JPH11177396A - Sawtooth wave generation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of noises from a constant voltage diode by providing on the power source-side of a switching element a constant voltage diode to determine the charging voltage of a capacitor. SOLUTION: In a sawtooth wave generation circuit, a constant voltage diode D1 to determine the charging voltage (reference upper limit voltage) of a capacitor C1 is inserted between the power source Vcc-side of a transistor (switching element) Q2 and the ground. Bias current is always supplied to the constant voltage diode D1 from a power source Vcc through a resistor R2 independent of on/off operation of the transistor Q2, so that the current value does not fall below a level where a noise is produced. Since a noise is not produced from the constant voltage diode D1, shaking in a vertical direction is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sawtooth wave generating circuit suitable for use in a vertical deflection circuit of a monitor or a television.

[0002]

2. Description of the Related Art FIG. 3 is a diagram showing a sawtooth wave generating circuit used in a conventional vertical deflection circuit, and FIG. 4 is an operation waveform diagram thereof. In these figures, a pulse having a vertical cycle of Hi during the vertical synchronization period and Lo during the scanning period is input to the base of the transistor Q1, and performs a switching operation of ON during the vertical synchronization period and OFF during the scanning period. The transistor Q2 is driven by the transistor Q1, and performs a switching operation of turning on during a vertical synchronization period and turning off during a scanning period.

When the transistor Q2 is turned on, a current flows from the power supply Vcc to the capacitor C1 via the resistor R2, and the capacitor C1 is charged to a voltage determined by the constant voltage diode D1 (reference upper limit voltage). When the transistor Q2 is turned off, the current for charging the capacitor C1 does not flow, and the constant current source Z discharges the constant current. In this way, a sawtooth voltage having a vertical period is output from the output terminal Vo.

[0004]

In the conventional sawtooth wave generating circuit described above, the bias current of the constant voltage diode D1 is intermittently interrupted at a vertical cycle. This causes a problem that vertical rattling occurs due to this.

Accordingly, an object of the present invention is to provide a sawtooth wave generating circuit which does not generate noise from a constant voltage diode.

[0006]

In order to achieve the above object, a sawtooth wave generating circuit according to the present invention comprises a switching circuit in which a pulse signal of a predetermined cycle is turned on in a first level period and turned off in a second level period. An element, a capacitor charged by a power supply voltage when the switching element is turned on, a constant current source interposed in parallel with the capacitor and discharging the capacitor at a constant current when the switching element is turned off, and a power supply for the switching element. A constant voltage diode interposed between the side and the ground to determine a charging voltage of the capacitor.

According to this structure, since the constant voltage diode for determining the charging voltage of the capacitor is provided on the power supply side of the switching element, the bias current is always applied to the constant voltage diode regardless of the on / off state of the switching element. It does not fall below the value at which flow and noise occur. Therefore, since no noise is generated from the constant voltage diode, no vertical play is caused by the noise.

[0008]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a sawtooth wave generating circuit according to an embodiment of the present invention. FIG. 1 is a diagram showing an embodiment of a sawtooth wave generating circuit according to the present invention, and FIG. 2 is an operation waveform diagram thereof. Note that, in FIG. 1, the same reference numerals are given to portions common to FIG. 3 described above.

The sawtooth wave generating circuit of this embodiment includes a constant voltage diode D1 for determining a charging voltage (reference upper limit voltage) of a capacitor C1 and a transistor (switching element).
It is interposed between the power supply Vcc side of Q2 and the ground. The constant voltage diode D1 is connected to the power supply V of the transistor Q2.
By providing the constant voltage diode D1 on the cc side, a bias current is always supplied to the constant voltage diode D1 from the power supply Vcc via the resistor R2 irrespective of the on / off state of the transistor Q2, and does not become lower than the value at which noise occurs. As a result, no noise is generated from the constant voltage diode D1, so that no rattling occurs in the vertical direction.

In the sawtooth wave generating circuit of this embodiment, the emitter potential of the transistor Q2 is controlled by the constant voltage diode D1.
When the transistor Q2 is turned on (vertical synchronization period), the capacitor C1 is charged to the voltage Vz determined by the constant voltage diode D1. Then, when the transistor Q2 is turned off (scanning period), there is no current for charging the capacitor C1, and the constant current source Z discharges the current at a constant current. Therefore, a sawtooth voltage having the same vertical period as that of the above-described conventional sawtooth generating circuit is output to the output terminal Vo. Needless to say, the sawtooth wave generating circuit of the present invention is mainly used for a vertical deflection circuit of a monitor or a television.

[0011]

According to the sawtooth wave generating circuit of the present invention, no bias current less than a value at which noise is generated does not flow through the constant voltage diode, so that no noise is generated from the constant voltage diode and noise is generated. It does not cause vertical rattling.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a sawtooth wave generating circuit according to the present invention.

FIG. 2 is an operation waveform diagram of the sawtooth wave generating circuit of FIG. 1;

FIG. 3 is a diagram illustrating a conventional sawtooth wave generation circuit.

FIG. 4 is an operation waveform diagram of the sawtooth wave generation circuit of FIG. 3;

[Explanation of Signs] Q1 transistor Q2 transistor (switching element) C1 capacitor Z constant current source D1 constant voltage diode R1, R2 resistance

Claims (2)

[Claims] 1. A switching element in which a pulse signal of a predetermined cycle is turned on in a first level period and turned off in a second level period, a capacitor charged by a power supply voltage when the switching element is turned on, and the capacitor A constant current source that is interposed in parallel with the switching element and discharges the capacitor with a constant current when the switching element is turned off; and a constant current source that is interposed between a power supply side of the switching element and ground to determine a charging voltage of the capacitor. A sawtooth wave generating circuit, comprising: a voltage diode; 2. The sawtooth wave generating circuit according to claim 1, wherein the sawtooth wave generating circuit is used for a vertical deflection circuit of a monitor or a television.