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June 8, 1948.
R, F, FOSTER
I
2,443,030 '
PICTURE SIZE CONTROL CIRCUIT FOR TELEVISION RECEIVERS
' Filed Nov. 9, 1946
24
PICTURE
SIGNAL
2%I
2|
- Inventor":
Raymond F.F‘ost,er~,
bymbm'
H is Attorney.
Patented June 8, 1948
2,443,036
UNITED STATES PATENTy'OFFlC“
PICTURE- SIZE CONTROL CIRCUITFOR
TELEVISION RECEIVERS
Raymond F. Foster, Stratford, Conn, assignor to
General Electric Company, a corporation of
New York
Application November 9, 1946, Serial No. 709,034
4 Claims. (01. 315-27)
I
My invention relates to television receiver cir
cuits and particularly to circuits for supplying
potentials to the anode and beam de?ecting coils
of a cathode ray tube employed in a television
receiver.
It is customary in television receiver circuits
2
the beam de?ecting current is controlled to regu
late the size of the picture by means of a vari
able inductance connected in series with the sec
ondary winding of the transformer. The vari
ation of inductance in the secondary winding cir
cuit is effective to introduce a change of in
to provide to the horizontal beam de?ecting coils
cuctance in the primary winding circuit suf
of the cathode ray tube a current which increases
at a constant rate for a length of time equal to
I?cient to compensate for any undesirable changes
one side to the other of the ?uorescent screen
or end wall of the tube. This uniformly vary
secondary winding circuit.
in the anode potential supply circuit otherwise
the picture signal portion of a received television 10 caused by the change in the primary winding cur
rent incident to the variation of the load in the
signal so that the cathode ray beam travels from
'
For a better understanding of my invention,
reference may be had to the following description
ing current is repeated at regular intervals spaced
apart by the time required to return the beam to 15 taken in connection with the accompanying
drawing and its scopewill be pointed out in the
its starting position. It is known to utilize the
appended claims. In the drawing, the single ?g~
pulse of voltage incident to the current employed
ure is a circuit diagram of a portion of a tele
to return the cathode ray beam to its starting
vision receiver suitably embodying my invention.
position to produce a high potential which may
Referring to the drawing, there is shown an
be recti?ed and supplied to the anode of the 20
output power tube I which applies current to the
cathode ray tube. When the same transformer
horizontal de?ecting coils 2, 3 of the cathode ray
is employed in both the horizontal beam de?ect
tube 4 through a transformer 5. The power tube
ing generating circuit and the anode voltage sup,
l is of the tetrode type having a cathode 6 which
ply circuit, di?‘iculty is encountered in control
ling the amplitude of the horizontal beam de 25 is connected to ground through a cathode resistor
7; Control electrode 8 of tube 1 is connected to
?eeting current to control the size of the tele
an input terminal 9 through a coupling capacitor
vision picture without a?ecting undesirably the
l0 and to ground through a grid resistance H.
magnitude of the anode voltage. When an at
The anode l2 of the tube l is connected to an
tempt is made to control picture size by increas
ing or decreasing the horizontal driving current, 30 intermediate point I3 on the primary winding
comprising coils [4, I5 of transformer 5. The
a change appears also in the voltage supply cir
lower terminal of the coil 14 is supplied with
cuit to produce an undesired change in picture
operating potential from the usual anode supply
size which nulli?es the result produced by the
indicated by the legend B+. The screen electrode
change in driving current magnitude.
