JPH04158389A - Horizontal deflecting circuit - Google Patents

Abstract

PURPOSE:To perform a stable operation when a power source is turned on and protect a deflecting stage by holding the power voltage of a horizontal output circuit at the low voltage with a horizontal output control circuit when the power source is turned on. CONSTITUTION:A horizontal output control circuit 7 is kept at the low voltage when a power source is turned on. The power voltage of a horizontal output circuit 6 is held at the low voltage even if a DAC (D/A converting circuit) 3 is set to any value. The power voltage of the circuit 6 is held at the low voltage even if the output of a DAC 5 is uncertain and a horizontal oscillating circuit 4 starts oscillation at any frequency, thus the deflecting stage of a horizontal deflecting circuit can be protected. An MPU 2 starts operating and outputs a gate signal to the circuit 7 to stop the output of the circuit. The MPU 2 detects the frequency fh of the horizontal synchronization signal with a counter circuit 1 and outputs the control value in response to the frequency to the circuit 4 through the DAC 3 and outputs it to the circuit 6 through the DAC 5.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a horizontal deflection circuit that stably oscillates when the power is turned on.

(Prior Art) In recent years, there has been a strong demand for display devices to display finer characters, figures, images, and the like. Therefore, the frequency of the synchronization signal is becoming higher, and devices for synchronization signals of various frequencies have appeared. Therefore, recently, display devices have been developed in which the deflection frequency can be changed according to each frequency.

The configuration of the horizontal deflection circuit of such a display device is realized as shown in FIG.

In FIG. 3, the horizontal synchronization signal fh is a voltage signal v1 corresponding to the horizontal synchronization frequency in the frequency/voltage conversion circuit 11.
is converted into and applied to the limiter circuit 12. The limiter circuit 12 limits this voltage signal v1 up and down in consideration of the dynamic range of the subsequent circuit, and controls the horizontal oscillation circuit 1.
given to 3. In this way, the horizontal oscillation signal O8C
The oscillation frequency is controlled.

Generally, when the power is turned on, it is desirable to change the control of the horizontal oscillation frequency from a high frequency to a predetermined horizontal oscillation frequency in order to protect the deflection stage of the horizontal deflection circuit.

By the way, when the power is turned on, the voltage is not converted by the frequency/voltage conversion circuit 11, so the horizontal oscillation circuit 13 will not perform an oscillation operation if this continues. Therefore, a lower limit value is outputted from the limiter circuit 12 and applied to the horizontal oscillation circuit 13 to cause horizontal oscillation operation.

At this time, in a small range of power supply voltage, the limiter circuit 12 does not have a lower limit value obtained in proportion to the power supply voltage;
Since the auxiliary voltage of the auxiliary voltage supply circuit 14, which is larger than that, is set as the lower limit value, the horizontal oscillation operation can be started quickly. In addition, the auxiliary voltage is made relatively larger as the power supply voltage becomes smaller than the lower limit value obtained in proportion to the power supply voltage, and the horizontal oscillation frequency gradually changes from a high frequency to a low frequency. The deflection stage of the horizontal deflection circuit can be protected.

The horizontal deflection circuit of such a display device is
For example, there is a horizontal deflection circuit J described in Japanese Unexamined Patent Publication No. 64-85478.

(Problem to be Solved by the Invention) Recently, the horizontal oscillation frequency of the horizontal deflection circuit and the output voltage of the horizontal output circuit are controlled by counting horizontal synchronizing signals using a counter circuit, and by using a microprocessor (hereinafter referred to as MPU). ), and the control value according to the count value is passed through a digital/analog converter circuit (hereinafter abbreviated as DAC).In such a configuration, even if the conventional control is performed by the MPU, Since the output value of the DAC is uncertain from the time the power is turned on until the MPU starts operating and sets the initial value to the DAC, the horizontal oscillation frequency is set to a low frequency when the power is turned on, and the horizontal oscillation frequency of the horizontal output circuit is There is a risk that the output voltage will be set to a high voltage. Therefore, there was a drawback that there was a risk that the horizontal deflection circuit would be destroyed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a horizontal deflection circuit which eliminates the drawbacks of the prior art, operates stably even when the power is turned on, and is capable of protecting the deflection stage.

(Means for Solving the Problems) The horizontal deflection circuit of the present invention includes a counter circuit for detecting the frequency of a horizontal synchronizing signal, an MPU that performs control according to the detected frequency, and a horizontal oscillation circuit that is controlled from the MPU. a first DAC for converting a control value outputted from the MPU into a control voltage, and a second DAC for converting a control value outputted from the MPU into a control voltage for controlling the power supply voltage of the horizontal output circuit. DAC, and a horizontal output control circuit for maintaining the power supply voltage of the horizontal output circuit at a low voltage when the power is turned on.

