JPS6250959B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dimmer circuit for controlling the light of a fluorescent lamp. A transistor inverter 1 consisting of an oscillation transistor and an oscillation transformer OT that lights up the light lamp L is provided, and the input side of a base drive circuit 3 that supplies a DC control current to drive the oscillation transistor and the DC main current of the transistor inverter 1 are provided. The input sides of the rectifiers DB ₁ for converting into 1 are connected to the AC power supply e via bidirectional control elements 2 for phase control, respectively, and the base drive circuit 3 is connected between the rectifiers DB ₁ and the input side of the transistor inverter 1 or the base drive circuit 3. This relates to a dimming circuit characterized in that a delay circuit 6 is inserted on the output side of the dimmer circuit to delay the rise of the main current or control current.

A conventional dimming circuit for controlling the light of a fluorescent lamp L is shown in FIG. The conventional example shown in FIG. 1 is a dimmer circuit for controlling the phase of the input of a push-pull type transistor inverter 1.As a basic configuration, the dimmer 5 is of the phase control type, and the phase-controlled voltage is applied to the fluorescent lamp. Transistor inverter 1 for L lighting
In addition, the sine wave voltage of the AC power source e continuously preheats the fluorescent lamp L via the preheating transformer FT, and has the following configuration. In other words, a preheating transformer FT is connected in parallel to the AC power supply e.
This preheating transformer FT is connected to the primary winding N ₁ of
The two secondary windings N ₂₁ and N ₂₂ are connected to the filaments F ₁ and F ₂ of the fluorescent lamp L, respectively. Furthermore, a bridge rectifier DB ₁ consisting of a diode is connected to the AC power supply e via a bidirectional control element 2 which is a triax for phase control, and the output of the bridge rectifier DB ₁ is connected to a transistor inverter 1 via a chain coil CH. It is connected to the midpoint of the primary winding _N1 of the oscillation transformer OT. The output winding _N2, which is the secondary winding of the oscillation transformer OT, is connected to both filaments _F1 and _F2 of the fluorescent lamp L, respectively. In addition, a bidirectional control element 2 is connected to the AC power source e.
The primary side of the transformer T for the power supply of the base drive circuit 3 that drives the oscillation transistor of the transistor inverter 1 is connected through the transformer T.
The secondary side of is connected to a bridge rectifier DB ₂ for full-wave rectification, and its DC voltage output is input to the bases of two oscillation transistors T _r1 and T _r2 via resistors R _B1 and R _B2 , respectively. are doing. A base drive circuit 3 is constituted by the transformer T, bridge rectifier _DB2 , and resistors R _B1 and R _B2 . The collectors of both transistors T _r1 and T _r2 are respectively oscillating transformers.
It is connected to both ends of the primary winding _N1 of OT, and its emitters are both connected to ground level. Further, the bases of both transistors T _r1 and T _r2 are respectively connected to the feedback winding N _B of the oscillation transformer OT.
A transistor inverter 1 is constituted by these two transistors T _r1 and T _r2 and an oscillation transformer OT. The base drive circuit 3, the transistor inverter 1, the preheating transformer FT, the bridge rectifier DB ₁ , and the choke coil CH constitute a ballast 7. The dimmer 5 includes a bidirectional control element 2 using a triac and a control section 4 that changes the phase of the bidirectional control element 2, and outputs the output of the control section 4 to the gate of the bidirectional control element 2. It is input to control the phase.

The operation of the conventional dimming circuit will be described below.
(As shown in Figure 1, a simple preheating transformer system is used to preheat the fluorescent lamp L.) When AC power e is applied to the input side of the dimmer circuit, as shown in Figure 1, A voltage whose phase is controlled at a conduction angle α as shown in FIG. 2a is applied between B and C,
This voltage is full-wave rectified by a bridge rectifier _DB1 , and then applied between the collectors and emitters of the two transistors _Tr1 and _Tr2 via the choke coil CH and the primary winding _N1 of the oscillation transformer OT. In parallel with this, a voltage as shown in FIG. 2a is applied to the primary side of the transformer T of the base drive circuit ₃ , and _{the two transistors T r1 , T} A base current, which is a control current, is supplied to each of _r2 . At this time, due to a slight imbalance between the two transistors T _r1 and T _r2 , either the transistor T _r1 or the transistor T _r2 is turned on first. Now suppose transistor T
Assuming that _r1 is turned on first, the main collector current begins to flow through the transistor T _r1 , current flows through the winding _N11 on one side of the primary winding _N1 of the oscillation transformer OT, and the current flows through the secondary winding N1. A voltage is induced in ₂ . At the same time, a voltage is also induced in the feedback winding N _B of the oscillation transformer OT connected between the bases of the two transistors T _r1 and T _r2 , thereby promoting turning on of the transistor T _r1 . Then, due to the saturation of the magnetic flux in the core of the oscillation transformer OT, the induced voltage in the feedback winding N _B becomes zero, turning off the transistor T _r1 . On the other hand, the transistor T _r2 , which had been off until now, turns on, and the two transistors T _r1 and T _r2 alternately switch the voltage whose phase is controlled by the conduction angle α, causing oscillation. A high frequency voltage is supplied to the fluorescent lamp L by the output winding _N2 of the transformer OT, so that the fluorescent lamp L is turned on. Figure 2a shows the output voltage of the dimmer 5 when the conduction angle is α;
Figure b shows the lamp voltage of the fluorescent lamp L at that time, and Figure 2c shows the waveform of the lamp current. These lamp voltages and lamp currents perform high frequency oscillation only during a period defined by the conduction angle α, and the fluorescent lamp L is dimmed by changing the conduction angle α. The preheating transformer FT is used to preheat the fluorescent lamp L at a constant voltage even at the so-called dimming level, and is connected between A and C in FIG. 1 to always receive a sine wave.

