JPH0574582A - Incandescent lamp lighting device - Google Patents

Abstract

PURPOSE:To prevent a fire and injuring a human body by preventing the on-duty of the output signal from exceeding a specific value even though a driving circuit generates a trouble or an error operation. CONSTITUTION:A driving circuit 1 to determine the on-duty of a switching element SW is provided. A protective circuit 2 to suppress the ON period of the switching element SW not to exceed a specific time is provided. When the driving circuit 1 generates a trouble, and the on-duty signal of the switching element SW is made larger than in the rating time, the protective circuit 2 detects it. The protective circuit 2 controls forcibly the ON period of the switching element SW so as not to exceed a specific time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an incandescent lamp lighting device for lighting an incandescent lamp including a mini halogen bulb through a lighting device that performs voltage conversion (step-down, frequency, etc.) or on / off control from a commercial power source. It is about.

[0002]

2. Description of the Related Art It is desirable to use a light source whose light distribution is easy to design in order to design an appropriate illumination according to the purpose and application. The light source with the greatest degree of freedom is a point light source. is there. As a light source close to the point light source, a low-voltage mini halogen bulb has recently been widely used. In order to light this lamp, a lighting device is usually required to reduce the commercial power supply voltage to the rated voltage of the lamp.

An example of the lighting device is shown in FIG. In this conventional example, a commercial power source is converted into a high frequency low voltage by a lighting device to light a low voltage mini halogen bulb.
Hereinafter, FIG. 7 will be described. The commercial power supply AC is full-wave rectified by the rectifier Re to make a power supply for a self-excited half-bridge inverter. In order to start the oscillation of the inverter, the capacitor C ₄ is charged through the resistor R _3, and when the breakover voltage of the trigger element Q ₃ (for example, SBS) is reached, the trigger element Q ₃ turns on and the oscillation transistor Turn on Q ₂ . At this time, the electric charge charged in the capacitor C ₃ flows in the transistor Q ₂ via the primary side of the step-down transformer T _{1 and} the primary side of the current transformer T ₂ .

[0004] transistor Q ₂ begins to turn on in the process of the current rises, the secondary winding of the current transformer T ₂ which is connected to the base of the transistor Q ₂ is, current in a direction to forward bias the transistor Q ₂ Flows. Eventually, the current on the primary side of the current transformer T ₂ is limited to a current substantially equivalent to the equivalent resistance of the lamp (low-voltage mini halogen bulb) L. At this time, the secondary side of the current transformer T ₂ is in a non-biased state. Since the transistor Q ₂ has no bias, it turns off after the accumulation time. Therefore, the current flowing through the transistor Q ₂ starts to decrease.

When the collector current of the transistor Q ₂ decreases, the current transformer T ₂ causes the transistor Q ₂ to be reverse biased and the transistor Q ₁ to generate a forward bias voltage. Eventually, the transistor Q ₂ is turned off and the other transistor Q ₂ is turned off. ₁ turns on. Hereafter, repeat this operation,
Continue oscillation. When the self-excited half-bridge type inverter as described above is used, _two resonance capacitors C ₂ and C ₃ and _two transistors Q ₁ and Q ₂ are required, and the transistors Q ₁ and Q are used. _A current transformer T ₂ is required for driving ₂ and the number of parts increases, resulting in a larger circuit.

On the other hand, the one-stone type inverter requires only one resonance capacitor and one transistor, which is advantageous for miniaturization. For example, JP-A-58
-51496 and the like. However, even in the one-stone type inverter, the self-excited type cannot freely control the oscillation frequency and the on-duty, so that high value-added functions such as dimming and soft start cannot be realized, or even if they can be realized. There are problems such as high cost, and large circuit.

Therefore, in the one-stone type inverter, a separately excited type in which the on-duty can be freely controlled is considered. FIG. 8 shows a second conventional example. In this circuit, a series circuit of a primary winding t ₁ of a transformer T and a switching element SW is connected to both ends of a DC power source E (commercial AC voltage may be rectified by a rectifying circuit). A capacitor C is connected to both ends of the primary winding t ₁ of the transformer T,
A lamp L is connected to both ends of the secondary winding t ₂ via a diode D.
(Low voltage mini halogen bulb) is connected. The capacitor C may be connected in parallel with the switching element SW.

The drive circuit 1 is connected to the gate of the switching element SW composed of an FET. This drive circuit 1
This allows the switching element SW to freely control its oscillation frequency and on-duty.
The output voltage can be varied to dimm the lamp L, or the output voltage can be gradually increased at startup to add a soft start function.

FIG. 9 shows operation waveforms of respective parts of the conventional example of FIG. 8, and the operation will be described below. In addition, a to e of FIG.
It is a waveform of points A to E in FIG. B is an output signal from the drive circuit 1, and its oscillation frequency and on-duty can be arbitrarily changed. First, when the output signal a is turned on, as shown in d, an oscillating current flows through the capacitor C from the inductance of the wiring or the like, and is attenuated. Then, + charges are accumulated on the + side of the DC power source E of the capacitor C. After that, when the output signal a is turned off, the electric charge stored in the capacitor C is discharged through the primary winding t ₁ of the transformer T, but in this direction, the diode connected to the secondary winding t ₂ is discharged. The current flows in the forward direction of D, the inductance of the primary winding t ₁ is very small, and a steep current flows instantaneously to charge the capacitor C in the opposite manner to when it is turned on.

