Method of operating a low standby power system for a television receiver

A television receiver includes a microprocessor, a switched mode power supply and a storage capacitor. The storage capacitor supplies standby power to the microprocessor when the television receiver is off and the switched mode power supply is disabled. While the television receiver is off, the microprocessor monitors the capacitor voltage and turns on the switched mode power supply to recharge the capacitor when its voltage level falls to a predetermined minimum. The microprocessor turns off the switched mode power supply when the capacitor voltage indicates that the capacitor has been recharged.

BACKGROUND OF THE INVENTION AND PRIOR ART 
This invention relates in general to television receiver power supplies and 
in particular to an efficient power supply for a television receiver that 
requires a small amount of standby power when in the off condition. 
Modern television receivers are both microprocessor controlled and remotely 
controllable and require a low level of standby power when the television 
receiver is off to maintain the microprocessor and remote control 
functions. Such receivers generally include a very efficient switched mode 
power supply which has the undesirable characteristic of being inefficient 
when supplying low levels of power. The standby power requirement of a 
typical television receiver is on the order of a couple of watts whereas 
its normal operating power requirement may be on the order of one hundred 
watts. Because of the switched mode power supply's inefficiency at low 
power levels, as much as 10 to 12 watts may be consumed in the standby or 
off mode of the television receiver in order to supply its small standby 
power needs. The bulk of the power is dissipated as losses in the switched 
mode power supply. A few television receivers incorporate a separate 
standby power supply for supplying the minimal standby power requirements 
of the television receiver and simply turn off the switched mode power 
supply when the television receiver is turned off. That is a relatively 
expensive solution to the problem and the invention solves the problem in 
a much more practical manner. 
OBJECTS OF THE INVENTION 
A principal object of the invention is to provide an improved power supply 
for a television receiver. 
Another object of the invention is to provide an efficient standby power 
system for a television receiver. 
A further object of the invention to provide a method of efficiently 
operating a television receiver power supply that must supply relatively 
high operating power and low standby power.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to the single figure of the drawing, a television receiver is 
generally indicated by block 10. The television receiver includes a 
conventional fused connection to an AC power source, a bridge rectifier 
and a filter capacitor, all identified by reference 11, and a switched 
mode power supply (SMPS) 12 of conventional construction that drives a 
transformer 13. Transformer 13 includes a primary winding 14, three 
secondary windings 15, 17 and 19 for developing the various voltages 
required by the television receiver load and control circuits and an 
auxiliary winding 27 for supplying power to SMPS 12. A switch transistor 
16 has its collector coupled through winding 14 to the source of B+ (from 
circuit 11) and its emitter connected to ground through a resistor 18. 
Winding 15 is used to supply power to the sweep circuit of the television 
receiver and the other secondary windings 17 and 19 supply lower voltage 
DC power to the other receiver circuits. As mentioned, auxiliary winding 
27 supplies SMPS 12 with operating voltage via a rectifier and filter 
network 29. The secondary windings 15, 17 and 19 are connected to suitable 
diode and capacitor combinations for converting the AC voltage into DC. 
Thus winding 15 is coupled to a diode 20 which supplies a capacitor 23 for 
supplying the approximate 130 volt DC voltage required by the deflection 
system (not shown) of the television receiver. Winding 17 supplies a diode 
21 and a capacitor 24 for supplying lower level DC voltage to the audio 
circuits of the receiver, also not shown, and winding 19 similarly 
supplies approximately 12 volt DC via diode 22 and capacitor 25 for 
control and other still lower voltage circuits. The latter circuits are 
coupled through transistors 26 and 28, respectively, which have their base 
control electrodes coupled to a transistor 30 that is activated by an 
on/off signal. This arrangement precludes energization of the low voltage 
B+circuitry when the television receiver is turned off while the switched 
mode power supply is still activated to supply standby power. While the 
transistors 26, 28 and 30 are used in prior art television receivers, they 
continue to be used with the arrangement of the invention. 
An opto coupler 32 of conventional construction supplies a switch 
transistor 34 for controlling the activation and deactivation of switched 
mode power supply 12. This is accomplished by means of a standby signal 
that is applied to opto coupler 32 through a resistor 36. The standby 
signal and the on/off signal are generated by a microprocessor 40 that is 
supplied with Vcc operating potential. The Vcc is taken from the output of 
a 5 volt regulator 42 that is supplied with DC voltage from the 
combination of secondary winding 19, diode 22 and capacitor 25. An energy 
storage capacitor 44 is coupled across the output of 5 volt regulator 42. 
The Vcc is also supplied to the IR remote control receiver in the 
television receiver. 
In operation, under normal conditions when the television receiver is 
turned on, switch mode power supply 12 is energized from the auxiliary 
winding 27 and opto coupler 32. Transistor 34 is operated when the standby 
signal is high which results in conduction of the photo transistor. When 
transistor 34 conducts, switched mode power supply 12 is turned on and 
repetitively enables switch transistor 16 to develop an AC current in 
transformer 13. Transformed voltage is supplied by the secondary windings 
15, 17, 19 and auxiliary winding 27, rectified and supplied to their 
respective circuits, including the 5 volt regulator 42 which supplies Vcc 
to capacitor 44 and to microprocessor 40. In the on condition of the 
television receiver, the standby signal assumes its off (high) state and 
the on/off signal is on. Therefore, transistors 26, 28 and 30 are operated 
and permit power flow to the appropriate circuitry in the television 
receiver. 
When the television receiver is turned off, the on/off signal from 
microprocessor 40 goes to its off state and disables transistors 26 and 28 
via transistor 30. The microprocessor also places the standby signal in 
its on (low) state which, via opto coupler 32, turns off switched mode 
supply 12. Thus there is no voltage developed across transformer 13. 
Microprocessor 40 now receives Vcc from energy storage capacitor 44 which, 
being on the output side of 5 volt regulator 42, is isolated from the 
circuits on the input side of the regulator. When the Vcc supplied to 
microprocessor 40 falls to a predetermined minimum, microprocessor 40 will 
turn off the standby signal (making the standby signal high) to enable 
activation of switched mode power supply 12 via opto coupler 32 and 
transistor 34, and once again, voltage will be developed across secondary 
windings 15, 17 and 19. The potential developed across winding 15 is 
ineffective to operate the television receiver deflection circuit because 
the necessary lower DC voltages from capacitors 24 and 25 are cut off by 
transistors 26 and 28 which remain nonconductive. The voltage developed 
across capacitor 25 however is taken before transistor 28 and supplied to 
the 5 volt regulator 42 to recharge capacitor 44. When capacitor 44 has 
been recharged, the reappearance of Vcc at the appropriate level causes 
microprocessor 40 to turn the standby signal back on and shut down 
switched mode power supply 12. Thus switched mode power supply 12 is 
periodically activated to replenish the energy of storage capacitor 44 and 
deactivated when the energy is replenished. All of the other circuits of 
the television receiver are deactivated so that the only power required 
while the switched mode power supply is on (when the television receiver 
is off) is that for replenishing energy storage capacitor 44. 
Consequently, the average power required by the television receiver in the 
standby mode is minimal and only slightly above the actual power used by 
the microprocessor 40 in its standby mode and by the IR receiver. The 
novel power supply is therefore cost effective, simple and energy 
efficient. 
It is recognized that numerous changes in the description of the invention 
will be apparent to those skilled in the art without departing from its 
true spirit and scope. The invention is to be limited only as defined in 
the claims.