JP2729077B2 - EL lighting circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement relating to a circuit of an inverter power supply necessary for lighting of a distributed EL or the like.

2. Description of the Related Art A distributed EL is lit by an AC AC power supply of, for example, 100 V and 400 Hz. Usually, this power supply is generated from a DC power supply by an inverter circuit.

In general, there are many types of inverters in addition to large categories of self-excited type and separately excited type, but for inverters for EL, the blocking oscillation type has few circuit components and EL
It is most often used because it can be easily matched with characteristics.

On the other hand, the need for distributed EL was previously limited to relatively small areas (10
0~150cm ²⁾ those which was a found size of the power supply, is particularly thin and improvement of the inverter conversion efficiency is strongly demanded together with proceeds to have a large area, such as a backlight for a liquid crystal display (about 400 cm ²⁾ recently It has become.

In the blocking oscillation method, if the EL has a large area, the transformer capacity will increase, making it difficult to reduce the size and thickness.
Even if it is small, there is a problem that a product with high efficiency cannot be obtained, and improvement is desired.

On the other hand, in the series resonance inverter system, even for a large-area EL, it is possible to make the inductor small and thin. Features such as high inverter conversion efficiency are generally accepted.

A conventional example of the series resonance inverter system will be described with reference to the drawings. FIG. 4 shows an example of a series resonance inverter system, in which a primary winding L1 of a transformer T and a capacitor C form a series resonance circuit, and the other end of the capacitor is grounded. The other end of primary winding L1 is connected to secondary winding L2 of transformer T and P
The positive DC power supply + V and the negative DC power supply -V are connected to the point P via switching elements Q5 and Q6, respectively.

On the other hand, the other end of the secondary winding L2 of the transformer T is connected to a control terminal of a switching element via a parallel connection of a resistor R5 (R6) and a capacitor C5 (C6). These resistors R5 (R6)
The capacitor C5 (C6) is inserted for impedance matching between the secondary winding L2 and the control terminal circuit of the switching element Q5 (Q6). Arrows A and B indicate the direction of the current flowing in the series resonance circuit.

FIG. 5 shows a series resonance circuit current waveform (upper diagram) and a voltage waveform at point P (lower diagram) during operation of the circuit of FIG.

In operation, when the voltage at the point P is positive, the switching element Q5 is conductive and the switching element Q6 is nonconductive, and during the negative period, the conductive and nonconductive states are reversed.

As shown in FIG. 5, the period during which the switching elements Q5 and Q6 switch between conduction and non-conduction is the period during which the current is at a maximum.

Problems to be Solved by the Invention By the way, in the above-described series resonant inverter, switching of the switching element is performed at a time when the current is maximum, and at this time, the rate of change of the current is the lowest,
Therefore, this is when the electromotive voltage of the secondary winding L2 is low. Therefore, there is a disadvantage that a sufficient current cannot be sent to the control element of the switching element, and the switching loss of the switching element cannot be reduced.

Further, if the secondary winding L2 is enlarged to improve the loss of the switching element, the load of the resonance circuit will cause a change in the oscillation constant, and the power consumption will increase. It was difficult.

Means for Solving the Problems The present invention has been made in view of the above circumstances, and enables a switching element to be driven by the current polarity of a series resonance circuit, and switches between conduction and non-conduction at a time when a current is small, thereby reducing switching loss. The aim is to realize a series resonance inverter type EL lighting circuit with low fluctuation and high fluctuation efficiency.

This EL lighting circuit comprises a switching element for switching power supply, comprising a first PNP transistor and a second NPN transistor, a third NPN transistor for driving the switching element, and a fourth PNP transistor. A current resonance detection transistor consisting of a transistor of the type described above, constitutes a series resonance circuit consisting of the capacitance of the EL and the inductance of the inductor connected in series with the EL, and supplies power in synchronization with the resonance frequency In the circuit for lighting the EL by the series resonant inverter method, the third and fourth transistors are connected so that the base poles and the emitter poles of the third and fourth transistors have the same potential, and are connected in series between the base pole and the emitter pole. A part of the current of the resonance circuit is passed to detect the current polarity, and the collector poles of the third and fourth transistors are respectively connected via resistors. A connection is made to the base poles of the first and second transistors, and a connection point between the collector poles of the first and second transistors is connected to a connection point between the base poles of the third and fourth transistors. Series resonant inverter EL
It is a lighting circuit.

In the circuit of the present invention, the switching of the power supply voltage to the resonance circuit is performed at the timing when the resonance circuit power supply becomes zero, and the current to the control terminal of the switching element increases with the increase in the resonance circuit power supply. Loss can be reduced.

In general, the conversion efficiency is higher in the series resonance inverter system than in the blocking oscillation system, but the EL lighting circuit of the present invention can further improve the conversion efficiency. In addition, the sensitivity of the current polarity detection unit using a transistor is high, and since the secondary winding L2 is not used, power consumption is negligible and the design is simple.

Examples Hereinafter, examples of the present invention will be described with reference to the drawings.

 FIG. 1 is a circuit diagram of one embodiment of the present invention.

FIG. 2 shows the current waveform (upper diagram) and the voltage waveform at point C (lower diagram) of the resonance circuit of FIG. 1 together with time.

In FIG. 1, the inductance L0 of the choke coil CH is shown.
(H) and the capacitance CEL of the distributed EL form a series resonance circuit. The EL loss REL is equivalent to the power consumed for light emission or the like. One end of the EL is grounded, and one end of the choke coil CH detects the positive and negative polarities of the current flowing to the resonance circuit, respectively, and detects the positive and negative polarities of the positive and negative polarities for amplification, and the transistors Q3 and Q4 with different polarities for the amplification. And the bases of transistors Q3 and Q4 are short-circuited at point C.

