JPH07320885A - Lighting device for electric discharge lamp - Google Patents

Abstract

PURPOSE:To provide an electric discharge lamp lighting device capable of preventing the heat generation of a filament preheating winding or the like, even if the filament of an electric discharge lamp is shortcircuited. CONSTITUTION:Transistors Q1 and Q2 are alternately turned on and off through the maturity of a current transformer CT, thereby generating high frequency current and lighting a fluorescent lamp FL at a high frequency. Also, filaments FL1 and FL2 are preheated with filament preheating windings Tr2 and Tr3. When one of the filaments FL1 and FL2 is shortcircuited, shortcircuit current flows to either the winding Tr2 or the winding Tr3. Thus, no voltage is induced in a detection winding Tr4 and a capacitor C5 is not charged. Furthermore, no current flows to the base of a transistor Q4 and this transistor Q4 is turned off, thereby applying voltage from a DC power supply El to the gate of a field effect transistor Q5. As a result, the transistor Q5 is turned on, and current is made to bypass the base of the transistor Q2 at low voltage. Consequently, the transistor Q2 is turned off, and the oscillation of an inverter circuit 1 is stopped.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discharge lamp lighting device which can cope with a short circuit of a filament of a discharge lamp.

[0002]

2. Description of the Related Art A conventional discharge lamp lighting device is shown in FIG.
It has the configuration shown in.

That is, for example, a commercial AC power source is rectified,
A series circuit of a collector and an emitter of the transistor Q1 and a collector and an emitter of the transistor Q2 is connected in series to the smoothed DC power source E, and the transistor Q1 and the transistor Q2 form a half-bridge type inverter circuit 1. .

A series circuit of a resistor R1 and a capacitor C1 is connected in parallel to the DC power source E, and a diode D1 is connected between the connection point of the resistor R1 and the capacitor C1 and the emitter of the transistor Q1 and the collector of the transistor Q2. At the same time, it is connected from the connection point of the resistor R1 and the capacitor C1 to the base of the transistor Q2 via the trigger element Q3.

Between the collector and the emitter of the transistor Q2, an input winding CT1 of a current transformer CT, a ballast choke L1, a filament FL1 and a filament FL2 of a fluorescent lamp FL as a discharge lamp, and a DC cut capacitor C2. The series circuit of is connected.

A series circuit of a resistor R2 and a control winding CT2 of the current transformer CT is connected between the base and the emitter of the transistor Q1, and a resistor R3 and a current transformer CT are connected between the base and the emitter of the transistor Q2. Control winding CT3
The series circuit of is connected.

Further, between the ballast choke L1 and the negative electrode of the DC power source E, a capacitor C3 and a series circuit of an input winding Tr1 of the filament transformer Tr and a capacitor C4 are connected.

The filament transformer Tr includes a filament preheating winding Tr2 and a filament preheating winding Tr.
3 is provided, the filament preheating winding Tr2 is a diode
The filament preheating winding Tr3 is connected to the filament FL1 of the fluorescent lamp FL via D2, and the filament preheating winding Tr3 is connected to the filament FL2 of the fluorescent lamp FL via the diode D3.

Here, as shown in FIG. 3, the fluorescent lamp FL has a stem 6 formed inside a lamp socket 5 formed at an end portion of a lamp bulb 4, an inner lead 7,
7 are provided, and the filaments FL1 and FL2 are connected between the inner leads 7 and 7.

When the power source is turned on, the capacitor C1 is charged with the DC voltage from the DC power source E, and the capacitor C1 is charged.
When the voltage of the voltage rises above the voltage set by the trigger element Q3, the trigger element Q3 breaks over and the transistor Q2
Current is supplied to the base of and turns on transistor Q2,
After the transistor Q2 is turned on, due to the saturation of the current transformer CT, the transistor Q1 and the transistor Q2 are turned on and off alternately to generate a high frequency alternating current, and the fluorescent lamp FL is lit at a high frequency.

