JPH02273079A - Self-exciting inverter circuit and fluorescent lamp driver using same - Google Patents

Abstract

PURPOSE:To reduce the generation of a spike voltage by connecting the emitter of a transistor to one end of a coil, the other end of which serves as a dividing top for a DC supply. CONSTITUTION:Respective base voltage-inducing coils L1, L2 connecting respective bases and emitters of transistors Tr1, Tr2 and an output voltage coil L connecting the emitter of said transistor Tr1 and controller of said transistor Tr2 and one output terminal are wound around the same transformer T. Both sides of the output terminal from said coil L are connected with the DC power supply side via capacitor and the other output terminal is a terminal obtained by voltage-dividing a DC power supply. Thus, it is possible to reduce a leakage inductance formed between the primary and secondary windings and to lessen the frequency of generation of a spike voltage.

Description

DETAILED DESCRIPTION OF THE INVENTION (Object and Field of the Invention) The present invention relates to a self-excited inverter circuit using transistors and a fluorescent lamp driving device using the same.

A half-bridge inverter shown in FIG. 1, for example, is known as a self-excited inverter circuit using transistors.

The operation of the half-bridge inverter circuit is as follows (the operation of 5 or less is common not only to the half-bridge inverter circuit but also to other self-excited inverter circuits).

■When conduction is established between the collector and emitter of one transistor Trt, collector current flow occurs due to conduction. ,
increases.

■ Due to the increase in the collector current ICI, the base voltage V of the transistor Trt is increased through the transformer T! 11, thereby maintaining conduction from the collector to the emitter of transistor T1.

(2) The collector current Iel is also saturated due to the saturation of the magnetic flux in the core of the transformer T, and this causes the induced voltage on the base side to decrease and even stop.

■Cutoff of collector current Iel.

(2) The magnetic flux φ flowing in the transformer T suddenly decreases due to the cutoff of the collector current Ic+, but due to such a sudden change in the magnetic flux φ, the base voltage V of the other transistor T1.

is induced to have a positive value, the collector current ICa of the transistor Tr2 flows to the emitter side, and the transistor Tra becomes conductive.
The + base voltage V is induced in the opposite direction by the aforementioned change in which the magnetic flux φ decreases rapidly after decreasing and stopping as described above, but the base voltage V□ has a negative value. Therefore, transistor Tr+ does not conduct.).

In the step, for example, the transistor T r of FIG.
In the process of changing from the cut-off of the + collector current Ic+ to the conduction of the collector current IC2 of the transistor Tra (the process of changing from ■ to ■), the leakage inductance of the primary coil L is With the conduction of the current ■, the excitation energy 1/
2 ・L'Ie, (where Lo: coil inductance and cage inductance), but transistor Tr+
is cut off, the circuit for discharging this energy is lost, and a back electromotive voltage is generated between the emitter and base of the transistor Tr+.

Therefore, a sharp spike voltage as shown in FIG. 2 is applied between the emitter and base of the transistor T1 at the moment when the collector current Ll becomes non-conductive.

In order to reduce such spike voltages, various attempts have been made such as reducing the magnetic resistance of the core or adding innovations to the winding of the coil L, but what is usually done is, for example, the first As shown in the figure, an RC circuit is provided at one terminal of the coil L (in FIG. 1, a resistor R and a capacitor C are arranged in parallel, but they may also be arranged in series.

), the energy generated in the leakage inductance is absorbed by the capacitor C, and the emitter of the transistor
In addition to preventing the generation of spike voltage between the collectors, the electric charge accumulated in the capacitor C is gradually discharged and dissipated in the resistor R as thermal energy.

However, in such a configuration, the voltage generated in the coil is always shunted through the resistor R and is taken away as thermal energy, which inevitably lowers the efficiency of the entire circuit.

The present application provides an inverter circuit that has an extremely simple design compared to conventional self-excited inverter circuits and can alleviate the generation of spike voltage without reducing energy efficiency, and also provides a fluorescent lamp using the inverter circuit. The object of the present invention is to provide a drive device for the following.

(Structure of the Invention) As shown in FIG. 3, the self-excited inverter circuit of the present invention connects the emitter of the transistor T1 and the collector of the transistor T1, and connects the collector of the transistor Tr+ and the collector of the transistor Tr+. In a circuit in which the emitter is connected to the DC power supply side, each coil L1. Lt and transistor Trt
An output voltage coil L that connects the emitter of the transistor T r m and the collector of the transistor T r m and one output terminal is wound around the same transformer T, and the output terminal from the coil L is connected to a DC power source via a capacitor on both sides. It is connected to the side.

