JPH06140182A - Discharge lamp lighting device - Google Patents

Abstract

PURPOSE:To provide a discharge lamp lighting device in which no load is generated in a lighting circuit even at preheating of a discharge lamp or secondary short-circuit. CONSTITUTION:At normal lighting, the voltage across a second capacitor C2 has almost the same waveform as the output of a rectifying circuit. The base voltage of a transistor Q3 is lowered, the base capacitance of a transistor Q1 is increased to generally oscillate an inverter circuit 3, and a fluorescent lamp FL is lighted as usual. At an abnormality such as long-time preheating state or secondary side short-circuit, the voltage of the second capacitor C2 becomes a voltage in which a high frequency is superposed on the voltage of the rectifying circuit 1. The base voltage of the transistor Q3 is raised, and the base capacitance of the transistor Q1 is lowered to lower the output of the inverter circuit 3. The stress added to a part such as the transistor Q1 is reduced, and the stress of a semiconductor part such as the transistor Q1 is protected.

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 for lighting a discharge lamp by a lighting circuit based on electric power obtained by rectifying an AC power supply.

[0002]

2. Description of the Related Art Conventionally, there is known a discharge lamp lighting device that rectifies a voltage of a commercial AC power source by a rectifier circuit and converts the rectified voltage into a high frequency by an inverter circuit to light a discharge lamp.

In order to keep the voltage supplied to the discharge lamp constant, the output voltage of the inverter circuit is kept constant regardless of the fluctuation of the voltage of the commercial AC power source.

As a method of keeping the output voltage of the inverter circuit constant, the voltage of the commercial AC power supply is detected, and when the voltage of the commercial AC power supply drops, the output of the inverter circuit is increased to increase the output voltage of the inverter circuit. On the contrary, when the voltage of the commercial AC power supply rises, the output of the inverter circuit is lowered so that the output voltage of the inverter circuit is always kept constant.

[0005]

However, in the case of the above-mentioned conventional discharge lamp lighting device, it is not possible to cope with the load fluctuation, for example, when the discharge lamp is preheated or when a secondary short circuit occurs, and the output voltage of the inverter circuit is reduced. Has a problem that, for example, a semiconductor switching element or the like in the inverter circuit is destroyed or stress is generated.

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 that does not burden the lighting circuit or the like even when the discharge lamp is preheated or a secondary short circuit occurs.

[0007]

DISCLOSURE OF THE INVENTION A discharge lamp lighting device according to the present invention comprises a rectifying circuit for rectifying an AC power source, a first capacitor connected between the outputs of the rectifying circuit, and one end of the first capacitor. A rectifying element connected to the first capacitor, a second capacitor connected in parallel to the first capacitor through the rectifying element in a forward polarity, and a discharge lamp connected between both terminals of the second capacitor. Is provided with a lighting circuit for lighting up, a voltage detection circuit for detecting the voltage of the second capacitor, and a control circuit for varying the output of the lighting circuit based on the voltage detected by the voltage detection circuit. .

[0008]

According to the present invention, the AC power supply is rectified by the rectifier circuit, and the first
The second rectifier through the rectifying element in the forward polarity and the first capacitor and the second capacitor are used as power sources to supply power to the lighting circuit, and the lighting circuit discharges the discharge lamp. Light up. In addition, the voltage detection circuit detects the voltage of the second capacitor,
Since the output of the lighting circuit is varied by the control circuit based on the voltage detected by the voltage detection circuit, the output of the lighting circuit can be controlled based on the voltage of the second capacitor in which the state of the discharge lamp appears. The burden can be prevented.

[0009]

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.

In FIG. 1, E is a commercial AC power source, and a rectifier circuit 1 for rectifying the AC voltage of the commercial AC power source E is connected to the commercial AC power source E. The rectifier circuit 1 serves as a surge absorbing element. For example, a ceramic varistor TNR1 is provided.

