JP3397314B2 - Inverter circuit - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter circuit having a soft start function for slowly raising an output.

Heretofore, for example, soft start of to launch slowly the output of one stone self-excited inverter circuit, an input line of the inverter circuit input voltage control circuit such as a regulator, as shown at 20 in FIG. 6 Was done by inserting into the series. That is, when a DC voltage is applied from the DC power supply 1 to the collector of the transistor 2 that constitutes the regulator 20, the transistor 2
Since a current is temporarily supplied to the base of the transistor through the resistor R1, the transistor 2 is turned on once.

Therefore, a direct current flows from the emitter side of the transistor 2 to the base side of the transistor 3 through the capacitor C1 and turns on the transistor 3. The timing at which the transistor 3 turns on is given by the Zener voltage of the Zener diode 4 inserted on the emitter side of the transistor 3, and this Zener voltage becomes the reference voltage.

When the transistor 3 is turned on, the base current of the transistor 2 is extracted through the collector side of the transistor 3, so that the conduction resistance between the collector and the emitter of the transistor 2 increases, and the collector-emitter current of the transistor 2 is narrowed. Becomes As a result, the primary coil L of the transformer 7 of the one-stone self-excited inverter circuit
Voltage that will be inputted to 1 initially lowered.

After that, the capacitor C1 is charged by the time constant determined by the resistor R3, so that the base current of the transistor 3 is gradually reduced. As a result, the collector-emitter current of the transistor 3 decreases, and conversely, the base-emitter current of the transistor 2 increases. Therefore, the collector-emitter current of the transistor 2 gradually increases, and the above-mentioned transformer 7 Primary coil L1
The voltage input to will gradually increase.

On the other hand, when the voltage input from the collector side of the transistor 2 rises, a current gradually flows between the base and emitter of the transistor 5 via the resistor R4, and the conduction resistance of the transistor 4 gradually decreases. As a result, a current gradually starts to flow in the coil L1 through the collector / emitter of the transistor 5, and accordingly, a positive voltage is induced in the coil L3. The voltage induced in the coil L3 is differentiated by the differentiating circuit of the resistor R5 and the capacitor C2, and then applied to the base of the transistor 5 to completely turn on the transistor 5. As a result, the current flowing through the coil L1 increases.

Since the increase in the current flowing through the coil L1 saturates at a certain time point, a voltage of the opposite polarity is induced in the coil L3 at this time point, and this voltage is differentiated by the differentiating circuit so that the voltage of the transistor 5 is changed. Applied to the base,
This transistor 5 is turned off rapidly. This allows
The current flowing through the coil L1 decreases rapidly and reaches zero at some point.
At this point, however, a positive voltage is again induced in the coil L3, which is differentiated in the same manner as above and applied to the base of the transistor 5, so that the transistor 5 is turned on again and flows into the coil L1 again. The current increases. After that, the above-described operation is repeated and the transistor 5 is switched, so that an alternating current flows through the coil L1.

Therefore, the coil L on the secondary side of the transformer 7
An alternating voltage corresponding to the winding ratio of the coil L1 and the coil L2 is generated in the second coil 2. The alternating voltage is converted into a direct current by a rectifying / smoothing circuit including a diode 8 and a capacitor C3, and a load on the secondary side (not shown). Is supplied to. afterwards,
The voltage fB on the secondary side of the transformer 7 is fed back to the base of the transistor 3, and the voltage input to the inverter circuit is adjusted so that the voltage on the secondary side is stabilized.

A regulator 20 including transistors 2 and 3 on the input side of the above-mentioned one-stone self-excited inverter circuit.
By inserting the DC voltage from the DC power source 1 to the Ichiishi self-exciting inverter circuit in an initially low state, and then increasing the voltage, the transistor 5
The switching operation can be slowly started and the output thereof can be gradually started, so that a so-called soft start of the inverter circuit is realized.

However, in order to realize such soft start of the inverter circuit, the regulator 20 having a considerably complicated circuit as described above is required, which increases the cost of the inverter circuit and increases the circuit scale. However, there is a drawback that the space property is deteriorated. In addition, in the above-mentioned conventional example, the regulator 20 performs not only the soft start of the one-stone self-excited inverter circuit but also the function of the stabilizer for stabilizing the output voltage of the one-stone self-excited inverter circuit, but only for the soft start function. When the regulator 20 is used, the above-mentioned drawback becomes remarkable.

