Note: Descriptions are shown in the official language in which they were submitted.
`` ~2~
RCA 77,856
1 TELEVISION RECEIVER STANDBY CIRCUIT
This invention relates to the standby operation of
television receivers and, in particular, to a power supply
which powers remote control circuits within the television
receiver during standby operation. The invention may be
used in retrace driven main power supplies, and in
particular, may be used in a single conversion system
(SICOS) power supply such as ~escribed in UK published
application 2094058A, published 8 September 1982.
Several types of standby television receiver
circuits are known. Known, for e~ample, is a small AC
line mains transformer which powers the remote control
circuits of the television receiver, and a relay which
turns the television receiver on and offO Such a standby
circuit may consume only about 6 watts, but is a relatively
costly approach to standby power supply.
Another type of standby circuit is a switched
mode power supply with an integrated circuit control such
as with a TDA4600 control circuit IC, and a relay which
turns off most of the switched mode power supply secondary
voltages during standby. The switched mode power supply
operates at around 70 KHz during standby to obtain the
required large range of regulation. Standby dissipation
of such a system, however, is relatively large,between 10
and 20 watts.
Still another type of standby circuit is a mains
transformer coupled to a switched mode regulator without a
relay. During standby the horizontal oscillator is
deenergized by the remote control circuit. The use of
a mains transformer is a relatively cumbersome approach
to the design of a standby circuit.
A feature of the standby circuit of the invention
is the initiation of standby operation by short circuiting
the horizontal trace switch by, for e~ample, maintaining
the horizontal output transistor continuously in saturation
during standby operation. When using a main power supply
such as the above referred to SICOS power supply, short
. _ .. . . . . .. . , . . , _ ... , . . . _ . ... .. .. .. .. . . . .. .. . . . .... . . . . ..
. ... .
~2~
- -2- RCA 77,856
1 circuiting the trace switch results in the SICOS power
supply going into free-running oscillation at around the
horizontal deflection frequency, with a duty cycle ratio
nearly that of the ratio between the trace to retrace
intervals. ~uring standby, the power for the remote
control circuit flows through the short circuited trace
switch from a secondary winding of the flyback transformer.
Standby power consumption may be less than 10 watts and
typically around 6 watts. Usable power for the remote
control circuit may be around 1.5 watts at 12 volts.
In the Drawing:
FIGURE 1 illustrates a television receiver power
supply and deflection circuit with standby remote control
circuitry embodying the invention;
FIGURE 2 illustrates waveforms associated with
the circuit of FI~URE 1 during normal mode operation;
FIGURE 3 illustrates waveforms associated with the
cixcuit of FIGURE 1 during standby mode of operation; and
FIGURE 4 illustrates a detailed embodiment of
20 the output circuitry of a SICOS power supply. .
In FIGURE 1, a SICOS power supply 20, described
in the aforementioned UK published application,
operates to txansfer power from an unregulated B+ supply
terminal to various television receiver load circuits
coupled to secondary windings of a flyback-transformer Tl,
including a high voltage ultor load 33 coupled to a high
voltage winding W4. During normal mode operation,
horizontal retrace pulses, voltage V3 illustrated in
FIGURE 2c, developed by horizontal deflection generator 21,
are transformer coupled from secondary winding W2 of
flyback transformer Tl to the primary winding Wl.
From the tap of primary winding Wl~ the positive
retrace pulses are peak rectified by a diode Dl, filtered
by a capacitor Cl and applied to the SICOS regulator
control circuit 22 along a signal line 34. Regulator
control circuit 22 is synchronized to horizontal deflection
by the retrace pulse voltage applied along a signal line 29
to develop pulse-width modulated signals 23 having a
.; duty cycle that varies with variations in retrace pulse
.. . . . . . , . . .. . _, .
~3~9D~
-3- RCA 77,856
1 voltage amplitude. The pulse-width modulated signals are
- applied to an input terminal 24 of the SICOS power supply 20
to pulse-width modulate push-pull switches Sl and S2.
