JPS635950B2 - - Google Patents

Description

BACKGROUND OF THE INVENTION This invention relates to a power supply for a television receiver, and more particularly to a power supply that provides an regulated output voltage that is controlled in response to changes in the load of an output circuit.

A television power supply supplies one or more precisely regulated voltages to ensure reliable operation of the load circuits it supplies. Uncontrolled changes in the voltage supplied to the load circuit can cause distortion in the reproduced television signal.

In some types of power supplies, the primary winding of the transformer is connected via a switch to an unregulated voltage source, typically drawn from an AC dry wire, which allows the current flowing through the primary winding to flow at a horizontal deflection period. Therefore, a voltage is induced in the secondary winding, and this induced voltage is rectified and filtered to become a supply voltage to each load circuit of the receiver. The level of this secondary voltage, or load circuit voltage, controls the operation of the primary winding switch to control the conduction period of the primary winding so that the secondary winding voltage is maintained at a regulated constant level. used for monitoring.

Despite the need to maintain the load circuit voltage at a constant value as mentioned above, under certain circumstances it may be desirable to adjust the level of the supply voltage of at least one load circuit depending on the operating state of the receiver. There is. In particular, when the brightness of the reproduced object increases, or when the brightness controller of the receiver is adjusted to increase the brightness, the scanning electron beam current increases.
This increase in electron beam current increases the current in the high voltage winding that supplies the anode potential of the picture tube.
This increase in current increases losses in this high voltage winding due to transformer leakage inductance and rectifier diode resistance losses, thereby causing a drop in the high voltage level.

The high voltage, i.e. the reduction in the electron beam accelerating potential, reduces the speed of the electron beam as it traverses the distance between the electron gun and the video tube display screen, thus reducing the time that the deflection field, especially the horizontal deflection field, acts on each electron. becomes longer and the size of the scan raster increases.
If the program material causes sudden or extreme changes in subject brightness, the change in image size can be noticeable and unsightly, so the scan raster size is reduced as the beam current increases. It is essential to reduce the supply voltage level of the deflection circuit.

One solution to this problem is to provide a beam current information return path in the voltage regulation control circuit to reduce the regulation voltage level of the deflection circuit power supply as the beam current increases. This configuration may reduce the supply voltage of other circuits in the receiver, necessitating the addition of voltage adjustment circuits to each of these power supplies, making the receiver expensive and complex. Another solution is to insert a resistor in series between the power transformer's primary winding and the regulated B+ supply, but the increased beam current will load the B+ supply and cause the primary winding to The increased current flowing creates a voltage drop across that resistor, reducing the regulation B+ voltage level. This solution therefore unnecessarily increases the power consumption of the receiver.

The present invention relates to a power supply that reduces the deflection circuit supply voltage in response to a reduction in high voltage without causing unnecessary interaction with the power supplies of other load circuits and without increasing the power consumption of the receiver.

<Summary of the Invention> A television receiver according to the invention includes a power supply with a plurality of load circuit voltage sources, one of which is used to generate a high voltage; The high voltage is a voltage whose level decreases as the beam current increases.

A deflection circuit is also energized by this high voltage generating power supply and provides a deflection current that deflects one or more electron beams, the level of which deflection current being determined by the average DC level of the supply voltage to the deflection circuit. . A control circuit controls operation of the power supplies in response to the detected voltage levels to maintain the voltage level of each voltage source substantially constant. A peak detection circuit detects the voltage supplied to the high voltage generation deflection circuit and supplies a voltage representing the peak level of the voltage to the control circuit. The average DC level of the deflection circuit supply voltage decreases as the beam current increases, compensating the electron beam deflection current for the decrease in high voltage level.

DISCLOSURE OF THE INVENTION The operating power for the illustrated circuit is provided by an AC mains power supply 1 connected to a bridge rectifier 11 and a filtering capacitor 12 to produce an unregulated DC voltage at terminal 13.
Supplied from 0. This unregulated voltage is applied to one terminal of a primary winding 14 of a power transformer 15, to the other terminal of which a switching transistor 16 and a buffer network 17 are connected to control the switching. 1 due to conduction of the switching transistor 16.
The secondary winding 14 is adapted to receive current from the unregulated power supply. This current causes transistor 1
6 is non-conducting, the secondary windings 20, 2 of the transformer 15
The energy transferred to 1, 22, 23 is stored in the primary winding 14. Due to imperfect magnetic coupling between the primary winding 14 and each secondary winding, some of that energy remains in the primary winding, but the residual energy in the diode 24, capacitor 25 and resistor 2
6, the transistor 16 is protected from the risk of voltage breakdown.

