JPH0574581A - Incandescent lamp lighting device - Google Patents

Abstract

PURPOSE:To reduce a switching loss when a switching element is ON, and to reduce a temperature rise of the switching element. CONSTITUTION:A transformer T in which a capacitor C is connected to the primary winding t1, and a switching element SW are connected in series. A driving circuit 1 to control the ON and OFF of the switching element SW is provided. A constant of the driving circuit 1 is set to make the starting of the on duty of a signal output from the driving circuit 1, to the lowest valley of the oscillation voltage VDS. The oscillation voltage VDS applied to both ends of the switching element is made lower than the VE (the voltage of a DC power source E), and a power loss which consists of the product of the applied voltage and current is reduced.

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. 5 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. 6 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. 7 shows operation waveforms of each part of the conventional example of FIG. 6, and the operation will be described below. In addition, a-e in FIG.
It is a waveform from point a to point 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.

[0011]

As shown in FIG. 8, the switching loss of the switching element SW at the time of turning on when performing the above-described circuit operation is as shown in FIG.
Is a shaded portion surrounded by the fall of the drain-source voltage V _DS and the rise of the drain current I _D.

It can be seen that the steep current flowing through the capacitor C has a large area and a large loss.
The present invention has been provided in view of the above points, and reduces the switching loss at the time of turning on and the temperature rise of the switching element, thereby reducing the size of the radiation fins and downsizing the circuit. The purpose is to improve the reliability of the circuit.

[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 next winding or in parallel with the switching element, and a diode is connected to the secondary winding of the transformer in a direction in which a current flows when the switching element is turned on to light the incandescent lamp. The incandescent lamp lighting device is provided with a drive circuit set so that the switching element is turned on at a phase at which the switching element becomes lower than the DC power supply voltage.

According to a second aspect of the present invention, a voltage detection circuit for detecting the voltage across the switching element and outputting a signal to the drive circuit when the detected voltage is lower than the DC power supply voltage is provided, and the drive circuit switches. An ON signal for turning on the element is output.

[0015]

Since the oscillating voltage applied to the switching element is lowered, the voltage when the switching element is turned on can be performed at a low place, the switching loss can be suppressed, and the temperature rise of the switching element can be suppressed. To reduce
It is possible to provide a compact and highly reliable lighting device in which the heat radiation fins can be made small.

According to a second aspect of the present invention, a voltage detection circuit for detecting the voltage across the switching element and outputting a signal to the drive circuit when the detected voltage is lower than the DC power supply voltage is provided, and the drive circuit switches the switching element. By outputting an ON signal to turn on the switching element, the voltage when the switching element is turned on can be performed at a low place, the switching loss can be suppressed, the temperature rise of the switching element can be reduced, and the heat radiation fin etc. can be made small. Therefore, a compact and highly reliable lighting device can be provided.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. According to the present invention, when the on-duty of the switching element in the one-stone inverter circuit starts, the oscillation voltage V _DS applied across the switching element is V
_By providing it at a position lower than _E (voltage of the DC power supply E), power loss due to the product of applied voltage and current is reduced.

FIG. 1 shows a circuit and an operation waveform diagram. The circuit configuration is similar to that of the second conventional example, and therefore detailed description is omitted. The characteristic of this circuit is that the beginning of on-duty is at the lowest valley of the oscillating voltage of V _DS .
That is, the constant of the drive circuit 1 is set. A specific example of such a drive circuit 1 is shown in FIG. In this specific example, a switching regulator IC (μPC1094) 2 is used, and the oscillation frequency can be arbitrarily set by the resistor R ₂ and the capacitor C _2, and the on-duty can be arbitrarily set by the volume VR. Therefore, FIG.
By adjusting the volume VR in the main circuit of, the start phase of on-duty can be set to the valley portion of the oscillating voltage V _DS .

(Embodiment 2) Embodiment 2 is shown in FIG. Basic
The circuit configuration is the same as that of the second conventional example, and detailed description is omitted.
I will omit it. The drive circuit 1 will be described below. switch
Resistor R at both ends of the switching element SW₁And R₂Connect a series circuit of
And the resistance R ₂Zener diode ZD on both ends of₁And
Anti-R₃Connect a series circuit of the Zener diode Z
D₁And resistance R₃Connect the connection point of to the base of transistor Q
It continues. In addition, Zener diode ZD₁Has voltage detection
It constitutes a circuit.