The other output terminal is a self-excited inverter circuit, which is a terminal obtained by dividing the voltage of the DC power supply.

As is clear from FIG. 3, the self-excited inverter circuit of the present application does not provide a secondary winding on the output side in the half-bridge inverter circuit shown in FIG. (Transistor Trz collector side) The other end of the coil is set as one output terminal, and the other output terminal is a terminal obtained by dividing the voltage of the DC power supply (in Fig. 3, , a circuit in which a diode D and a capacitor C° are connected in parallel is used as a voltage dividing circuit, but the voltage dividing circuit of the present application is not limited to such a circuit. A circuit using a resistor and a capacitor in series or in parallel may also be used.)

The operating principle of the self-excited inverter circuit of the present invention shown in FIG. 3 is the same as that of the half-bridge inverter circuit shown in FIG.

However, in the self-excited inverter circuit of the present application, since the transformer T does not have a secondary winding on the output side,
Since the leakage inductance formed between the primary and secondary windings is extremely small,
The frequency of spike voltage occurrence is extremely low compared to conventional self-excited inverter circuits.

In addition to this, in the self-excited inverter circuit of the present application shown in FIG. 3, for example, the collector current I at of the transistor T r r is cut off.

When the collector currents of transistors Trz and 2 start conducting, the coil current and cage inductance are as follows:
As mentioned above, the collector current Ie+ that has been conducting so far
By 1/2・L゛Work. , (L': coil thickness - cage inductance) has been accumulated, and since the transistor T r + has become non-conductive, a back electromotive force is generated due to the accumulated energy λ. The back electromotive force is charged and absorbed by the capacitor C1 that divides the voltage of the DC power supply.

That is, the excitation energy accumulated in the leakage inductance L° is absorbed and charged by the capacitor C1,
It is possible to avoid applying a spike voltage directly between the collector and emitter of the transistor T r +, and the electric charge charged in the capacitor C1 is
It is discharged through the load Z on the output terminal side.

That is, in the self-excited inverter circuit of the present invention,
It is possible to reduce the generation of spike voltages between the emitter and collector of the transistor Tr+ as shown in FIG. It is also possible to dissipate the energy generated in the coil and avoid reducing energy efficiency.

Considering the waveform of the output voltage of the self-excited inverter circuit of the present application, when the transistor Tr+ is conductive in FIG. 3, the collector current is higher than the input DC voltage to the transistor. , the voltage drop due to the internal resistance between the collector and emitter of the transistor Tr+, the voltage drop due to L-dIe/dt due to the coil L of the transformer T, the voltage drop due to the resistance of the coil L itself, Mutual inductance M between coil L and coil L1.

Ml ・Voltage drop due to dI□/dt (however, Ia
+:) Based on the base current of the transistor T r □
Voltage rise due to conduction (voltage rise due to internal resistance between the collector and emitter of transistor Tr2, transformer T
The back electromotive force L-dIct/
Voltage increase due to dt, voltage increase due to the resistance of coil L itself, voltage increase due to mutual inductance M2 between coil L and coil 2, M2 ・d I a, / d t (However, ■, l!: Transistor T r Since the potential is high by () based on the base current of If designed, a rectangular high frequency wave will be generated as shown in FIG.

FIG. 5 shows an improved circuit by adding other elements to the circuit of FIG. 3 (actually, it is often used in the state shown in FIG. 5).

In FIG. 5, the base-emitter winding and the collector-emitter winding of the transistor Tr+ are drawn consecutively, but the polarity of the windings is reversed (if not so). For example, the collector current I of transistor T r +
The base voltage v1 is not induced to a positive value when ct is conducting).

Furthermore, in the transistors Tr+ and Tr, diodes D, D, whose forward direction is from the emitter to the base, and resistors Rg and Ra are connected between the base and the emitter.
When is conductive, a voltage is induced not only in the coil L2 but also in the coil (a voltage is induced in the direction opposite to the direction in which the base voltage V□ is induced when the transistor Trt is conductive). ), current ■ through diode D6 and resistor R2. , conducts.

As a result, the base potential V□ of the transistor T r 1 drops by IOI·82, and the transistor T
1 will act to ensure that conduction does not occur.

