JPH11252940A - Self-excited resonance power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply which lowers the withstand voltage required for a resonance capacitor, requires no protective means for transistors, and at the same time enables a circuit to operate stably with self-excited oscillation. SOLUTION: In a self-excited resonance power supply of a push-pull configuration, a resonance capacitance part Cre connected in parallel with a primary winding N1 of a transformer T is constituted of first to fourth capacitors C1, C2, C3, C4 connected in series. A junction (A) between the second capacitor C2 and the third capacitor C3 is connected to the common junction of each source of first and second transistors Q1, Q2. A junction (B) between the first capacitor C1 and the second capacitor C2 is connected to the gate of the second transistor Q2, and a junction (C) between the third capacitor C3 and the fourth capacitor C4 to gate of the first transistor Q1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention solves the problems of withstand voltage and protection of resonance capacitors and transistors in a self-excited resonance type power supply circuit to which a lower oscillation circuit is applied.
At the same time, the present invention relates to a technique for improving the stability of oscillation operation of a circuit.

[0002]

2. Description of the Related Art There are various types of power supply circuits for supplying a drive voltage to loads such as a fluorescent display tube and a discharge tube.
Here, especially when an alternating current is required for the drive voltage, a self-excited, resonance type power supply circuit applying a lower oscillation circuit is often used. As such a self-excited resonance type power supply, there has been a power supply circuit having a circuit configuration as shown in FIG. The circuit configuration and operation of the power supply circuit shown in FIG. 2 were generally as follows.

In FIG. 2, an input terminal 1a is connected to an intermediate tap of a primary winding N1 of a transformer T via a choke coil L1, and an input terminal 1b is connected to the ground. A resonance capacitor C5 is connected between the terminals of the primary winding N1 as a resonance capacitor, and both ends of the primary winding N1 are respectively connected to main terminals of a first transistor Q1 and a second transistor Q2 each formed of a field effect transistor. It is connected to earth via a current path. The both ends and the intermediate tap of the secondary winding N2 are output terminals 2a, 2b,
2c. The gates of the transistor Q1 and the transistor Q2 are connected in the form of a cross, respectively, to the winding end opposite to the winding end of the primary winding N1 to which its own main current path is connected, by a resistor R3 or a resistor R4. Connected through. DZ1 and DZ2 connected between the respective gates and the ground are constant voltage diodes for protecting the transistors Q1 and Q2.

In the circuit having the above configuration, when an input voltage V _IN is supplied from the outside between the input terminals 1a and 1b, one of the transistor Q1 and the transistor Q2 becomes conductive like a multivibrator. Here, it is assumed that the transistor Q1 is turned on first. A current flows through the primary winding N1 due to the conduction of the transistor Q1, and a voltage is induced in the primary winding N1. The voltage induced at this time is applied as a feedback voltage to the gates of the transistor Q1 and the transistor Q2. Then, a forward bias is applied to the transistor Q1,
2 are given reverse bias, respectively, and the transistor Q
1 is turned on, and the transistor Q2 is turned off. The voltage induced at this time is the resonance capacitor C5.
Causes a resonance phenomenon in a resonance circuit formed by the primary winding N1.

[0005] The occurrence of the resonance phenomenon causes the primary winding N
A voltage (resonance voltage) appearing between the terminals of the first terminal changes in a sinusoidal manner. According to the change in the resonance voltage appearing between the terminals of the primary winding N1, the transistors Q1 and Q2
Are turned on or off alternately, and thereafter, the self-excited oscillation operation is continuously performed. In the power supply circuit having the circuit configuration described above and performing the self-excited oscillation operation, the primary winding N1 is directly connected to each of the transistors Q1 and Q2.
Is supplied as a feedback voltage for driving. For this reason, the number of circuit elements was small, and the power supply circuit was small and highly efficient.

