JP2008061369A - Resonant switching power supply - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resonant switching power supply having high degree of freedom in design and performing stable self oscillation. <P>SOLUTION: In the resonant switching power supply, a resonance capacitor Co is connected in parallel with the primary winding N1 of a transformer T, control terminals of a first switching element Q1 and a second switching element Q2 are connected with the winding end side of the primary winding of main current path of a switching element on the opposite side through a first capacitor C1 or a second capacitor C2 for dividing the applied voltage, and a third capacitor C3 or a fourth capacitor C4 for dividing the applied voltage is connected with the common joint of each control terminal of the first and second switching element and the main current path of two switching elements. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique for solving the breakdown voltage and protection problems of a switching element and simultaneously improving the stability of oscillation operation of a circuit in a resonant switching power supply using a Royer oscillation circuit.

  There are various circuit systems for a power supply circuit that supplies a driving voltage to a load such as a fluorescent display tube or a discharge tube. Here, especially when an alternating current is required for the drive voltage, a self-excited and resonant power supply circuit using a Royer oscillation circuit is often used. As such a self-excited resonance type power supply, there has conventionally 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 are generally as follows.

  In FIG. 2, the input terminal 1 is connected to an intermediate tap of the primary winding N1 of the transformer T through a choke coil L1. A resonance capacitor Co is connected as a resonance capacitor between the terminals of the primary winding N1, and both ends of the primary winding N1 are connected to a first switching element Q1 and a second switching element made of a field effect transistor (MOSFET), respectively. The switching element Q2 is connected to the ground via the main current path. Then, both ends and the intermediate tap of the secondary winding N2 of the transformer T are connected to the output terminals 2a, 2b, and 2c, respectively. The gates of the first and second switching elements Q1 and Q2 are in the form of brushes, respectively, at the winding end opposite to the winding end of the primary winding N1 to which the main current path is connected, They are connected via a resistor R1 or a resistor R2. Z1 and Z2 connected between the respective gates and the ground are constant voltage diodes for protecting the first switching element Q1 and the second switching element Q2.

  In the circuit configured as described above, when the input voltage Vin is supplied to the input terminal 1 from the outside, either the first switching element Q1 or the second switching element Q2 conducts like a multivibrator. For example, it is assumed that the first switching element Q1 is turned on first. Since the first switching element Q1 is turned on, a current flows through the primary winding N1, 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 first and second switching elements Q1 and Q2. Then, a forward bias is applied to the first switching element Q1, and a reverse bias is applied to the second switching element Q2, so that the first switching element Q1 is turned on and the second switching element Q2 is turned off. . The voltage induced at this time causes a resonance phenomenon in the resonance circuit formed by the resonance capacitor Co and the primary winding N1.

When the resonance phenomenon occurs, the voltage (resonance voltage) appearing between the terminals of the primary winding N1 changes in a sine wave shape. The first and second switching elements Q1 and Q2 are alternately turned on or off in accordance with the change in the resonance voltage appearing between the terminals of the primary winding N1, and thereafter, the self-oscillation operation continues. Will do.
In the power supply circuit having the circuit configuration as described above and performing the self-excited oscillation operation, the resonance voltage appearing in the primary winding N1 is directly supplied to the first and second switching elements Q1 and Q2. The feedback voltage for driving is used. Therefore, the number of circuit elements can be reduced, and a small and highly efficient power supply circuit can be obtained.

However, the following problems exist when the power supply circuit having the configuration shown in FIG. 2 is actually manufactured.
Can not be obtained a resonance voltage exceeding the gate-Tososu Withstand voltage _{V GS} of the MOSFET, the input voltage Vin is limited to withstand the voltage _{V GS} between the MOSFET gate and source of. That is, the gate-source withstand voltage V _GS of the MOSFET is generally 20 V or less, and practically as small as 10 V or less. Further, because of the limitation on the gate-source withstand voltage V _{GS of} the MOSFET, the circuit load (circuit operation Q) cannot be increased, and the distortion rate cannot be lowered.
In addition, the first and second switching elements Q1 and Q2 are directly driven by the resonance voltage, but the driving voltage applied to the gate of each switching element is not limited to the load side short circuit or the like when the load state changes. At the time of abnormality, it may change greatly with the change of the resonance voltage. Therefore, in the circuit of FIG. 2, constant voltage diodes Z1 and Z2 are used to protect the first and second switching elements Q1 and Q2, but the cost of the power supply circuit increases due to this protection measure. .

