JP2893463B2 - Push-pull inverter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a push-pull inverter used as a driver of, for example, a cold cathode discharge tube or a hot cathode discharge tube.

[Prior Art] Push-pull inverters having various circuit configurations are known, one example of which is shown in FIG.

FIG. 2 shows an inverter circuit configured as a driver for the fluorescent tube 11, which is a push-pull circuit including a boosting transformer 12, transistors 13 and 14 for switching operation, a choke coil 15, and the like.

In this inverter circuit, when the power switch 16 is closed, the transistor 17 serving as a power supply switch is turned on,
DC power is supplied from the DC power supply 18.

From this, through the resistor 19 to the transistor 13,
A base current flows into each of the transistors 14 through the resistor 20. For this reason, the transistors 13 and 14 move in a direction in which both transistors are turned on, but one of the transistors greatly advances in a conductive state in terms of transistor characteristics and circuit configuration.
This transistor turns on first.

For example, if the transistor 13 is turned on first, the DC power supply 18
The current sent from the transformer passes through the choke coil 15
The current flows through the primary coil 12P, and a voltage in the direction indicated by the solid line is generated in the primary coil 12P. The collector potential of the transistor 13 is lower than the collector potential of the transistor 14.

At this time, an induced voltage is generated in the secondary coil 12S in the direction of the solid line in the figure, and the lighting of the fluorescent tube 11 is started.

In addition, the transistor 13,
Since the biasing capacitors 21 and 22 connected between the base and the collector of 14 are charged to the polarity shown, the transistors
13 receives positive feedback and the collector current increases rapidly.

Since the increase in the current of the transistor 13 is suppressed when the saturation point determined by the base current and the amplification degree is reached, the primary coil of the transformer 12 decreases as the increase in the current decreases.
12P generates a voltage in the direction of the dotted line in FIG.
Switches from ON to OFF, and the transistor 14 switches from OFF to ON.

As a result, an induced voltage is generated in the secondary coil 12S in the direction indicated by the dotted line, and the lighting of the fluorescent tube 11 is continued.

In addition, the capacitors 21 and 22 are charged to polarities opposite to the illustrated polarities, and positive feedback is applied to the base of the transistor 14.

Thereafter, the transistors 13 and 14 are alternately turned ON in the same manner as described above, and generate a high alternating voltage in the secondary coil 12S.

The above-described inverter circuit has been developed by the inventor of the present application, and a patent application has already been filed as Japanese Patent Application No. 274825/1999.

[Problems to be Solved by the Invention] The output voltage of the inverter circuit described above is not a sine wave AC voltage but a distorted wave close to the AC voltage.
There is practically no problem in lighting 11 and, in addition, in this inverter circuit, a feedback coil can be omitted from the step-up transformer 12, and a resonance capacitor connected in parallel with the primary coil 12P is not required. As a result, an extremely efficient inverter circuit that generates less heat from the step-up transformer 12 is obtained.

However, when the above-described inverter circuit is operated with no load with the fluorescent tube 11 removed, unstable oscillation occurs.

That is, when the fluorescent tube 11 is removed, the transistor
Since the regular feedback is not applied to the transistors 13 and 14, the operations of the transistors 13 and 14 become unstable.

Such unstable oscillation is a problem particularly when the inverter circuit supplies power to another load.

SUMMARY OF THE INVENTION It is an object of the present invention to improve the above-described inverter circuit and to develop an inverter circuit that operates stably even when there is no load and is capable of supplying power to the first load and the second load.

[Means for Solving the Problems] In order to achieve the above-described object, the present invention provides a primary coil having an intermediate tap, a step-up transformer having a secondary coil connected to a load, and a primary coil on one side of the intermediate tap. A first and a second switching element with a control pole for alternately interrupting the current flowing through the coil and the primary coil on the other side; a capacitor connected between the control poles of the first and second switching elements; In a push-pull inverter provided with a feedback circuit that allows a load current to flow around, an input coil connected in parallel to a primary coil of the step-up transformer, an output coil thereof, and control electrodes of the first and second switching elements are connected. We propose a push-pull inverter characterized by providing an auxiliary transformer having a feedback coil.

"Operation" Since the boosting transformer and the auxiliary transformer output both when the two switching elements are turned on alternately,
The first load connected to the step-up transformer and the second load connected to the auxiliary transformer can be supplied by one inverter circuit.

Further, since positive feedback is applied to the two transistors by the feedback coil provided in the auxiliary transformer, a stable oscillation operation is performed regardless of whether the first load is connected to the step-up transformer.