[0006]

However, when the power supply circuit having the structure shown in FIG. 2 is actually manufactured, there are the following problems. That is, if the input voltage V _IN is applied between the input terminals 1a and 1b, the peak value of the resonance voltage appearing between the primary winding N1 and the terminal of the resonance capacitor C5 is approximately 2V _IN × (2) ^{1. / 2} high voltage. For this reason, a high withstand voltage equal to or higher than the peak value of the resonance voltage is required for the resonance capacitor C5. However, high withstand voltage components are expensive and have few types, and it is difficult to find a component that meets the required specifications. Although the transistors Q1 and Q2 are directly driven by the resonance voltage, the drive voltage applied to the gate of each transistor changes when the load state changes, especially when there is an abnormality such as a load-side short circuit. May greatly change with the change. Therefore, in the circuit of FIG. 2, the constant voltage diode D is used to protect the transistors Q1 and Q2.
Although Z1 and DZ2 are connected, the cost of the power supply circuit increases due to this protection measure.

In order to solve such a problem, the present inventor has disclosed in Japanese Patent Application No. 9-343820 that a resonance capacitor is formed by a series circuit of a plurality of capacitor elements, and a control terminal of each transistor is connected to a predetermined capacitor. A circuit connected to the connection point is proposed. However, when actually commercializing the circuit proposed here, it is necessary to narrow down the circuit specifications such as the load fluctuation range and the input voltage application range in order to perform stable self-excited oscillation operation. there were. In view of the above problems, the present invention eliminates the need for using a high withstand voltage component for the resonance capacitor, eliminates the need to provide a special protection means for the transistor, and has a wide range of self-excited oscillation operation of the circuit. It is an object of the present invention to provide a self-excited resonance type power supply that is performed stably under the above conditions.

[0008]

A self-excited resonance type power supply according to the present invention has a primary winding having a predetermined inductance, and is connected in parallel to the primary winding of the transformer to resonate with the primary winding. First and second transistors having one end of each main current path connected to a predetermined position of a primary winding of a transformer, a resonance capacitor forming a circuit, and a predetermined position of a primary winding of a transformer. A choke coil connected with an external input voltage source between the tap and the common connection point at the other end of the main current path of the first and second transistors;
The resonance capacitor is constituted by a plurality of capacitor elements connected in series, and a connection point (A) between predetermined capacitors of the resonance capacitor is set to a common connection point of a main current path of the first and second transistors. The control terminals of the first and second transistors are connected to at least one capacitor element of the resonance capacitor from the winding end of the primary winding, and to a connection point (A) between the capacitors. Both are characterized in that they are connected to connection points (B) and (C) between predetermined capacitors in a resonance capacitor section separated by at least one capacitor element.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A resonance capacitor connected in parallel to a primary winding of a transformer is constituted by four or more capacitor elements connected in series. One ends of the main current paths of the first and second transistors are connected to both ends of the primary winding of the transformer, respectively, and the other ends of the main current paths of the first and second transistors are commonly connected. A choke coil is connected between the common connection point and the intermediate tap of the primary winding together with an external voltage supply, and a connection point (A) between the common connection point and a predetermined capacitor of the resonance capacitor is connected. Connecting. And the first
And a control terminal of the second transistor is connected to a connection point (B) between predetermined capacitors of the resonance capacitor section, which separate at least one capacitor element from both the winding end of the primary winding and the connection point (A). ) And (C). Also, the first
A resistance element is connected between each of the control terminals of the second transistor and the other end of the main current path.

[0010]

[Embodiment] A high-withstand-voltage resonance capacitor is not required, and protection measures for transistors are not required. In addition, it is possible to stably perform the oscillation operation of the circuit under a wide range of conditions.
FIG. 1 shows a circuit of an embodiment of the self-excited resonance type power supply according to the present invention. In FIG. 1, the same components as those shown in FIG. 2 are denoted by the same reference numerals. The circuit configuration of the self-excited resonance type power supply of the present invention is as follows. The input terminal 1a is connected to the intermediate tap of the primary winding N1 of the transformer T via the choke coil L1, and the input terminal 1b is connected to the ground. Both ends of the primary winding N1 are first transistors Q each formed of a field effect transistor (FET).
The first and second transistors Q2 are connected to ground via a main current path, and a resonance capacitor Cre corresponding to the resonance capacitor C5 in FIG. 2 is connected between the terminals of the primary winding N1. Here, as for the resonance capacitor portion Cre, the first capacitor C
1, a second capacitor C2, a third capacitor C3, and a fourth capacitor C4.