The energy transferred to the secondary windings 20, 21, 22, 23, shown as portions of one winding with multiple taps, induces a respective voltage across each winding, which voltage is associated with The voltage is rectified and smoothed by a diode and a capacitor to form a DC voltage source for supplying power to each load circuit of the receiver. For example, winding 20 has 127V at terminal 30.
The winding 21 generates a +24V class voltage at the terminal 31, the winding 22 generates a +16.5V class voltage at the terminal 32, and the winding 23 generates a -16.5V class voltage at the terminal 33. .

The 127V voltage developed at terminal 30 is passed through primary winding 34 of high voltage transformer 35 to horizontal deflection circuit 36.
is supplied to The horizontal deflection circuit 36 includes a horizontal output switching transistor 37, a retrace capacitor 40, a damper diode 41, a horizontal deflection yoke winding 42, and an S-shaped capacitor 43, and generates a horizontal deflection current in the deflection yoke winding 42. This deflection current produces a time-varying magnetic field in the vicinity of a deflection yoke winding 42 located at the neck of a television picture tube (not shown). This time-varying magnetic field imparts a desired deflection or scanning motion to one or more electron beams in the picture tube.

The operation of horizontal output switching transistor 37 is controlled by a switching signal applied to its base from horizontal drive circuit 44, which is also powered from the 127V power supply as shown. The correct timing of the switching signal for transistor 37 is provided by a horizontal oscillator 45, which is powered from the +16.5V supply as shown.

The current that periodically flows through the primary winding 34 of the high voltage transformer 35 induces a voltage in the high voltage winding 46, which generates a 25KV class anode voltage at the terminal 47, which is transferred to the picture tube high voltage terminal (Fig. (not shown). A voltage is also induced in the secondary winding 50 of the high voltage transformer, and this voltage is rectified and smoothed by associated diodes and capacitors, producing a +230V class DC voltage at terminal 51, which is used, for example, in a video tube. It may also be used to power an electron beam drive circuit (not shown).

By controlling the conduction time of switching transistor 16, and thus the amount of energy stored in primary winding 14, the level of the supply voltage produced by secondary windings 20, 21, 22, 23 is controlled or adjusted. You can also do that. This is a Matsushita integrated circuit that detects one or more supply voltages and supplies a pulse width modulated drive signal to the base of the switching transistor 16 via a drive circuit 53.
This is achieved by a constant voltage control circuit 52 such as AN5900. The voltage detected by the constant voltage control circuit 52 is drawn from the 127V power supply used to generate the high voltage for the picture tube and to feed the horizontal deflection circuit 36, as described above. Drive circuit 53 includes an isolation transformer which, together with power transformer 15, electrically isolates the receiver load circuit from the AC mains power supply and facilitates coupling of the receiver to external program sources and regeneration components. .

As the picture tube electron beam current increases, i.e., for example, when the brightness adjustment of the receiver is increased or the subject brightness increases, the number of electrons that impinge on the picture tube anode increases, but the current path for these electrons increases. Since the electron current passes through the voltage winding 46, this increased electron current increases energy loss in the winding 46 due to leakage inductance loss and resistance loss, lowering the high voltage level and further reducing the accelerating potential of the electron beam in the picture tube. let Therefore, since the time required for the electrons to reach the screen is increased, the scanning area for a given deflection field strength is increased. Therefore, unless this deflection magnetic field or deflection current is corrected, the raster displayed on the display screen of the picture tube will inconveniently expand or contract as the brightness level changes.

The increase in energy loss in the high voltage winding 46 is reflected in the primary winding 34, requiring a corresponding increase in its current, but this increase in current must be provided by the 127V supply, so that the picture tube beam As the current increases, the load on the 127V power supply increases, and the AC ripple component of the rectified and smoothed voltage generated at terminal 30 increases. According to the present invention, a diode 55 and a capacitor are provided in the detection return path from the 127V power supply to the adjustment control circuit 52 to detect the peak level of the voltage drawn from the 127V power supply and to supply the voltage to the adjustment control circuit 52. A peak detector 69 including 62 is provided. The amount of AC ripple in a 127V power supply is the smoothing capacitor 54
The capacitor 54 is selected to ensure that when the beam current exceeds a predetermined threshold, an appropriate amount of AC ripple occurs to provide the desired correction effect of the present invention. do.