Each switch comprises a transistor, Trl or Tr2, having an
antiparallel diode, not illustrated in FIGURE 1, coupled
between its collector and emitter electrodes. By pulse-
width modulating the operation of switches Sl and S2, the
retrace pulse amplitude is maintained relatively constant
under varying load and B+ voltage conditions.
The positive voltage developed across capacitor Cl
holds a transistor Ql in saturation, thereby bringing its
collector voltage to the potential o~ earth ground 25 and
reverse biasing a diode Dl0. On the secondary side of
flyback transformer T1, a standby switching transistor,
Darlington transistor Q2, is held in saturation by base
current flowing from a hold rail 26 through a resistor R9
and a zener diode D5. Thus, horizontal trace switch 27
and horizontal driver transistor Q5 are connected to
chassis ground 28 by way of the conducting, remote control
switch Q2.
The waveforms of FIGURES 2a-2e iliustrate
normal mode operation of the SICOS power supply and
- horizontal deflection circuit of FIGURE 1. FIGURE 2a
illustrates the switching voltage Vl at the junction of
25 output switches Sl and S2 of SICOS power supply 20.
~he dashed-line waveforms of FIGURE 2 indicate the
regulation range of the power supply~ The solid~line
waveforms represent waveforms taken at a typical working
point of the power supply.
FIGURE 4 illustrates a detailed embodiment of the
circuitry of SICOS power supply 20 of FIGURE 1. Switch Sl
becomes conductive at a controllable instant, T4, within
the trace interval of the horizontal deflection cycle,
coupling energy storage inductor Ll to the B+ input
35 voltage terminalO Switch Sl becomes conductive because
near time T4 the positive-going edges of pulse-width
modulated signal 23 has turned on transistor Tr4, thereby
turning off transistor Tr2 of switch S2. To maintain the
; current il in main winding Lla of inductor Ll, the dotted
-4- RCA 77,856
1 terminal of winding Lla becomes positive relative to the
undotted terminal, thereby forward biasing diode DSl of
switch Sl. A now decreasing current in winding Lla flows
to the B+ terminal of FIGURE 1.
The positive voltage at the dotted terminal of
winding Lla induces a positive voltage at the dotted
terminal of control winding Llc to forward bias the
base-emitter junction of transistor Trl. Transistor Trl
takes up current conduction in winding Lla when the
current il of FIGURE 2b becomes positive at some instant
after time T4 but within the trace interval T2-T6.
At the end of the trace interval,-at time
T6, a controllable amount of energy has been s~tored in
inductor Ll. Much of this stored energy is then
1~ transferred to the load circuits coupled to flyback
transfarmer Tl during the horizontal retrace interval
T -T .
At time T6~ the positive retrace pulse voltage
developed at the dotted terminal of winding Wl of flyback
transformer Tl is applied to the undotted terminal of
winding Lla of inductor Ll making positive the undotted
terminals of winding Lla and control windings Llb and Llc.
Transistor Tr3 becomes conductive, turning off transistor
Trl. The positive current il is now taken up by diode
~5 DS2 of switch S2 until near the center of retrace when
transistor Tr2 takes over conduction when current il
becomes negative. During retxace, a resonant transfer of
energy takes place, by way of flyback transformer Tl,
between inductor Ll and the retrace resonant Gircuit
comprising capacitor CR and horizontal deflection winding
LH and the load circuits coupled to secondary windings
W3 and W4 of flyback transformer Tl.