The resonance capacitor Cre is connected to the first capacitor C1.
Series circuit of the second capacitor C2 and the third capacitor C3
A connection point (A) between the second capacitor C2 and the third capacitor C3 so as to be divided into a series circuit of the capacitor C4 and the fourth capacitor C4.
To earth. The gate of the second transistor Q2 is connected to the connection point (B) between the first capacitor C1 and the second capacitor C2, and the gate of the first transistor Q1 is connected to the connection point (C) between the third capacitor C3 and the second capacitor C2.
Connect to A resistor R1 or R2 is connected between each gate and source of the first transistor Q1 and the second transistor Q2, respectively. The secondary winding N2 of the transformer T
Are connected to output terminals 2a, 2a and 2b, respectively.
b, 2c.

The circuit of FIG. 1 having the above configuration is shown in FIG.
In comparison with the circuit of the above, the resonance capacitor is formed by a plurality of capacitor elements, a predetermined position of the resonance capacitor is connected to the ground, and the feedback voltage supplied to the transistor is converted to a part of the capacitor of the resonance capacitor. To enter through, is different. For this reason, the circuit of FIG. 1 has the following operations and effects. Since the self-excited oscillation operation of the entire circuit is not much different from the circuit of FIG. 2, a detailed description of the self-excited oscillation operation is omitted here. First, in the circuit of FIG. 1, a resonance phenomenon occurs due to the inductance of the primary winding N1 and the overall combined capacitance of the resonance capacitance portion Cre. Here, inside the resonance capacitance portion Cre, the capacitors connected in series share and take charge of a voltage (having a value inversely proportional to the capacitance) according to the capacitance. Therefore, the voltage value applied per capacitor element is lower when a plurality of capacitor elements are used as shown in FIG. 1 than when only a single capacitor element is used as a resonance capacitor as shown in FIG. Become. Therefore, each of the capacitor elements forming the resonance capacitance section Cre can be used with a low withstand voltage.

In the circuit of FIG. 1, the second capacitor C2
The connection point (A) of the first and second capacitors C3 and C3 is connected to the commonly connected sources of the first and second transistors Q1 and Q2, substantially to ground. From this circuit configuration,
The voltage between the gate and source of the first transistor Q1 appears between the terminals of the third capacitor C3, and the voltage between the gate and source of the second transistor Q1 returns between the terminals of the second capacitor C2. It is applied as a voltage. Here, the voltage between the terminals of the second capacitor C2 and the voltage between the terminals of the third capacitor C3 are the divided voltages of the resonance voltages shared by the four capacitors, and the capacitance values of the first to fourth capacitors are calculated as follows. By adjusting, it is possible to set a desired value. For this reason, by setting the feedback voltage of each of the first and second transistors Q1 and Q2 to an appropriate value, transistor protection means such as a constant voltage diode, which is required in the circuit of FIG. 2, becomes unnecessary. .

Further, in the circuit of FIG. 1, resistors R1 and R2 are connected between the gate and the source of the first transistor Q1 and the second transistor Q2. Since the connection point (A) is connected to the ground, the third capacitor C3 and the resistor R
1, the third capacitor C3 in the path of ground, connection point (A)
A current loop for supplying a feedback signal to the first transistor Q1 from the second capacitor C2, the resistor R2, the ground, and the feedback signal from the second capacitor C2 to the second transistor Q2 via the path of the connection point (A). A current loop for the supply is respectively formed. With this current loop, the first
The bias state between the gate and the source of the transistor Q1 and the second transistor Q2 is stabilized, and the stability of the self-excited oscillation operation of the circuit is improved. In addition,
In an actual transistor element, there is a very small current leakage from the gate to the source.
It can be considered that a high-resistance element is connected between the sources. Therefore, depending on the circuit specifications, the resistance R
1, it is also possible to omit R2.

