JPS61121296A - 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 [Field of Application of the Invention] The present invention relates to a lighting device for a discharge lamp such as a fluorescent lamp, and particularly to a lighting circuit suitable for reducing circuit loss.

[Background of the invention]

The lighting circuit for a light bulb-shaped fluorescent lamp described in Japanese Patent Application Laid-Open No. 58-103758 uses a choke coil as a ballast, so the power factor is poor and sufficient conversion efficiency cannot be obtained. Therefore, a highly efficient light bulb-shaped fluorescent lamp has been realized in which the power utilization rate is increased by using an electronic lighting circuit as a lighting circuit, and the luminous efficiency of the fluorescent lamp is improved by high-frequency lighting. FIG. 1 shows a conventional two-stone push-pull inverter circuit as a typical example of an electronic lighting circuit for a light bulb type fluorescent lamp.

In Figure 1, vl is the aftereffect rectified voltage obtained from the commercial power supply,
1 is a current limiting choke, 2 is a magnetic leakage type oscillation transformer, 3 is a resonant capacitor, 4 and 5 are switching transistors, 6, 7 and 8 are base bias resistors, 9
10 is a fluorescent lamp, and 10 is a capacitor for stabilizing the base potential.

The operation of the circuit shown in FIG. 1 will be explained below. Oscillation transformer 2
The collectors of switching transistors 4 and 5, whose emitters are connected in common, are connected to both ends of the primary windings N and N2, respectively, and the resonant capacitor 3 is connected in parallel, and both ends of the feedback winding N and Connect each to the base of 5. The voltage v1 is applied to the primary winding N of the oscillation transformer 2 via the current limiting choke 1.

and N2, and further apply the voltage V to the base bias resistor 6. The switching transistors 4 and 5 are
By supplying a base current to the switching transistors 4 and 5, the switching transistors 4 and 5 are alternately turned on and off to continue oscillation, and an excitation voltage for the secondary winding N of the oscillation transformer 2 is generated. By passing a preheating current through the filament of the fluorescent lamp 9, the fluorescent lamp is lit at high frequency.

By the way, the DC current amplification factor of the switching transistor has a large temperature dependence, and has a characteristic that the DC current amplification factor also decreases as the temperature decreases.

Further, unless a current equal to or greater than the value obtained by dividing the collector current by the DC current amplification factor is supplied to the bases of the switching transistors 4 and 5, stable oscillation operation cannot be performed. Therefore, the base bias resistors 6 and 7 are set to a value that can supply sufficient base current to perform stable oscillation operation even when the switching transistors 4 and 5 are cold, such as immediately after lighting, that is, when the DC current amplification factor is low. and 8
If the resistance value is set, the temperature of switching transistors 4 and 5 will rise over time after lighting, and the DC current amplification factor will increase, which will supply extra base current and cause extra power loss. There was a drawback.

[Purpose of the invention]

The purpose of the present invention is to eliminate the above-mentioned drawbacks of the prior art, improve oscillation stability during the period immediately after lighting when the temperature of the switching transistor is low and the DC current amplification factor is low, and reduce power loss in the base bias circuit under steady lighting conditions. The object of the present invention is to realize the electronic lighting circuit by suppressing the temperature rise of the circuit elements, and to provide a light bulb-shaped fluorescent lamp with high conversion efficiency.

[Summary of the invention]

A feature of the present invention is that a temperature sensing element is used as the base bias resistance of the switching transistor, and the ambient temperature of the switching transistor is detected and a change in the resistance value of the temperature sensing element is used to control the base current of the switching transistor. By adjusting it according to the ambient temperature, a base current sufficient to stabilize the oscillation operation is supplied during the period when the ambient temperature of the switching transistor is low and the DC current amplification factor is low, such as immediately after the first lighting, and the ambient temperature gradually increases after lighting. As the temperature rises and the DC current amplification factor increases, the resistance value of the temperature sensing element increases and the base current is reduced, thereby suppressing circuit loss, thereby suppressing the temperature rise of the circuit elements and relieving stress on the elements. By doing so, a lighting circuit for a fluorescent lamp with high efficiency and long life is constructed.

[Embodiments of the invention]

Embodiments of the present invention will be described below based on the drawings.

FIG. 2 shows an embodiment of the invention. 11 in Figure 2
is a temperature sensing element, and the other 1. The same reference numerals as in the figures indicate the same or equivalent parts.

In the above configuration, when the entire circuit is cold, such as immediately after one light is turned on, the DC current amplification factors of switching transistors 4 and 5 are small, and the base current required for stable oscillation operation is large. However, at this point, the resistance value of the temperature sensing element 11 is small, so the current value determined by the voltage Vu and the resistance value of the temperature sensing element 11 is I, lx =
Vx / (K (tz-to)+R,>,, (
Here, IIIL is the base current when the ambient temperature is 70°C, and is the temperature coefficient of the temperature sensing element 12.

Ro is the resistance value when t1=t0), and since l1li is large when tl is small, the switching transistor 4
and 5 can be sufficiently driven and stable oscillation operation can be obtained. As the temperature of the entire circuit rises as time passes after lighting, the DC current amplification factors of switching transistors 4 and 5 also increase, so the required base current value decreases. At this time, the resistance value of the temperature sensing element 11 increases due to the inherent temperature coefficient K, so the current value equivalent to the base current I mz = V1/
When t2 increases from (K (tz-to)+Ro) (where XSS is the base current at ambient temperature t2), I
. decreases.

Therefore, according to the present embodiment, by setting the temperature coefficient of the temperature sensing element 11, it is possible to simultaneously achieve two contradictory objectives: stability of oscillation at low temperatures and reduction of circuit loss during steady lighting.

Other embodiments of the present invention made from this point of view will be described in the third embodiment.
In FIG. 3, the parts with the same reference numerals as in FIG. 1 indicate the same or equivalent parts, and 12 and 13 are temperature sensing elements. Detected at 13, 2nd C! The same control as in the It embodiment is performed, and the operation is the same as that shown in FIG. 2, so a description thereof will be omitted.

〔Effect of the invention〕

As explained above, according to the present invention, sufficient base current can be supplied to obtain stable operation even when the direct current amplification factor of the transistor is low during cold periods, such as immediately after lighting the fluorescent lamp lighting circuit, and As time passes after lighting, the temperature of the circuit rises and the DC current amplification factor of the transistor increases, which reduces the necessary base current. By automatically limiting the amount of base current supplied, Suppresses circuit loss and temperature rise of circuit elements. Therefore, it is possible to realize a lighting circuit for a fluorescent lamp that is stable, highly efficient, and has a long life.

[Brief explanation of the drawing]

Figure 1 shows a conventional electronic lighting circuit for fluorescent lamps.
FIG. 2 is a circuit diagram showing one embodiment of the present invention, and FIG. 3 is a circuit diagram showing another embodiment of the present invention. Broom 1

Claims (1)

[Claims] 1. A transistor inverter using a DC power supply as a power supply source and a fluorescent lamp connected to the output side of the transistor inverter, the transistor inverter being an oscillation transformer having a primary winding, a secondary winding, and a feedback winding. A fluorescent lamp configured to include a base bias circuit that supplies a base current to a transistor that is connected in series between a primary winding, a collector emitter, and an input end, and that is connected to supply a feedback signal from the feedback winding to the base. The base bias circuit of the lighting circuit includes temperature detection means and means for providing a current value according to the detected temperature,
A discharge lamp lighting device characterized in that by supplying a base current to the transistor according to temperature, an optimum base current can be supplied even if the direct current amplification factor of the transistor changes depending on the temperature.