JPS62128495A - Hot-cathode discharge tube burner - 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 the Invention] The present invention relates to an improvement in a high-frequency lighting device for a discharge tube having a hot cathode.

[Prior art and its problems]

Recently, inverter-type electronic ballasts using semiconductors such as transistors have been put into practical use as lighting devices for discharge tubes with hot cathodes such as fluorescent lamps, replacing the conventional teak coil ballasts made of iron and copper. , is becoming popular.

FIG. 2 is a typical circuit diagram of an inverter type electronic ballast. It is called a constant current inverter that uses two transistors, and converts the DC power into high frequency power to light the discharge lamp at high frequency.

In the same figure, E is a DC power supply, L is an auxiliary inductor, and Q
a, Qh are power transistors, R, L.

R& is the starting resistance, C is the oscillation capacitor, T is the output transformer using a ferrite core, and Nz is the output transformer T.
The secondary first winding of , D is a thermoelectric generator like a fluorescent lamp,
This is a discharge tube having HjL'.

Nj is the return winding.

It is well known that this electronic ballast has the characteristics of high efficiency (low loss), small size, and light weight compared to conventional steel choke ballasts.

However, as shown in Fig. 2, which is becoming commonly used,
Stone inverter type ballasts have high costs for main parts such as semiconductors and transformers, and the price of the entire device is also high.
The problem is that it is not widely available. In particular, the output transformer T needs to generate the high voltage (400V or more) required to start the discharge lamp, so the number of turns of the secondary first winding Nz is large, resulting in a large shape, which causes an increase in manufacturing costs. It has become.

[Purpose of the invention]

An object of the present invention is to provide a novel lighting circuit based on a different step-up method that does not use a step-up transformer in an output circuit like a conventional inverter circuit.

[Structure and operation of the invention]

FIG. 1 shows an embodiment of the present invention. In the figure, C+, Cz
, C3 is a capacitor, Lm is a main inductor, D is a diode, Q is a transistor, and R is a resistor. Other symbols are used in common with FIG. 2.

The present invention basically consists of one transistor as shown in FIG.
This is a self-excited oscillation circuit using a stone. Self-oscillation is sustained by feeding back part of the voltage generated in the main inductor Lm to the base of the transistor through the winding Nf, and Lm,
A sinusoidal high frequency alternating current is generated in the main current circuit including Cz and D, lighting the discharge tube. Note that the second conventional example
The case shown in the figure is also a self-excited oscillation circuit, and the main point here is that self-oscillation is generated by feeding back a part of the output voltage of the output transformer T to the base of the transistor Q (, Qb) through the It' line N4. Similar to invention.

A feature of the circuit of the present invention is that the discharge tubes are connected without an output transformer. This circuit is basically the main inductor Lm after the discharge tube starts.

It is a series oscillating circuit of a capacitor Cz and a discharge tube, and the main current flows between Lm-Cz-D. Before starting the discharge tube, there is high impedance between the hot cathode H+ and Hz, so the series oscillation circuit is Lm, Cz, ) (11 capacitor C3
, Hi. However, the hot cathodes H+ and H
Since the resistance value of the heater coil z is relatively small, the series oscillating circuit becomes extremely oscillatory and a large voltage is generated in the circuit.

The frequency of the vibration is higher than that during normal lighting after startup, in which only the capacitor Cλ is dominant because the capacitors Cz and 03 are connected in series. This high frequency is applied as a high voltage between the hot cathode H+ and the hot cathode H+ as a current.

Since the current flows at Hz, starting of the discharge tube occurs easily.

The voltage and current conditions to ensure starting can be selected within an appropriate range depending on the size and ratio of capacitors C+ and C. Incidentally, even when using a DC power source obtained by rectifying an input power source of 100 V, a secondary voltage with an effective value of 300 V or more can be easily obtained between the terminals of the capacitor C3.

After the discharge tube starts, the impedance of the discharge tube decreases and the tube voltage (voltage between hot cathodes HI and HL) decreases, so the current flowing through the path of capacitor CJ (heater circuit) decreases and the current flowing through capacitor C2L decreases. The current in the main current circuit increases and the discharge tube reaches its normal lighting state.

As described above, the present invention differs in that it uses the resonance phenomenon of the L-C-R series oscillation circuit to generate the high voltage for starting the discharge tube, instead of relying on boosting the output voltage as in the conventional method, and has various advantages as follows. It is something that has.

[Effect of invention idea]

Since no output transformer is used, it can be made small and inexpensive. Not only does it require a single transistor, it also has fewer circuit parts, making it compact, economical, and less likely to break down.

Furthermore, it is possible to design a circuit with a conversion efficiency of 90% or more, while making the entire device smaller and lighter than the conventional two-stone type (circuit conversion efficiency of 80-85%).

Although the present invention has been described with respect to a self-excited circuit, the effects of the present invention are the same even if the transistor is driven by a separately excited type using the voltage of another signal source instead of relying on the feedback voltage from the main inductor.

4. Brief Description of the Figures FIG. 1 shows an embodiment of a lighting device according to the present invention, and FIG. 2 shows an embodiment of a conventional lighting device.

Claims (2)

[Claims] (1) A main inductor and a second capacitor connected in parallel to a parallel connection circuit consisting of at least a transistor and a first capacitor, which is connected via an auxiliary inductor from a DC power source obtained by rectifying a DC power source or an AC power source. and a discharge tube having two hot cathodes connected in a series circuit, and a third capacitor being connected between the hot cathodes. (2) The discharge tube lighting device according to claim 1, wherein the transistor is configured to self-oscillate by being driven by a feedback voltage generated in the main inductor.