A power supply for a television apparatus

Abstract: During a power-up mode of a television receiver power supply, a first run supply voltage (V+) is generated by rectifying a retrace voltage (V W2 ) in a flyback transformer (T1) of a horizontal output stage (99) of the television receiver. The first voltage (V+) is coupled (through a resistor (R111) and a diode (D2)) to a power supply voltage receiving terminal (120) of a load circuit (998). A voltage regulator (105), typically including a pass transistor (Q3), regulates the voltage at the terminal (120) during both the power-up and standby modes. During the power-up mode, when the ambient temperature is higher than during the standby mode, the current in the transistor (Q3) is lowered, as a result of a current (i R ) that is coupled to the terminal (120) via the diode (D2). This reduces the power dissipation in the transistor (Q3) during the power-up mode. Optionally, a second transistor (Q2), having a base electrode that is coupled to the anode of the diode (D2), generates a second, temperature compensated run supply voltage (V RUN ) at an emitter electrode of the transistor (Q2).

Description: The invention relates to a power supply for supplying a supply voltage to circuitry of a television apparatus during, for example, both run and standby modes of operation of the power supply. In a television receiver, for example, that is capable of operating in a standby mode, in which power dissipation and heat generation in the television circuit components is low, a standby power supply is typically required for energizing television circuitry that includes, for example, a remote control unit that enables start-up operation during a transition from the standby to the power-up mode. US-A-4 651 214 discloses a power supply of a television apparatus comprising: a source of input supply voltage; an unregulated stand-by power supply coupled to said source including a storage capacitor for developing a standby supply voltage during both standby mode and power-up mode of said supply; a load circuit of the television apparatus coupled to the storage capacitor of the standby power supply via a disconnect diode and being energised thereby during the standby mode; a source of an on-off control signal such as a remote control signal receiver; and a source of run supply voltage responsive to the on/off signal for generating run-mode power to at least the said load circuit during power-up mode; the arrangement being such that during the transition from stand-by to power-up mode, the unregulated power supply provides an increased load current which discharges the storage capacitor, and the disconnect diode which was forward biased by the standby power supply during stand-by mode becomes reverse biased by the source of run supply voltage so that only the run-supply powers the load circuit during power-up mode. A standby/power-up power supply may include a standby transformer having a primary winding that is coupled to an alternating current (AC) mains supply source. A voltage that is developed at a secondary winding of the transformer is rectified to produce a DC energizing voltage. The energizing voltage is applied to a supply voltage receiving terminal of the television circuitry that is required to be energized during the standby mode via a series regulator; whereas, during the power-up mode, a run-mode power supply that is inoperative during the standby mode provides a portion of the energizing current. The series regulator regulates the energizing voltage at such terminal during both the power-up and standby modes. It may be desirable to reduce the power dissipation in the regulator during the power-up mode when the ambient temperature caused by power dissipation in the various circuit components of the television receiver is higher than during the standby mode. Thereby, for example, the temperature at a P-N junction of a series coupled transistor of the regulator is prevented from exceeding a safe level, during the power-up mode. In accordance with an aspect of the invention, there is provided power supply of a television apparatus, comprising: a source of an input supply voltage; a voltage regulator coupled to said source of input supply voltage for developing at an output terminal of said regulator a first output supply voltage both during a standby mode and during a power-up mode of said power supply; a load circuit of said television apparatus coupled to said output terminal of said regulator and being energized by said first output supply voltage such that a first supply current that is generated in said regulator is coupled to said load circuit to form a load current that flows in said load circuit during said standby mode; a source of an on/off control signal; a source of a run supply voltage responsive to said on/off control signal for generating a second supply current during operation in said power-up mode; switching means, responsive to said on-off control signal, and forming a main current path between said source of said run supply voltage and said output terminal of said regulator when said switching means is conductive for coupling therethrough said second supply current