Further, the filament preheating winding Tr2 and the filament preheating winding Tr3 preheat the filaments FL1 and FL2 of the fluorescent lamp FL, respectively.

[0012]

However, as shown in FIG. 4, for example, the filament FL1,
If FL2 is melted and the inner leads 7 and 7 are short-circuited, a short-circuit current flows through the filament preheating windings Tr2 and Tr3, and the filament preheating windings Tr2 and Tr3 may generate heat.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a discharge lamp lighting device which prevents heat generation in a filament preheating winding or the like even when the filament of the discharge lamp is short-circuited.

[0014]

According to the present invention, a direct current of a direct current power source is oscillated by a switching element of an inverter circuit to be converted into an alternating current, and a filament of a discharge lamp is preheated by a filament preheating winding formed in a transformer. , In the discharge lamp lighting device for lighting the discharge lamp,
A detection winding magnetically coupled to the filament preheating winding in the transformer; and a protection means for stopping the oscillation of the switching element when the voltage detected by the detection winding drops below a predetermined value. It is equipped with.

[0015]

According to the present invention, the transformer is provided with the detection winding which is magnetically coupled to the filament preheating winding, and when the voltage detected by the detection winding falls below a predetermined value, the protection means prevents the switching element from oscillating. Since the discharge lamp is stopped, no electric power is supplied to the discharge lamp, which prevents the filament preheating winding from generating heat.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the discharge lamp lighting device of the present invention will be described below with reference to the drawings. It should be noted that the portions corresponding to the conventional example shown in FIG.

As shown in FIG. 1, for example, a collector and an emitter of a transistor Q1 as a switching element and a collector and an emitter of a transistor Q2 as a switching element are connected in series with a DC power source E obtained by rectifying and smoothing a commercial AC power source. A series circuit is connected, and the transistor Q1 and the transistor Q2 form a half-bridge type inverter circuit 1.

A series circuit of a resistor R1 and a capacitor C1 is connected in parallel to the DC power source E, and a diode D1 is connected between the connection point of the resistor R1 and the capacitor C1 and the emitter of the transistor Q1 and the collector of the transistor Q2. At the same time, it is connected from the connection point of the resistor R1 and the capacitor C1 to the base of the transistor Q2 via the trigger element Q3.

Between the collector and the emitter of the transistor Q2, an input winding CT1 of a current transformer CT, a ballast choke L1, a filament FL1 and a filament FL2 of a fluorescent lamp FL as a discharge lamp, and a DC cut capacitor C2. The series circuit of is connected.

A series circuit of a resistor R2 and a control winding CT2 of the current transformer CT is connected between the base and emitter of the transistor Q1, and a resistor R3 and a current transformer CT of the transistor Q2 are connected between the base and emitter. Control winding CT3
The series circuit of is connected.

Further, between the ballast choke L1 and the negative electrode of the DC power source E, a capacitor C3 and a series circuit of an input winding Tr1 of the filament transformer Tr and a capacitor C4 are connected.

The filament transformer Tr includes a filament preheating winding Tr2 and a filament preheating winding Tr.
3 is provided, the filament preheating winding Tr2 is a diode
The filament preheating winding Tr3 is connected to the filament FL1 of the fluorescent lamp FL via D2, and the filament preheating winding Tr3 is connected to the filament FL2 of the fluorescent lamp FL via the diode D3.

Further, the filament transformer Tr is provided with a detection winding Tr4 of the protection means 11, and a series circuit of a diode D4 and a capacitor C5 is connected to the detection winding Tr4. The base of the transistor Q4 is connected to the connection point of the diode D4 and the capacitor C5 via the resistor R4, and the resistor R5 and the series circuit of the resistor R6 and the DC power source E1 are connected between the collector and the emitter of the transistor Q4. Are connected in parallel. Further, the capacitor C6 is connected to the resistor R5, the gate of the field effect transistor Q5 is connected to the collector of the transistor Q4, the source is connected to the negative electrode of the DC power source E, and the drain is connected to the transistor Q2 via the diode D5. It is connected.