In order to soft start the output of the above-mentioned one-stone self-excited inverter circuit,
It was necessary to insert a regulator or the like in series to the input line of the inverter circuit.

However, since this regulator has a more complicated circuit than the one-stone self-excited inverter circuit, it has the drawback of increasing the overall circuit cost and increases the circuit scale, which deteriorates the space of the inverter circuit. There was a drawback that

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an inverter circuit which eliminates the above-mentioned drawbacks and realizes a soft start capable of slowly raising the output with an inexpensive and simple circuit configuration.

SUMMARY OF THE INVENTION An inverter circuit of the present invention comprises a transformer having at least one primary winding, one control winding, and at least one secondary winding, and an alternating current generated in the control winding of the transformer. A switching element that keeps switching with a voltage and flows a switching current through the primary winding; a rectifying and smoothing circuit that rectifies an alternating voltage generated in the control winding to generate a potential of a predetermined polarity; and the switching element Is inserted between the control terminal and the potential of the specified polarity generated by the rectifying and smoothing circuit to hold the voltage after the soft start.
Multiple constant voltage elements connected in series with constant voltage set so that the influence of functions is eliminated , capacitors connected in parallel to some of these constant voltage elements, and anti-parallel to switching elements. It has the structure provided with the connected diode element.

According to the inverter circuit of the present invention, when the input voltage is turned on, the impedance of the capacitor connected in parallel to a part of the plurality of constant voltage elements connected in series is substantially 0, so that the constant voltage connected in series is changed. The control terminal of the switching element to which the element is connected is held at a low electric potential, and the electric potential of the control terminal of the switching element is held at a low electric potential as the capacitor is charged. By gradually increasing the conduction resistance of the switching element,
Soft start is performed by slowly starting the switching operation of the switching element.

After that, since a predetermined potential generated from the rectifying / smoothing circuit is applied to the other end of the constant voltage element connected in series, the voltage of the constant voltage element connected in series to the control terminal of the switching element is applied. The effect of retention is eliminated,
After starting, the switching element performs the switching operation as usual. As a result, the soft start of the inverter circuit can be performed by the constant voltage element, the capacitor, and the rectifying / smoothing circuit connected in series, and the components associated with the soft start can be simplified and the circuit can be configured at low cost. In addition, since the circuit size is not increased, the space property of the inverter circuit can be improved.

Further, the pulse voltage generated between the control terminal and the conduction terminal of the switching element due to the counter electromotive force excited in the primary winding of the transformer during the OFF period of the switching element due to the switching operation is the switching element. Since the diode elements connected in anti-parallel with respect to the above are short-circuited, the malfunction of the switching element due to the pulse voltage is suppressed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a circuit diagram showing an embodiment of the inverter circuit of the present invention.

1 is a DC power supply for supplying operating power of the one-stone self-excited inverter circuit, 5 is a switching transistor of the one-stone self-excited inverter circuit, and 6 is connected in antiparallel to the switching transistor 5 to protect the transistor 5. A diode, 7 is a transformer of the one-stone self-excited inverter circuit, 8 is a rectifying diode that rectifies an alternating voltage induced in the secondary coil L2 of the transformer 7, and 9 is a rectified induced voltage of the coil L3 (control winding). Rectifier diodes 10, 11 are Zener diodes that keep the base potential of the transistor 5 at the beginning of activation low, and C2 is a coil L.
3, a capacitor forming a differentiating circuit for differentiating the voltage generated in C3, a smoothing capacitor C3 for smoothing the output current of the rectifying diode 8, a capacitor C4 connected in parallel with the Zener diode 11, and a capacitor C5 rectified by the diode 9. Smoothing capacitor for smoothing the current, R4 is a resistor for supplying the current for starting the transistor 5, R5
Is a resistor forming a differentiating circuit that differentiates the voltage generated in the coil L3.