FIGURE 2d illustrates the base current i3 in
horizontal output transistor Q4, flowing from a winding
Wb f a horizontal driver transformer T2. FIGURE 2e
illustrates the current i2 flowing in a winding Wc of
driver transformer T2. Near time To~ a horizontal driver
transistor Q5 is turned on, generating a reverse base
current i ~hat cuts o~f horizontal output transistor Q4
, 3
~2~
-5- RCA 77,856
1 at time Tl. Also beginning near time Tol a current i2 is
generated that charges a capacitor C8 through a diode D20
The currents i2 and i3 during normal mode operation are
therefore generated by the switching action of horizontal
driver transistor Q5~
To switch the television receiver into the
standby mode of operation, a remote control circuit 30
applies chassis ground potential for about l second duration,
as an OFF command signal, to the base of remote control
switching transistor Q2 via a control rail 31. With
transistor Q2 cut off, the current in winding W2 of
flyback transformer Tl is forced to flow to chassis
ground 28 via winding Wc of horizontal driver transformer
T2. When conventional current il flows out of the dotted
terminal of flyback transformer winding W2, the return
current path for that current is through horizontal output
transistor Q4 into the dotted terminal of winding Wc of
driver transformer T2, then through diode D2 to charge
capacitor C8 to a positive voltage. When conventional
current il flows out of the undotted terminal of flyback
transformer winding W2, the return path is through the
diode of Darlington transistor Q2, the damper diode D7 of
trace switch 27, and the diode formed by the base-col]ector
junction of horizontal output transistor Q4.
The positive current i2 induces in winding W~
of horizontal driver transformer T2 a positive base
current i3 for horizontal output transistor Q4. The
current i3 keeps horizontal output transistor Q4 conductive.
Transformer T2, therefore, serves as a bootstrapping
transformex that provides positive feedback from the output
of transistor Q4, to ~eep the transistor in saturation.
During standby, transistor Q4 is either in a
condition of saturated forward conduction or in a condition
of reverse collector conduction with damper diode D7
also conducting. These conditions produce in effect a
short circuited trace switch 27 connecting the dotted
terminal of flyback transformer winding W2 to the dotted
terminal of driver transformer winding Wc. With trace
switch 27 continuously short circuited, the retrace resonant
-6- RCA 77,856
1 circuit is prevented from forming, thereby collapsing the
retrace pulse voltages. The supply currents through
diodes D4 and D6 become zero, as well as the supply
voltage Vb and the current through hold rail 26. Remote
control transistor Q2 therefore remains in cutoff, even
after elapse of the aforementioned one~second OFF command
signal interval.
The voltage Va across capacitor C4 is the source
voltage for the 12 volt supply rail energizing remote
control circuit 30 and horizontal oscillator 32. This
voltage is developed, in the standby mode of operation,
via diodes D2 and D3, from the positive current of
current il, that flows in driver tran~former windin~ Wc
as the current i2. ~orizontal oscillator 32 is in operation
during standby to facilitate the turn-on of the television
receiver, as explained later. A Darlington transistor Q3
acts as a shunt regulator to limit the voltage across
capacitor C8.
On the primary side o flyback transformer Tl,
as the retrace pulses collapse upon initiation of standby
mode of operation, SICOS power supply 20 begins to operate
in a free-running mode. The collapse of the retrace pulse
voltages disables control circuit 22 and brings transistor
Ql into cutoff. With transistor Ql cutoff, an RC network
comprising resistors Rl-R4 and a capacitor-C2 is enabled
to form an astable multivibrator arrangement with SICOS
switches Sl and S2.
The waveforms of FIGURE 3 illustrate waveforms
associated with the circuit of FIGURE 1 in the standby mode
of operation. As indicated in the voltage Vl of FIGURE 3a,
a~ter time tl,switch Sl of SICOS power supply 20 is
conducting. Also near time tl, the left plate of capacitor
C2 is positive relative to the right plate. Therefore,
when switch Sl becomes conductive, capacitor C2 begins
to discharge through resistors R2 and R3 as indicated
in FIGURE 3b by the decreasing voltage V2 at the collector
of ~ransistor Ql after time tl.
Switch Sl of SICOS power supply 20 remains
r ~ conductive due to the regenerative action provided by
.. . . . ..
æ
.
7- RCA 77,8~6
1 control windings Llb and Llc of FIGURE 4. As indicated in
- FIGUR~ 3a, switch Sl remains conductive until time t3,
at which time transistor Trl of switch Sl begins to turn
off. ~y time t4, transistor Trl is in cutoff and switch S2
has been turned on due to conduction in diode DS2, thereby
bringing the voltage Vl to earth ground potential.
