JPH02312191A - Inverter circuit for lighting fluorescent lamp - Google Patents

Abstract

PURPOSE:To obtain a fluorescent lamp lighting inverter circuit capable of realizing high power rate by charging a condensor with a high frequency voltage generated by switching operation, and returning the charging voltage to power source side. CONSTITUTION:A fluorescent lamp FL is connected to the output side of a half bridge switching circuit HSW, and this switching circuit HSW includes two switching transistors TR1, TR2 and an oscillating transformer T. During switching operation, the output current of the switching transistor TR1 is allowed to flow through a diode D4, an inductor L2, and a condensor C4. Energy is accumulated in the inductor L2 by the current, and when the transistor TR1 is turned off, stored energy is emitted through a diode D3, and the condensor C4 is charged with a current allowed to flow at that time. The voltage charged in the condensor C4 is returned to power source side through the diode D2. High power rate is thereby realized.

Description

DETAILED DESCRIPTION OF THE INVENTION (Al Industrial Field of Application) The present invention relates to an inverter circuit for lighting a half-bridge type fluorescent lamp.

(b) Prior Art Inverter circuits for lighting fluorescent lamps include a push-pull type, a forward type, a half-bridge type, and the like. Fourth
The figure shows a schematic diagram of a conventional half-bridge system.

This half-bridge inverter circuit uses a switch SWI that alternately switches the fluorescent lamp FL.
, SW2 are half-bridge connected. The half-bridge switching circuit consists of these two switches SWI, S
It is composed of W2, two capacitors Co, C1, and an inductor L1. The series circuit of capacitors Co, C1 and inductor Ll constitutes a resonant circuit with respect to the switching frequency. Large capacity capacitor C3 is installed on the output side of power supply E.
is connected. In this half-bridge inverter circuit, the switches SWI and SW2 are turned on and off alternately, and the current 1. ．． 12 alternately flows to the fluorescent lamp FL. As this operation is repeated several times, the filament of the fluorescent lamp FL is heated up, and the fluorescent lamp FL is ignited by the resonance voltage generated across the capacitor CI, resulting in continuous lighting.

(C) Problems to be Solved by the Invention However, since the above circuit has a capacitor input type circuit configuration in which the capacitor C3 is connected to the rear stage of the power supply rectifier circuit, there is a problem that the inrush current is large and the power factor is low.

An object of the present invention is to provide an inverter circuit for lighting a fluorescent lamp that can realize a high power factor by charging a capacitor with a high frequency voltage generated by a switching operation and returning the charged voltage to the power source.

(Means for Solving Problem d1) This invention provides a rectifying circuit for a commercial AC power supply voltage, a half-bridge switching circuit in which two switching transistors are connected in a half-bridge to a fluorescent lamp, and the half-bridge switching circuit. An LC series circuit through which the output current of one switching transistor flows, a flyback diode connected in a direction to release the energy stored in the inductor of the LC series circuit to the capacitor, and a flyback diode that discharges the charge in the capacitor to the fluorescent lamp. and a capacitor discharging diode connected in the direction of.

FIG. 1 is a block diagram of an inverter circuit according to the present invention.

A fluorescent lamp FL is connected to the output side of the half-bridge switching circuit H3W, and this switching circuit HS W
is equipped with two switching transistors TRI and TR2 and an oscillation transformer T.

In addition, this switching circuit HS W includes a starter circuit S.
T is connected so that the switching transistor TR2 is activated first when the power is turned on.

The output current of the upper switching transistor TRI of the switching circuit H3W flows into an LC series circuit consisting of an inductor L2 and a capacitor C4. Further, a fly bank diode D3 is connected in parallel to this LC series circuit, and a capacitor C of the LC series circuit is connected in parallel.
A discharge diode D2 is connected between the power supply terminal 4 and the power supply terminal.

(In an inverter circuit having a configuration of 81 or more functions, when the power is turned on, the starter circuit ST operates first and starts the switching transistor TR2 of the half-bridge switching circuit H3W. After this, the switching transistors TRL and TR2 are alternately activated. A switching operation is performed by repeatedly turning on and off, and a switching output current is supplied to the fluorescent lamp FL.When the filament of the fluorescent lamp FL is sufficiently heated, the capacitor ( The fluorescent lamp FL is ignited by the resonant voltage generated at both ends of the lamp (not shown), resulting in continuous lighting.

On the other hand, during the switching operation, the output current of the switching transistor TRI flows through the diode D4. Inductor L2. flows through capacitor C4. Energy is stored in the inductor L2 by this current, and then when the transistor TRI is turned off, the Ma energy is released through the diode D3, and the current flowing at that time charges the capacitor C4. The voltage charged in the capacitor C4 is returned to the power supply side through the diode D2. Therefore, the power supply voltage is charged to the capacitor C4 by the chopper operation of the switching transistor TR1, and this charged voltage becomes a voltage close to direct current and is the pulse of the output of the rectifier circuit D1. It will be superimposed on AL. In this case, the magnitude of the charging current flowing through the capacitor C4, ie, the charging voltage of the capacitor C4, can be changed by selecting the magnitude of the inductor L2. FIG. 2(A) shows the inverter input voltage waveform and the lamp current waveform flowing through the fluorescent lamp when the charging voltage of the capacitor C4 is set to an appropriate level. Voltage VC4 is the charging voltage of capacitor C4. At time t1, the load current is supplied from the rectifier circuit Dl side, and at time 1. Then, the load current is supplied from capacitor C4. If this time t2 is very short, that is, if the charging voltage VC4 of the capacitor C4 is very low, oscillation stops during the period when the voltage is low, and a rest period occurs in the lamp current. FIG. 2(B) shows the inverter input voltage waveform and lamp current waveform in an extreme case where the charging voltage VC4 of the capacitor C4 is O, that is, when there is no LC series circuit of the capacitor C4 and the inductor L2.