to said load circuit during said power-up mode, that causes a reduction in said first supply current from said regulator such that both said second supply current and said first supply current each form corresponding substantial portions of said load current during said power-up mode. In accordance with another aspect of the invention, there is provided a television apparatus, comprising: a source of an input supply voltage; a voltage regulator coupled to said source of input supply voltage for developing at an output terminal of said regulator a first output supply voltage both during a standby mode and during a power-up mode; a load circuit of said television apparatus coupled to said output terminal of said regulator and being energized by said first output supply voltage such that a first supply current that is generated in said regulator is coupled to said load circuit to form a load current that flows in said load circuit during said standby mode; a source of an on/off control signal; a deflection winding; a deflection circuit output stage for generating a deflection current in said deflection winding; a source of a run supply voltage coupled to said deflection circuit output stage and responsive to said on/off control signal for generating a second supply current during operation in said power-up mode; and switching means, responsive to said on/off control signal, and forming a main current path between said source of said run supply voltage and said output terminal of said regulator when said switching means is conductive for coupling there-through said second supply current to said load circuit during said power-up mode that causes a reduction in said first supply current from said regulator such that both said second supply current and said first supply current each form corresponding substantial portions of said load current during said power-up mode. In the Drawing: The sole FIGURE illustrates a standby/power-up television power supply including a supply regulator embodying an aspect of the invention. The sole FIGURE illustrates a portion of a television receiver incorporating a control circuit 100. Such portion of the television receiver includes a bridge rectifier 101 that rectifies a mains supply voltage V AC to produce a DC, unregulated voltage V UR . A conventionally designed output stage, or switched regulator 102 that may include a silicon controlled rectifier (SCR) produces, in a power-up or run mode, a regulated voltage B+ that is coupled to a flyback transformer T1. An input terminal 102c of regulator 102 is coupled to unregulated voltage V UR . Regulated voltage B+ is developed at an output terminal 102d of switch regulator 102. Transformer T1 is coupled to a collector electrode of a deflection switching transistor Q1 of a horizontal circuit output stage 99 operating at a horizontal rate f H . A control signal H r , at the horizontal rate f H , that is produced in a horizontal processor portion, not shown in the FIGURE, of control circuit 100, is coupled via a horizontal driver 666 to the base electrode of transistor Q1. Signal H r controls the switching of transistor Q1 to generate a deflection current i y in a deflection winding L Y of output stage 99. A retrace voltage V w2 is produced in a conventional manner across a winding W2 of transformer T1 in each retrace interval of each horizontal period H. Each retrace interval occurs immediately after transistor Q1 becomes nonconductive. A DC, run-mode supply voltage V+, that is illustratively +16 volts, is produced by rectifying voltage V w2 in a rectifier arrangement 104 that is coupled to winding W2. Voltage V+ is also coupled to various circuits of the receiver to provide them with energy during a power-up mode of the television receiver. Such circuits are depicted as a load 900. Voltage V+ is also coupled to a switch mode regulator and pre-driver portion, not shown in the FIGURE, of control circuit 100 to provide a feedback signal. A pulse width modulated signal S C is generated that controls the duration, in each horizontal interval H, in which switch regulator 102 is conductive. The duty cycle of signal S C varies, in accordance with a difference between a voltage that is proportional to voltage V+ and a reference voltage that may be produced in a conventional manner. Signal S C causes regulated voltage B+ to be at a predetermined DC voltage level such as, illustratively, +125 volts. Signals S c and H r , and voltages B+ and V+ are produced, illustratively, when control circuit 100 operates in the power-up mode, but are not produced during television receiver standby-mode operation. A standby transformer TO steps down voltage V AC . The stepped down voltage is rectified in a rectifier arrangement 106 to produce a standby voltage V SB . Standby voltage V SB is coupled to an energizing voltage receiving terminal 120 of control circuit 100 through a series pass regulator 105 that includes a transistor Q3 having a base electrode that is coupled to a cathode of a zener diode 131. Transistor Q3 produces at its emitter an energizing voltage V cc which is filtered by capacitor 66. Voltage V cc is coupled to terminal 120 of control circuit 