JPS6160668B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a resonant transistor inverter device that does not cause abnormal oscillation even when the load fluctuates.

Conventionally, various self-excited and resonant transistor inverter devices have been proposed. However, a problem with the conventional device is that when the load fluctuates, the oscillation operation becomes abnormal. In other words, if the load is a discharge lamp, for example, and the resistance increases due to the life of the discharge lamp, the resonance conditions determined by the resonance capacitor, transformer, load, current-limiting inductor, etc. will change, and the pre-designed resonance will change. This is different from the phenomenon. For this reason, the bias voltage applied to the base of the transistor differs from the designed one, and the transistor switching does not occur as planned, increasing power loss during switching, causing heat generation, and in the worst case scenario. It was something that could destroy transistors.

The present invention has been made to eliminate these drawbacks of conventional devices.Even when the load fluctuates, the bias voltage of the transistor is kept the same as during normal oscillation, thereby eliminating abnormal oscillation and reducing power loss during switching. Prevents the increase in temperature and
It is an object of the present invention to provide a transistor inverter device that can prevent destruction of transistors.

The present invention provides a resonant circuit that resonates at the fundamental frequency of the resonant output of the inverter between the feedback winding of the transformer and the base of the transistor. The present invention is characterized in that a bias voltage similar to that during normal oscillation is applied to the base of the transistor to cause oscillation as designed in advance.

Embodiments of the present invention will be described below with reference to the drawings. Reference numeral 1 denotes a DC power supply, which can be a rectified power supply obtained by rectifying commercial AC power, or a rectified smoothed power supply. 2 and 3 are transistors connected to this power supply 1. These transistors 2 and 3 have their respective emitters connected to the negative electrode side of the DC power supply 1, and in this embodiment, a push-pull type inverter is shown. Note that in the present invention, connecting the transistor to the DC power supply 1 includes, for example, connecting the transistor to the DC power supply 1 via the constant current inductor 4 as in this embodiment. next,
A transformer 5 has both ends of an input winding 5a connected to the collectors of the transistors 2 and 3, and the positive electrode of the DC power supply 1 is connected to the midpoint of the input winding 5a. AC power is output from the output winding 5b based on the switching. The transformer 5 also has a feedback winding 5c, which is connected to the bases of the transistors 2 and 3, respectively. 6 is a resonant capacitor connected to the transformer 5 to output sinusoidal resonant power from the output winding 5b;
In this embodiment, it is connected in parallel with the input winding 5a. However, this resonant capacitor 6
may be connected in parallel or in series with the output winding 5b. Such a resonant capacitor 6
is used to determine the switching timing of the transistors 2 and 3, and by applying a bias voltage to the bases of the transistors 2 and 3 through the feedback winding 5c, the transistors 2 and 3 are switched. This resonant frequency is selected, for example, from about 15 KHz to 30 KHz. Next, 7 is a load such as a discharge lamp, which is supplied with high frequency AC power by the output winding 5b of the transformer 5 and is turned on. When the load 7 is a discharge lamp as described above, a current limiting device 8 constituted by an inductor, a capacitor, a leakage inductance of the transformer 5, etc. is provided. Further, preheating circuits 9 and 10 for the discharge lamp are provided. Next, 11 is a resonant circuit provided between the feedback winding 5c of the transformer 5 and the bases of the transistors 2 and 3. In this embodiment, it consists of an inductor 12 connected in series to the feedback winding 5c, and a capacitor 13 connected in parallel to the series circuit of the inductor 12 and the feedback winding 5c. This resonant circuit 11 resonates with the fundamental frequency of the sinusoidal resonant power of the transformer 5 and supplies this resonant output to the bases of the transistors 2 and 3, and performs a so-called filter function. That is, if there is no fluctuation in the load 7 and there is no abnormality in the resonant capacitor 6 and the transformer 5, the transformer 5 outputs the resonant power as designed. Therefore, the feedback winding 5c also outputs a sinusoidal voltage, but in this case the resonant circuit 11 is designed to have almost no effect on this output.
In addition, the resonance conditions change due to load fluctuations, etc.
As a result, when a distorted waveform that is not sinusoidal appears in the feedback winding 5c, the resonant circuit 11 resonates so as to output a voltage with the same waveform as the output waveform during normal oscillation. 14 and 15 are base resistances of the transistors 2 and 3.