It is the primary object of the present inven 35 [6 of tube 1 is connected to the lower terminal
of winding I4 for unidirectional currents and is
tion to provide a new and improved anode voltage
by-passed to ground through a capacitor I‘! for
supply circuit and horizontal beam de?ecting
alternating currents. ‘
circuit in which the magnitude of the beam de
Preferably, the input terminal 9 is supplied
?ecting current may be varied over a substan
tial range without affecting substantially the in 40 with a sawtooth .wave of voltage, such as the
wave l8, from preceding portions of the televi
tensity of anode voltage.
sion receiver. In the usual television receiver
It is still another object of my invention to
circuit, the duration of each sawtooth wave cor
provide a new and improved circuit for control
responds to the horizontal scanning period and
ling the size of the picture of a television re
45 adjacent of the'sawtooth waves vare separated by
ceiver.
a pulse of voltage having a duration correspond
It is a further object of my invention to provide
ing to the usual horizontal retrace period. The
a new and improved circuit for controlling the
power tube I utilizes the input voltage wave M5
size of the picture of a television receiver which
to produce, in its anode circuit, a sawtooth wave
is simple in construction and operation.
Brie?y stated, in accordance with one aspect 50 of current. The voltage wave across the wind
ing l4 generated by this sawtooth current is as
of the present invention a transformer is em
indicated at H). The wave I9 comprises slightly
ployed for supplying both horizontal beam de
decreasing ‘sawtooth portions separated by high
?ecting current to the picture tube of a tele
positive pulses of a duration corresponding to
visionreceiver and to generate a high intensity
anode voltage for that tube. The intensity of 55 the duration of the horizontal sweep retrace
2,443,030
3
cuit for controlling the size of the picture of a
cathode ray tube of a television receiver circuit is
that the inductance required for size control is
period of the cathode ray tube. The sharp posi
tive peaks of wave [9 caused by the rapid change
of flux in transformer 5 produce across the wind
ings M, l5 a high potential which is recti?ed by
diode recti?er 20 and utilized to provide a high
unidirectional operating potential which is sup
relatively small and, furthermore, has no dele
terious effect upon the anode voltage supply cir
cuit.
A still further advantage lies in the fact that
the variable size control inductance 36 is con
plied to the anode terminal 2| of cathode ray
tube 1.1. The high potentials for the anode 21 are
nected into the horizontal sweep coil circuit in
obtained by connection between the cathode of
recti?er 20 and a capacitor 22 connecting the 10 advance of the variable tap 35 so that the lin
earity of the sweep ?eld may be satisfactorily
cathode to ground.
maintained by controlling the position of the
Since the wave of voltage i-9, vwhich is across
the primary winding of transformer 5, contains‘ ' tap 35 on resistance 29.
positive pulses, the wave of current in secondary @
While I have illustrated my invention as in
winding 23 of transformer 5 is not entirely saw- ~
cluding various devices diagrammatically shown,
tooth in form, but varies therefrom at periods
following the positive peaks by shock oscilla
tions. To eliminate such variations and to pro-'
it will be obvious to those skilled in the art that
changes and modi?cations may be made without
departing from my invention and I, therefore,
aim to cover in the appended claims all such
vide to the de?ection coils 2, 3 a sawtooth wave
of current 24, I provide a damping tube 25 to
changes and modi?cations as fall within the true
supply a compensating current to the horizontal
spirit and scope of my invention,
de?ection coils. The control electrode 26 of the
What I claim as new and desire to secure by
damping tube 25 is connected ‘through a re»
Letters Patent of the United States is:
sistance 21 to a differentiating circuit compris
l. ‘The combination, in a television receiver
ing a capacitor 28 and a variable resistor 29. 25 circuit, including a cathode ray tube having an
The cathode 30 of damping tube 25 is connected
anode and a beam de?ecting coil, a transformer
having ‘a primary winding and a secondary wind
to ground through a load resistor 3| shunted by
ing, means supplying a sawtooth wave of cur
a by-pass capacitor 32. Bias for the control
rent to a portion of said primary winding, means
electrode of the damping tube 25 is obtained by
grid voltage recti?cation and grid current in 30 utilizing the voltage across said primary Wind
ing to provide a unidirectional potential to said
resistor 33 shunted by a by-pass capacitor 313.
anode, said coil being connected in series cir
One terminal of resistor 33 is connected to the
cuit with said secondary winding, and variable
cathode 36 and the opposite terminal is connected
to a variable tap 35 on resistor 29.
reactance means included in said series circuit
In this cir
cuit, the differentiation of the elements 28, 29 35 for varying the current in said coil without
changing the intensity of said potential to con
trol the size of a picture produced on said cath
ode ray tube.