100. Regulated voltage V+ is coupled to terminal 120 via a resistor R111 and series coupled diode D2, to supply a corresponding portion of a current i ps from voltage V+ only when control circuit 100 operates in the power-up mode. Diode D2, that is nonconductive during the standby mode, prevents current drain via loads 900 and 999 from standby transformer TO. Voltage V cc provides the operating voltage of a receiver 107 which responds to remotely generated signals. The receiver 107 generates an ON/OFF signal that is coupled via a drain electrode of an MOS transistor 108 to control circuit 100. When transistor 108 is conductive, a low impedance is formed at terminal 109 of control circuit 100. The low impedance occurs after, for example, a user initiates a power-on command via an infra-red communication link that causes a start-up interval to occur. When transistor 108 becomes conductive, it causes a horizontal oscillator, not shown in the FIGURE, to begin operating. Consequently, signals H r and S c are generated. At the beginning of the start-up interval, horizontal driver 666 is energized by standby voltage V SB through diode 67. A current i c of regulator 105 supplies, by itself, current i ps prior to operation in the power-up mode. Thus, regulator 105 provides the entire current requirement, such as 50 milliamperes, of control circuit 100 and of other television circuitry, referred to herein as a load 998, prior to operation in the power-up mode. During the start-up interval, voltage V+, that was zero before, begins increasing. At the end of the start-up interval, when voltage V+ is sufficiently large, it causes diode D2 to turn-on for developing voltage V cc in the power-up mode from voltage V+. In accordance with an aspect of the invention, diode D2 supplies a current i R that is combined with current i c to supply current i ps during the power-up mode, such that the contribution of each to current i ps is significant. In the example of the invention shown in the FIGURE, each of currents, i c and i R contributes 50% to current i ps during the power-up mode. Because of the flow of current i R to terminal 120, current i c that is supplied by regulator 105 is, advantageously, significantly reduced relative to its value during standby. At the same time, voltage V cc is maintained regulated by regulator 105. During run-mode or power-up mode operation, the ambient temperature increases inside the cabinet of the television receiver relative to the inside temperature during standby. The increase in ambient temperature is caused by the heat dissipation of the television receiver circuitry that has become powered up during run-mode operation. The rise in ambient temperature would tend to cause a temperature rise in transistor Q3, requiring a more massive heat sinking structure for the transistor. In accordance with a feature of the invention, heat dissipation in transistor Q3 is reduced during run-mode relative to that during standby mode. The reduction in the power dissipation enable operation of transistor Q3 at, advantageously, approximately the same collector P-N junction temperature during both the power-up and the standby modes. Advantageously, by utilizing current i R to provide the corresponding portion of current i ps , a heat dissipation arrangement for transistor Q3, such as, for example, a heat sink, may not be required. In the power-up mode, the television receiver is fully operative. Conversely, after a power-off command is initiated by the user, transistor 108 becomes nonconductive and forms a high impedance circuit at terminal 109 that causes a standby mode to occur. In the standby mode, deflection current i y and the raster scanning on the display device of the television receiver are turned-off. Input supply current i ps is coupled through terminal 120 for providing the energizing current of control circuit 100 and of remote receiver 107. During operation in the power-up mode, a significant portion of current i ps is supplied by rectifier arrangement 104 through diode D2 and D4; whereas, during operation in the standby mode, current i ps is supplied entirely from standby transformer 106 via regulator 105. Various circuits in the receiver such as, for example, a second IC of the television receiver that provides video processing, that are depicted as a load 999 in the FIGURE, may require, during the power-up mode, a regulated supply voltage, that is depicted as a voltage V RUN in the FIGURE. Voltage V RUN may be required to be at a level that is equal to that of, for example, voltage V cc . It may be desirable to utilize voltage V cc that is regulated by regulator 105 to also provide regulation of voltage V RUN . Therefore, transistor Q2, having a collector electrode that is coupled to voltage V+, produces regulated voltage V RUN at an emitter electrode of transistor Q2. The base electrode of transistor Q2 is coupled to the anode of diode D2. The base current of transitor Q2 is provided by resistor R111. The forward voltage drop across diode D2 is summed with voltage V cc to produce at the base of transistor Q2 a voltage that is higher by diode D2 voltage drop that is, approximately, 0.7 volts in a silicon