Next, the operation of the above embodiment will be described.

First, when the DC voltage from the DC power source E is turned on, the capacitor C1 is charged, the voltage of the capacitor C1 rises according to the time constants of the resistor R1 and the capacitor C1, and is set by the trigger element Q3. When the voltage rises above the threshold voltage, the trigger element Q3 breaks over and current is supplied to the base of the transistor Q2, turning on the transistor Q2, and after turning on the transistor Q2, the saturation of the current transformer CT causes the transistors Q1 and Q2 to Are alternately turned on and off to generate high-frequency alternating current, and the fluorescent lamp FL is lit at high frequency.

Further, the filament preheating winding Tr2 and the filament preheating winding Tr3 preheat the filaments FL1 and FL2 of the fluorescent lamp FL, respectively.

When the fluorescent lamp FL is in a normal state, since a normal current flows through both the filament preheating winding Tr2 and the filament preheating winding Tr3, a voltage is similarly induced in the detection winding Tr4. Is rectified by the diode D4 to charge the capacitor C5. When this capacitor C5 is charged, current flows through the base of the transistor Q4,
Since the voltage is not applied to the gate of the field effect transistor Q5 when the transistor Q4 is turned on, the field effect transistor Q5 is in the off state and the base current of the transistor Q2 is not bypassed, so that the inverter circuit 1 oscillates normally.

On the other hand, the filaments FL1 of the fluorescent lamp FL,
If any of FL2 is shorted, filament preheat winding Tr
2 or filament preheating winding Tr3, a short circuit current flows, so no voltage is induced in the detection winding Tr4.
Capacitor C5 is not charged. When the voltage of the capacitor C5 is low, current does not flow to the base of the transistor Q4, and the transistor Q4 is turned off.
Since the voltage of the DC power supply E1 is applied to the gate of Q5, the field-effect transistor Q5 turns on and the low-voltage side transistor Q2
Bypassing the base current of, the transistor Q2 is turned off and the oscillation of the inverter circuit 1 is stopped.

Therefore, even if one of the filaments FL1 and FL2 of the fluorescent lamp FL is short-circuited, the filament preheating winding Tr2 and the filament preheating winding Tr3 do not generate heat.

The inverter circuit 1 is not limited to the half-bridge type inverter circuit, and the same effect can be obtained by using a one-stone type inverter circuit.

[0031]

According to the discharge lamp lighting device of the present invention, the transformer is magnetically coupled with the filament preheating winding to provide the detection winding, and the voltage detected by the detection winding is lowered to a predetermined value or less. Then, since the protection means stops the oscillation of the switching element, the electric power is not supplied to the discharge lamp, so that the filament preheating winding can be prevented from generating heat.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a discharge lamp lighting device of the present invention.

FIG. 2 is a circuit diagram showing a conventional discharge lamp lighting device.

FIG. 3 is a view showing the vicinity of a filament of a fluorescent lamp at a normal time.

FIG. 4 is a diagram showing the vicinity of a filament when the fluorescent lamp is broken.

[Description of symbols] 1 Inverter circuit 11 Protection means E DC power supply FL Fluorescent lamp as discharge lamp FL1, FL2 Filament Q1, Q2 Transistor as switching element Tr Filament transformer Tr2, Tr3 Filament preheating winding Tr4 Detection winding

Claims (1)

[Claims] 1. A discharge lamp for activating a direct current of a direct current power source to oscillate a switching element of an inverter circuit to convert it into an alternating current, preheating a filament of a discharge lamp by a filament preheating winding formed in a transformer and lighting a discharge lamp. In the lighting device, a detection winding provided magnetically coupled to the filament preheating winding in the transformer, and the oscillation of the switching element is stopped when the voltage detected by the detection winding falls below a predetermined value. A discharge lamp lighting device, comprising: