KR20010088753A - Electronic ballast which comprising a control circuit of cathode pre-heating current therein - Google Patents

Abstract

PURPOSE: An electronic ballast including cathode preheating current control circuit is provided to control a cathode preheating current of a fluorescent lamp filament by lowering a resonance voltage on both ends of a resonance condenser connected with a lamp. CONSTITUTION: A rectification unit(200) rectifies an AC(alternating current) signal into a DC(direct current) signal. A lighting unit(600) oscillates the voltage permitted from the rectification unit(200) to a resonance frequency and turns on a lamp. An inverter unit(400) receives the voltage rectified in the rectification unit(200) and gives rise to the resonance of the lighting unit(600). A starting circuit unit(300) performs an initial starting of the inverter unit(400). A switching element(Q3) has access to one of the trigger elements(Q1,Q2) of the inverter unit(400). A constant voltage diode(D11) has access to a control tab of the switching element(Q3). A cathode preheating current control circuit unit(500) has access to a secondary or a third winding(T2,T3) of a drive transformer, and the junction point consists of a voltage dividing resistance(R7,R8) connected to the constant voltage diode(D11).

Description

ELECTRONIC BALLAST WHICH COMPRISING A CONTROL CIRCUIT OF CATHODE PRE-HEATING CURRENT THEREIN

The present invention relates to an electronic ballast for fluorescent lamps, and more particularly to an electronic ballast incorporating a cathode preheating current control circuit of a fluorescent lamp.

Electronic ballasts contain a starter element in the ballast, which preheats the electrode with its switching action or electrode heating winding and starts the lamp by the switching action of the switching circuit, while the lamp is turned on by the lamp current and the electrode heating winding during lighting. As the ballast used in the circuit system to be heated, there are self-excited equations oscillated by its own LC resonant circuit and the perception equation related to the present invention using a separate oscillator.

Electronic ballasts have several advantages over conventional ballasts, but they have built-in protection circuits due to their weaknesses in voltage fluctuations and surge voltages. Nevertheless, special measures for start-up are necessary due to the high voltage at lighting. .

Fluorescent lamps also shorten lamp life if they blink frequently. It is discharged when the electronic material of the filament is not heated sufficiently (for example, up to 110 ° C.) at the initial stage of lighting, so that the electronic material is scattered and the lamp rapidly blackens and the life is shortened.

However, if the lamp current and cathode preheating current specified in KSC 8100 are within the specified values, no significant lamp life change and short time blackening will occur. In order to control the cathode preheating current within a specified value, a control method using an IC is used, but this has a disadvantage in that the circuit is complicated and the unit price is high.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electronic ballast for a fluorescent lamp which can reliably control the cathode preheating current while having a simple circuit and low cost.

Further objects and effects of the present invention will become more apparent from the following detailed description of the invention described with reference to the accompanying drawings.

1 is a circuit diagram of an electronic ballast according to the present invention.

<Description of the symbols for the main parts of the drawings>

100: input power supply 200: rectification and smoothing unit

300: start circuit 400: inverter

500: cathode preheat current control circuit 600: lighting unit

Electronic ballast according to the present invention for achieving the above object, the rectification and smoothing unit 200 for rectifying the input AC signal to supply a DC voltage, and the given resonance frequency supplied with the voltage applied from the rectifying and smoothing unit A lighting unit 600 which oscillates and turns on the lamp, an inverter unit 400 which generates a resonance of the lighting unit by receiving the rectified voltage from the rectifying and smoothing unit, and a starting circuit unit for initial starting of the inverter unit ( 300, the lighting unit 600 includes resonant capacitors C12, C5, and C6 and an inductor L2. The inverter unit 400 has one winding of the resonant inductor L2. ) And the drive transformer T1, T2, and T3 electrically connected to each other and the secondary or tertiary windings of the drive transformer are turned on or off and trigger high frequency output by triggering the resonance circuit of the lighting unit. And a starter circuit (C8, R6, TD) for operating any one of the trigger elements when the lamp is started, and the start-up circuit unit (300) including trigger elements (Q1, Q2) for generating. A switching element Q3 which includes circuits R8 and D13 for later stopping the operation of the starting circuit, and which is connected to any one of the trigger elements Q1 and Q2 of the inverter unit 400, and the switching The voltage divider R7 and R8 connected to the constant voltage diode D11 connected to the control terminal of the element Q3 and the secondary or tertiary windings T2 and T3 of the drive transformer, and the connection point of which is connected to the constant voltage diode. And further comprising a negative electrode preheating current control circuit unit 500 configured to include a negative preheating current control circuit 500. Q3) to operate the The gate supply voltage of one of the trigger elements Q1 and Q2 is controlled, and the cathode voltage of the filament of the fluorescent lamp is controlled by lowering the resonance voltage across the resonance capacitor C12 connected to the lamp. It is characterized by soft start.

Preferably, the source side of the switching element Q3 of the cathode preheat current control circuit unit 500 is connected to the gate of one of the trigger elements Q1 and Q2 through a resistor R4, and the gate side thereof is It is characterized in that it is connected to the constant voltage diode (D11) and at the same time is grounded through the capacitor (C9).

EMBODIMENT OF THE INVENTION Hereinafter, the electronic ballast which concerns on this invention is described, referring FIG.

As shown in FIG. 1, the electronic ballast according to the present invention includes a voltage stabilizer 100, a rectification and smoothing unit 200, a starter circuit unit 300, an inverter unit 400, and a lighting unit 600. However, it is characterized in that the negative electrode preheating current control circuit 500 is connected to the start circuit 400.

First, a general ballast circuit without the cathode preheating current control circuit unit 500 according to the present invention will be described.

The voltage stabilization unit 100 receives a two-phase AC power in the form of a general AC power supply through two terminals A and B. The alternating current is filtered and stabilized again by a filter circuit consisting of three capacitors C1-C3 through a parallel circuit of varistor TNR and transformer LF1 functioning as a filter through fuse F1. The power stabilized by the filter circuit is applied to the next stage rectification and smoothing unit 200.

The rectification and smoothing unit 200 is full-wave rectified by the bridge diodes D1-D4, by the choke coil L1 and the condenser C4, and by the diodes D7, D8 and the smoothing capacitor C7. As smoothed and filtered, the rectified and smoothed voltages are applied to the start circuit unit 300 and the inverter unit 400, which are the next stages.

The inverter unit 400 includes a first and second switching transistors Q1 and Q2, to which a rectified DC power supply is applied, and which are connected to the gate terminal and the source terminal of each of the switching transistors. R15) (R3, R4) and secondary and tertiary transformer circuits (T2) (T3) connected to the gate terminals of the respective switching transistors, and diodes (D16, D5) (D10, D9) for maintaining a constant voltage. It is composed. The primary side T1 of the transformer circuits T2 and T3 is connected to one side of the lamp LAMP of the lighting unit 600 to detect the output of the lamp.

That is, the contacts P1 and P2 of the inverter unit 400 are connected to the source and the drain of the MOSFETs Q1 and Q2 respectively serving as trigger elements of the inverter unit, and the other input terminals of both trigger elements Q1 and Q2 are connected to the contacts. Meet at P4 and at the same time the primary winding T1 of the drive transformer is connected to the contact P4. In addition, the gate of the trigger element is connected to the secondary and tertiary side windings T2 and T3 of the drive transformer through resistors R15 (R3 and R4). Reference numerals D16 and D10 denote non-return diodes, and D5 and D9 denote constant voltage diodes.

On the other hand, both ends of the smoothing capacitor C7 of the rectifying and smoothing unit 200 are simultaneously connected to the starting circuit unit 300. That is, the series circuit of the resistor R6 and the capacitor C8 of the starting circuit portion is connected to the terminals P1 and P2, and the DIAC DIAC is connected to the connection point P3 of the resistor R6 and the capacitor C8 and It is connected to the gate of the trigger element Q2. Further, circuits R8 and D13 for stopping the operation of the starting circuit are connected between the terminals P3 and P4.

In addition, the lighting unit 600 has one electrode connected to the resonant circuit inductor L2 and the primary winding T1 of the driving transformer, and the other terminal is connected to the connection terminals of the output voltage distribution capacitors C6 and C5. That is, the other side of the lamp LAMP is connected to the output terminal and the ground terminal of the rectifying and smoothing unit 200 through the capacitors C5 and C6, respectively, and the capacitor C13 for impedance and resonance adjustment is inserted between both electrodes of the lamp. do.

Hereinafter, the operation of the voltage stabilization unit 100 to the inverter unit 400 will be described.

The supply voltage stabilized by the voltage stabilizer 100 is converted into a DC power supply by the rectification and smoothing unit 200 and applied to the inverter unit 400 and the starter circuit unit 300. Is charged in the charging capacitor C8, and when the charged voltage exceeds a predetermined value, the trigger diode TD is conducted by the time constants of the RC circuits R6 and C8 to eventually turn on the second switching transistor Q2. By operating, it starts by autonomously starting from the resonance of the LC resonant circuits L2, C12, C5, C6 of the lighting unit.