Next, an embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, reference numeral 25 denotes an auxiliary transformer, a primary coil 25P of which is connected in parallel to a primary coil 26P of a step-up transformer 26, and a second load 28 which is connected to a secondary coil 25S.
Is connected. The auxiliary transformer 25 is provided with a feedback coil 25F. One end of the coil 25F is connected to the base of the transistor 13 via the capacitor 27, and the other end is connected to the base of the transistor 14.

Other configurations are the same as those of the inverter circuit shown as a conventional example in FIG. Although the step-up transformer 26 has a winding start direction of each coil opposite to that of the conventional step-up transformer 12, these transformers 12 and 26 operate similarly.

In the inverter circuit of this embodiment, both the boosting transformer 26 and the auxiliary transformer 25 generate an output voltage by alternately turning on the switching circuits.

For example, when the transistor 14 is switched from OFF to ON, a voltage in the direction indicated by the solid line in the drawing is generated in the primary coil 26P of the step-up transformer 26, and the voltage of the primary coil 26P is Generates a voltage in the direction of the solid line in FIG.

As a result, the fluorescent tube 11, which is the first load, is supplied with the output voltage of the secondary coil 26S of the step-up transformer 26 in the direction indicated by the solid line. Is fed.

In this operation stage, the bias capacitors 21 and 22 are charged to the illustrated polarity by the load current of the fluorescent tube 11, and
The voltage generated in the feedback coil 25F of the auxiliary transformer 25 in the direction indicated by the solid line in the drawing is positively fed back to the base of the transistor 14.

Transistor 14 changes from ON to OFF, transistor 13 turns OFF
To ON, a voltage in the direction indicated by a dotted line is generated in each coil of the step-up transformer 26 and the auxiliary transformer 25, so that the fluorescent tube 11 and the second load 28 as the first load are supplied with power. Become.

On the other hand, in the above inverter circuit, when the fluorescent tube 11 is removed, the load current flowing into the capacitors 21 and 22 disappears, but the base of the transistors 13 and 14 generates the voltage generated in the feedback coil 25F of the auxiliary transformer 25. As a result, the step-up transformer 26 operates stably regardless of no load.

Also, when the second load 28 is removed, the feedback coil 25
A stable operation is also performed by the feedback action of F.

In the inverter circuit described above, the step-up transformer 26 is used.
The output voltage of the auxiliary transformer 25 and the auxiliary transformer 25 becomes an alternating voltage including a distorted wave. Output voltage.

However, since the capacitor 29 causes a rise in the transformer temperature, it is preferable to use a capacitor having an appropriate capacity in consideration of the improvement of the output voltage waveform and the transformer temperature. Therefore, the capacitor 29 is not necessary if the output voltage waveform does not need to be improved.

As mentioned above, although one Example of this invention was described, when implementing this invention, the transformer 26 for boosting and the transformer 25 for assistance may be made into a separate transformer, and these are integrally comprised. Is also good.

[Effects of the Invention] As described above, in the present invention, in a push-pull inverter in which two switching elements are alternately turned on using a load current, an input coil is connected in parallel to a primary coil of a step-up transformer of the inverter. And a feedback coil provided in the auxiliary transformer performs a feedback operation on the control poles of the two switching elements. Therefore, two loads are supplied by one inverter circuit. Can be done,
A push-pull inverter with stable oscillation operation even when the load is removed and no load is applied.

[Brief description of the drawings]

FIG. 1 is a push-pull inverter circuit diagram showing one embodiment of the present invention, and FIG. 2 is a push-pull inverter circuit diagram shown as a conventional example. 11 Fluorescent tube 13, 14 Transistor 15 Choke coil 21, 22 Bias capacitor 25 Auxiliary transformer 26 Boost transformer 27 Capacitor 28 Second load

Claims (1)

(57) [Claims] 1. A step-up transformer having a primary coil having an intermediate tap, a secondary coil connected to a load, and a current flowing through a primary coil on one side and a primary coil on the other side of the intermediate tap alternately intermittently. A push-pull inverter including first and second switching elements having a control pole, a capacitor connected between the control poles of the first and second switching elements, and a feedback circuit configured to allow a load current to flow around the capacitor. , An auxiliary transformer having an input coil and an output coil thereof connected in parallel to a primary coil of the step-up transformer and a feedback coil connected to control poles of the first and second switching elements is provided. Push-pull inverter.