Next, the operation of this embodiment will be described. When a DC voltage generated from the DC power supply 1 is applied to the resistor R4 and the primary winding L1 of the transformer 7, a DC current is applied to the resistor R4.
Through the zener diode 10 side. Initially, since the capacitor C4 connected in parallel to the Zener diode 11 is not charged, the impedance of the capacitor C4 is very low, which is equivalent to the case where only the Zener diode 10 is connected to the anode side of the diode 9. Become.

After that, since the capacitor C4 is gradually charged with a time constant determined by the resistor R4, assuming that the Zener voltage of the Zener diode 10 is Z1, the voltage at the point A which is the base potential of the transistor 5 is shown in FIG. As described above, it will rise from Z1 over time T. For this reason, the conduction resistance (collector-emitter resistance) of the transistor 10 gradually decreases. Therefore, the current supplied from the DC power supply 1 to the primary coil L1 of the transformer 7 gradually increases as the conduction resistance of the transistor 10 decreases.

Thus, when a current starts to flow through the coil L1 through the collector / emitter of the transistor 5, a positive voltage is induced in the coil L3. The voltage induced in the coil L3 is differentiated by the differentiating circuit of the resistor R5 and the capacitor C2, and then applied to the base of the transistor 5 to completely turn on the transistor 5. As a result, the current flowing through the coil L1 increases.

Since the increase in the current flowing through the coil L1 saturates at a certain time point, a voltage of the opposite polarity to the above is induced in the coil L3 from this time point, and this voltage is differentiated by the differentiating circuit to cause the transistor 5 to pass. Applied to the base, this transistor 5 turns off rapidly. As a result, the current flowing through the coil L1 rapidly decreases and becomes 0 at a certain time point, but from this time point, a positive voltage is again induced in the coil L3, and this is differentiated in the same manner as described above, and the transistor 5 of the transistor 5 is differentiated. Applied to the base. As a result, the transistor 5 is turned on again, and the current flowing through the coil L1 increases again.

After that, the above operation is repeated and the transistor 5 is switched, so that the coil L
An alternating current flows through 1.

When the switching operation of the transistor 5 is started in this way, the voltage generated in the coil L3 is converted into a DC voltage by the rectifying / smoothing circuit including the diode 9 and the capacitor C5, and the DC voltage of the negative electrode is zener diode. 11 will be applied to the anode side. Therefore, the sum of the Zener voltages of the Zener diodes 10 and 11 is (Z1 + Z2), whereas the base potential, which is the voltage at the point A of the transistor 5, is maintained at a potential sufficient for normal operation. The zener diodes 10 and 11
Also, the influence of the soft start circuit composed of the capacitor C4 is eliminated.

Here, as described above, when the DC voltage from the DC power supply 1 is applied to the one-stone self-excited inverter circuit to start this inverter circuit, the soft start composed of the Zener diodes 10 and 11 and the capacitor C4. As the circuit operates, initially the current from the DC power supply 1 gradually starts to flow in the primary winding L1 of the transformer 7. This corresponds to the switching operation of the transistor 5 starting slowly over the time T of FIG. 3 (A), and the output voltage of the inverter circuit generated in the secondary winding L2 of the transformer 7 ends up slowly. It will stand up and a soft start will be realized.

Therefore, the time for soft starting the above-mentioned inverter circuit is determined by T in FIG. This T is the resistance R4 and the capacitor C4 shown in FIG.
Since there is a relation of T = α · R1 and C1, the time constant T can be adjusted by changing the resistance value of the resistor R4 and the capacitance value of the capacitor C4.

Further, the voltage rise at point A which is the base potential of bets transistor 5 Zener - Zener diodes 10 and 11 - can be adjusted by the ratio of the voltage Z1, Z2.

In the example of FIG. 1, the Zener diode 1
Zener voltages Z1 and Z2 of 0 and 11 are equal, for example, 4
It is set to about V. Therefore, the total operating voltage of the series circuit of the Zener diodes 10 and 11 is 8V.
During the period when the transistor 5 is normally switching,
Since a negative potential is applied to the anode side of the Zener diode 11, it is necessary to prevent the voltage holding function of the Zener diodes 10 and 11 from operating during inverter operation.
A voltage of V has been selected. Further, if the soft start circuit described above is not provided for reference, when the DC power supply 1 is applied to the inverter circuit, the base potential of the transistor 5 rises almost instantaneously as shown in FIG. Therefore, the output voltage output from the secondary side of the transformer 7 also rapidly rises accordingly.