2. The combination, in a television receiver
circuit, including a cathode ray tube having an
supplied to the de?ection coils may be varied
anode and a beam de?ectingr coil, a transformer
to control the size of the picture produced on
having a primary winding and a secondary wind
the cathode ray tube 4, I provide a variable in
ing, means supplying a sawtooth wave of current
ductance 36 which is connected in series be
‘to a portion of said primary winding, means
tween the lower terminal of secondary winding
23 and ground. Preferably, the inductance 36 45 utilizing the voltage across said primary Wind
ing to provide a unidirectional potential to said
has a relatively low Q and may be shunted if
is varied by varying the position of tap 35 to con
trol the amount of compensating current supplied
to the de?ection coils by tube 25.
In order that the magnitude of the current
desired by a resistance 3'! to reduce the amount
of oscillatory energy stored in the inductance 36.
In the operation of the above-described cir
cuit, the size of the picture on the ?uorescent 50
screen or end wall of the cathode ray ‘tube 4
anode, said coil being connected in series circuit
with said secondary winding, and means for
varying the current in said coil without chang
ingthe intensity of said potential comprising a
variable impedance connected in said series cir
cuit.
may be controlled by varying the inductance 36.
3. In a television receiver circuit, the com
The effect of this variation is either to increase
bination comprising a cathode ray tube having
or decrease the magnitude of the ‘sawtooth cur
rent supplied to the horizontal de?ection coils 55 ‘an anode and a beam de?ecting coil, a trans
former having a' primary winding and a sec
2, 3. Such a change in current in the secondary
ondary winding, means supplying a substantially
winding produces an undesirable change in the
sawtooth wave of current to said primary Wind
current flow in the loading of the primary Wind
ing, means utilizing the voltage across said pri
ing of transformer 5 which tends to reduce the
magnitude of the voltage supplied to the anode 60 mary winding to provide a. unidirectional po
of the cathode ray tube.
Such a reduction of
anode voltage, however, is compensated by the
change of inductance in the secondary circuit
tential to said anode, a variable inductance and
said coil being connected in series circuit with
said secondary winding, the size of the picture
produced on said‘ cathode ray tube being vari
which is transferred to the primary circuit to vary
the reactance thereof in a direction to maintain 65 able by variation of said inductance, and said
inductance being of sufficient value to maintain
the anode supply voltage at a desired value. Such
said potential at a substantially constant value
a result is in contrast to that obtained by at
tempts to regulate the size of the picture by, using
as the current in said transformer is varied to
control the size of a picture,
4. The combination, in a television receiver cir
of the secondary Winding 23, the effect of which 70
cuit, of a cathode ray tube having an anode
is opposite to that produced by the inductance 38
and a horizontal beam de?ecting coil, a trans
and which tends to produce achange of high volt
an inductance or resistor in shunt with a portion
age which nulli?es the change in picture size pro
duced by such a shunt circuit.
'
An important advantage of my improved cir
former having a primary Winding and a sec
ondary winding, means supplying .a substantially
75 sawtooth wave of current to said primary Wind
2,443,030
5
6
ing, means for rectifying the voltage across said
primary winding to provide a unidirectional po-
REFERENCES CITED
tential to said anode, said coil being connected
in series circuit with said secondary winding,
The following references are of record in the
?le Of this Patent:
means connected in shunt with said secondary 5
winding for compensating for non-linearities 1n
the current thereof to provide a sawtooth wave
of current to said coil, and reactance means
connected in said series circuit for controlling
the magnitude of the current supplied to said 10
coil.
RAYMOND F. FOSTER.
UNITED STATES PATENTS
Number
10741495
2,183,647
2,212,217
Name
Date
Vance —————————— —— Mar- 23’ 1937
3115,55 ———————————— —— Jan- 30: 1940
Whlte et a1 ------- -- Aug- 20, 194°