JPS5843998B2 - Inverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an inverter that obtains high frequency power suitable for using a non-smoothed rectified power source.

Japanese Unexamined Patent Publication No. 54-29022 discloses an invention for reducing power loss in a drive circuit as much as possible by obtaining a drive current for a transistor constituting a switching element from a feedback winding of an output transformer. .

That is, in this prior art, as shown in the first diagram, a pair of feedback windings 2 and 3 are provided in the output transformer 1, and one of the feedback windings 2 and 3 is
is used to obtain an excitation signal for self-oscillation like a general inverter, but a diode 4 and a capacitor 5 are connected in series between both ends of the other winding 3, and a base resistor is connected between both ends of the capacitor 5. The inverter is connected between the base and emitter of each transistor 8 and 9 via transistors 6 and 7, and the other parts are almost the same as a general known inverter.

Since a smoothed DC voltage appears across the capacitor 5, a required drive current is supplied to each transistor 8, 9.

According to this prior art, since it is sufficient to supply a low voltage of at most several volts from the feedback winding 3, the power loss in the base resistors 6 and 7 can be kept low.

The above prior art has no problems when the power source is a smoothed rectified power source or a battery power source, but it is difficult to set the constant of the capacitor 5 when a non-smoothed rectified power source is used.

In other words, if the capacitance is small and the smoothness is insufficient, Fig. 3a
During the phase where the power supply voltage is low, the drive is insufficient and an oscillation pause period occurs.

On the other hand, if the capacitance is large and completely smoothed, overdrive will occur as shown in Figure 3, causing overshoot in oscillation.

SUMMARY OF THE INVENTION An object of the present invention is to provide an inverter with an improved drive circuit suitable for use with a non-smoothed rectified power supply.

In the present invention, the smoothing circuit in a drive circuit having a rectifier and a smoothing circuit connected to the feedback winding of a transformer is connected in parallel to the first capacitor, which is composed of a first capacitor, a resistor, and a second capacitor. It is characterized by its structure including a series circuit.

According to the present invention, since the degree of freedom in setting the constants of the smoothing circuit is improved, it is possible to easily perform the desired oscillation operation even when using a non-smoothed rectified power supply.

Hereinafter, details of the present invention will be explained with reference to an embodiment shown in the second drawing.

A first rectifier 11 is connected to the AC power supply 10, and the positive output terminal of the rectifier 11 is connected to the common connection point of the input windings 14 and 15 of the output transformer 13 via the reactor 12. The terminals are connected to the emitters of NPN transistors 16 and 17, respectively.

The collector of transistor 16 is connected to the other end of input winding 14, and the base is connected via resistor 18 to the common connection point of input windings 14,15.

In addition, the collector of the transistor 17 is connected to the other end of the input winding 15, and the base is connected to the input winding 14,
Connect to 15 common connection points.

A capacitor 21 is connected to both ends of the output winding 20 of the transformer 13 to form a resonant circuit with the output winding 20.

22 is a load connected to the output winding 20, furthermore, the transformer 13 has feedback windings 23 and 24, and one end of the feedback winding 23 is connected to a switching element such as the transistor 1.
6 and the other end thereof are connected to the base of a switching element, for example, a transistor 170, respectively.

Furthermore, a smoothing circuit 26 is connected to both ends of the feedback winding 24 via a second rectifier 25 .

The smoothing circuit 26 includes a series circuit of a first capacitor 27, a resistor 28, and a second capacitor 29, and this series circuit is connected in parallel to the first capacitor 27.

The positive terminal of the capacitor 27 is connected to the base of the transistor 16 through the resistor 30, and the base of the transistor 17 is connected through the resistor 31, and the negative terminal is connected to the emitters of the transistors 16 and 17, respectively, to form a drive circuit. Configure.

Next, the operation will be explained.

When an AC voltage is applied by the AC power supply 10, a non-smoothed rectified output is generated in the first rectifier 11, and this output provides a drive current to the bases of the transistors 16 and 170 via the resistor 18. , transistor 16°1
Due to the unbalance of transistor 7, for example, transistor 16 turns on first.

As a result, an output is induced in the output winding 20, and
The differential voltage between the output winding 20 and the resonant circuit of the capacitor 21 generates an electromotive force in the feedback winding 23, and the transistors 16 and 17 are turned on and off alternately, thereby starting high frequency oscillation.

When oscillation starts in this way, an electromotive force is also generated in the feedback winding 24.

This electromotive force is rectified by the second rectifier 25, and the above-mentioned oscillation high frequency component is smoothed by the filter effect of the first capacitor 2T of the smoothing circuit 26, and the voltage across the capacitor 27 is as shown in curve A in FIG. According to the output of the first rectifier 11, a low frequency pulsating waveform is formed.