On the other hand, when the state of conduction of the transistor T r z changes to the state of conduction of the transistor Trl, the coil 2 generates a current I in the direction opposite to the direction in which the base voltage V1g was previously induced. 2 will flow through the diode Dtt resistor R3, but such a reverse current I. 2, the magnetic flux formed in the coil and cage inductance L' is canceled (because at the stage when the collector current Ict is conducting and the base voltage V□ is induced, the coil L and coil L
The direction of the magnetic flux formed in 2 and 2 is the same,
Therefore, the direction of the magnetic flux formed in the coil length and the cage inductance L° is the same as the direction of the magnetic flux of the coil L2, but the conduction of the current Ioz in the opposite direction is the direction that induces the base voltage VB□. Since it is the opposite, the direction of the magnetic flux formed in the coil inductance and cage inductance will be canceled out. ).

Therefore, as shown in FIG. 4, even if one of the transistors is not in operation, it is coiled as described above or the current is supplied by the coil L2. , or current I. By making the transistors Tr+ conductive, the transistors Tr+ and Tr
This contributes to preventing the generation of spike voltage at the moment when z becomes non-conductive (however, the diode D
, ,D, and the resistors R, ,R, are not themselves essential components of the present invention).

In the invention of the present application, the transistor T r + or T r
It is necessary for one side of t to become conductive first, but
For this purpose, the transistor T r + or.

It is preferable to apply a trigger voltage or pulse voltage to one base of Trz.

In particular, if the DC input power source is not a complete DC source such as a battery, but is simply a regular AC power source that has been rectified and smoothed by a smoothing circuit, fluctuations may remain in the DC power source itself. Therefore, it is preferable to apply a trigger pulse to the base side of the transistor Tr+ or Tr2 using a trigger circuit such as a trigger diode, diac, or uni-junction transistor.

FIG. 5 shows an example in which a trigger diode D6 is used to apply a trigger pulse to the base side of the transistor Trz (addition of such a trigger pulse itself is not an essential requirement of the present invention). do not have,)
.

Also, in FIG. 5, the transistor T r l % same T r
In order to prevent x from heating (overheating), diodes D6 and D9 are connected between the base and emitter of the transistor, but this is because the resistance between the base and emitter decreases due to heating of the transistor.

This causes a large amount of current to flow from the base side to the emitter side, which poses a risk of further heating the transistor, so the current is shunted to diodes D8 and D to prevent the transistor from overheating. (Using such a diode between base and emitter is not necessarily an essential requirement of the present invention.)
.

FIG. 6 shows a circuit diagram of a device for driving a fluorescent lamp using the high frequency generated by the self-excited inverter circuit of the present invention.

In recent years, fluorescent lamps have been lit using high-frequency power sources.

This is because when using a high frequency, the flicker is extremely reduced; the gas inside the fluorescent lamp is more easily excited, improving the efficiency of the entire light source; and the frequency is high, so it is used in fluorescent lamps. This technology has been attracting attention in recent years because it has advantages such as making the ballast smaller and lighter and cheaper.

When a conventional self-excited inverter circuit is used as a high-frequency power source, the emitter and
In order to absorb the spike voltage that occurs between the collectors, an RC circuit as shown in Figure 1 is provided, and as a result, the energy efficiency of the primary coil is reduced, or the transistor is damaged due to the spike voltage. The voltage of a DC power supply applied to a self-excited inverter circuit has been reduced without providing an RC circuit or the like.

On the other hand, in the invention of the present application, as described above, the charge accumulated in the voltage dividing capacitor generated by the spike voltage generated between the collector and emitter of the transistor is discharged to the load side, so there is no deterioration in energy efficiency. Especially when diodes D, D, are used between the base and emitter of the transistor as shown in FIG.
Since the generation of spike voltage can be canceled considerably, the self-excited inverter circuit of the present invention is extremely suitable as a power source for fluorescent lamp voltage.

FIG. 6 shows an embodiment in which the invention of the present application is used as a fluorescent lamp driving device.

In FIG. 6, choke coils L, , L smooth the waveform from the self-excited inverter circuit and also serve as a ballast in the input circuit for the fluorescent lamp.

On the other hand, capacitors C,,C, and diodes DIO,D
11 in parallel is useful not only for adjusting the output voltage of the self-excited inverter circuit, but also for shaping the waveform of the output voltage. It also adjusts the phase delay caused by L4 and improves the power factor. Although it is not an essential requirement, such a voltage dividing circuit is most convenient, at least as a drive device for fluorescent lamps.)