By time t4, capacitor C2 has charged to an
opposite polarity voltage such that the right plate of
the capacitor is positive relative to the left plate. With
the positive, right plate of capacitor C2 clamped to ground
by switch S2, the base-collector junctlon of transistor Ql
becomes forward biased, clamping the voltage V2 to just
below ground potential, between times t4 and t6 of FIGURE
3b. ~etween times t~ and t6, capacitor C2 discharges
through the base-collector ju~ction of transistor Ql and
through resistor R2 from the B+ terminal. Near time t6,
the voltage across capacitor C2 reverses polarity, reverse
~iasing the base-collector junction of transistor Ql.
Capacitor C2 begins to charge from the B~ termi~al,
charging the left plate of the capacitor positive relative
to the right plate.
By time t7 of FIGURE 3b, capacitor C2 has
charged suffi~iently to forward bias diode D10 and turn on
control transistor Tr4 of SICOS power supply 20. Turning
on control transistor Tr4 turns off output~switching
transistor Tr2. When Tr2 turns off, diode DSl of switch Sl
is turned on to take up current conduction from main
winding Lla of inductor Ll of FIGURE 4. The voltage Vl
therefore increases to the B+ voltage level as illustrated
in FIGURE 3a.
The duration of one complete free-running
oscillation of switches Sl and S2 is illustratively 70
microseconds, a duratio~ that is near that of the
horizontal deflec-tion duration TH = 64 microseconds.
3~ The 70 microseconds free-running period is selected to be
short enough so as to be inaudible to most persons
in standby mode. Adjustment of the free-running
period may be made by adjusting the value of resistor R2
of the astable multivibrator.
-8- RCA 77,856
1 FIGURE 3c illustrates the current il in winding
Wl of flyback transformer Tl during standby operation.
Because windings Wl and W2 are tightly coupled to each
other and have approximately the same number of turns,
the current il in winding W2 and thus in the collector
of horizontal output transistor Q4 in the standby mode
has about the same shape and amplitude as the current il.
Compared to the currents il and il during normal mode
operation, the currents il and il during standby mode of
operation are substantially reduced. The power consumption
of SICOS power supply 20 during standby is therefore
relatively low, illustratively 6 watts.
FIGURE 3d illustrates the voltage V4 across
remote control switching transistor Q2 during standby
15 operation. Between time to and time t2, an interval when
the currents in windings Wl and W2 of flyback transformer
Tl are negative, the diode of Darlington transistor Q2 is
forward biased, clamping the voltage V4 to chassis ground
potential. Between time t2 and time t3, the currents il
20 and i are positive and ramping upwardly. In this interval
the current i2 in winding Wc of transformer T2 is positive,
forward biasing diode D2 and charging capacitor C8 to a
voltage of approximately 20 volts. In this interval, the
voltage V4 is positive and clamped to the voltage level
25 established by the voltages being developed-across windings
Wc of driver transformer T2 and across capacitor C8.
Near time t3, switch S2 of SICOS power supply 20
becomes conductive, initiating the negatively sloping
portion of the currents il and il. After time t3,
30 the current il flowing to winding Wc of drivex transformer
T2 causes a reversal in the polarity of the voltage
developed across winding Wc. The Voltage V4 therefore
decreases from time t3 until time t5, the zero-crossover
instants of the current il. At time t5, the current il
35 becomes negative, forward biasing the diode of Darlington
transistor Q2, again clamping the voltage ~4 to chassis
ground potential.
Because trace switch 27 is a short circuit during
standby mode operation, the voltage developed across
2~
-9- RC~ 77,856
1 flyback transformer winding W2 is the same voltage V4
- illustrated in FIGURE 3d, but at a different, AC, zero
volt reference level. Thus, during standby operation,
the peak-to-peak volta~e across winding W2 is approximately
25 volts, illustratively, compared to 900 volts,
illustratively, during normal mode operation, a peak-to-peak
voltage reduction to about 3% of that obtained during
normal operation.
