JPH06325878A - Brightness reducing circuit for fluorescent lamp - Google Patents

Abstract

PURPOSE: To provide a luminance lowering circuit which is capable of easily controlling the luminance of a fluorescent lamp and preventing an overcorrect in a no-load state, caused by the contact failure of the fluorescent lamp. CONSTITUTION: In a luminance lowering circuit, having a magnetic force oscillating means having a transformer 18 with three windings, a second winding or the transformer 18 is connected to a DC power source, and a third winding is connected to a fluorescent lamp 21. The second winding is also connected to an oscillating circuit, and this oscillating circuit has a first resistor 12, transistors 16, 17 and first winding. This circuit comprises a variable resistor 14 to be connected in series with the first resistor 12, and the variable resistor 14 includes a movable arm to be connected to the first winding, the operating frequency of the fluorescent is controlled, and as a result the luminance is controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fluorescent lamp control circuit for operating a fluorescent lamp by a direct current source, and more particularly to a brightness dimming circuit for such an illumination. The invention further relates to a protection circuit which operates when the circuit is unloaded to control the lamp.

[0002]

2. Description of the Related Art An invention circuit for providing an oscillation source for driving a fluorescent lamp by using magnetic force is disclosed in Japanese Utility Model Publication (Japanese Utility Model Publication).
Lity Model Gazette No. 54-2598, 48-23181). However, the device cannot control the brightness of the lamp. In addition, the poor contact of the lamp filament may cause the lamp to be imperfectly connected to the circuit, and overcurrent may damage the brightness lowering circuit and sometimes cause a fire. It does not include emergency mechanisms to protect the circuit in the event of a situation. Despite the importance of limiting overcurrent under no-load conditions, most lamp control circuits proposed to date do not provide sufficient protection and use no protective device at all. Some do not. On the other hand, the means for controlling the brightness of the lamp is generally devised, but the circuit configuration of such a controller is very complicated, and the device generates flicker light at low level illumination and controls it. The range is not enough. Moreover, the manufacturing costs of conventional products are high and therefore such control is generally not easy.

[0003]

SUMMARY OF THE INVENTION It is, therefore, an object of the present invention to provide a brightness lowering circuit which can easily control the brightness of a fluorescent lamp and can turn on the lamp by using an electronic circuit.

Another object of the present invention is to provide a brightness lowering circuit capable of preventing an overcurrent in a no-load state caused by poor contact.

According to the present invention, there is provided a brightness lowering circuit for logically detecting the connection state of a fluorescent lamp in a control circuit.
If the fluorescent lamp is disconnected from the circuit, or if the fluorescent lamp is broken or does not work, the circuit current is cut off to protect the circuit. Further, according to the present invention, the fluorescent lamp can be turned on by the oscillation mechanism by the magnetic force, and the illumination is optimized by regulating the oscillation frequency and controlling the current amount.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the following description, a brightness lowering circuit according to an embodiment of the present invention is a fluorescent lamp of low power, for example 40 mW, and uses a DC power supply.

In FIG. 1, the brightness lowering circuit of the present invention includes a DC power source such as a battery 1, and the battery 1 is connected via a voltage divider composed of series resistors 12 and 14. Positive side of battery, that is, battery 1
The connection point of the resistor 12 and the resistor 12 is connected to the base of the first transistor 16 via the resistors 13 and 15. The emitter of this transistor is connected to the negative side of the battery 1. The collector of the transistor 16 is the first of the transformer 8.
It is connected to the tap of the resistor 14 through the winding N1,
This tap is also connected to the negative side of the battery 1 via the capacitor 22.

The collector of the transistor 16 is also connected to the base of the second transistor 17, the emitter of this transistor is connected to the negative side of the battery 1, and the collector is connected via the winding N2 of the transformer 18 to the battery 1.
Is connected to the connection point between the positive side of and the resistor 12. The third winding N3 of the transformer 18 is connected to the fluorescent lamp 21. The filament 20 provided at one end of the lamp is connected between the taps of the windings N3 and N3, the filament on the opposite side of the lamp is connected to the second end of the winding N3, and the diode 19
Is connected to the second tap of the winding N3. The connection point between the diode 19 and the lamp 21 is connected to the junction of the resistors 13 and 15.

In FIG. 1, the transistor 17 is turned on or off according to the cycle of the oscillation frequency. This frequency is determined by the values of resistors 12 and 14, the value of capacitor 22, and the value of winding N2 of transformer 18. The switching of the transistor 17 is performed by the winding N1 of the transformer 18.
To generate an alternating current, and a high voltage to the winding N3 to turn on the fluorescent lamp 21.