In order to solve such a problem, the inventor of the present application disclosed in Patent Document 1 that a resonant capacitor is constituted by a series circuit of a plurality of capacitor elements (C1, C2, C3), and predetermined capacitors are connected to the control terminal of each switching element. The circuit (FIG. 3- (a)) which connected these connection points is proposed. Further, in Patent Document 2, the resonance capacitor is configured by a series circuit of a plurality of capacitor elements (C1, C2, C3, C4), and a predetermined position of the resonance capacitor portion is connected to the ground, and feedback is supplied to each switching element. The circuit (FIG. 3- (b)) which connected the voltage to the control terminal through the capacitor | condenser of a part of resonance capacity is proposed.
As described above, Patent Document 1 and Patent Document 2 both have a resonance action and a voltage dividing action by connecting a plurality of resonance capacitors in series, and the voltage divided by the resonance capacitor is applied between the gate and the source of the MOSFET. It is something to try.

JP 11-164563 A Japanese Patent Laid-Open No. 11-252940

However, when the coil and the capacitor are connected in parallel and resonated, the voltage and current between both ends, that is, one end of the connection point between the coil and the plurality of capacitors and the connection point between the other coil and the capacitor are The phase difference is zero, and if the coil or capacitor is viewed individually, the phase on the capacitor side is advanced by 90 degrees and the phase on the coil side is delayed by 90 degrees according to the ratio between the connection points of the coil and the capacitor.
By the way, the oscillation action is generally caused by feeding back an output signal having the same phase as the input signal. However, the voltage divided from the resonance capacitor having a plurality of capacitors in series does not meet this condition and is stable. It is difficult to continue oscillation and it is inevitable from instability.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-described problems and to provide a resonant switching power supply having a high degree of design freedom and capable of stably performing a self-excited oscillation operation.

  In order to solve the above-described problem, a resonant switching power supply according to the present invention has a resonance capacitor connected in parallel to a primary winding of a transformer, and a first switching element and a second switching coil are respectively connected to winding ends of the primary winding. Switching elements are connected, a direct current is supplied between a common connection point of the main current paths of the two switching elements and a predetermined winding position of the primary winding, and an AC output obtained by a self-excited oscillation operation In the resonance type switching power supply that supplies the load to the load, the control terminals of the first switching element and the second switching element are respectively connected to the switching element on the opposite side via the first capacitor or the second capacitor that divides the applied voltage. Connected to the winding end side of the primary winding of the main current path, the common connection of the control terminals of the first switching element and the second switching element and the main current path of the two switching elements Characterized in that connecting the third capacitor or fourth capacitor for dividing each voltage applied to the point.

The resonant switching power supply of the present invention maintains a stable self-excited oscillation operation by obtaining a feedback signal for oscillation from both ends of the resonance capacitor, and prevents the switching element from being destroyed by a voltage dividing action by a plurality of capacitors. be able to. In addition, since the voltage applied between the gate and the source of the switching element can be applied with an arbitrary voltage equal to or lower than the withstand voltage V _GS (Max) between the terminals by the voltage dividing action by a plurality of capacitors, The source-to-source voltage application voltage is no longer limited by the inter-terminal withstand voltage V _GS (Max), and design is possible even when the input voltage is high. For the same reason, the settable range of the circuit load (circuit operation Q) is widened, the degree of design freedom is widened, and the distortion rate can be lowered.

  FIG. 1 shows an embodiment of a resonant switching power supply according to the present invention.

  In the present invention, a capacitor for dividing the applied voltage is connected to the control terminal of each switching element in the self-excited resonant power supply circuit of FIG. 2, an intermediate tap is provided on the secondary winding, and a full-wave rectifier circuit is added. Thus, parts corresponding to those of the conventional example in FIG.

In FIG. 1, an input terminal 1 is connected to an intermediate tap of a primary winding N1 of a transformer T via a choke coil L1. A resonance capacitor Co is connected as a resonance capacitor between the terminals of the primary winding N1, and both ends of the primary winding N1 are respectively connected to a first switching element Q1 and a second switching element made of a field effect switching element. The resistor R3 is connected to the ground via the main current path of the switching element Q2.
Here, the choke coil L1 is for preventing the inrush current of the circuit, and the resistor R3 prevents the inrush current of the circuit and sets the operating points (self-bias method) of the first and second switching elements Q1, Q2. This may be omitted depending on the specification.