A smoothing circuit 2 is connected in parallel with the ceramic varistor TNR1. In this smoothing circuit 2, a first capacitor C1 is connected in parallel to the ceramic varistor TNR1, the anode of a diode D1 as a rectifying element is connected to the positive electrode side of the first capacitor C1, and the diode D1 is connected in order. First capacitor via polarity
A second capacitor C2 is connected between both terminals of C1. In addition, an inductor L1, a charging capacitor C3 and a diode D2 are placed between both terminals of the second capacitor C2.
, A series circuit for performing valley filling smoothing is connected. Further, the anode of the diode D3 is connected to the connection point of the charging capacitor C3 and the diode D2.

Further, between both terminals of the second capacitor C2,
The inverter circuit 3 as a lighting circuit is connected.
This inverter circuit 3 connects a parallel circuit of a primary winding Tr1a of an inverter transformer Tr1 and a resonance capacitor C4 via a diode D3 between both terminals of an inductor L1 and a charging capacitor C3. The collector and the emitter of the transistor Q1 are connected between the connection point of the Tr1a and the capacitor C4 and the negative electrode of the rectifier circuit 1.
Further, a starting resistor R1 is connected between the cathode of the diode D1 and the base of the transistor Q1. In addition, a series circuit of a capacitor C5 for DC cutting and a detection winding CT1a of a current transformer CT1 for current detection is connected to one end of a secondary winding Tr1b of the inverter transformer Tr1.
The resistor R2 is connected to the series circuit of the capacitor C5 and the detection winding CT1a.

Further, between the secondary winding Tr1b of the inverter transformer Tr1 and the connection point of the resistor R2 and the detection winding CT1a, a filament FL of a fluorescent lamp FL as a discharge lamp is provided.
a and FLb are connected, and a starting capacitor C6 is connected between the filaments FLa and FLb.

A control circuit 4 is connected between the base and emitter of the transistor Q1. That is, a current transformer is placed between the base and emitter of the transistor Q1.
The control winding CT1b of CT1 is connected to the capacitor C7 and the series circuit of the drain and source of the capacitance varying field effect transistor Q2. In addition, between the drain and source of the capacitor C7 and field effect transistor Q2,
A series circuit of C8 and a capacitor C9 is connected, and further, a diode D4 and a diode D5 are connected in antiparallel in parallel with the capacitor C8, and a diode D6 is connected in parallel with the capacitor C9. A series circuit of a diode D7 and a resistor R3 is connected between the base and emitter of the transistor Q1.

On the other hand, the voltage detection circuit 5 is connected to the output terminal of the rectifier circuit 1. In the voltage detection circuit 5, a series circuit of a resistor R4 and a smoothing capacitor C11 is connected between the output terminals of the rectifier circuit 1, and the capacitor C1
A zener diode ZD1 for constant voltage is connected in parallel to 1 and a series circuit of a resistor R5, an emitter and collector of a transistor Q3, a resistor R6 and a resistor R7 is connected between both terminals of this zener diode ZD1. There is. A series circuit of a resistor R8 and a smoothing capacitor C12 is connected between both terminals of the rectifier circuit 1 via a diode D1, and a zener diode ZD2 for constant voltage is connected in parallel to this capacitor C12. ing. Furthermore, Zener diode
A series circuit of a resistor R9 and a variable resistor R10 is connected in parallel with ZD2. The base of the transistor Q3 is connected to the connection point of the resistors R8 and R9.

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

First, when the commercial AC power source E is turned on, full-wave rectification is performed by the rectifier circuit 1, and a pulsating current is applied to the first capacitor C1 and the second capacitor C2. And
The inverter circuit 3 supplies the DC voltage supplied from the second capacitor C2 to the base of the transistor Q1 via the resistor R1 to activate the transistor Q1. Also, the transistor Q1 is switching-controlled at high frequency, and the inductance of the primary winding Tr1a of the inverter transformer Tr11 and the capacitor
A voltage resonating with the capacitance of C4 is induced in the secondary winding Tr1b and supplied to the fluorescent lamp FL. Then, the capacitor C5 preheats the filaments FLa and FLb of the fluorescent lamp FL, and at the same time, the generated voltage of the capacitor C6 is applied to the fluorescent lamp FL to start and light the fluorescent lamp FL.