On the other hand, if the charging voltage of capacitor C4 is too large,
Time t1 during which current flows from the rectifier circuit DI side to the load
There is an inconvenience that the power factor deteriorates because the time becomes too short.

In this invention, since the charging voltage of the capacitor C4 can be changed to an arbitrary value as described above depending on the size of the inductor L2, the lamp current waveform shown in FIG. 2(A) continues to flow. The size of inductor L2 is adjusted to obtain an appropriate inverter input voltage waveform.

In this way, the time t can be made sufficiently long, that is, the power factor can be improved, and stoppage of oscillation can be prevented, allowing the lamp current to flow continuously.

([1 example FIG. 3 shows a circuit diagram of an embodiment of the invention.

In the same figure, circuit A consists of inductor L2 and capacitor C.
LC series circuit consisting of 4, flyback diode D3
, discharge diode D2 and backflow prevention diode D
Contains 4. The starter circuit ST also includes a time constant circuit consisting of a resistor R1 and a capacitor C5, and a capacitor C5.
diverging circuit D5 that provides a starting pulse to the switching transistor TR2 when the charging voltage reaches a certain level.
and a diode D6 for discharging the charge in the capacitor C5 during operation. In addition, a capacitor C6 is connected to the base of the switching transistor TRI.
A bias circuit consisting of a parallel circuit of a capacitor C7 and a resistor R3 is connected to the base of the transistor TR2. This bias circuit is intended to rapidly release accumulated carriers when the switching transistor is switched from on to off, thereby reducing losses during switching operations. Furthermore, in this embodiment, a surge absorbing element S and a noise prevention filter F are connected to the input side of a rectifier circuit Di formed of a bridge circuit.

Next, the operation of the above circuit will be explained. 'When the power is turned on, the commercial AC power supply voltage that has passed through the surge absorption element S and the noise prevention filter F is rectified by the rectifier circuit D1, becomes a pulsating current, and is applied to the starter circuit ST and switching transistors TR1 and TR2. applied. When the switching transistor TR2 is started after a certain period of time, a current flows through the series circuit of the capacitor CO1 ballast LL, the filament capacitor C1 of the fluorescent lamp FL, the filament of the fluorescent lamp FL, the oscillating transformer T, and the transistor TR2. current and charges the capacitor CO. At this time, the fluorescent light FL
filament is preheated. As charging of the capacitor CO progresses and the induced voltage in the secondary winding of the oscillation transformer T begins to decrease, the transistor TR2 suddenly turns off and the transistor TRI turns on. When the transistor TRI is turned on, the charge stored in the capacitor CO is transferred to the transistor TR1, the oscillation transformer T, the filament of the fluorescent lamp FL, the capacitor CI, the filament of the fluorescent lamp FL,
It is discharged through the series circuit of ballast L1. This discharge current preheats the filament of the fluorescent lamp FL.

As the above operation is repeated, the preheating of the filament of the fluorescent lamp FL becomes sufficient, and at a certain stage, the resonant charging voltage generated across the capacitor CI causes the fluorescent lamp F to
L is ignited and from then on it continues to light up.

On the other hand, when the switching transistor TR1 is on, current is supplied from the rectifier circuit D1 to the LC series circuit via the oscillation transformer T and the die 1-D4,
Energy is stored in inductor L2. Next, when the transistor TRI is turned off and the transistor TR2 is turned on, the energy stored in the inductor L2 is released through the diode D3, and the current at that time charges the capacitor C4. As a result of the above operations being performed continuously, a constant voltage is charged to the capacitor C4, but this voltage is returned to the power supply side through the discharging diode D2 and is superimposed on the pulsating voltage output from the rectifier circuit D1. is supplied to the load. The voltage at this time, ie, the inverter input voltage waveform, is as shown in FIG. 2(A).

The size of the inductor L2 is determined so that the lamp current flowing through the fluorescent lamp FL does not fade out, as shown in Fig. 2 (A), that is, the inverter input voltage waveform is such that oscillation occurs continuously. Set.

The above operation prevents inrush current from the power supply side.
Since the power factor is improved and the oscillation operation of the switching circuit is performed continuously, it is possible to prevent flickering of fluorescent lamps and the like.

(g) Effects of the Invention As described above, according to the present invention, one switching transistor of the half-bridge switching circuit is also used as a chopper, so that the capacitor of the LC series circuit is charged with a constant voltage, and the voltage is transferred to the power supply side. The input voltage waveform to the inverter can be optimized from the viewpoint of high power factor and continuous oscillation.

[Brief explanation of the drawing]

Figure 1 shows the configuration diagram of this invention, Figure 2 (A),
(B) is a diagram for explaining the operation of the LC series circuit, and FIG. 3 shows the inverter circuit of the embodiment.
FIG. 4 shows a schematic diagram of a conventional half-bridge inverter circuit. Di-rectifier circuit, L2. C4-4, C series circuit, D3-flyback diode, D2-discharge diode.

Claims (1)

[Claims] (1) A rectifying circuit for a commercial AC power supply voltage, a half-bridge switching circuit in which two switching transistors are connected in a half-bridge to a fluorescent lamp, and an LC through which the output current of one switching transistor of the half-bridge switching circuit flows. a series circuit; a flyback diode connected in a direction to discharge the energy stored in the inductor of the LC series circuit to the capacitor; and a capacitor discharging diode connected in a direction to discharge the charge in the capacitor to the fluorescent lamp. An inverter circuit for lighting a fluorescent lamp, comprising: and.