JPH0729752Y2 - Self-exciting inverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a self-excited inverter using a saturation transformer.

[Conventional technology]

Conventionally, as a self-excited inverter circuit of this type,
There is a royer circuit as shown in the figure. In the figure, 1 is a saturation transformer, and 2 and 3 have their emitters a DC power supply 5.
Is a NPN transistor connected to the negative polarity side, and the bases of the transistors 2 and 3 are connected to the negative polarity side of the DC power supply 5 via the base windings 1a and 1b of the saturation transformer 1. The collectors of the transistors 2 and 3 are connected to one end and the other end of the collector winding 1c of the saturation transformer 1, and the neutral point thereof is connected to the positive side of the DC power supply 5 via the switch 4. That is, 2 at its neutral point
The number of turns n _C1 and n _C2 of the first collector winding 1c ₁ and the second collector winding 1c ₂ of the divided collector winding 1c are set to be equal. Also, the base winding 1a of the saturation transformer 1
And 1b are set to have the same number of turns n _B1 and n _B2 , and their respective base windings are connected to a polarity that causes positive feedback due to the collector current. Further, the saturation transformer 1 uses a core having magnetic characteristics with rectangular hysteresis as shown in FIG. 1d
Is the secondary output winding of the saturation transformer 1.

In the royer circuit configured in this way, the switch 4
When one of the transistors is closed, one of the transistors becomes conductive by positive feedback due to the induced voltage in the base winding. As a result, the collector current flowing in the transistor on the conductive side increases linearly with time, and the core of the saturation transformer 1 is excited. Eventually, when the core reaches its saturation flux (eg, + Φ _s ), the induced voltage in the base winding decreases and the collector current also decreases rapidly. As a result, the transistor that has been conducting until now is cut off, and on the contrary, the other transistor is turned on and its collector current starts to increase. This increase also continues until the core reaches the saturation magnetic flux −Φ _S , after which the transistor cuts off and returns to the initial state again. The oscillation is continued in this way, and the oscillation frequency is expressed by the following equation.

f = V / 4N _C Φ _S [Hz] In this expression, V is the power supply voltage [V], Φ _S is the saturation magnetic flux [Wb] of the core, and N _C is the number of turns of the collector winding.

[Problems to be solved by the invention]

However, according to such a conventional self-excited inverter, the magnetic saturation characteristic of the transformer is used for its principle, so that the period from when the switch is closed until the oscillation becomes stable
Excessive voltage surge is transiently applied to the transistor,
In the worst case, there was a problem of destroying the transistor. For this voltage surge that is applied between the collector and emitter of the transistor,
This can be easily avoided by selecting a transistor with a high emitter breakdown voltage or adding a CR circuit for absorbing surge between the collector windings of the transformer. But,
Regarding the voltage surge applied in the reverse direction between the base and emitter of the transistor, there is no effective protection means because the reverse withstand voltage V _EBO of the base and emitter of the transistor is as low as 5 to 7V.

[Means for solving problems]

In order to solve such a problem, the present invention provides first and second emitters whose common ground is connected, whose collector is connected to a collector winding of a saturation transformer and whose base is connected to a base winding of a saturation transformer. A constant voltage diode is connected between the base and the emitter of the second transistor, with its cathode on the emitter side.

[Action]

Therefore, according to the present invention, the excessive reverse voltage applied between the base and the emitter is suppressed below the zener voltage of the zener diode.

[Embodiment] Hereinafter, a self-excited inverter according to the present invention will be described. First
The figure is a diagram showing a royer circuit as an example of the self-excited inverter. In the figure, the same reference numerals as those in FIG. 3 denote the same components, and the description thereof will be omitted. That is, in this royal circuit, constant voltage diodes 6 and 7 are connected between the bases and emitters of the transistors 2 and 3, respectively, with their cathodes arranged on the emitter side.

Therefore, an excessive voltage surge that is applied between the base and the emitter of the transistor immediately after the switch 4 is closed until the oscillation is stabilized is suppressed to the zener voltage of the constant voltage diode or less, and the transistor protection function is achieved. . Moreover, since the forward voltage drop of the constant voltage diodes 6 and 7 is generally larger than the base-emitter voltage of the transistors 2 and 3, the basic operation of the above-mentioned royer circuit is not impaired.

FIG. 2 is an example in which the present invention is applied to an inverter for high frequency lighting of a fluorescent lamp. Here, the capacitor 8 constitutes a parallel resonance circuit with the collector winding 1c of the saturation transformer 1,
The choke coil 9 prevents the DC power supply 5 from generating noise. 10 and 11 are transistors 2 and 3
Reference numeral 12 is a resistor connected between the base of the switch and switch 4, and reference numeral 12 is a capacitor connected in front of the fluorescent lamp 13. Also in the high-frequency lighting inverter configured in this manner, the constant voltage diodes 6 and 7 are connected between the bases and emitters of the transistors 2 and 3 with their cathodes arranged on the emitter side and are connected at the time of startup. The excessive reverse voltage that is applied in the meantime is suppressed below the zener voltage of the constant voltage diode to protect the transistor.

[Effect of device]

As described above, according to the self-excited inverter according to the present invention, since the cathode is arranged on the emitter side and the constant voltage diode is connected between the bases and the emitters of the first and second transistors, the start-up of the inverter is started. At times, an excessive reverse voltage that tends to be applied between the base and the emitter is suppressed below the zener voltage of the zener diode, thus protecting the transistor.

[Brief description of drawings]

FIG. 1 is a diagram showing a royer circuit as an embodiment of the self-excited inverter according to the present invention, FIG. 2 is a circuit diagram showing an inverter for high frequency lighting of a fluorescent lamp to which the present invention is applied, and FIG. 4 is a diagram showing the royal circuit of FIG. 4, and FIG. 4 is a diagram showing the magnetic characteristics of the core used in the saturation transformer of this royal circuit. 1 …… Saturation transformer, 2,3 …… NPN transistor, 4 ……
Switch, 5 ... DC power supply, 6, 7 ... Constant voltage diode.

Claims (1)

[Scope of utility model registration request] 1. A first and a second device having their emitters connected to a common ground and having their collectors connected to a collector winding of a saturation transformer and their bases connected to a base winding of a saturation transformer.
In the self-excited inverter including the transistor, the cathode is arranged on the emitter side between the base and the emitter of the first and second transistors, and the constant voltage diode is connected. Excitation type inverter.