The subsequent steady-state operation will be described by dividing it into a period in which the voltage value of the first capacitor C1 is higher than the voltage value of the charging capacitor C3 and a low period.

First, the first from the voltage of the charging capacitor C3
During the period when the voltage of the capacitor C1 is low, when the transistor Q1 of the inverter circuit 3 is turned on, the first capacitor
Inverter transformer from C1 and second capacitor C2
Electric power is supplied to the primary winding Tr1a of Tr1. The current of the transistor Q1 is the diode D2, the diode D3, the capacitor C4 and the primary winding Tr of the inverter transformer Tr1.
It flows in the loop of 1a. At this time, the inverter transformer Tr
The primary winding Tr1a of 1 and the capacitor C4 vibrate to generate an oscillating voltage. Then, the reverse blocking state is maintained by the diode D1, the primary winding Tr1a of the inverter transformer Tr1 and the capacitor C4 vibrate, and an oscillating voltage is generated.

Further, since the capacity of the second capacitor C2 is not sufficient to maintain the oscillation of the inverter circuit 3, the voltage value gradually decreases, and the voltage value of the second capacitor C2 is the first capacitor C2. When the voltage value of C1 is reached, power is also supplied from the first capacitor C1. Further, when the transistor Q1 is turned off, the charge of the charging capacitor C3 is discharged and resonates with the inductor L1 and the capacitor C4 to charge the second capacitor C2 in a sine wave shape.

Next, the first from the voltage of the charging capacitor C3
When the transistor Q1 of the inverter circuit 3 is turned on while the voltage of the capacitor C1 of the first capacitor is high, the first capacitor
Inverter transformer from C1 and second capacitor C2
Electric power is supplied to the primary winding Tr1a of Tr1. The current of the transistor Q1 is the diode D2, the diode D3, the capacitor C4 and the primary winding Tr of the inverter transformer Tr1.
It flows in the loop of 1a. At this time, the inverter transformer Tr
The primary winding Tr1a of 1 and the capacitor C4 vibrate, and an oscillating voltage is generated in the secondary winding Tr1b of the inverter transformer Tr1.

Further, at this time, in the voltage detecting means 5, a voltage is generated in the time constant circuit composed of the resistor R4 and the capacitor C11 connected between the output terminals of the rectifying circuit 1, and the emitter voltage is applied to the transistor Q3 via the resistor R5. Added. At the same time, a base signal is given to the base of the field effect transistor Q2 by the voltage divided by the resistor R8 and the Zener diode ZD2 by the voltage division of the resistors R10, R11, R12.
Therefore, the field-effect transistor Q2 is turned on by the potential difference between the emitter and the base and energizes the resistors R13 and R14, so that a voltage is generated in the resistor R14 and the field-effect transistor
Join the gate of Q2 and turn it on.

When the field effect transistor Q2 is turned on, the capacitor C3 and the capacitor C8 are connected in parallel, and the combined capacitance becomes large, so that the frequency for the inverter circuit 3 becomes low and a sufficient output of the inverter circuit 3 is obtained. Then, it can be supplied to the fluorescent lamp FL.

On the other hand, by operating the variable resistor R10 provided in the base circuit of the field effect transistor Q2, the base potential changes, the collector current of the transistor Q3 also changes, and the gate voltage of the field effect transistor Q2 changes. , The output of the inverter circuit 3 can be changed. For example, if the resistance value of the variable resistor R12 is increased and the base potential of the field effect transistor Q2 is increased, the potential difference between the field effect transistor Q2 and the emitter is reduced and the collector current is reduced, so that the gate voltage of the field effect transistor Q2 is also reduced. Therefore, the current value flowing through the field effect transistor Q2 decreases,
The combined capacitance of the capacitors C7, C8 and C9 decreases, the base current of the transistor Q1 decreases, the frequency of the inverter circuit 3 increases, and the output of the inverter circuit 3 decreases. That is, the output supplied from the inverter circuit 3 to the fluorescent lamp FL decreases.