The collector of the transistor Q has a resistor R ₄
A control power supply Vcc is connected via a capacitor C ₁ and a resistor R ₅ to a differentiating circuit, and the capacitor C 1
The connection point between ₁ and the resistor R ₅ is input to the timer circuit 3. The output of the timer circuit 3 is connected to the gate of the switching element SW. Next, the circuit operation will be described with reference to FIG. Both ends of the resistor R ₂ are shown in FIG.
A divided voltage waveform of the drain-source voltage of the switching element SW is applied as shown in (3) and is detected by the zener voltage V _ZD1 of the zener diode ZD ₁ (this zener voltage V _ZD1 is lower than V _E , and the vibration is generated). It is set higher than the valley of the voltage V _DS ).

Since the transistor Q is turned on for the period shown in FIG.
The emitter-to-emitter voltage V _CE has a waveform as shown in FIG.
This waveform of (c) is input to the differentiating circuit, and its rising signal ((f) in the same figure) is input to the timer circuit 3 of the next stage, and the ON signal (determined by the time constant in the timer circuit 3 The same figure (g) is input to the gate of the switching element SW.

As described above, the ON phase of the switching element SW is always the valley of the oscillating voltage V _DS , and the switching loss at the ON time is minimized.
The temperature rise can be suppressed, the heat radiation fins of the switching element SW, etc. can be designed small, and the circuit can be miniaturized. As shown in FIG. 4, the Zener diode ZD ₁
If the zener voltage of is set to a voltage V _ZD2 lower than the valley portion, the valley portion cannot be detected and control cannot be performed.

[0023]

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 next winding or in parallel with the switching element, and a diode is connected to the secondary winding of the transformer in a direction in which a current flows when the switching element is turned on to light the incandescent lamp. Since the incandescent lamp lighting device is provided with a drive circuit set so that the switching element is turned on at a phase at which the switching element becomes lower than the DC power supply voltage, vibration applied to the switching element is provided. Since the voltage becomes low, the voltage when the switching element is turned on can be performed at a low place, and the switching loss can be suppressed. Reduces the temperature rise of, etc. can be reduced radiating fin, in which the effect capable of providing a highly reliable lighting device compact.

According to a second aspect of the present invention, a voltage detection circuit that detects the voltage across the switching element and outputs a signal to the drive circuit when the detected voltage is lower than the DC power supply voltage is provided. By outputting an ON signal to turn on the switching element, the voltage when the switching element is turned on can be performed at a low place, the switching loss can be suppressed, the temperature rise of the switching element can be reduced, and the heat radiation fin etc. can be made small. Therefore, a compact and highly reliable lighting device can be provided.

[Brief description of drawings]

FIG. 1A is a circuit diagram of an embodiment of the present invention.
(B) is an operation waveform diagram of the above.

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

FIG. 3 is a circuit diagram of a second embodiment of the above.

FIG. 4 is an operation waveform diagram of FIG. 3 above.

FIG. 5 is a circuit diagram of a conventional example.

FIG. 6 is a circuit diagram of a second conventional example.

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

8 is an operation explanatory diagram showing a switching loss at the time of turning on of FIG. 6 above.

[Explanation of symbols]

 1 Drive circuit E DC power supply C Capacitor T Transformer D Diode L Lamp SW Switching element

Claims (2)

[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, in the incandescent lamp lighting device, a capacitor is connected in parallel with the switching element, and a diode is connected to the secondary winding of the transformer in a direction in which a current flows when the switching element is turned on to light the incandescent lamp. An incandescent lamp lighting device provided with a drive circuit set so that a switching element is turned on at a phase at which the switching element is lower than the DC power supply voltage. 2. A voltage detection circuit that detects the voltage across the switching element and outputs a signal to the drive circuit when the detected voltage is lower than the DC power supply voltage, and turns on the switching element from the drive circuit. The incandescent lamp lighting device according to claim 1, wherein a signal is output.