The voltage across this capacitor 27 supplies a drive current to the bases of transistors 16 and 17 through resistors 30 and 31.

On the other hand, since a low frequency filter consisting of a series circuit of a resistor 28 and a second capacitor 29 is connected in parallel with the first capacitor 21, the voltage across the second capacitor 290 is determined by the time constant of the resistor 28. 1 capacitor 27
The fourth voltage is lower than the highest value of the voltage across the terminal and higher than the lowest value.
This is shown by curve B in the figure.

This curve B is almost linear because the time constant of the capacitor 290 charging/discharging circuit consisting of the second capacitor 29, the resistor 28, and the resistors 30 and 31 is set large.

However, even if it does not have a linear shape, the effect described below will remain the same.

As shown in FIG. 4, the voltage across the second capacitor 29 is higher than the voltage across the first capacitor 27 during the phase α.

During this phase α, the second capacitor 29 is in a discharge state and supplies an appropriate drive current to the transistors 16 and 17 via the resistor 28 and resistors 30 and 31.

That is, since the lack of output of the first capacitor 27 is compensated for, the constant setting of the smoothing circuit 26 is easy and the setting range can be widened, and the oscillation voltage waveform of the transistor 16 or 17 is changed to irregular oscillation as shown in FIG. 3C. There is no occurrence of oscillation, and stable oscillation corresponding to the output of the first rectifier 11 is achieved, whereby AC power is supplied to the load 22.

Since the first capacitor 27 smoothes high-frequency voltage, it can be made smaller and has a smaller capacity than the second capacitor 29 that smoothes low-frequency voltage, and if a plastic film capacitor or the like is used, loss can be reduced. (can.

Further, by using an electrolytic capacitor as the second capacitor 29, the capacitance can be increased, and the second capacitor 29 can be made small and inexpensive.

FIG. 5 shows the main part of another embodiment of the present invention, that is, the smoothing circuit 32. The same parts as in FIG. It is omitted because it is the same as the original.

33 is a third rectifier such as a diode, which is connected in parallel with the resistor 28 in a direction opposite to that of the second rectifier 25.

In FIGS. 2 and 5, the second capacitor 29,
The time constant of the discharge circuit consisting of the rectifier 33, the resistor 30 or 31 and the base-emitter of the transistor 16 or 17 is independent of the resistor 28.

Therefore, the voltage across the second capacitor 29 can be adjusted by the resistor 28, and the drive currents of the transistors 16 and 17 can be adjusted appropriately, so that the transistors 16 and 17 can be driven in a good condition.

Note that the present invention is not limited to the above-mentioned embodiments,
This can be implemented in an inverter that uses at least one switching element, and a normal rectifier can be used.

Further, the high frequency output may be rectified or frequency converted and then supplied to the load.

As described in detail above, the present invention provides a smoothing circuit connected to the feedback winding of a transformer via a rectifier, which is made up of a first capacitor, a resistor, and a second capacitor and is connected in parallel to the first capacitor. Since the smoothing circuit includes a series circuit, even in the case of a non-smoothed rectified power supply, the degree of freedom in setting the constants of the smoothing circuit is improved, and the optimum drive current can be stably supplied. Therefore, the desired high frequency oscillation output can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing a conventional example, Fig. 2 is a circuit diagram showing an embodiment of the present invention, Figs. 3 and 4 are voltage waveform diagrams for explanation, and Fig. 5 is a circuit diagram showing an embodiment of the present invention. FIG. 2 is a circuit diagram showing main parts of the embodiment. 10... AC power supply, 11... first rectifier, 13
...Transformer, 16.17...Switching element,
25... Second rectifier, 26... Smoothing circuit, 27
...First capacitor, 28...4EL29...Second capacitor.

Claims (1)

[Claims] 1. A transformer having a human power winding, an output winding, and a feedback winding, an AC power supply, a first rectifier connected between the power supply, this first rectifier and the above-mentioned input. A switching element interposed between the windings and turned on and off periodically, and a drive circuit having a second rectifier and a smoothing circuit and connected between the feedback windings and driving the switching element. An inverter characterized in that the smoothing circuit includes a first capacitor and a series circuit including a resistor and a second capacitor and connected in parallel to a fourth capacitor. 2. The inverter according to claim 1, wherein the first capacitor has a smaller capacity than the second capacitor and is superior in high frequency customization. 3. The inverter according to claim 1 or 2, wherein the first capacitor is a plastic film capacitor, and the second capacitor is an electrolytic capacitor. 4. Claims 1 to 3, characterized in that a third rectifier is connected in parallel to the resistor included in the smoothing circuit in a direction opposite to the second rectifier.
Any one of 1 = ffi inverter.