When the lighting is turned on by the operation of the second switching transistor Q2, the voltage induced in the self oscillating coils T1, T2, and T3 is changed by the time constants of the windings of the first and second switching transistors Q1, The driving voltage is supplied to Q2) to continue oscillation, and once started, the charging voltage at both ends of C8 is discharged by the discharge circuit portions D13 and R8, and further starting operation is prohibited.

At this time, when the initial oscillation, the LC resonance voltage is high across the capacitor C12, and when the resonance voltage is higher than the discharge start voltage of the fluorescent lamp while preheating the filament, the fluorescent lamp is turned on. The filament of the fluorescent lamp is damaged, resulting in rapid blackening and shortening of lamp life.

Therefore, in the present invention, the negative electrode preheat current control circuit 500 is inserted into the inverter unit 400, that is, for example, in the gate terminal of the second switching transistor Q2. This is composed of the third switching element Q3, the constant voltage diode D11, the voltage divider R7 and R8, and the capacitor C9. The source side of the third transistor Q3, which is another switching element, is the second side. It is connected to the gate of the transistor Q2 through the resistor R4 (drain side is grounded), and the gate side is connected to the connection point of the voltage divider resistors R7 and R8 through the constant voltage diode D11 and at the same time through the capacitor C9. Grounded. The voltage divider resistor is connected to both ends of the tertiary winding T3 of the self oscillating coil.

Therefore, the high resonance voltage generated at the time of lighting is detected by the primary winding T1 of the transformer for detecting the output voltage, and divided by the voltage dividing resistors R7 and R8 in the tertiary winding T3 coupled thereto. When the detected voltage is an overvoltage greater than or equal to the breakdown voltage of the diode D11, the third transistor Q3 is operated to control the gate supply voltage of the second transistor Q2, and is connected to the lamp. It controls the cathode preheating current of the filament of the fluorescent lamp by lowering the resonance voltage across the capacitor (C12) and gradually turns on (soft start) to prevent blackening of the lamp and extend the lamp life. The necessary preheating current can be adjusted by changing the parameter values of the voltage divider resistors R7 and R8 or the constant voltage diode D11.

Although the present invention has been described above with reference to one embodiment shown in the accompanying drawings, the present invention is not limited thereto, and various modifications may be made within a range easily understood by those skilled in the art. Therefore, the limitation of the present invention should be limited only by the following claims.

As described above, according to the ballast according to the present invention, the resonant voltage across the capacitor C12 connected to the lamp is lowered at the start of the lamp to control the cathode preheating current of the filament of the fluorescent lamp and gradually turn on (soft start). This prevents blackening of the lamp and extends its life.

Claims (2)

A rectifying and smoothing unit 200 for rectifying an input AC signal to supply a DC voltage, a lighting unit 600 for receiving a voltage applied from the rectifying and smoothing unit and oscillating at a given resonance frequency to turn on a lamp; In the electronic ballast comprising an inverter unit 400 that receives the rectified voltage from the rectification and smoothing unit to cause resonance of the lighting unit, and a starter circuit unit 300 for initial starting of the inverter unit. The lighting unit 600 includes resonance capacitors C12, C5 and C6 and an inductor L2. The inverter unit 400 may be turned on by one side of the drive transformer T1, T2, and T3 electrically connected to the resonance inductor L2, and whether the secondary or tertiary windings of the drive transformer are energized. And on / off trigger elements (Q1, Q2) for triggering the resonance circuit of the lighting unit to generate a high frequency output, The starter circuit unit 300 includes starter circuits C8, R6, and TD for operating any one of the trigger elements when the lamp is started, and circuits R8, which stop the operation of the starter circuit after the lamp is turned on. D13), The electronic ballast includes a switching element Q3 connected to any one of the trigger elements Q1 and Q2 of the inverter unit 400, and a constant voltage diode D11 connected to a control terminal of the switching element Q3. And a cathode preheating current control circuit part 500 which is connected to the secondary side or tertiary side windings T2 and T3 of the drive transformer and whose connection point is connected to the constant voltage diode. by doing, When the output voltage dividing voltage detected by the voltage dividing resistors R7 and R8 is an overvoltage greater than or equal to the breakdown voltage of the diode D11, the switching element Q3 is operated to operate the one of the trigger elements Q1 and Q2. And controlling the gate supply voltage to control the cathode preheating current of the filament of the fluorescent lamp by lowering the resonance voltage across the resonance capacitor (C12) connected to the lamp. The method of claim 1, The source side of the switching element Q3 of the cathode preheat current control circuit unit 500 is connected to the gate of one of the trigger elements Q1 and Q2 through a resistor R4, and the gate side thereof is the constant voltage diode D11. ) And grounded through a capacitor (C9) at the same time.