Conduction in hoxizontal driver transistor Q5
is prevented due to the reverse biasing of either diode D8
or diode D9. Operation of horizontal oscillator 32 during
standby mode of operation will not therefore interfere
with the free-running operation of SICOS power supply 20,
Standby power for remote control circuit 30 and
15 horizontal oscillator 32 is derived from winding Wc of
horizontal driver transformer T2 by way of the current i2
which charges capacitor C8 and capacitor C4 during standby
operation. The a~erage value of the positive portion of
the current i2, illustrated in FIGURE 3f, amounts to
20 about 150 milliamperes, amounting to about 1.8 watts of
usable power at the output of the 12 volt regulator~
The positive current i3 in w;nding Wb of transformer T2,
illustrated in FIGURE 3e, is induced by the current i2.
The current i3 is higher in amplitude because winding Wb
25 has only about half the number of turns of winding Wc.
For example, the inductance of winding Wb may be about
200 microhenries, and thus, the inductance of winding Wc
may be about 800 micrPhenries.
Resistors R7 and R8 serve to smooth the base
30 current i3. Via resistor R7, some energy is stored in
winding Wc to lengthen the base current i3 when D2 cuts
off. Horizontal output transistor Q4 is kept safely in
saturation until the current through its collector is zero.
To bring the television receiver back to normal
3~ operation, remote control circuit 30 applies a positive
puls2, ON commana signal to the base of switching
transistor Q2 via control rail 31 for approximately 1 second
until sufficient hold current for the transistor
subsequently becomes available fxom hold rail 26.
. _ . , . . . _ . _ _ .. ... _ .. .. .. . .
æ
-10- RCA 77,856
1 Deflection generator 21, including trace switch 27, is
again connected to chassis ground 28 directly through
switching transistor Q2, bringing ground potential to
the emitter of horizontal output transistor Q4. As a
result~ the current il in flyback t~ansformer winding W2
is bypassed to ground by transistor Q2 awa~ from winding
Wc of driver transformer T2. As a result, current i2
diminishes significantly, and horizontal output transistor
Q4 is not in continuous saturated conduction.
The operation of SICOS power supply 20 changes
to a start-up sequence of operation similar to that
described in the aforementioned UK Published application
of P. Haferl. This sequence is controlled by retrace
ringing until the retrace voltage coupled to primary
winding Wl of flyback transformer Tl is high enough in
amplitude to reenable the SICOS regulator control circuit
22. With the regulator control circuit reenabled, the
turn-off of output switch Sl is synchronized with
horizontal retrace. At the same time, the retrace pulse
voltage produces the saturation of transistor Ql, disabling
the multivibrator network of resistors Rl-R4 and
capacitor C2.
During the transition from standby to ON operation,
current i3 changes from ~eing induced by the current in
winding Wc of driver transformer T2 to being induced by
the current in winding Wa. Similarly, during the transition
from ON operation to standby, the current i3 changes from
being induced by winding Wa to being induced by winding WCO
To make these transitions safely without damaging
horizontal output transistor Q4, the switching
sequence of transistor Q4 is not interrupted
during the transitions. Transistor Q4 is not
turned on when a significant positive voltage V3 is present
at its collector.
In standby, horizontal oscillator 32 is
operating, but is only in-circuit with the base of
horizontal driver transistor Q5 when the voltage V4 is
low. Current il, when voltaye V4 is low, flows in a
negative direction, from the diode of Darlington
. .
~æ~
~ RCA 77,856
1 transistor Q20 Thus, even though switching signals are
b~ing applied to the base of driver transistor Q5 in
standby, only a small negative current i3 flows and does
not disturb operation of transistor Q4.
When current il becomes positive, voltage V4
goes high. Conduction in the collector of transistor Q5
is cut off by diodes D8 and D9. A positive current i3
flows to keep transistor Q4 biased into saturation.