Next, the effect will be explained. If the load 7, for example, the discharge lamp has not reached the end of its life, and the load 7 does not change from its design value, the resonance conditions determined by the resonance capacitor 6, transformer 5, load 7, or leakage inductance of the transformer, etc. This is the same as the design value, and the transformer 5 outputs sinusoidal resonant power due to normal resonance. Therefore, by applying such a bias voltage, transistors 2 and 3 perform a switching operation. At this time, as described above, the resonant circuit 11 does not affect the output of the feedback winding 5c.

If the load 7 fluctuates and, for example, the discharge lamp reaches the end of its life and the resistance increases and becomes overloaded, the resonance conditions will naturally change. That is, for example, if the resistance increases as the discharge lamp reaches its end of life, the resonant system may enter a damped state and become unable to resonate. Therefore, as shown by the broken line in FIG. 2, a voltage is generated in the feedback winding 5c that cannot completely reverse the polarity at the time when the polarity should be reversed due to resonance, which keeps one transistor conductive for a long time. Sometimes I let it go. Therefore, switching of the transistors requires a long time, power loss increases, heat is generated, and in the worst case, the transistors 2 and 3 may be destroyed. On the other hand, when the resonant circuit 11 of the present invention is provided, the resonant circuit 11 resonates with the output of the feedback winding 5c as shown by the broken line in FIG. 2, resulting in normal oscillation as shown by the solid line in FIG. Outputs the same voltage as when That is,
It outputs a voltage whose polarity is reversed at the same time as during normal oscillation. Therefore, since this output is applied and transistors 2 and 3 are biased,
Since the transistors 2 and 3 switch according to their designed values, power loss does not increase due to abnormal oscillation, and problems such as heat generation and destruction of the transistors 2 and 3 can be eliminated.

Note that the present invention is not limited to the above-mentioned embodiments, and various modifications are possible. For example, similar actions and effects can be obtained with a single-stone type inverter instead of a push-pull type inverter. In short, the effects of the present invention can be obtained with any resonant type inverter device that outputs resonant power that determines the switching timing of transistors. Further, the resonant circuit can be modified without departing from the technical idea of the present invention, and the resonant frequency of the resonant circuit and the fundamental frequency of the resonant output of the inverter do not necessarily have to completely match. In short, any material may be used as long as it can reduce distortion of the bias voltage to the transistor due to load fluctuations or the like. Furthermore, the load is not limited to discharge lamps.

As described in detail above, the present invention provides a resonant type inverter with a resonant circuit that resonates at the fundamental frequency of the resonant output of the inverter between the base of the transistor and the feedback winding, so that the resonant circuit that resonates at the fundamental frequency of the resonant output of the inverter can be used to reduce load fluctuations. Since the same bias voltage as the design value is always applied to the base of the transistor, there is no abnormal oscillation, which prevents an increase in power loss during switching, and prevents inconveniences such as heat generation or transistor destruction. Therefore, it is possible to provide a transistor inverter device that eliminates the problem.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a waveform diagram for explaining the operation. 1...DC power supply, 2, 3...Transistor, 5
...transformer, 6...resonant capacitor, 7...load, 11...resonant circuit.

Claims (1)

[Claims] 1. A DC power source, a transistor that switches the output of this power source, an input winding that inputs the switching output of this transistor, and a feedback winding that applies a bias voltage to the base of the transistor. a transformer; a resonant capacitor provided in association with the transformer to generate a resonant output in the transformer; a load energized by the output of the transformer; and a resonant capacitor provided between the base of the transistor and the feedback winding; A transistor inverter device comprising: a resonant circuit that resonates at the fundamental frequency of the resonant output and supplies the resonant output to the base of the transistor. 2. The transistor inverter device according to claim 1, wherein the resonant circuit comprises an inductor connected in series to the feedback winding of the transformer, and a capacitor connected in parallel to the inductor and the feedback winding.