JPH0237278Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit configuration of a so-called DC-AC inverter that converts a DC voltage source into an AC voltage source.

A DC-AC inverter is widely used, for example, as an AC pulse source for roll-calling an AC type plasma display panel or as an AC pulse source for heating the filament of a fluorescent display tube.

An example of a conventional circuit configuration of this type of DC-AC inverter will be explained using drawings.

FIG. 1 is a drawing showing the circuit configuration of a conventional DC-AC inverter.

In FIG. 1, the primary winding 9 of the transformer 1, the transistor 2, and the additional resistor 7 and capacitor 8 connected to the base terminal of the transistor 2 together constitute a well-known separately excited oscillator circuit. The primary winding is driven at a frequency determined mainly by a high-frequency pulse input to the transistor 2. Therefore, the secondary winding 10 has the primary winding 9
An AC voltage is induced by the current change, and by specifying the turns ratio of the primary winding 9 and the secondary winding 10 for a given DC power supply voltage value, a desired AC amplitude value can be obtained at the output end. Can be done. by the way,
AC for fluctuations in DC power supply voltage or load fluctuations
In order to keep the AC amplitude value appearing at the output terminal stable, it is necessary to add a negative feedback circuit (hereinafter referred to as NFB).
Generally, the negative amplitude of the output of the NFB winding 11 is rectified and smoothed by a diode 3, a capacitor 4, and a resistor 5, and then returned to the base of the transistor 2 via a Zener diode 6.

Now, in the conventional DC-AC inverter shown in FIG. 1, as mentioned above, only the negative amplitude of the output of the NFB winding 11 is observed to control the transistor 2, so the negative amplitude of the AC output is Although it is stabilized, it has the serious drawback that the positive amplitude is completely unprotected. Also, among the switching characteristics of transistor 2, the off characteristics are determined by the inductance load of transformer 1, and the frequency characteristics and 2 It is clear that it has a serious drawback in that the output amplitude of the secondary winding 10 is limited.

The purpose of this invention is to prevent DC power supply voltage fluctuations or
An object of the present invention is to provide a DC-AC inverter that has an NFB method that can stabilize the total amplitude value of AC output against load fluctuations on the AC output side, and has improved frequency characteristics.

The present invention comprises a transformer having at least one primary winding and at least one feedback winding, a separately excited oscillator circuit comprising at least one transistor, and at least one secondary winding of the transformer. In the DC-AC inverter,
The negative potential obtained by voltage-doubling rectification of the output of the feedback winding of the transformer to the negative potential side is coupled to the base terminal of the transistor via the Zener diode, and is connected in opposite phase to the separately excited oscillation circuit on the primary side of the transformer. This objective is achieved by coupling a switching circuit comprising at least one switching transistor to the secondary winding.

Next, embodiments of the present invention will be described.

FIG. 2 shows an embodiment of the present invention, which supplies an AC voltage source for lighting a plasma display panel.

In FIG. 2, the primary winding 9 of the transformer 1, the transistor 2, the additional resistor 7, and the capacitor 8 collectively constitute a separately excited oscillator circuit, which converts the high-frequency pulse input to the base of the transistor 2 into a current. The pulse current is amplified and passed through the primary winding of transformer 1. An AC voltage is induced in the secondary winding 13 by the current change in the primary winding 9, and a DC power supply voltage of 10 to 30
The turns ratio is chosen so that the total amplitude of the AC output is approximately 300 volts. In this embodiment, the output of the NFB winding 11 is voltage doubled and rectified to the negative side by a capacitor 12 and diodes 13 and 3, and the negative potential obtained by smoothing it by a capacitor 4 and a resistor 5 is passed through a Zener diode 6. and is coupled to the base terminal of transistor 2. Here, the negative potential obtained by voltage double rectification is
Since it is equal to the total amplitude of the output of the NFB winding 11,
Therefore, in the NFB method according to this embodiment, the transistor 2 is controlled by observing the total amplitude of the output, and the total amplitude value can be kept constant over a wide range of DC power supply fluctuations and AC output load fluctuations. was done
AC output can be obtained.

Furthermore, in this embodiment, the output of the secondary winding 10 is connected to the AC
A transistor 16 that level shifts the output and switches the output in an opposite phase to transistor 2.
Collectors are connected. Here, the additional resistor 17, capacitor 18, and inverter 19 connected to the transistor 16 operate in the opposite phase to the circuit constituted by the transistor 2.

Next, the principle of operation in which a switching circuit is provided on the secondary side with a phase opposite to that on the primary side will be explained.

When the primary side transistor 2 is turned on by the input high frequency pulse, current flows through the primary winding 9 and a positive voltage is induced in the secondary winding 10. Next, when the primary side transistor 2 turns off, the secondary side transistor 16 turns on, switching the induced voltage to the negative side. At this time, a current flows through the secondary winding 10, and a positive voltage is induced on the collector side of the transistor 2 connected to the primary winding 9. Furthermore, when transistor 2 on the primary side is turned on by the next high-frequency pulse, the positive potential induced from the secondary winding can further flow current, so the voltage induced on the secondary side increases, and transistor 2
Since a voltage is induced from the secondary side when the switch is turned off, the switching speed is improved. Therefore, according to this embodiment, by combining the above-mentioned NFB method with a switching circuit on the secondary side in opposite phase to the separately excited circuit on the primary side, it is possible to overcome a wide range of DC power supply fluctuations and AC output load fluctuations. A stabilized AC output with a constant total amplitude value can be obtained, and the frequency characteristics and efficiency of the transformer can be improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the circuit configuration of a conventional DC-AC inverter, and FIG. 2 shows a first embodiment of the present invention.

Claims (1)

[Scope of utility model registration request] a separately excited oscillator circuit comprising a transformer having at least one primary winding and at least one feedback winding and at least one transistor;
In a DC-AC inverter including at least one secondary winding of the transformer, the negative potential obtained by voltage-doubling rectification of the output of the feedback winding of the transformer to the negative potential side is connected to a Zener diode. means having a negative feedback circuit coupled to the base terminal of the transistor through the secondary winding; and at least one transistor switching in an opposite phase to the separately excited oscillation circuit on the primary side of the transformer. A DC-AC inverter characterized by having one on the side.