However, in such a conventional example, the fluorescent lamp L
When the transistor inverter 1 starts to oscillate, a phase-controlled voltage as shown in FIG. The oscillation becomes unstable for several cycles, which causes noise. This is dv/
The conduction angle α, where dt is the largest, is largest near 90°.

The present invention has been provided in view of the above-mentioned points, and provides a dimming circuit whose purpose is to reduce noise when a transistor inverter starts oscillating by smoothing the steep rise of a phase control voltage waveform. It is something.

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 3a shows a first embodiment of the invention, and FIG. 3b shows a second embodiment. That is, it is basically the same as the conventional example shown in FIG. ₁ , and the difference from the conventional example is that in FIG. In addition, in the case of FIG. 3b, a bridge rectifier DB ₂ and resistors R _B1 and R _B2 of the base drive circuit 3 are inserted.
However, in practice, the second embodiment, in which the delay circuit 6 is inserted on the output side of the base drive circuit 3, requires lower voltage and current. This is advantageous in terms of circuit parts, etc.

FIG. 4 shows an example of the delay circuit 6. That is, a resistor _R3 , a parallel circuit of a diode D and a resistor _R1 , and a series circuit consisting of a capacitor _C1 are connected in parallel to the input terminal 8, and a transistor T is connected in series between the input terminal 8 and the output terminal 9. Insert _r and resistor
A resistor R ₂ is connected to the base of the transistor T _r from the connection point between R ₁ and the capacitor C ₁ . This delay circuit 6 is a basic circuit with a delay using a resistor and a capacitor, and consists of a resistor _R1 and a capacitor _C1 .
The degree of delay is determined by a time constant determined by and. Transistor T _r performs the function of a switch, and resistor R ₂ is the base resistance of transistor T _r . Diode D and resistor _R3 are capacitors
This is a reset circuit for leaving the charge on _C1 to zero every half cycle. Here, when a phase-controlled voltage with a conduction angle α of 90° as shown in Figure 5a is applied to the input terminal 8, the rising part of the waveform is determined by the time constant of the resistor R ₁ and the capacitor C ₁ . The voltage rises according to a flat curve determined by the voltage, and the transistor T _r is switched to output a voltage having a waveform as shown in FIG. 5B to the output terminal 9. By inserting this delay circuit 6 at the location shown in FIG. 3a or 3b, the rise of the main current input to the transistor inverter 1 for each cycle is delayed,
Further, by delaying the rise of the control current, which is the base current of the oscillation transistors T _r1 and T _r2 , every half cycle, the oscillation operation of the transistor inverter 1 is stabilized, and noise generation is reduced.
The operation of the entire dimming circuit is the same as that of the conventional example, so a description thereof will be omitted.

As described above, in the present invention, a delay circuit is inserted between the rectifier and the input side of the transistor inverter or on the output side of the base drive circuit, so that the steep voltage whose phase is controlled at a certain conduction angle every half cycle is By blunting the rising edge, the oscillation operation of the transistor inverter is stabilized and the noise is reduced, and the entire dimming circuit becomes a noise reduction measure.

[Brief explanation of the drawing]

FIG. 1 is a specific circuit diagram of the conventional example, FIGS. 2 a to c are operational waveform diagrams of the same as above, FIGS. 3 a and b are specific circuit diagrams of the first and second embodiments of the present invention, and FIG. 4 is a specific circuit diagram of the conventional example. A specific circuit diagram of the same delay circuit as above, and FIGS.
is a bidirectional control element, 3 is a base drive circuit,
6 is a delay circuit, e is an AC power supply, FT is a preheating transformer, L is a fluorescent lamp, DB ₁ is a rectifier, and OT is an oscillation transformer.

Claims (1)

[Claims] 1. A preheating transformer connected in parallel to an AC power source to preheat the fluorescent lamp is provided, and a transistor inverter consisting of an oscillation transistor and an oscillation transformer is provided to light the fluorescent lamp, and a DC control current for driving the oscillation transistor is provided. The input side of the base drive circuit to be supplied and the input side of the rectifier that converts the main current to the DC main current of the transistor inverter are connected to an AC power source through bidirectional control elements for phase control, respectively, and the input side of the rectifier and transistor inverter is A dimming circuit characterized in that a delay circuit is inserted between the base drive circuit and the output side of the base drive circuit to delay the rise of the main current or control current.