diode. Consequently, voltage V RUN , that is smaller than the base voltage of transistor Q2 by approximately the same voltage drop that is developed across diode D2, is equal to voltage V cc . A current i RUN that is supplied via transistor Q2 to load 999 is outside the current path of current i ps that is coupled to control circuit 100 via terminal 120. Temperature related changes of the voltage across the base-emitter junction of transistor Q2, are temperature compensated by diode D2 to render voltage V RUN regulated and temperature compensated. Using resistor R111, diode D2 and regulator 105 for controlling transistor Q2 to obtain regulation of voltage V RUN , advantageously, eliminates the need for separate resistor, diode and regulator that would have otherwise been required for providing the base voltage of transistor Q2. During operation in the power-up mode, voltage V+, that is coupled via resistor R111, causes diode D2 to be conductive. Resistor R111 is required for developing a voltage drop that is equal to the difference between voltage V+ and a sum voltage of voltage V cc and the forward voltage drop across diode D2. During the standby mode, it is undesirable to load standby transformer TO by any of load 900, load 999, resistor R111 and transistor Q2, because the cost of transformer TO is directly related to the standby current requirement from, or loading of, transformer TO. Diode D2, advantageously, prevents the loading of transformer TO during the start-up interval, as long as voltage V+ is not sufficiently large to turn on diode D2. Similarly, during the standby mode, each of load 900, load 999, resistor R111 and transistor Q2 is, advantageously, isolated from standby transformer TO by diode D2 that is non-conductive.

Claims: A power supply of a television apparatus, comprising: a source (V AC ) of an input supply voltage; a voltage regulator (105) coupled to said source of input supply voltage for developing at an output terminal (120) of said regulator a first output supply voltage (V CC ) both during a standby mode and during a power-up mode of said power supply; a load circuit (998) of said television apparatus coupled to said output terminal (120) of said regulator and being energized by said first output supply voltage such that a first supply current (i C ) that is generated in said regulator is coupled to said load circuit to form a load current (i PS ) that flows in said load circuit during said standby mode; a source (107) of an on/off control signal; a source (104) of a run supply voltage (V+) responsive to said on/off control signal for generating a second supply current (i R ) during operation in said power-up mode; switching means (D2), responsive to said on-off control signal, and forming a main current path between said source (104) of said run supply voltage (V+) and said output terminal (120) of said regulator (105) when said switching means (D2) is conductive for coupling therethrough said second supply current (i R ) to said load circuit (998) during said power-up mode, that causes a reduction in said first supply current (i C ) from said regulator (105) such that both said second supply current (i R ) and said first supply current (i C ) each form corresponding substantial portions of said load current (i PS ) during said power-up mode. A power supply according to claim 1 characterized in that said switching means (D2) also couples, during said power-up mode, said first output supply voltage (V CC ) that is developed at said output terminal (120) of said regulator (105) to a second output terminal (emitter of Q2) to regulate at said second output terminal a second output supply voltage (V RUN ) that during said standby mode is isolated by said switching means (D2) from said output terminal (120) of said regulator (105). A power supply according to claim 2 characterized in that said switching means comprises a diode (D2) having a first terminal (anode) that is coupled to said source (104) of said run supply voltage (V+) and a second terminal (cathode) that is coupled to said output terminal (120) of said regulator (105). A power supply according to claim 3 characterized in that said switching means further comprises, a transistor (Q2), wherein said diode (D2) is interposed between a control electrode (base) of said transistor (Q2) and said output terminal (120) of said regulator (105) and wherein a resistor (R111) is coupled between said control electrode (base) of said transistor (Q2) and said source (104) of said run supply voltage (V+) that causes said diode (D2) to be conductive only when said run supply voltage (V+) is generated. A power supply according to claim 4 characterized in that said diode (D2) isolates said source (104) of said run supply voltage (V+) from said regulator (105) prior to said power-up mode. A power supply according to claim 5 characterized in that a second load (999) is coupled to a main current conducting electrode (emitter) of said transistor (Q2) and wherein said diode (D2) isolates said regulator (105) from said second load (999) prior to said mode when said run supply voltage is turned-off. A power supply according to claim 4 characterized in that said diode (D2) provides temperature compensation for variations of a base-emitter junction voltage in said transistor (Q2) to produce a temperature compensated third output supply voltage (V RUN ) at an emitter electrode of said transistor (Q2). A power supply according to claim 1 characterized in that said source (106) of said input supply voltage (V SB ) comprises a step-down transformer (TO) coupled to a main supply voltage (V AC ), and a rectifier (106) having an input terminal that is coupled to said step-down transformer (TO) for generating said input supply voltage (V SB ) by rectifying a voltage that is developed at said step-down transformer (TO). A power supply according to claim 1 characterized in that said source of said run supply voltage comprises a deflection circuit (99) responsive to a control signal (H r ) at a frequency that is related to a deflection frequency. A power supply according to claim 9 characterized in that said source of said run supply voltage further comprises a flyback transformer (T1) for generating in a winding (W2) of said flyback transformer (T1) a voltage (V W2 ) at a frequency that is related to said deflection frequency and a rectifier (D4) coupled to said winding (W2) of said flyback transformer (T1) for rectifying a voltage that is generated in said winding (W2) to generate said run supply voltage (V+). A power supply according to claim 1 characterized in that said on/off control signal is generated in a remote receiver (107). A power supply according to claim 1 characterized in that said regulator (105) comprises a transistor (Q3) having a first main current conducting electrode (collector) that is coupled to said source (106) of said input supply voltage (V SB ), having a second main current conducting electrode (emitter) that is coupled to said output terminal (120) of said regulator (105) and having a control electrode (base) that is coupled to a source (131) of a reference signal at a reference level that causes said first output supply voltage (V CC ) to be maintained at substantially the same level both during and prior to said power-up mode. A power supply according to claim 12 characterized in that said source of reference signal comprises a zener diode (131) such that said reference level is produced at a terminal (cathode) of said zener diode (131). A power supply according to claim 12 characterized in that, during said power-up mode when said second supply current (i R ) is generated, said second supply current (i R ) causes said first output supply voltage that is developed at an emitter electrode of said transistor to increase slightly that, in turn, causes an emitter current (i C ) that flows in an emitter electrode of said transistor (Q3) to decrease significantly relative to its value prior to said power-up mode. A power supply according to claim 1 characterized in that, during said power-up mode, when an ambient temperature inside an enclosure that includes said television apparatus is higher than during said standby mode, said first supply current (i C ) is lower than during said standby mode and therefore causes power dissipation in said regulator (105) to be less than prior to said power-up mode, to provide temperature compensation in a P-N junction of a transistor (Q3) that is said regulator (105). A television apparatus, comprising: a source (V AC ) of an input supply voltage; a voltage regulator (105) coupled to said source of input supply voltage for developing at an output terminal (120) of said regulator a first output supply voltage (V CC ) both during a standby mode and during a power-up mode; a load circuit (998) of said television apparatus coupled to said output terminal (120) of said regulator (105) and being energized by said first output supply voltage (V CC ) such that a first supply current (i C ) that is generated in said regulator is coupled to said load circuit to form a load current that flows in said load circuit during said standby mode; a source (107) of an on/off control signal; a deflection winding (L Y ); a deflection circuit output stage (99) for generating a deflection current (i y ) in said deflection winding; a source (104,D4) of a run supply voltage (V+) coupled to said deflection circuit output stage (99) and responsive to said on/off control signal for generating a second supply current (i R ) during operation in said power-up mode; and switching means (D2), responsive to said on/off control signal, and forming a main current path between said source (D4) of said run supply voltage and said output terminal (120) of said regulator (105) when said switching means (D2) is conductive for coupling therethrough said second supply current to said load circuit during said power-up mode that causes a reduction in said first supply current (i c ) from said regulator (105) such that both said second supply current (i R ) and said first supply current (i a ) each form corresponding substantial portions of said load current during said power-up mode.

Inventors: LENDARO JEFFERY BASIL, LENDARO, JEFFERY BASIL
Applicants: RCA THOMSON LICENSING CORP, RCA THOMSON LICENSING CORPORATION
Application year: 1989
Main classification: H04N5
IPC codes: H04N5