JP2644538B2 - Bipolar sawtooth power amplifier circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a push-pull amplifier for a convergence correction circuit of a display device using a CRT, and in particular, achieves vertical keystone distortion correction of a projection display device with low power. And a bipolar sawtooth power amplifier circuit.

[Prior Art] In a projection display device, three colors of red, green and blue are used.
In general, a projection tube (CRT) of a book is horizontally juxtaposed with a projection lens, and a color image is projected and synthesized on one screen.

And in this type of projection display device, red,
The blue image is projected obliquely to the screen,
Since the image is superimposed on the image of the force projected from the front, a trapezoidal distortion as shown in FIG. 3 is generated based on the projection geometry, and this results in a color shift. This color shift pattern is called a vertical keystone.

In order to correct the color shift, it is necessary to correct the deflection of the electron beam of the projection tube. For the deflection correction, an electromagnetic yoke means is mounted on the neck of the projection tube, and
This is achieved by passing a current having a waveform whose horizontal axis is shown as a time axis t in FIG. This waveform is usually called a butterfly waveform, and is generated by multiplying a sawtooth wave of a horizontal scanning period (T _H ) and a sawtooth wave of a vertical scanning period.

FIG. 5 is a block diagram of a correction circuit according to the prior art, wherein 1 is the above-mentioned butterfly signal, 2 is a negative feedback amplifier, 3
Is a class B push-pull output circuit, 4 is an electromagnetic yoke for deflecting the electron beam, 5 is a current detecting resistor, and the detected voltage is negatively fed back to two negative feedback amplifiers. Therefore, a current proportional to the butterfly signal of the input 1 flows through the electromagnetic yoke 4. In addition, those related as this kind of circuit include:
Home projection TV, C4 manufactured by Hitachi, Ltd.
The 5-K55 has a conversion sense circuit and an output up circuit.

[Problem to be Solved by the Invention] In the above-mentioned conventional technology, there is a problem that the power consumption of the power supply is extremely large. That is, the horizontal scanning frequency is about
In a 64 KHz high-definition display device, it is necessary to supply an average of 50 mA each from a ± 60 V power supply, and the total is 6 W per color. The circuit shown in FIG. 5 is required for each of red and blue, and the total of red and blue requires about 12 W of electric power.

SUMMARY OF THE INVENTION An object of the present invention is to provide a bipolar sawtooth power amplifier circuit configured to significantly reduce the power consumption for correcting the convergence distortion, particularly trapezoidal distortion.

[Means for Solving the Problems] The above object is achieved by providing an output section of a class B push-pull amplifier circuit with two outputs.
A series connected diode is connected, and an output is obtained from a connection midpoint of this diode, and a canta paster is added between the connection midpoint serving as the output node and the ground,
It is also achieved by reducing the power supply voltage by a factor of several compared to the prior art.

[Operation] The capacitor resonates with the inductance of the electromagnetic yoke based on the initial current of the electromagnetic yoke in response to a sudden change in the input signal during the horizontal feedback period to generate a flyback pulse. This flyback pulse voltage has a positive polarity in the upper part of the screen and is generated with an amplitude several times the positive side power supply voltage of the class B push-pull output circuit. In the lower part of the screen, the polarity is negative, and it is several times larger than the negative power supply voltage. The output voltage can exceed the power supply voltage due to the addition of two diodes. This is because for each of the positive / negative flyback pulses, each of the two diodes performs a cut-off operation.

Therefore, the power consumption can be reduced to a fraction of that of the prior art.

The above description has been made on the assumption that an electromagnetic yoke having the same inductance value as that of the conventional technology is used for easy understanding. However, since the essential parameter is electromagnetic energy, the product of the power supply voltage and the required current is reduced even when another inductance value is used.

[Example] Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a circuit configuration diagram of one embodiment of the present invention, and the main portions thereof are portions indicated by reference numerals 6, 7, and 8.

 The operation of the figure will be described below.

1 is the butterfly signal described above, 9 and 10 are differential intensifiers, and 11 is a current source for supplying a bias current of about 6 mA. 12, 13, and 14 are current mirror circuits. Reference numeral 15 denotes a diode for temperature compensation.

16 and 17 are class B push-pull output transistors, 7 and 8 are two diodes constituting a main part of the present invention, 6 is a capacitor constituting a main part of the present invention, 4 is an electromagnetic yoke, and a horizontal scanning cycle number is 64 KHz. In the use of the above, about 80 μH is used. Reference numeral 5 denotes a current detection resistor having a resistance value of about 2Ω and a power supply voltage ± V _CC of about ± 12V.

In the figure, the value C of the capacitor 6 is selected to be approximately the value of the following equation (1).

Therefore, a value of 4 mμF is selected.

The voltage detected by the detection resistor 5 is fed back to the differential amplifiers 9 and 10, and the current mirror circuits 12, 13, and 14 output transistors 1
6, 17 A negative feedback loop passing through the electromagnetic yoke 4 is formed. Therefore, the current flowing through the electromagnetic yoke 4 is similar to the input signal 1.