The voltage divider circuit 59 in the detection feedback path consists of a resistor 60 and parallel resistors 61, 63, 64, 65, and serves several functions, one of which is the regulation control circuit 5.
2 is to provide the necessary input voltage correction level. Voltage divider 59 also reduces the amplitude of the detection voltage provided to peak detector 69 from +127V power supply terminal 30 to a level low enough that only low voltage capacitor 62 is required. If peak detection diode 55 and capacitor 62 are connected to voltage divider 59
If it is located earlier, a capacitor with a higher rated voltage will be required. The voltage divider 59 is connected to the peak detector 6
In conjunction with capacitor 62 at 9, it also serves the function of determining the response time of the voltage regulation loop. Therefore, the value of capacitor 62 should be selected to satisfy both the desired value for detecting the peak value of the ripple component of the +127V power supply and the value necessary to make the response time of normal voltage regulation sufficiently fast. You have to choose. The values of the parallel resistors 61, 63, 64, 65 are selected such that at least one of them can be omitted and still provide a detection voltage such that the supply voltage at terminal 30 is regulated to the desired level, i.e. 127V. There is.

Using the AN5900 integrated circuit described above as shown, the cathode of diode 55 is connected to input pin 2 of this integrated circuit. This AN5900 integrated circuit needs to provide a reference voltage at pin 1, which is a 6.2V Zener diode 70 bypassed by a resistor 71 and a capacitor 72 as shown.
Provided from a +16.5V power supply grounded through the In this configuration, capacitor 62 should be fed back to reference voltage terminal pin 1. A resistor 73 is connected between pins 1 and 2 of the adjustment control circuit 52,
It forms a discharge path for the capacitor 62 and facilitates the starting operation.

The regulation control circuit 52 functions to maintain the peak voltage of the 127V power supply constant at 127V. As mentioned above, due to the increase in the AC ripple of the 127V supply voltage due to the increase in beam current, the average DC value of this 127V supply voltage decreases slightly, to, for example, 124V, thereby decreasing the DC supply voltage of the horizontal deflection circuit 36. This reduction in supply voltage results in a reduction in the deflection current amplitude produced by deflection circuit 36, thereby compensating for the reduction in high voltage level discussed above. Furthermore, this reduction in the high voltage level due to the reduction in the average value of the B+ power supply voltage does not produce any untoward effects because the sensitivity of electron beam scanning to changes in the high voltage level is lower than the sensitivity to changes in the 127V power supply voltage.
Correct selection of the values of the filtering and supply capacitors associated with the secondary load circuit voltage source of transformer 15 will result in:
Any adverse changes in these supply voltage levels due to increased AC ripple on the regulated 127V power supply are virtually eliminated. This secondary load circuit power supply is inherently regulated to the peak voltage level of the regulated B+ power supply. Since this level is regulated and maintained at a substantially constant value, changes in the electron beam current do not substantially change the voltage supply level of the secondary voltage power supply of the transformer 15.

The invention further protects the receiver under severe power load conditions such as picture tube discharge. Under such conditions, the average DC supply voltage is significantly reduced, thereby reducing electrical stress on receiver components such as the horizontal output transistors.

[Brief explanation of the drawing]

The figure is a circuit diagram of a portion of a television receiver including a power supply constructed according to the present invention. 16...Means comprising a plurality of load circuit voltage sources,
36...Deflection circuit, 46...Extracting means, 52...Controlling means, 59...Coupling means, 69...Detecting means.

Claims (1)

Claims: 1. A first device coupled to means for deriving a high voltage level.
means for forming a plurality of load circuit voltage sources including a load circuit voltage source; energized by the first load circuit voltage source;
a deflection circuit that supplies an electron beam deflection current at a level determined by the average DC level of its output voltage; and a deflection circuit that maintains the voltage level of each load circuit voltage source approximately constant according to the supplied voltage level. , comprising a control means for controlling the operation of the voltage source forming means, and a detection means for generating a voltage level representing a peak value of the output voltage of the first load circuit voltage source and supplying it to the control means; means for coupling the first load circuit voltage source to the control means, wherein the high voltage level exhibits a tendency to change in response to fluctuations in the high voltage load; The load circuit voltage source generates a corresponding AC ripple in its output voltage in response to variations in the high voltage load, and the resulting changes in the average DC level of the output voltage cause a change in the high voltage level. 1. A television receiver, characterized in that it compensates for changes in the amount of electron beam deflection caused by changes in electron beam deflection.