JPH1188057A - Frequency modulation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inexpensive frequency modulation device of low precision with simple constitution by connecting a resistor and a photocoupler to a resistor for oscillation in parallel or in series and generating a frequency modulation wave. SOLUTION: Alternating current flows in the series circuit of the resistor RM and a capacitor CM in a multi-vibrator by two inverters. The period is decided by the value of RM×CM. The series circuit constituted of the resistor R1, a diode bridge DB1 and the photo-transistor Q1 of the photo-coupler PC is connected to the resistor RM in parallel. The resistance component of the series circuit is decided by the conduction state of the photo-transistor Q1, namely, the value of current flowing in lightemitting diode LED 1. Since the series circuit is connected to the resistor RM in parallel, the oscillation frequency of the multi-vibrator changes when the resistance component of the series circuit changes. Thus, the oscillation frequency of the multi-vibrator controls current flowing in LED 1 and it can be changed.

Description

DETAILED DESCRIPTION OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for obtaining a low-cost, low-precision frequency modulated wave with a very simple structure.

2. Description of the Related Art Conventionally, using a variable capacitance diode,
Although a method of obtaining an M wave has been generally used, this method has been adopted for a high frequency circuit of relatively several hundred KHz or more, and has been difficult to use in an oscillation circuit of several tens KHz.

When a metal halide lamp or the like is lit at a high frequency, an acoustic resonance phenomenon occurs, causing arc instability and extinguishing. As a means for avoiding the acoustic resonance phenomenon, there is a method of constantly changing the lighting frequency at the time of lighting. However, when a conventional FM oscillation circuit using a variable capacitance diode is used, it is necessary to increase the oscillation frequency of the lighting device to several hundred KHz. Therefore, there is a disadvantage that the noise terminal voltage of the lighting device is increased, and a method of obtaining a modulated wave at a relatively low frequency is required.

According to the present invention, as a method of modulating an oscillation frequency of several tens of KHz, an RC oscillator is combined, and a resistor and a photocoupler are connected in parallel or series with a resistor for oscillation to generate a frequency modulated wave. It is something that you get.

Since the resistance and the photocoupler are connected in parallel or series with the R of the RC oscillator, by changing the conduction state of the photocoupler, the substantial resistance of the RC oscillator changes and frequency modulation is performed.

FIG. 1 shows an embodiment of the present invention. In a multivibrator with two inverters, an alternating current flows through a series circuit of a resistor RM and a capacitor CM, and the cycle thereof is determined by the value of RM × CM. A series circuit including a resistor R1, a diode bridge DB1, and a phototransistor Q1 of a photocoupler PC is connected in parallel with the resistor RM. The resistance component of this series circuit is determined by the conduction state of Q1, that is, the value of the current flowing through the light emitting diode LED 1 of the photocoupler. Since the series circuit is connected in parallel with the resistor RM, if the resistance component of the series circuit changes, the oscillation frequency of the multivibrator also changes. Therefore, the oscillation frequency of the multivibrator can be changed by controlling the current flowing through the LED 1. That is, if no current flows through the LED1, the resistor R1 does not contribute to the oscillation frequency of the multivibrator at all because Q1 is in a non-conducting state, and the multivibrator uses RM and CM.
Oscillates at the fundamental frequency determined by As the current flowing through LED1 is increased, the conduction state of Q1 advances and R
The resistance component connected in parallel with M gradually decreases,
Accordingly, the oscillation frequency of the multivibrator increases. When the current flowing through the LED is further increased, the conduction state of Q1 reaches a saturation point and finally becomes a full conduction state. At this time, D
If the resistance component of B1 is ignored, the resistance R1 is equal to the resistance RM.
Is connected in parallel to the multi-vibrator,
Oscillates at the highest frequency. In other words, the multivibrator operates according to the magnitude of the current flowing through the LED 1 according to RM × CM.
From the frequency f0 determined by The frequency f1 changes in a range up to the frequency f1, which is determined by the following equation. If the current flowing through the LED 1 is controlled by the AC power supply as in the example of FIG. 1, the oscillation frequency of the multivibrator repeatedly changes from f0 to f1 in the cycle of the AC power supply. FIG. 2 shows another embodiment of the present invention, in which a frequency modulation device including a resistor R3 is connected in series to an oscillation resistor RM of a multivibrator. The highest oscillating frequency can be obtained with sufficient current flowing through LED1. Diode bridge D
B1 is connected so that an alternating current flows through the resistor R1 so that it can be controlled by a polar phototransistor. This is not necessary if the light receiving element of the photocoupler is a non-polar one such as a cadmium sulfide element (CdS). . If the duty of the obtained output waveform does not have to be 50%, it can be omitted. If two photocouplers are used, the diode bridge DB1 can be eliminated. All parts directly connected to the oscillation resistor RM of the multivibrator are composed only of passive elements,
Moreover, since it is completely insulated from the LED 1 for frequency control, it does not adversely affect the oscillator. Therefore, the present invention can be applied to an oscillator whose oscillation frequency is controlled by a resistor other than the multivibrator. Since the light receiving element of the photocoupler is mainly used in a semi-conducting state, it is easily affected by variations in its characteristics. However, if the frequency modulation range is determined based on the point where the light receiving element is in a non-conductive state or a fully conductive state, even if the characteristics of the photocoupler fluctuate, the fundamental frequency is almost constant and only the frequency modulation range fluctuates. And can be used for low-precision applications.

As described above, according to the present invention, it is possible to perform relatively low frequency modulation at a low accuracy, but at a very simple and low cost, and it is used for an acoustic resonance of a high frequency lighting device of a metal halide lamp. It is the best way to avoid the phenomenon.

[Brief description of the drawings]

FIG. 1 and

FIG. 2 is a circuit diagram showing one embodiment of the present invention.

Claims (1)

[Claims] 1. An oscillator utilizing charge and discharge of a resistor and a capacitor, wherein the frequency modulator comprises a resistor and a photocoupler connected in parallel or in series with an oscillation resistor of the oscillator.