Also, when the power is turned on, the horizontal output control circuit controls the first
The deflection stage of the horizontal deflection circuit can be protected by keeping the power supply voltage of the horizontal output circuit at a low voltage regardless of the outputs of the DAC and the second DAC. Furthermore, after the MPU starts operating and initializes the first DAC and second DAC, the output of the horizontal output control circuit is stopped, the horizontal oscillation frequency of the horizontal deflection circuit is controlled through the first DAC, and the horizontal The power supply voltage of the output circuit is controlled through the second DAC.

(Function) With the above configuration, the deflection stage of the horizontal deflection circuit can be protected when the power is turned on.

(Example) An example of the present invention will be described based on FIGS. 1 and 2.

FIG. 1 is a block diagram of a horizontal deflection circuit according to the present invention. In the figure, l is a counter circuit for detecting the frequency of the horizontal synchronization signal, 2 is an MPU that performs control according to the detected frequency, and 3 is a control value output from the MPU 2 to control the horizontal oscillation circuit 4. A first DAC 15 for converting the control value into a control voltage is outputted from the MPU 2 to control the power supply voltage of the horizontal output circuit 6. A second DAC 17 for converting the control value into a control voltage outputs the horizontal output when the power is turned on. This is a horizontal output control circuit that maintains the power supply voltage of the circuit at a low voltage.

When the power is turned on, the horizontal output control circuit 7 is held at a low voltage. At this time, no matter what value the first DAC 3 is set to, the power supply voltage of the horizontal output circuit 6 is maintained at a low voltage. On the other hand, even if the output of the second DAC 5 is uncertain and the horizontal oscillation circuit 4 starts oscillating at any frequency, the power supply voltage of the horizontal output circuit 6 is maintained at a low voltage, so the deflection of the horizontal deflection circuit is It can protect the steps.

Next, after the MPU 2 starts operating and initializes the first DAC 3 and the second DAC 5, the MPU 2 outputs a gate signal to the horizontal output control circuit 7 and stops the output of the horizontal output control circuit 7. And MPU2 is counter circuit 1
detects the frequency fh of the horizontal synchronizing signal, and outputs a control value corresponding to the frequency to the horizontal oscillation circuit 4 through the first DAC 3.
output to control the horizontal oscillation frequency. Also the second D
It is output to the horizontal output circuit 6 through the AC 5, and the power supply voltage of the horizontal output circuit 6 is controlled.

FIG. 2 shows a specific circuit of the horizontal output control circuit 7. The base of transistor Q1 is connected to the output port of MPU2 and is further pulled down by resistor R1. The collector is connected to ground. The emitter is connected to the output of the second DAC and horizontal output circuit 6
supplied to When transistor Q1 is turned on, the second
The output of the DAC 5 can be forcibly held at ground level.

When the power is turned on, the output port of the MPU 2 is in a high impedance state, and the base of the transistor Q is brought to a low level by the resistor R. Then, the transistor Q is turned on, and the output of the second DAC 5 is forcibly held at the ground level.

Next, the MPU 2 initializes the first DAC 3 and the second DAC 5, and then sets the output port to a high level. And transistor Q.

is turned off, and the output of the second DAC 5 is supplied to the horizontal output circuit 6.

(Effects of the Invention) According to the present invention, in a method in which the horizontal oscillation frequency of the horizontal deflection circuit and the output voltage of the horizontal output circuit are controlled through a DAC, a control value according to the frequency of the MPU is controlled. The MPU starts operating for the first time after being turned on, and the DA
Even if the output value of the DAC is uncertain until the initial value is set for can be provided, and its practical effects are great.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a horizontal deflection circuit according to an embodiment of the present invention, FIG. 2 is a connection diagram showing the detailed configuration thereof, and FIG. 3 is a block diagram of a conventional horizontal deflection circuit. 1... Counter circuit, 2... MPU, 3
...First DACl 4...Horizontal oscillation circuit, 5...
- Second DACl 6...Horizontal output circuit, 7...Horizontal output control circuit.

Claims (1)

[Claims] A counter circuit that receives a horizontal synchronization signal as an input and detects the frequency of the horizontal synchronization signal, a microprocessor that performs control according to the frequency detected by the counter circuit, and controls a control value output from the microprocessor. a first digital/analog conversion circuit for converting the control value output from the microprocessor into a control voltage and controlling the horizontal oscillation circuit; and a first digital/analog conversion circuit for converting the control value output from the microprocessor into a control voltage and controlling the power supply voltage of the horizontal output circuit Second digital/
A horizontal deflection circuit comprising an analog conversion circuit and a horizontal output control circuit for maintaining the power supply voltage of the horizontal output circuit at a low voltage when the power is turned on.