The gates of the first and second switching elements Q1, Q2 are in the form of brushes, respectively, at the winding end opposite to the winding end of the primary winding N1 to which the main current path is connected, The resistor R1, the first capacitor C1, and the diode D3 are connected in parallel, or the resistor R2, the second capacitor C2, and the diode D4 are connected in parallel. Also, third and fourth capacitors C3 and C4 are connected between the gate sources of the first and second switching elements Q1 and Q2.
Here, the resistors R1 and R2 are for starting the first and second switching elements Q1 and Q2, and the first and third capacitors C1 and C3 or the second and fourth capacitors C2 and C4 are switching element protections. This is a voltage divider capacitor. The diodes D1 and D2 are used for speeding up the switching on / off transition of the switching elements Q1 and Q2, and it has been confirmed that the power conversion efficiency is improved by about 1 to 3%. May be omitted depending on the specifications.

  Then, full-wave rectifying diodes D1 and D2 and a smoothing capacitor C5 are connected to both ends of the secondary winding N2 of the transformer T and connected to the output terminal 2. The intermediate tap of the secondary winding N2 is connected to the ground.

  In the circuit configured as described above, when the input voltage Vin is supplied to the input terminal 1 from the outside, one of the first and second switching elements Q1 and Q2 conducts like a multivibrator. For example, it is assumed that the first switching element Q1 is turned on first. When the switching element Q1 becomes conductive, a current flows through the primary winding N1, 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 first and second switching elements Q1 and Q2. Then, a forward bias is applied to the first switching element Q1, and a reverse bias is applied to the second switching element Q2, so that the first switching element Q1 is turned on and the second switching element Q2 is turned off. . The voltage induced at this time causes a resonance phenomenon in the resonance circuit formed by the resonance capacitor Co and the primary winding N1.

  When the resonance phenomenon occurs, the voltage (resonance voltage) appearing between the terminals of the primary winding N1 changes in a sine wave shape. The first and second switching elements Q1 and Q2 are alternately turned on or off in accordance with the change in the resonance voltage appearing between the terminals of the primary winding N1, and thereafter, the self-oscillation operation continues. Will do. Then, the AC voltage appearing in the secondary winding N2 is rectified and smoothed, and the DC voltage Vo is output to the output terminal 2.

In the present invention, a stable self-oscillation operation is maintained by the resonant capacitor Co, and the voltage applied between the gate and source of the first and second switching elements Q1, Q2 is applied to the first, third capacitors C1, C3 or The voltage is divided according to the impedance (reactance) of the second and fourth capacitors C2 and C4, and the gate-source voltage is less than or equal to the withstand voltage V _GS (Max) between the terminals of the first and second switching elements Q1 and Q2. Since an arbitrary voltage can be applied, the gate-source voltage is not limited by V _GS (Max), and design is possible even when the input voltage Vin is high. For that reason, the settable range of the circuit load (circuit operation Q) is widened, the distortion can be lowered, the harmonics can be reduced, and the degree of freedom in design can be increased.

  In the above embodiment, the input / output is not insulated, but may be an insulated type. One ends of the third and fourth capacitors C3 and C4 are connected to the sources of the switching elements Q1 and Q2, respectively, but may be connected to the ground. The third and fourth capacitors C3 and C4 may be replaced with gate input capacitances that are parasitic on the switching elements Q1 and Q2.

The circuit diagram of the Example of the resonant type switching power supply by this invention Conventional Royer circuit Main circuit diagram (a, b) with improved conventional Royer circuit

Explanation of symbols

1 Input terminal 2 Output terminal Q1, Q2 Switching elements Co, C1, C2, C3, C4, C5 Capacitors D1, D2, D3, D4 Diodes R1, R2, R3 Resistor L1 Choke coil T Transformer

Claims (3)

A resonance capacitor is connected in parallel to the primary winding of the transformer, and a first switching element and a second switching element are connected to the winding ends of the primary winding, respectively. In a resonant switching power supply in which a direct current is supplied between a connection point and a predetermined winding position of a primary winding and an alternating current output obtained by a self-excited oscillation operation is supplied to a load.
The control terminals of the first switching element and the second switching element are respectively wound with the primary winding of the main current path of the opposite switching element via the first capacitor or the second capacitor that divides the applied voltage. A third capacitor or a fourth capacitor which is connected to the end side and divides the applied voltage at the common connection points of the control terminals of the first switching element and the second switching element and the main current path of the two switching elements. Resonant type switching power supply characterized by connecting. 2. The resonant switching power supply according to claim 1, wherein a parallel circuit of a resistor and a diode is connected in parallel with the first capacitor or the second capacitor. The resonant switching power supply according to claim 1, wherein the switching element is a MOSFET.

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