Power Supply Regulator for Television

The invention relates to an arrangement for regulating a run supply voltage of a television apparatus.

In, for example, a television receiver, a pulse-width modulator, or voltage regulator may generate a pulse-width modulated control signal, at a horizontal deflection related frequency. The control signal may be coupled to a power supply switching stag that supplies a regulated B+ supply voltge to a horizontal output stage. The voltage regulator circuitry may be combined with horizontal circuit (IC) that is referred to herein as the deflction IC. The deflection IC may be required to operate, selectively, in a power-up mode and in a standby mode, in accordance with an on/off control signal provided by a remote rceiver. Such pulse-width voltage regulator may be required to supply, in the power-up mode, the pulse-width modulated control signal for controlling the power supply that generates the regulated B+ supply voltage used for operating the horizontal output stage of the receiver. When operation in the standby mode is required, such control signal may be required to prevent the power supply from energizing the deflection output stage until such time as a user initiates a power-up command that is provided via the remote receiver.

The deflection IC that includes, for example, the voltage regulator, may include other portions that are required to be energized during both the power-up and the standby modes. A second voltage regulator such as a shunt regulator integral to the IC, for example, may be coupled between a supply voltage receiving terminal of the deflection IC and ground for regulating the supply voltage of the deflection IC during both the power-up and standby modes. Similarly, the remote receiver may also be required to be energized during both the power-up mode and the standby mode.

A standby power supply for the deflection IC 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 may be rectified to produce a DC, standby energizing voltage. The standby energizing voltage may be applied to the supply voltage receiving terminal of the deflection IC to energize, for example, that portion of the deflection IC that is required to be energized by the standby power supply during the standby mode; whereas, during the power-up mode, the run-mode power supply provides the energizing voltage to such terminal. The shunt regulator may regulate the energizing voltage at such terminal during both the power-up and standby modes.

The regulated, energizing voltage, developed at the supply voltage receiving terminal during the power-up mode, may be at, for example, the same level that is required by other integrated circuits of the television receiver. Therefore, it may be desirable to utilize such regulatd energizing voltage to regulate a second supply voltage that is coupled to various other circuits of the television receiver and that provides a corresponding supply current during operation in the power-up mode.

It may be desirble to obtain such regulation of the second supply voltage with as few circuit components as possible. Furthermore, it may be desirable that, during operation in the standby mode, the second supply voltage generating and regulating circuitry will not load the standby power supply that is coupled to the supply voltage rceiving terminal of the deflection IC. Reduction of the supply current that is required from the tnadby transformer during the standby mode is desirable so as to reduc the cost of such transformer.

In accordance with an aspect of the invention, a television apparatus power supply generates a first supply voltage during a normal operation power-up mode of the power supply. a second supply voltage is coupled to a first terminal of a first load circuit to develop a first terminal supply voltage prior to operation in the power-up mode. A switching arrangement is coupled between the first supply voltage and the first terminal for coupling, during the power-up mod, the first supply voltage to the first terminal to develop, during the power-up mode, the first terminal supply voltage at the first terminal. A voltage regulator supply voltag such that the regulated first terminal supply voltage is coupled through the switching arrangement, during the power-up mode, to a second terminal of the switching arrangement to regulate at the second terminal a third supply voltage that, prior to the operation in the power-up mode, is isolated by the switching arrangment from the first terminal.

The sole FIGURE illustrates a television power supply including a supply regulator embodying the invention.

The sole FIGURE illustrates a portion of a television reciever incorporating a deflection IC 100. Such portion of the television receiver includes a bridge rectifier 101 that rectifies a mains supply voltage V.sub.AC to produce a DC, unregulated voltage V.sub.UR. A conventionally designed output stage, or switch regulator 102 that may include a silicon controlled rectifier (SCR) produces, in a power-up 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.sub.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.sub.H. A control signal H.sub.r, at the horizontal rate f.sub.H, that is produced in a corresponding portion of deflection IC 100, referred to herein as a horizontal processor 100a, is coupled via a horizontal driver 666 to the base electrode of transistor Q1. Signal H.sub.r controls the switching of transistor Q1 to generate a deflection current i.sub.y in a deflection winding L.sub.Y of output stage 99. A retrace voltage V.sub.w2 is produced in a conventional manner across a winding W1 of tranformer 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.sub.w2 in a rectifier arrangement 104 that is coupled to winding W1. 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 corresponding portion of deflection IC 100 that is referred to herein as switch mode regulator and pre-driver 100b to provide a feedback signal. Regulator and pre-driver 100b generates a pulse width modulated signal S.sub.c that controls the duration, in each horizontal interval H, in which switch regulator 102 is conductive. The duty cycle of signal S.sub.c varies, in accordance with a difference between a voltage that is proportional to voltage V+ and a reference voltage V.sub.NIN that may be produced in a conventional manner. Signal S.sub.c causes regulated voltage B+ to be at a predetermined DC voltage level such as, illustratively, +125 volts. Signal S.sub.c, voltage B+ and voltage kV+ that may be produced in a conventionally known manner are produced, illustratively, when deflection IC 100 operates in the power-up mode, but are not produced during television receiver standby-mode operation.

