output winding 160. That impedance being a func-
tion of the number of turns in winding 160, the parallel
capacitance of tuning capacitor 130, the magnetic circuit
. length in the core of transformer 100, and the current
.~ in secondary winding 160 which is the load current
of gas discharge tube 166. Thus, a change in load
current as seen when the gas discharge tube is no longer
, in the circuit, effects the impedance of winding 160
and is reflected into the impedance of the primary
winding 125.
; ,~ ~ . ~....
.
- ,~'' ' ' '
,: . .
i., . - ~ -
~;~'7'30'~0
--40--
sy creating a variable inductance whose impedance
is inversely proportional to the load current, a limited
voltage can be generated by control of the collector
current responsive to the load conditions.