From these operations, the variable resistor R1 is normally operated.
The inverter circuit 3 is driven to obtain the output set by 0, and the output is supplied to the fluorescent lamp FL.

The lamp current of the fluorescent lamp FL is detected by the detection winding CT1a of the current transformer CT1, and the output of the control winding CT1b controls the base current of the transistor Q1 to control the oscillation of the transistor Q1.

When the output from the rectifier circuit 1 rises and the voltage detected by the voltage detection circuit 5 rises, the base current of the transistor Q3 increases and the gate voltage of the field effect transistor Q2 decreases. Then, the switching of the transistor Q1 is accelerated to reduce the output of the inverter circuit 3.

On the other hand, when the output from the rectifier circuit 1 decreases and the voltage detected by the voltage detecting circuit 5 decreases, the base current of the transistor Q3 decreases and the gate voltage of the field effect transistor Q2 increases. Thus, the switching of the transistor Q1 is delayed to increase the output of the inverter circuit 3.

As described above, when the output voltage of the rectifier circuit 1 increases, the output of the inverter circuit 3 decreases, and conversely,
When the output voltage of the rectifier circuit 1 drops, the inverter circuit 3
, The output of the inverter circuit 3 can always be kept constant.

Further, during normal lighting, the voltage across the second capacitor C2 has substantially the same waveform as the output of the rectifier circuit 1, that is, a frequency twice that of the commercial AC power source E, as shown in FIG. . Then, in this case, as shown in FIG. 4A, the base voltage of the transistor Q3 decreases, the base capacitance of the transistor Q1 increases, and the inverter circuit 3 normally oscillates to turn on the fluorescent lamp FL as usual.

Further, in the case of a preheated state for a long time or an abnormality such as a secondary side short circuit, the voltage of the second capacitor C2 becomes
The voltage of the rectifier circuit 1 is a voltage in which a high frequency is superimposed. Then, in this case, as shown in FIG. 4B, the transistor Q3
Since the base voltage of the transistor Q1 increases, the base capacitance of the transistor Q1 decreases, and the output of the inverter circuit 3 decreases, stress on components such as the transistor Q1 is reduced, and semiconductor components such as the transistor Q1 are protected from stress. be able to.

[0032]

According to the discharge lamp lighting device of the present invention, the voltage detection circuit detects the voltage of the second capacitor, and the control circuit changes the output of the lighting circuit based on the voltage detected by the voltage detection circuit. The second state of the discharge lamp appears
Since the output of the lighting circuit can be controlled based on the voltage of the capacitor, it is possible to prevent the lighting circuit from being overloaded.

[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 voltage waveform diagram of a second capacitor in a normal state.

FIG. 3 is a voltage waveform diagram of the second capacitor when there is an abnormality in the same as above.

FIG. 4 is a graph showing the relationship between the base capacitance of the transistor Q1 and the base potential of the transistor Q3.

[Explanation of symbols]

 1 Rectifier circuit 3 Inverter circuit as lighting circuit 4 Control circuit 5 Voltage detection circuit C1 1st capacitor C2 2nd capacitor E Commercial AC power supply FL Fluorescent lamp as discharge lamp

Claims (1)

[Claims] 1. A rectifying circuit for rectifying an AC power source, a first capacitor connected between outputs of the rectifying circuit, a rectifying element connected to one end of the first capacitor, and the rectifying element in order. A second capacitor connected in parallel to the first capacitor via a polarity; a lighting circuit connected between both terminals of the second capacitor for lighting a discharge lamp; and a second capacitor of the second capacitor. A discharge lamp lighting device comprising: a voltage detection circuit that detects a voltage; and a control circuit that varies the output of the lighting circuit based on the voltage detected by the voltage detection circuit.