When a fluorescent lamp is turned on by a high-frequency power source, the electrode itself has the shape of a spiral coil.

Moreover, since it is a high frequency, the magnitude of the inductance due to the electrode itself cannot be ignored [If the current flowing through the electrode is I, and the inductance of the electrode itself is L, then L-d i / d t is This is a back electromotive voltage, but since it is a high frequency, d i / d t is extremely large).

Due to the inductance of such electrodes, the power factor of the power applied to the fluorescent lamp may deteriorate, so placing separate capacitors 01° and C11 in the wiring connecting the electrodes will overcome the above drawbacks. be able to.

Although Fig. 6 shows the case of driving two fluorescent lamps, it is also possible to drive one fluorescent lamp using the output terminal of the self-excited inverter circuit of the present application. is clear.

(Operations and Effects of the Invention) As described above, since the self-excited inverter circuit of the present invention has less leakage inductance than the conventional configuration, it generates less spike voltage and can efficiently alleviate spike voltage. It can be used in various high frequency circuits because it provides an AC output close to a rectangular wave.

Further, since the transformer T does not require an output winding on the secondary side, the circuit can be designed extremely simply and at low cost.

Such a self-excited inverter circuit of the present invention is most suitable as a high-frequency lighting device for a lamp using gas such as a fluorescent lamp.

In particular, in the high-frequency lighting lamp of the present application, in particular, in an embodiment in which a diode and a capacitor are installed in parallel, the voltage dividing circuit and the circuit for improving the power factor can also be used, which is compared to the case where both are installed separately. However, it is extremely simple and economical.

As described above, since the present invention has various advantages as described above, its utility value is extremely high.

[Brief explanation of drawings]

Figure 1: Shows a conventional half-bridge self-excited inverter circuit. Figure 2: A graph showing the voltage between the emitter and collector of a transistor in a non-conducting state (the rising peak portion indicates a spike voltage) Figure 3: A circuit diagram showing the basic configuration of the self-excited inverter circuit of the present invention Figure 4: A graph showing the output voltage of the self-excited inverter circuit of the present invention Figure 5: A circuit diagram showing an embodiment in which other components are added to the circuit shown in Figure 3 (D1 ~D4 is a diode that performs radio wave rectification, C, , C2 and R3
It is obvious that the circuit is a smoothing circuit.) Figure 6 - Circuit diagram of a fluorescent lamp drive device using the self-excited inverter circuit of the present invention Figure 1 Naoto Akao, attorney and patent attorney for the applicant Figure 2 Figure 3 Figure 4

Claims (8)

[Claims] (1) Connect the emitter of the transistor Tr_1 and the collector of the transistor Tr_2, and
In a circuit in which the collector of transistor Tr_1 and the emitter of transistor Tr_2 are connected to the DC power supply side, transistor Tr_
1. Base voltage induction coils L_1 and L_2 that connect the base and emitter of the same Tr_2, and an output voltage coil L that connects the emitter of the transistor Tr_1 and the collector of the transistor Tr_2 and one output terminal.
are wound around the same transformer T, and the output terminal from the coil L is connected to the DC power supply side via a capacitor on both sides, and the other output terminal is a terminal obtained by dividing the DC power supply. Self-excited inverter circuit by (2) In the transistors Tr_1 and Tr_2, a diode is connected from the emitter to the base side with the forward direction, and a resistor provided in series with the diode is connected to the base. Self-excited inverter circuit (3) The self-excited inverter circuit according to claim (1), characterized in that a trigger pulse input circuit is connected to the base of one of the transistors Tr_1 and Tr_2 from the positive side of the DC input. (4) A self-excited inverter circuit according to claim (1), characterized in that a heating prevention diode is connected between the base and emitter of the transistors Tr_1 and Tr_2, with the forward direction being from the base to the emitter. (5) Fluorescent lamp driving device using high frequency output from the self-excited inverter circuit according to claim (1) (6) The fluorescent lamp driving device according to claim (5), characterized in that a parallel circuit of a diode and a capacitor is used as a voltage divider circuit for dividing the input from the DC power source side. (7) The fluorescent lamp driving device according to claim (5), characterized in that a ballast by a chiyoke is provided at the output terminal from the self-excited inverter circuit. (8) The fluorescent lamp driving device according to claim (5), characterized in that a capacitor is interposed in the wiring connecting between the electrodes of the fluorescent lamp.