With the television receiver switched from
standby to ON operation, transistor Q2 is switched into
saturation. Immediately after receipt of the ON command
signal~ voltage Vb is at zero volts, resulting in zero
current i3 to drive horizontal output transistor Q4.
SICOS power supply circuit 20 continues to free run as
15 during standby. The retrace circuit LH, CR rings to
produce an increasing amplitude voltage V3 at the
retrace frequency during the interval tl-t3 of FIGURE 3.
The automatic frequency and phase control portion
of horizontal oscillator 32, not illustrated in FIGURE l,
20 begins to phase the oscillator output to the phase of
the ringiny voltage V3~ The increasing amplitude ringing
voltage developed across retrace capacitor CR is coupled
by way of flyback transformer winding Wl and control
winding Llc of inductor Ll to the base of transistor Tr3
25 to turn that transistor on, thereby turning-off transistor
Trl of output switch Sl. Therefore~ the increasing
amplitude ringing voltage V3 begins to synchronize the
turn-off of switch Sl to the phase of the output of
horizontal oscillator 32.
As the voltage Vb increases, the already
correctly phased oscillator 32 controls the switching of
horizontal driver transistor Q5 to supply correctly phased
base current i3 to horizontal output transistor Q4.
The increasing amplitude ringing voltage turns on
35 transistor Ql, thereby disabling the multivibrator
arrangement of resistors Rl-R4 and capacitor C2, and at
the same time enabling regulator control circuit 22.
Once regulator control circuit 22 is :enabled, the voltage
V3 increases smoothly to its nominal steady-state ON value.
... -12- RCA 77,856
1 When the television receiver is switched from ON operation to standby, the transition is a controlled one
and safely brings horizontal output transistor Q4 into
saturated conduction on a continuous basis. When the OFF
command si.gnal is received, remote control transistor Q2
is switched off, thereby disabling operation of horizontal
driver transistor Q5. If transistor ~2 happens to be
turned off during retrace, the current induced in winding
Wb of driver transformer T2 from winding Wa is higher than
that induced from winding Wc. Horizontal output transistor
Q~, remains in cutoff until the end of retrace. Subsequent
thereto, transistor Q4 is maintained in continuous
saturation.
For the first few milliseconds after receipt of
the OFF command signal, operation of SICOS power supply 2a
is at the lower free-running frequency described in the
aforementioned UK published application of P. Haferl.
When capacitor Cl of FIGURE 1 has discharged sufficiently
to turn off transistor Ql, the multivibrator arrangement
of resistors R1-R4 and capacitor C2 is enabled and
increases the frequency of operation of SICOS switches
Sl and S2 to a free-running frequency near that of the
horizontal deflection fre~uency, as previously discus;!3ed.
The standby circuit a~rangement of FIGURE 1, just
described, also prov.ides short circuit and overload
protection. Switching transistor Q2 is only controlled
by ON-OFF command pulses provided from remote control
circuit 30. When the transistor is turned on, it is held
in saturation by the base current supplied from hold
rail 260 A short circuit or an overload that produces
a decrease in the voltage Vb to a voltage below about
6.5 volts will turn off remote control switchi~g transistor
Q2 and place the television receiver and SICOS power
supply 20 into a standby mode of operation. In the
standby mode of operation, the voltage Vb ~ollapses
completely, preventing the excessive current condition
from continuing. Thus, the television receiver will
in general return to the standby mode of operation under
a persistent overload operating condition, even when
.. . ... ... . . . . ... . . . . . .
~2~
-13- RCA 77,856
1 repeated attempts are made to turn the television
receiver on.
~n example of horizontal driver transformer T2
is the followlng: Core: cylindrical 30 x 6 mm, material
N27; Wa: 350 turns of 0.2 mm wire, 4 mH; Wb: 80 turns of
0.4 mm wirel 200 ~H; Wc: 160 turns of 0.2 mm wire, 800 ~H. -
~25
'; ,,
. _ . , . ~ . ... . .. ... . .. . .. .... . . . .. . .. .. . .. . .