When the current flows in the opposite direction, the capacitor C is discharged in the same direction as when it was turned on.
Since the current flows in the opposite direction of the diode D connected to the secondary winding t ₂ and no current flows in the secondary winding t ₂ , the inductance of the primary winding t ₁ is Line t ₂
The output end of becomes the same condition as open and becomes larger. Therefore, the discharge current is small and the time constant is long. When off, the above damping vibration is performed, and finally the capacitor C
Current is zero. As a result, the switching element SW
An oscillating voltage as shown in C is applied to both ends of the. Further, since the current shown by E flows in the primary winding t ₁ of the transformer T, the current obtained by combining D and E flows in the switching element SW as shown in B. The capacitor C may be connected in parallel with the switching element SW.

[0011]

In the circuit configuration as described above, the switching element SW is turned on / off only by the output signal from the drive circuit 1. Therefore, when the drive circuit 1 fails or malfunctions, the output voltage changes. If the on-duty becomes short due to a failure or malfunction, the output voltage will drop and the optical output will drop,
Although it works on the safe side, when the on-duty becomes long, the output voltage becomes high and the temperature of the lamp L becomes high.
As a result, the appliance temperature may exceed the rating, which may cause a fire, or the switching element SW may cause thermal runaway to destroy the circuit. If the voltage applied to the lamp is high, at worst,
The lamp L may explode and cause harm to the human body.

The present invention has been provided in view of the above points, and prevents the on-duty of the output signal from exceeding a certain value even if the drive circuit malfunctions or malfunctions, thereby preventing a fire or a human body. An incandescent lamp lighting device is provided for the purpose of preventing harm.

[0013]

According to the present invention, a DC power source is connected to one end of a primary winding of a transformer, a switching element is connected to the other end of the primary winding of the transformer, and A capacitor is connected in parallel with the secondary winding or in parallel with the switching element to provide a drive circuit that determines the on-duty of the switching element, and a diode is provided in the secondary winding of the transformer so that a current flows when the switching element is turned on. In the incandescent lamp lighting device in which the incandescent lamp is connected to turn on the incandescent lamp, when the drive circuit outputs an on-duty signal that is longer than the rated time when an abnormality occurs, the on-period of the switching element is prevented from exceeding a certain value. A protection circuit is provided.

[0014]

By controlling the ON period of the switching element so as not to exceed a certain value, even if the ON duty signal that is longer than the rated time is output when the drive circuit has a failure, etc. The ON period of does not exceed a certain level, prevents the application of high voltage to the incandescent lamp, suppresses the temperature rise of the tube wall of the incandescent lamp, and the fixture temperature exceeds the rating,
It is possible to prevent a fire, prevent the explosion of incandescent lamps, and prevent harm to the human body.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. According to the present invention, even if the drive circuit 1 malfunctions or malfunctions, an on-duty signal above a certain level is not output. (Embodiment 1) FIG. 1 shows a circuit diagram. The basic circuit configuration is the second
The difference from the conventional example is that the protection circuit 2 is connected to both ends of the switching element SW and the output of the protection circuit 2 is input to the drive circuit 1.

FIG. 2 shows a concrete example of the drive circuit 1, which uses an IC3 (μPC1094) as a switching regulator. The oscillation frequency can be arbitrarily set by a resistor R ₂ and a capacitor C _2, and it is turned on by a volume VR. The duty can be set arbitrarily. Drive circuit 1
A rectangular wave signal as shown by C in FIG. 4 is output to the output terminal of.

FIG. 3 shows a concrete example of the protection circuit 2, in which resistors R ₄ and R _{5 are provided} between the drain and source of the switching element SW.
Of the Zener diode ZD ₁ is connected to the connection point of the resistors R ₄ and R ₅ , and the anode of the Zener diode ZD ₁ is connected to the base of the transistor Q via the resistor R _6. ing. The collector of the transistor Q is connected to the gate of the switching element SW, and the emitter of the transistor Q is connected to the source of the switching element SW.

Next, the circuit operation will be described with reference to the waveform chart of FIG. When the drive circuit 1 is normal, the rectangular wave signal shown in (c) is output, and the waveform shown in (a) and a similar waveform are applied to both ends of the switching element SW from the constant and the constant of the main circuit. On the basis of the oscillation waveform B divided by the resistor R ₅ , the base signal B is applied to the transistor Q for a period higher than the Zener voltage V _ZD1 of the Zener diode ZD ₁ , and the transistor Q is turned on. While the transistor Q is on, even if the gate signal for turning on the switching element SW is output from the drive circuit 1, the gate and source of the switching element SW are short-circuited by the transistor Q, and the switching element SW is turned on.
Does not turn on.