A standby transformer T0 steps down voltage V.sub.AC. The stepped down voltage is rectified in a rectifier arrangement 106 to produce a standby voltage V.sub.SB. Standby voltage V.sub.SB is coupled to an energizing voltage receiving terminal 120 of deflection IC 100 through a resistor R1 that charges a capacitor 66 to produce in capacitor 66 an energizing voltage V.sub.cc. Voltage V.sub.cc is coupled to terminal 120 of deflection IC 100. Regulated voltage V+ is coupled to terminal 120 via a resistor R11, that is coupled in series with a diode D2, to supply voltage V.sub.cc from voltage V+ only when deflecting IC 100 operates in the power-up mode. Diode D2 that is nonconductive during the standby mode prevents current drain via load 900 from standby transformer T0.

Standby voltage V.sub.SB is coupled to a remote receiver 107 to provide the operating voltage of remote receiver 107. Remote receiver 107 causes, via a drain of an MOS transistor 108, when transistor 108 is conductive, a a low impedance to be formed at a terminal 109 of deflection IC 100. The low impedance occurs after, for example, a user initiates a power-on command via an infra-red communication link that cuases a start-up interval to occur. When transistor 108 becomes conductive, it causes an on/off control circuit 555 to generate a control signal 555a that applies voltage V.sub.cc to horizontal processor 100a; consequently, a horizontal oscillator, not shown in the FIGURES, of processor 100a begins operating and signal H.sub.r is generated. Similarly, a control signal 555b of circuit 555 applies voltage V.sub.cc to pre-driver 100b that causes pre-driver 100b to generate signal S.sub.c.

At the beginning of the start-up interval, horizontal driver 666 is energized by standby voltage V.sub.SB. Voltage V.sub.cc is then obtained from the charge previously stored by arrangement 106 in capacitor 66. 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 supplying voltage V.sub.cc in the power-up mode from voltage V+.

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.sub.y and the raster on a display device of the television receiver are turned-off.

An input supply current i.sub.PS is coupled through terminal 120 to deflection IC 100 for providing the energizing current of deflection IC 100. During operation in the power-up mode, current i.sub.PS is supplied mainly by rectifier arrangement 104 through diode D2 and D4; whereas, during operation in the standby mode, current i.sub.PS is supplied from standby transformer 106 via rectifier arrangement 106 and resistor R1.

Voltage V.sub.cc is regulated in deflection IC 100 by a shunt regulator 131 that is required to regulate voltage V.sub.cc during operations in both the standby mode and the power-up mode. Regulation of voltage V.sub.cc during the standby mode may be desirable for protecting deflection IC 100 from an over-voltage condition at terminal 120 that may occur should voltage V.sub.cc exceed the voltage rating of deflection IC 100, during the standby mode. If permitted to occur, such over voltage condition may damage deflection IC 100. Voltage V.sub.cc may also be required to be a regulated voltage, during the standby mode, for operating, for example, on/off control circuit 555 of deflection IC 100. Shunt regulator 131 regulates voltage V.sub.cc, in accordance with a reference voltage V.sub.BG2, that is generated during both the power-up and standby modes. Voltage V.sub.BG2 is generated in, for example, in a bandgap type voltage source 105 that is, therefore, required to operate during both the standby and the power-up modes.

Various circuits in the receiver such as, for example, a second IC of the television reciver, 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.sub.RUN in the FIGURE. Voltage V.sub.RUN may be required to be at a level that is equal to that of, for example, voltage V.sub.cc. It may be desirable to utilize voltage V.sub.cc that is regulated by shunt regulator 131 to also provide regulation of voltage V.sub.RUN.

In accordance with an aspect of the invention, a transistor Q2 having a collector electrode that is coupled to voltage V+ at a terminal 104a produces regulated voltage V.sub.RUN at a emitter electrode of transistor Q2. The base electrode of transistor Q2 is ocupled to the anode of diode D2. The base current of transistor Q2 is provided by resistor R111. The forward voltage drop across diode D2 is summed with voltage V.sub.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.sub.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.sub.cc. A current i.sub.RUN that is supplied via transistor Q2 to load 999 is outside the current path of current i.sub.PS that is coupled to deflection IC 100 via terminal 120.

In accordance with another aspect of the invention, temperature related changes of the voltage across the base-emitter junction of transistor Q2, are temperature compensated by diode D2 to render voltage V.sub.RUN regulated and temperature compensated. Furthermore, using a bandgap type voltage source such as source 105 for regulating voltage V.sub.RUN provides, advantageously, temperature compensation with tighter tolerances than obtained by using a zener diode that is used in some prior art circuits. Also, unlike a zener diode, the bandgap type voltage source can be designed to provide any selected voltage within a given range of voltages. Using resistor R111, diode D2 and shunt regulator 131, that are used for operating deflection IC 100, also for controlling transistor Q2 to obtain regulation of voltage V.sub.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 ocupled via resistor R111, causes diode D2 to be conductive. Resistor R111 is required to developing a voltage drop that is equal to the difference between voltage V+ and a sum voltage of voltage V.sub.cc and the forward voltage drop across diode D2.

During the standby mode it is undesirable to load transformer TO and capacitor 66 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 T0. Diode D2, advantageously, prevents the loading of transformer T0 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 T0 by diode D2 that is switched off.