Magnetic force oscillators of the type described above are generally known. However, an excellent feature of the present invention is the inclusion of circuitry to control the brightness of the lamp as described below. According to the present invention, the switching characteristics of transistor 17 are controlled by a movable tap on resistor 14, the movement of which tap changes the high voltage on winding N1 of transformer 18, resulting in a change in the switching frequency. Therefore, the voltage of the second coil N3 of the transformer 18 changes according to the change of the frequency of the switching current in the primary winding of the transformer 18. This change in frequency level causes the fluorescent lamp 21
By changing the tube current inside, the fluorescent lamp 21
The brightness of changes. The optimum frequency range is 7 KHz to 25
It is KHz, and the brightness of the lamp can be controlled 95% in this range.

As shown in FIG. 2, in the preferred embodiment of the present invention, the oscillating transformer 18 is in the form of an annular magnetic circuit (toroid) having an annular core, around which coils N1 and N2 are wound. The size and number of turns of each winding of the annular magnetic circuit core are determined according to the requirements of the fluorescent lamp used.

The protection circuit of the present invention operating under no load will be described with reference to FIGS. In FIG. 3, the arrow indicates the current direction when the fluorescent lamp 21 is connected to the circuit and is conducting. In this case, the transistor is turned off. This is because a negative bias is supplied to the base of the transistor via the resistor 15 and the lamp filament 20. When transistor 16 turns off, transistor 17 performs its switching action in the normal way, and the circuit can be described as loaded.

FIG. 4 shows a case where the fluorescent lamp is non-conductive due to poor contact, for example. In this case, no current will flow,
The protection circuit functions to prevent damage. A positive bias current through the loop is formed via resistors 13 and 15. This is because the current path through the filament 20 is open due to poor contact. In this case, the transistor 17 is turned off, so that no current flows in the winding N2 of the transformer 18. as a result,
No current flows in the winding N3 and no power is supplied to the lamp.

As described above, the present invention provides a brightness lowering circuit having a lighting control function, which changes the frequency generated from the oscillator circuit by magnetic force and changes the current flowing through the secondary winding of the transformer. . Changes in the current flowing through this secondary winding change the brightness of the lamp. The present invention also has a protective function which operates when the lamp is in a non-conducting state which may be caused by poor contact between the control circuit and the lamp. INDUSTRIAL APPLICABILITY The brightness lowering device according to the present invention has a wide range of applications such as an emergency indoor lamp, an in-car lamp, a portable lamp, a lamp in a train, and an in-board lamp, and can be used for ensuring electrical safety and low power consumption.

[Brief description of drawings]

FIG. 1 is a preferred embodiment of a brightness lowering circuit according to the present invention.

FIG. 2 shows an oscillator circuit and a core used in the brightness lowering circuit of FIG.

FIG. 3 is a circuit diagram of a brightness lowering circuit according to the present invention, showing a current flowing when a fluorescent lamp is conducting, that is, when the lamp is operating.

FIG. 4 is a circuit diagram of a brightness lowering circuit according to the present invention, showing a state where a fluorescent lamp is non-conductive.

[Explanation of symbols]

1 ... Battery, 12.13.14.15 ... Resistance, 18
... transformer, 16/17 ... transistor, 21 ... fluorescent lamp, 20 ... filament, 19 ... diode.

Claims (4)

[Claims] 1. Resistors 12 and 14 provided at both ends of a DC power source, a transformer, a fluorescent lamp connected to a third winding N3 of the transformer, resistors 12, 14, a transistor 17, a first winding N1 and An oscillating circuit having a second winding N2; and a transistor 16 connected between the base and the emitter of the transistor 17, the collector of the transistor 16 being connected to the base of the transistor 17,
The emitter of the transistor 16 is the transistor 1
A base resistor 15 connected to the emitter of the transistor 7 and to the transistor 16, a filament resistor 20 of the fluorescent lamp, and a negative bias circuit including the emitter of the transistor 16; Lamp brightness reduction circuit. 2. A diode provided in series between the oscillation coil N3 and one terminal of a filament of the fluorescent lamp 20 to prevent reverse flow of a base current of a transistor,
The diode 19 and the filament are the resistor 13,
The brightness lowering circuit according to claim 1, wherein the brightness lowering circuit is connected to 15. 3. The core of the transformer is a ring-shaped Ni-
The first, second and third windings N1, which are made of Fe,
2. The brightness lowering circuit according to claim 1, wherein N2 and N3 are annular magnetic circuits. 4. The core of the transformer 18 is ring-shaped N
i-Fe, and includes the first, second and third windings N
3. The brightness reducing circuit according to claim 2, wherein 1, N2 and N3 are annular magnetic circuits.