In the normal drive signal as shown by C, since there is no portion overlapping with the signal of B, the drive signal D input to the gate has the same waveform as that of C. Drive circuit 1
Is malfunctioning due to a failure or the like and outputs a very long ON period signal of the switching element SW as shown in E, the ON period of the switching element SW is cut at the shaded portion where the waveform E and the waveform B overlap. , The switching element SW is turned on in the remaining portion shown in F, and the oscillation voltage V _DS
Waveform is generated.

(Embodiment 2) A protection circuit 2 of Embodiment 2 is shown in FIG.
Shown in. The entire basic circuit is the same as that of the second conventional example.
As shown in FIG.₁And R₂The series circuit of
The resistor R is connected to both ends of the ching element SW.₂On both ends of
Zener diode ZD₁, Capacitor C ₁And resistance R₃
Is connected to the series circuit.

The connection point between the capacitor C ₁ and the resistor R ₃ is connected to the trigger input terminal of the timer IC 5 of the timer circuit 4. The output terminal of the timer IC 5 has a resistor R ₅
Is connected to the base of the transistor Q via. Next, the circuit operation will be described with reference to FIG. A voltage division waveform a of the drain-source voltage of the switching element SW is applied to both ends of the resistor R ₂ , and it is compared with the zener voltage V _ZD1 of the zener diode ZD ₁ to obtain a waveform across the resistor R _3. The trigger waveform shown in (c) is generated, and the timer circuit 4 is operated thereby, and the timer signal D defined by the circuit constant is output.

The transistor Q is turned on by this timer signal D, and the driving circuit 1 is operated during this period as in the first conventional example.
The switching element SW does not turn on even if an erroneous signal is received from the switching element SW. That is, as shown in FIG. 6G, when the drive circuit 1 fails, a signal with a wide on-duty is output, but the protection circuit 2 causes the operation of the timer IC 5 as shown in FIG. , The on-duty is regulated to a certain value or less, and the gate input signal to the switching element SW is output.

In the first embodiment, the period during which the switching element SW is forcibly turned off is uniquely determined by the resonance voltage waveform of the main circuit and the zener voltage of the zener diode ZD ₁ and cannot be freely changed. But,
In the second embodiment, the time constant of the timer circuit 4 can be arbitrarily set, the degree of freedom is increased, and the ON period of the switching element SW can be regulated on the safer side.

[0024]

As described above, the present invention connects the DC power supply to one end of the primary winding of the transformer, connects the switching element to the other end of the primary winding of the transformer, and A capacitor is connected in parallel with the secondary winding or in parallel with the switching element to provide a drive circuit that determines the on-duty of the switching element, and a diode is provided in the secondary winding of the transformer so that a current flows when the switching element is turned on. In the incandescent lamp lighting device in which the incandescent lamp is connected to turn on the incandescent lamp, when the drive circuit outputs an on-duty signal that is longer than the rated time when an abnormality occurs, the on-period of the switching element is prevented from exceeding a certain value. Since the protection circuit is provided, the drive circuit can be protected by suppressing the ON period of the switching element from exceeding a certain value. If an on-duty signal that is longer than the rated value is output, the ON period of the switching element does not exceed a certain level, preventing the application of high voltage to the incandescent lamp, and By suppressing the temperature rise, it is possible to prevent the equipment temperature from exceeding the rating and to cause a fire, and also to prevent the explosion of the incandescent lamp and prevent the harm to the human body.

[Brief description of drawings]

FIG. 1 is an overall circuit diagram of an embodiment of the present invention.

FIG. 2 is a specific circuit diagram of the drive circuit of the above.

FIG. 3 is a specific circuit diagram of the above protection circuit.

FIG. 4 is an operation waveform diagram of the above.

FIG. 5 is a specific circuit diagram of the protection circuit according to the second embodiment.

FIG. 6 is an operation waveform diagram of the above.

FIG. 7 is a circuit diagram of a first conventional example.

FIG. 8 is a circuit diagram of a second conventional example.

FIG. 9 is an operation waveform diagram of the above.

[Explanation of symbols]

 1 Drive circuit 2 Protection circuit C Capacitor T Transformer D Diode L Lamp SW Switching element

Claims (1)

[Claims] 1. A DC power source is connected to one end of a primary winding of a transformer, a switching element is connected to the other end of the primary winding of the transformer, and in parallel with the primary winding of the transformer.
Alternatively, a capacitor is connected in parallel with the switching element to provide a drive circuit that determines the on-duty of the switching element, and a diode is connected to the secondary winding of the transformer in the direction in which current flows when the switching element is turned on, and an incandescent lamp is connected. In the incandescent lamp lighting device that is turned on, a protection circuit is provided to prevent the ON period of the switching element from exceeding a certain value when an on-duty signal that is longer than the rated time is output from the drive circuit during an abnormality. Characteristic incandescent lamp lighting device.