By the way, in the circuit shown in FIG.
Although the case where a channel field-effect transistor is used is illustrated, the circuit may be formed using another type of transistor. Further, in FIG. 1, the resonance capacitance section Cre is used.
Is composed of four capacitor elements, but may be composed of more capacitor elements. However, in actual commercialization, parts having the same characteristics are used for the first and second transistors Q1 and Q2, and the resonance capacitance section Cre is constituted by four capacitor elements. And the first
It would be realistic to design a circuit with the same capacitance for the capacitors C1 and C4 and the same capacitance for the second and third capacitors C2 and C3. And
The circuit in FIG. 1 is configured as an inverter circuit that supplies an AC voltage generated in the secondary winding N2 to a load.
It is also possible to connect a rectifying element to the next winding N2 and use it as a converter circuit.

[0016]

As described above, the self-excited resonance type power supply of the present invention is formed by a plurality of capacitor elements connected in series with a resonance capacitor forming a resonance circuit together with a primary winding of a transformer. A connection point (A) between predetermined capacitors of the resonance capacitor is connected to a common connection point of the main current paths of the first and second transistors. The control terminals of the first and second transistors are connected to the connection point (A) at both ends of the primary winding.
Connection points (B) and (C) between predetermined capacitors in the resonance capacitance portion, both of which separate at least one capacitor element.
It is characterized by a circuit configuration for connection to the. With such a configuration, the voltage applied between the terminals of the individual capacitors forming the resonance capacitor portion is reduced, so that the withstand voltage of the used capacitor can be reduced.

Further, by adjusting the capacitance of each of the capacitors forming the resonance capacitance section and setting the feedback voltage applied to the gate of the transistor to an appropriate value, the protection means for the transistor becomes unnecessary. be able to. Furthermore, by connecting the connection point (A) to the common connection point of the main current paths of the first and second transistors, a current loop for stabilizing the bias state of the first and second transistors is formed, and the circuit is self-contained. The stability of the excitation oscillation operation is improved. Therefore, according to the present invention, it is not necessary to use a component having a high withstand voltage for the resonance capacitor, it is not necessary to provide a special protection means for the transistor, and the self-oscillation operation of the circuit can be performed stably under a wide range of conditions. The self-excited resonance type power supply can be provided.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of a self-excited resonance type power supply according to the present invention.

FIG. 2 is a circuit diagram of an example of a conventional self-excited resonance type power supply.

[Explanation of symbols]

 1a, 1b Input terminal 2a-2c Output terminal (AC) Q1 First transistor Q2 Second transistor L1 Choke coil T Transformer N1 Primary winding N2 Secondary winding Cre Resonance capacitor C1 First capacitor C2 Second capacitor C3 Third capacitor C4 Fourth capacitor R1 First resistor R2 Second resistor (A) to (C) Connection point between predetermined capacitors

Claims (3)

[Claims] A transformer having a predetermined inductance in a primary winding; a resonance capacitor connected in parallel to the primary winding of the transformer to form a resonance circuit with the primary winding; First and second transistors each having one end of a main current path connected to a predetermined position of a primary winding of the transformer; a tap provided at a predetermined position of a primary winding of the transformer; A choke coil connected together with an external input voltage source between a common connection point at the other end of the main current path of the two transistors, and a plurality of capacitor elements having the resonance capacitor connected in series. And a connection point (A) between predetermined capacitors of the resonance capacitor unit.
Is connected to a common connection point of a main current path of the first and second transistors, and each control terminal of the first and second transistors is connected to a winding end of the primary winding by the resonance capacitor. At least one capacitor element of the portion and at least one capacitor element at a connection point (A) between the capacitors.
A self-excited resonance type power supply, which is connected to connection points (B) and (C) between predetermined capacitors of the resonance capacitor. 2. The semiconductor device according to claim 1, wherein first and second resistors are respectively connected between the control terminals of the first and second transistors and the other end of the main current path. Self-excited resonance power supply described in 1. 3. The resonance capacitor section includes four series-connected capacitors.
3. The self-excited resonance type power supply according to claim 1, wherein the first and second transistors comprise one capacitor element, and the first and second transistors comprise FETs.