JPH023190B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a horizontal amplitude control circuit used in a horizontal deflection circuit of a display device using a cathode ray tube (CRT).

Conventional configurations and their problems In recent years, display devices using CRTs have been used not only for television signals but also for various purposes as terminals for personal computers. Since there are various types of horizontal scanning frequencies depending on the display accuracy of characters and graphics, there is a phenomenon in which the horizontal amplitude changes depending on the frequency used. In order to cope with these problems, an increasing number of devices are changing the design for each model or having a built-in switching mode as a means for keeping the horizontal amplitude constant.

A conventional horizontal amplitude control circuit will be explained below.

Figure 1 shows a configuration diagram of a conventional horizontal amplitude control circuit. 1 is a DC power supply terminal connected to the collector of a voltage control transistor 2, and a capacitor 3 is grounded to the emitter, and the horizontal deflection It is applied to the input voltage terminal 8 of the circuit 41. The base of the transistor 2 is biased at a voltage dividing point between a resistor 4 and a resistor 5, and is grounded via a resistor 6 by a switching transistor 7. A control signal, which is the output of the _H detection circuit 17, is applied to the base of the transistor 7. The input synchronization signal _HD is applied to _{the H} detection circuit 17 and the horizontal AFC circuit 16,
The deflection output circuit is synchronized. Horizontal deflection path 41
The connection is that the horizontal output transformer 9 is connected to the input voltage terminal 8.
and the collector of the horizontal output transistor 10. 11 is a damper diode, 12 is a resonant capacitor, 13 is a deflection coil, and 14
is a DC blocking capacitor, which constitutes a well-known flyback pulse type horizontal deflection output circuit.

The operation of the conventional horizontal amplitude control circuit configured as described above will be explained.

Since the amplitude of the sawtooth current in the deflection coil is proportional to the scan time and input voltage (+V _C2 ),
Unless you change the inductance of the deflection coil.
+V _C2 needs to be lowered when the scanning time becomes longer. For this purpose, _{the H} detection signal is made high so as to lower the base potential of transistor 2, turning on transistor 7 and controlling the divided potential.

However, in the above configuration, the voltage between the collector and emitter of the transistor 2 increases as the scanning frequency becomes lower. As shown in Figure 5a
When _H changes by about twice from 31.5 KHz to 15.75 KHz, the collector loss P _c increases nonlinearly, requiring a transistor with a large capacity rating, and reliability also decreases. Also, since the input frequency is detected and switched, if the frequency is 15KHz or 22KHz when lowering from 31.5KHz to another frequency,
There is a problem in that it is necessary to set the variable resistor 16 each time.

Purpose of the Invention The present invention solves the above-mentioned conventional problems, and not only has a voltage control circuit with low loss and high power efficiency, but also provides a horizontal switching system that allows the switching frequency to be set arbitrarily and does not require readjustment. The purpose is to provide an amplitude control circuit.

Structure of the Invention The present invention provides a switching power supply that can vary the output by chopper control of a DC power supply, a sawtooth wave voltage generator that is formed by a switching discharge action using pulses shaped from the output of a horizontal AFC circuit, and This is a horizontal amplitude control circuit equipped with a comparator that controls the pulse width of the chopper control based on the voltage.The switching action can improve power efficiency, and the comparator action can eliminate the need to adjust the _H response. It is.

DESCRIPTION OF EMBODIMENTS FIG. 2 shows a configuration diagram of a horizontal amplitude control circuit in a first embodiment of the present invention. Components in FIG. 2 that have basically the same functions as those in FIG. 1 are designated by the same reference numerals. 20 is a chopper control transistor forming the switching power supply 42;
is a damper diode, and the filter 22 and capacitor 33 form a filter. The chopper control output voltage generated at the capacitor end is connected to the input voltage terminal 8 of the horizontal deflection circuit 41. The horizontal AFC circuit 16 and the horizontal drive circuit 15 have the same configuration as the conventional one, and are connected to the base of a switch transistor 25 via a shaping circuit 24 that pulse-shapes the oscillation output pulse of the horizontal AFC circuit 16. The collector of the transistor 25 is connected to a capacitor 26 for obtaining a sawtooth voltage and a constant current source circuit 27 for charging, and applies the sawtooth voltage to the base of a transistor 29 forming a comparator. 43 indicates a sawtooth voltage generator. 30 is another transistor of the comparator, a fixed bias is applied to its base by a resistor 31, and its emitter is connected to a negative power supply via a resistor 28. The comparator output is transistor 3
A current pulse is applied to the base of the chopper transistor 20.

