JPS61256594A - Discharge lamp lighting apparatus - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a discharge lamp lighting device using a half-bridge inverter.

[Background technology]

Conventionally, in a discharge lamp lighting device using a half-bridge inverter, when dimming the discharge lamp, there are two methods: one is to separately excite the transistors and change the control frequency, and the other is to change the input voltage of the inverter using phase control, etc. Alternatively, there is a method of switching the value of a current-limiting element such as an intagtance connected in series with the discharge lamp. All of these use separately excited drive, so they require an oscillation circuit as a drive source.
The drawback was that the circuit was complicated and expensive. To improve this, there is a self-exciting circuit that returns part of the circuit's voltage to the base of the transistor.
Since the feedback voltage is always obtained from a fixed circuit element, it was not possible to dim the discharge lamp even though it could be lit at its rated value.

[Purpose of the invention]

An object of the present invention is to control the current of a discharge lamp in stages to enable easy and inexpensive dimming, and to improve circuit efficiency by reducing switching loss of transistors.

[Disclosure of the invention]

Embodiment In FIG. 1, two transistors Q1. A 0-transistor Q1. An intagtance L1 and a capacitor C3 are connected between the connection point m of Q2 and the connection point n of capacitors C1 and C2.
, connect the series circuit of the discharge lamps 1a. A winding n2 that intersects with a part of the magnetic flux of the interface l, and a capacitor C3.
One end of the winding n2 is connected to one end of the transformer T2, the other end is connected to the common terminal of the changeover switch SW, and the secondary winding n
One end of the transformer T2 is connected to the other end of the transformer T2 and the contact point of the changeover switch SW, and the other end is connected to the contact point a of the changeover switch SW. Two secondary windings n4 of transformer T2. N5 is connected between the bases of transistors Q1 and Q2 through parallel circuits of resistors R1 and cocidencers C, respectively, to form a self-excited half-bridge inverter. still,
The DC power source E may be a rectified power source.

Operation First, the case where the changeover switch SW is on the contact side will be explained. The voltage applied between the bases of the transistors Ql and Q2 and the voltage v2 of the winding n2 appears as the primary winding voltage v3 of the transformer T2, which turns the transistors Ql and Q2 on and off alternately. do. Note that the drive is performed by a capacitor C connected to the base of the transistor Q2.
Transistor q is first turned on by the charging current to o. The secondary winding voltage v2 slightly advances in phase with respect to the voltage of intagtance 1 due to the leakage intertasis of the secondary winding, and as shown in Fig. 2 (C), V2 = V
As a result, the voltage V+, II], that is, the voltage between the collector and transistor Q2 of the transistor Q2 turns off at t2 and the transistor Q1 turns on, so the voltage V+, II becomes a rectangle as shown in Figure 2 (a). It becomes a wave. Note that the phase in which the voltage Vl becomes O is delayed between the phase in which the voltage vl becomes 0 and the phase in which the voltage v3 becomes O due to the drive voltage v of the transistors Ql and Q2.
Even if 3 becomes O, there is an accumulation time in the transistors Ql and Q2, so the phase in which the transistors Ql and Q2 are actually turned off is delayed. Further, FIG. 2(b) shows the voltage VC3 across the capacitor C3.

Next, the case where the changeover switch SW is on the contact a side will be explained. The primary winding voltage V3 of the transformer T2 shown in FIG. 3(d) K is the same as the voltage v2 shown in FIG.
Transformer TI of voltage Vca of capacitor C3 shown in b)
It is the sum of the voltages stepped down by . The difference from the case where the changeover switch SW is on the contact side is that the voltage VC of the capacitor C3
This is due to the addition of component 3. Since the capacitor voltage VC3 has a voltage that is 90 degrees out of phase with the circuit current, the addition of the capacitor voltage component means that the primary winding voltage of the transformer T2 is delayed, and the voltage of the primary winding of the transformer T2 is delayed.
The effect of delaying the on period of Q2 works, and the transistor Q
Extend the on and off periods of s and Qz. As a result, when the changeover switch SW is on the contact side, the vibration between the terminals m and n is caused by the transistors Qs and Q2 being turned off in synchronization with each half cycle of the circuit current, as shown in Fig. 2 (a).
), but if the changeover switch SW is on the contact a side, the transistors Ql,
The ON/S OFF period of Q2 becomes a steady state during one cycle of circuit vibration. In this way, the changeover switch S
On the side where W makes contact, the on/off period of the transistor (lb, Q2 is the period of the oscillating current Il of the circuit), and on the contact a side, the on/off period of transistors Q1, Q2 is the period of the oscillating current Il of the circuit. When examining the oscillating current 11 in these two types of states, it is found that the changeover switch S
It was found that the oscillating current becomes larger when W is on the b side. This is because when the contact is on the A side, current is always supplied from the DC power supply E during the ON period of one transistor, whereas when the contact is on the A side, the oscillating current I
zt:1. Since the polarity is reversed as shown in Figure 3(a),
A part of the current supplied from the DC power supply E flows through the diode Dl.
, D2, and as a result, the current flowing through the discharge lamp 1aK, that is, the electric power of the discharge lamp 1a also becomes smaller. Therefore, the discharge lamp la can be dimmed by switching the changeover switch SW.

〔Effect of the invention〕

As described above, the present invention switches the circuit elements that obtain the feedback voltage and changes the operating frequency to perform stepwise dimming, so that the current of the discharge lamp can be controlled stepwise and the dimming can be done easily and inexpensively. , the transistor current is 0 in both the turn-off phase and the turn-on phase of the transistor, and the transistor:
, the number of switching contacts of the I resistor can be reduced, and circuit efficiency can be improved.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the present invention, FIG. 2 is a diagram of voltage and current waveforms of main parts during steady lighting, and FIG. 3 is a diagram of voltage and current waveforms of main parts during dimmed lighting. E...DC power supply, Ql102...Transistor, D
+, D2...diode, CI, C2...capacitor, Ll...intagtance, C3...capacitor, la...discharge lamp, SW-°/changeover switch.

Claims (1)

[Claims] (1) Connect a series circuit of two transistors with diodes connected in reverse parallel to a DC power supply, and connect a series circuit of two capacitors, and connect the connection point of the two transistors and the two capacitors. In a discharge lamp lighting device, a series circuit of an intagtance, a capacitor, and a discharge lamp is connected between a connection point of A discharge lamp lighting device characterized in that the circuit element for obtaining the feedback voltage is switched and the operating frequency is changed so that stepwise dimming can be performed.