The negative feedback operation is performed within the horizontal scanning feedback. In the horizontal feedback period at the top / bottom of the screen, one of the transistors 16 and 17 is cut off and the other is saturated.

Figure 2 an alien waveform diagram showing the respective portions waveform corresponding to the top of the screen in FIG. 1 in a horizontal period, E _i is the input signal, E
_R is the potential difference across the current detecting resistor 5, the E _L in the potential difference across the electromagnetic yoke 4, E _L1 in the figure the upper peak value, E _L2 is lower peak value. Current flowing in the upper part of the screen to the electromagnetic yoke 4 (I _OP) is a sawtooth wave of about ± 0.4 A, becomes ± 0.8V (1.6V _PP) E _R correspondingly. The magnitude of the flyback pulse E _L1 is obtained from the following equation (2).

Equation (2) means that electromagnetic energy is converted to electrostatic energy in a resonance process during a retrace period.

On the other hand, E _{L2 in} FIG. 2 is given by the following equation (3), where T _S is the horizontal scanning period.

Accordance connexion, a power supply voltage required in the top of the screen the horizontal scanning period, the -5.8V a sum of the E _R and the E _L2,
A total of about −9 V is obtained by adding the subtotal of about 3 V of the loss voltage of the diode 8 and the transistor 17 shown in FIG.

The flyback pulse voltage of 56 V generated during the feedback period can exceed the positive power supply voltage because the diode 7 performs a cut-off operation. At this time,
12, 16 are in the "ON" state, and 13, 14, 15, 17 are in the "OFF" state. The operation at the upper part of the screen has been described above.

At the bottom of the screen, in the above description, positive / negative, ON
Inverts / OFF and performs the same operation as above.

Therefore, at the power supply voltage of ± 9 V, electromagnetic energy equivalent to the case of the class B push-pull amplifier with the power supply voltage of ± 60 V in the prior art can be supplied to the electromagnetic yoke 4. In the present invention, the average current supplied from each power supply of ± 9 V is I _OP = ±
Corresponding to 0.4 A, each becomes ± 50 mA as in the conventional technology. Referring butterfly waveform of FIG. 4 because the average current is because the respective 1/8 of I _OP.

Therefore, the required power in the present invention is 9V × 50mA × 2 = 0.
9W / color. This is about 1/1 of the power required 6W / color of the prior art.
It is 6 or less.

In the prior art, the reason why an efficient operation as in the present invention could not be achieved is that, for example, in the upper part of the screen, the diode 7 shown in FIG. 1 does not exist, and therefore, even if the capacitor 6 is added. This is because, during the horizontal feedback period, the transistor 16 is saturated, preventing the output voltage from exceeding the power supply voltage. Also at the lower part of the screen, the generation of the flyback pulse was prevented by the saturation of the transistor 17.

Reflecting on the concept of the present invention from another point of view, it can be seen that the concept is based on the same principle as the generation of the flyback pulse by the combination of the horizontal output transistor and the damper diode in the so-called horizontal deflection circuit means. That is, in the upper part of the screen, 14 and 17 in FIG. 1 are equivalent to horizontal output transistors, and 7 and 16 are equivalent to dipole diodes. In the lower part of the screen, 12, 16 act as horizontal output transistors, and 8, 17 act as dipole diodes.

The embodiment of the present invention has been described above. FIG. 1 shows a case where the transistors 16 and 17 are push-pull amplifiers of an emitter output type, but one or both of them can be replaced with a collector output type configuration.

Although the present invention has been disclosed for the purpose of correcting trapezoidal distortion of a projection optical system, it can be generally applied as a bipolar sawtooth power amplifier to an inductance load.

[Effects of the Invention] As described above, according to the present invention, a bipolar sawtooth wave having an excellent function of correcting trapezoidal distortion caused by a projection optical system with a fraction of low power as compared with the related art. A power amplifier circuit can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of one embodiment of the present invention, and FIG.
FIG. 3 is an explanatory diagram of a color shift distortion pattern of the projection optical system, FIG. 4 is an explanatory diagram of a butterfly waveform, and FIG.
The figure is a circuit configuration diagram of the prior art. 1 ... Input correction signal, 4 ... Electromagnetic yoke, 5 ... Current detection resistor, 6 ... Capacitor, 7,8 ... Diode, 9,10
…… Differential amplifier, 11… Current source, 12,13,14… Current mirror circuit, 15… Diode, 16,17 …… Output transistor.

Claims (1)

(57) [Claims] 1. A push-pull amplifier having an output transistor for supplying a bipolar sawtooth current to an inductance load, wherein the output transistor is connected by at least two diodes connected in series, and the output transistor is connected in series. Connecting the output current from the connection point of the diode to the inductance load, connecting a capacitor substantially in parallel with the inductance load, causing the capacitance of the capacitor to resonate with the inductance of the inductance load, A bipolar sawtooth power amplifier circuit which corrects convergence by generating positive and negative flyback pulses exceeding a power supply voltage at a connection midpoint.