The operation of the horizontal amplitude control circuit of this embodiment configured as described above will be explained below.

As explained in FIG. 1, generally the horizontal deflection circuit 4
1, it is necessary to control the voltage of +V _C2 depending on the value of _H , and the change in voltage due to change in horizontal frequency will be explained with reference to the operating waveform diagram shown in FIG. The pulse 4-a is an output pulse of the shaping circuit 24 synchronized with the input synchronization pulse. When the horizontal frequency _H decreases from _H1 to _H2 , the scanning time becomes longer as shown by the broken line. 4-b is a sawtooth wave voltage generated in the capacitor 26, which is compared with the base bias voltage _Eb of the transistor 30 to form a pulse current and make the chopper control transistor 20 conductive. 4-c indicates the collector voltage of the transistor 20, that is, the diode voltage υd. This pulse voltage is smoothed by a filter 22,
Output +V _C2 is the average value of the pulses. Now, when _H2 is reached, the duty ratio of the output pulse changes as shown by the broken line, so +V _C2 drops. That is,
The current value of the deflection coil 13 of the horizontal deflection circuit 41 can be made constant according to _H.

As described above, according to this embodiment, by providing the chopper control transistor 20 and using a sawtooth wave voltage with a constant slope synchronized with the input synchronization signal for its pulse width control, it is possible to control the horizontal frequency _H. , it is possible to obtain a constant horizontal amplitude and to have little loss in control of the power supply voltage. Since the transistor 20 does not perform class-A operation but performs switching operation, P _c is extremely small, and the heat sink can also be small, so it can be configured compactly.

A second embodiment of the present invention will be described below with reference to the drawings.

FIG. 3 is a block diagram of a horizontal amplitude control circuit showing a second embodiment of the present invention. In the figure, 32 is an error detection amplifier, and 33 is a reference voltage.
34 is a pulse detection transformer, and 35 is a rectifier diode, which is smoothed by a capacitor 36 and connected to the comparison terminal of the error amplifier 32. The output of error amplifier 32 is applied to the base of transistor 30.

In the horizontal amplitude control device of the second embodiment configured as described above, a pulse proportional to the amplitude of the deflection current is rectified and detected by the detection transformer 34, and a negative feedback circuit is formed. , the duty ratio of the chopper control transistor 20 can be changed. Therefore, even if +V _C1 changes while _H remains constant, +V _C2 is controlled so that the deflection current remains constant. Of course, even if _H changes,
Needless to say, this embodiment operates in the same way as the first embodiment, with little control loss in the power supply.

Effects of the Invention The horizontal amplitude control circuit of the present invention includes a switching power supply whose output can be varied by chopper control of a DC power supply, and a sawtooth wave voltage generator formed by a switching discharge action using pulses shaped by the output of a horizontal AFC circuit. By providing this, it is possible to perform efficient voltage control and to automatically control the horizontal amplitude to an initially set constant horizontal amplitude in accordance with the horizontal frequency. In addition, unlike the conventional example, the _H detection circuit is not required, and it can be realized with a small and simple configuration, which is very useful industrially.

[Brief explanation of drawings]

FIG. 1 is a block circuit diagram of a conventional horizontal amplitude control circuit, FIG. 2 is a block circuit diagram of a horizontal amplitude control circuit according to a first embodiment of the present invention, and FIG. 3 is a block circuit diagram of a horizontal amplitude control circuit according to a first embodiment of the present invention. 4 is a block circuit diagram, FIG. 4 is an operational waveform diagram of the main part of the present invention, and FIGS. 5a and 5b are characteristic diagrams of a conventional example. 15...Horizontal drive circuit, 16...Horizontal
AFC circuit, 24... Shaping circuit, 29, 30...
Transistors forming the comparator, 41...
Horizontal deflection circuit, 42...Switching power supply, 43
...Sawtooth wave generator.

Claims (1)

[Claims] 1. A switching power supply that can vary the output by chopper control of the DC power supply, a horizontal deflection output circuit that is switching driven by a horizontal drive circuit and whose input voltage terminal is connected to the switching power supply, and an oscillation output that is synchronized with the input synchronization pulse. a horizontal AFC circuit that applies the voltage to the horizontal drive circuit, a sawtooth wave voltage generator that is formed by a switching discharge action using a pulse shaped output of the horizontal AFC circuit, and one of the two differential input terminals. 1. A horizontal amplitude control circuit comprising: a comparator to which a bias voltage is applied and to which the sawtooth wave voltage is coupled; the switching power supply is controlled by the output of the comparator.