According to this embodiment, the original transformer 7
A rectifier circuit composed of a diode 6 and a capacitor C5 that generate a negative potential from a voltage generated in a coil L3 that is a control winding of the DC power supply 1, and a Zener diode 10 or 11 that suppresses the base potential of the transistor 5 to a low level immediately after a voltage is applied from the DC power supply 1.
Since the soft start function can be performed by the capacitor C4, the circuit related to the soft start can be simplified and the cost can be reduced. As a result, it is possible to prevent an increase in the circuit scale of the one-stone self-excited inverter circuit equipped with the soft start circuit or increase the cost of the circuit, and to maintain a good space property.

Further, the induced voltage of the primary winding of the transformer generated when the transistor 5 is turned off is generated by the Zener diodes 10 and 11 between the base of the transistor 5 and the potential of the predetermined polarity generated in the rectifying and smoothing circuit. However, the pulse voltage is short-circuited because the diode 6 is connected in parallel in the direction opposite to the conduction direction of the transistor 5 because it is inserted in the transistor 5. As a result, the transistor 5 is protected.

FIG. 4 is a circuit diagram showing a main part of another embodiment of the present invention. In this example, a resistor R6 is connected in series to the Zener diode 11 instead of the Zener diode, and the other configurations are the same as those of the soft start circuit shown in FIG.

Also in this embodiment, when switching of the transistor 5 is started, a voltage corresponding to the voltage drop flowing through the resistor R6 is applied to the base of the transistor 5 to suppress the base voltage to a low level, and then the capacitor C4 is charged. Therefore, the base potential of the transistor 5 rises and the switching operation is slowly started, which has the same effect as that of the embodiment shown in FIG.

However, since the voltage drop of the resistor R6 differs depending on the current flowing through the resistor R6, the change in the base potential of the transistor 5 is complicated, and the resistor R6 depends on the temperature.
Since the resistance value of No. 6 changes, the accuracy of setting the soft start time and the like is slightly deteriorated. However, since the resistance is cheaper than the Zener diode, the cost of the circuit can be reduced as compared with the embodiment of FIG.

FIG. 5 is a circuit diagram showing a main part of still another embodiment of the present invention. In this embodiment as compared with the embodiment shown in FIG. 4, Tsu E Na over the diode and the connecting position of the resistor R7 and is a reversed, Moreover, although the capacitor C4 is connected in parallel with the resistor R7, operation Figure It is exactly the same as that of 4 and has the same effect.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of an inverter circuit of the present invention.

2 is a diagram showing a main part of an embodiment for explaining a soft start time of the circuit shown in FIG.

FIG. 3 is a diagram showing a base potential rise characteristic of the transistor shown in FIG.

FIG. 4 is a circuit diagram showing a main part of another embodiment of the present invention.

FIG. 5 is a circuit diagram showing a main part of still another embodiment of the present invention.

FIG. 6 is a circuit diagram showing an example of a one-stone self-excited inverter circuit including a conventional soft start circuit.

[Explanation of symbols]

1 ... DC power supply 5 ... Transistor 6, 8, 9 ... Diode 7 ... trance 10, 11 ... Zener diode C2, C3, C4 ... Capacitor R4, R5 ... Resistance

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H02M 3/28

Claims (2)

(57) [Claims] 1. The number of primary windings, control windings and secondary windings is reduced.
With a transformer equipped with one each, The AC voltage generated in the control winding of this transformer switches
And the switching current is applied to the primary winding.
Switching element to flow, Rectify the alternating voltage generated in the control winding to a predetermined polarity
A rectifying and smoothing circuit that generates the potential of In the control terminal of the switching element and the rectifying and smoothing circuit
It is inserted between the electric potential of the predetermined polarity generated bySof
After the start, the influence of the voltage holding function is eliminated.
Constant voltage setMultiple voltage regulators connected in series
When, Capacitors connected in parallel to some of these constant voltage elements
When, Dio connected in anti-parallel to the switching element
And a device An inverter circuit comprising: 2. The inverter circuit according to claim 1, wherein a part of a plurality of constant voltage elements connected in series is replaced with a resistor.