The collectors of transistors Q3 and Q4 are resistors R2 and R3, respectively.
, Are connected to control terminals of the switching elements Q1 and Q2. The resistors R2 and R3 are current limiting resistors for the control terminals of the switching elements Q1 and Q2, and the switching elements Q1 and Q2 operate as power supply switches to the resonance circuit.

Emitter of transistor Q3 (Q4) for current polarity detection,
Diodes D1, D2 (D3, D
4) is connected in the same direction as the polarity of the transistor, and if necessary, a resistor R4 is connected in parallel.

The diodes D1 and D2 (D3 and D4) are the base current limiting circuits of the transistor Q3 (Q4), and together with the resistor R4, the transistor Q3 (Q3) , Has the function of limiting the base current of Q4.

The point C is grounded via the resistor R1 and is provided to allow the current at the time of polarity reversal to flow as the base current of the transistor Q3 or Q4.However, since the stray capacitance at the time of wiring can be substituted, even if the resistor R1 is not provided. May work.

The positive DC power supply + V (for example, + V = + 50 V) is connected to a point C via a switching element, and the negative DC power supply -V (for example, -V = -50 V) is connected to a point C via a switching element Q2. To explain the circuit operation,
If a current flows in the direction of arrow A in FIG. 1, the current is amplified by the transistor Q3 and the switching element Q1 is turned on.
To Transistor Q4 is reverse biased and switching element Q2 is turned off. Therefore, the voltage at point C is +
The current in the direction A increases with time (time zone 1 in FIG. 2), but starts to decrease due to an increase in the terminal voltage of the CEL. (Time period 2 in FIG. 2) The current eventually becomes zero due to the characteristics of the resonance circuit, and then begins to flow in the opposite direction through the resistor R1. Then, the transistor Q2 is reverse-biased, the switching element Q1 is turned off, a current flows through the base of the transistor Q4, the switching element Q2 is turned on, and the voltage at the point C is inverted to -V.

For this reason, the current in the direction B increases steadily (time period 3 in FIG. 2), and eventually begins to decrease due to the influence of CEL. (Time zone 4 in FIG. 2) After that, the polarity of the current is reversed and the current in the direction A starts to flow (time zone 5 in FIG. 2). Thereafter, the above-described operation is repeated and oscillation continues.

In this circuit, switching elements Q1 and Q2 are ON at the same time
Then, the power supply will be short-circuited. For this purpose, a current must flow through both the transistors Q3 and Q4. However, since the potentials of the emitters and the bases of the transistors Q3 and Q4 are always the same, such a situation cannot occur.

Oscillation of this circuit starts spontaneously if the amplification degree of the transistors Q3 and Q4 is large.
A few volt bird starts to start by applying a signal to point C in FIG.

Further, in the circuit of FIG. 1, since the positive and negative power supplies having the same absolute value and opposite polarities are used as the power supply of the series oscillation circuit, no DC voltage component is applied to EL.

If it is necessary to apply a voltage waveform including a DC voltage component to EL, the voltage waveform can be easily obtained by adjusting the voltage of the positive DC power supply and the voltage of the negative DC power supply.

However, when the distributed EL is turned on, the DC voltage component may cause a reduction in reliability, and a voltage waveform having no DC voltage component is often desired.

A second embodiment in which a voltage waveform having no DC component is desired by a single power supply instead of a positive and negative power supply will be described with reference to FIG.

As shown in FIG. 3, by arranging the switch circuit of FIG. 1 on both sides of the series resonance circuit, a DC resonance inverter in which a DC voltage component is not applied to the EL even with a single power supply can be realized.

Advantages of the Invention As described above, according to the circuit of the present invention, when applied to a large-area EL as compared with a blocking oscillation type inverter conventionally used as a lighting power supply of the EL, a reduction in size can be achieved. The switching of conduction and non-conduction of the switching transistor in the power supply of the series resonance inverter system with high conversion efficiency is performed at the point when almost no current flows, so that the switching loss can be reduced and the power supply for EL lighting with high conversion efficiency can be obtained. it can. More distributed
In the case of EL, a desired voltage waveform having no DC voltage component can be easily obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of one embodiment of the present invention, and FIG. 2 shows a resonance circuit power supply and a resonance circuit drive power supply waveform during the oscillation operation. FIG. 3 is a circuit diagram of another embodiment of the present invention at the time of a single power supply of a positive electrode, in which two sets of the circuit of FIG. FIG. 4 is a circuit diagram of an example of a conventional series resonance inverter system, and FIG. 5 shows a resonance circuit current and a resonance circuit driving power supply waveform during the oscillation operation. Q1, Q2: switching element, Q3, Q4: current polarity detection transistor, CH: choke coil, CEL: capacitance of EL, REL: equivalent circuit resistance of EL.

Claims (1)

(57) [Claims] A first transistor of a PNP type and a second transistor of an NPN type;
A switching element for switching a power supply composed of transistors and an NPN for driving the switching element
A current resonance detecting transistor including a third transistor of a PNP type and a fourth transistor of a PNP type, forming a series resonance circuit including an electrostatic capacitance of EL and an inductance of an inductor connected in series with EL. In a circuit for turning on EL by a series resonance inverter system in which power is supplied in synchronization with the resonance frequency, the base and emitter electrodes of the third and fourth transistors may have the same potential. Connected, a part of the current of the series resonance circuit is caused to flow between the base pole and the emitter pole to detect the current polarity, and the collector poles of the third and fourth transistors are respectively connected to the first and fourth transistors via resistors. Second
And the first,
A series resonance inverter type EL lighting circuit, wherein a connection point between collector electrodes of a second transistor and a connection point between base electrodes of the third and fourth transistors are connected.