JP2606635Y2 - Voltage resonant converter - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a voltage resonance converter used for a switching power supply or the like.

[0002]

2. Description of the Related Art FIG. 8 shows a circuit called an inductance commutation-side converter generally known as a voltage resonance converter. This circuit, MOS F between the input power supply V _in the input circuit input-side ground GND
A series circuit of a first switch element Q1 made of ET and a second switch element Q2 is interposed. Opposite diodes D1 and D2 are connected in parallel to these switch elements Q1 and Q2, respectively. Further, a first capacitor C11 is connected in parallel to the first switch element Q1, and a series circuit of a first inductor L11 and a second capacitor C12 is connected between both ends of the first capacitor C11. ing. Further, a series circuit of a second inductor L12 and a third capacitor C13 is connected between both ends of the series circuit. One end of the third capacitor C13 is connected to the ground GND, and the other end is an output terminal V _OUT .

The control circuit 14 controls the on / off timing and pulse width of the first and second switch elements Q1 and Q2 so that the output voltage taken out from the output terminal V _OUT becomes constant.

In this type of voltage resonance converter, both the switching elements Q1 and Q2 can perform zero voltage switching (perform on / off switching operation when the applied voltage is zero voltage), and the switching loss is eliminated. Thus, the control of the switch elements Q1 and Q2 can be performed at a fixed frequency. Further, the switching elements Q1 and Q2 are connected to the input power supply V.
since they are connected in series between _in and ground GND, and the peak voltage applied to the switch elements Q1, Q2 is used as the input voltage of the input power supply V _in, the switching elements Q1, Q2 MO
When configured with an SFET (field effect transistor),
Since it is not necessary to increase the withstand voltage of the switch elements Q1 and Q2, the on-resistance of the switch is reduced and the circuit efficiency is improved.

[0005]

However, in the voltage-resonant converter having the above-described structure, the voltage A between the input side and the output side is high.
There was a problem that it was not possible to meet the general requirements for a switching power supply to perform C insulation.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a highly efficient voltage resonance converter capable of performing AC insulation between an input side circuit and an output side circuit. Is to provide.

[0007]

The present invention is configured as follows to achieve the above object. That is, the primary side of the transformer is used as an input circuit, the secondary side of the transformer is used as an output circuit, and the first circuit is connected between the input power supply of the input circuit and the ground.
A series circuit of a switch element and a second switch element is interposed. A first diode is connected to the first switch element, and a second diode is connected to the second switch element in parallel in opposite directions. In addition, a first capacitor is connected in parallel on the equivalent circuit to the first switch element, and between the ground and either side of the input power supply and the connection portion of the first and second switch elements. Is connected to a series circuit of a primary coil of the transformer and a second capacitor. On the output circuit side, a series circuit of a secondary coil of the transformer and a third capacitor is connected to both ends of a third diode. At the same time, an LC smoothing circuit is connected to the third diode, and a first inductor is connected in series on an equivalent circuit to at least one of the primary coil and the secondary coil of the transformer. It is characterized in that there.

[0008]

According to the present invention, when the output voltage of the output circuit decreases, the ON period of the second switch element is controlled to be long and the ON period of the first switch element is controlled to be short. By this switch control, the energy stored in the inductor of the LC smoothing circuit during the ON period of the second switch element increases, and the decrease in output voltage is compensated for, and the output voltage is stabilized.

On the other hand, when the output voltage increases, the on-period of the second switch element becomes shorter, and the on-period of the first switch element becomes longer. The energy stored in the inductor of the LC smoothing circuit during the period decreases, and acts in a direction to offset the increase in the output voltage, thereby stabilizing the output voltage.

Also, since a transformer is interposed between the input circuit and the output circuit, A
C insulation is completely achieved.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the first embodiment of the voltage resonance converter according to the present invention.
Is shown. In this figure, the transformer T
The primary side of the transformer T1 is an input circuit, and the secondary side of the transformer T1 is an output circuit.

[0012] Between the input side ground GND1 and the input power supply V _in the input circuit and the first switching element Q1 consisting MOS FET series circuit of the second switching element Q2 is interposed. Opposite diodes D1 and D2 are connected in parallel to these switch elements Q1 and Q2, respectively. A first capacitor C1 is connected in parallel to the first switch element Q1, and both ends of the first capacitor C1, that is, each switch element Q1,
The series circuit of the first inductor L1, the primary coil N1 of the transformer T1, and the second capacitor C2 is connected between the connection point of Q2 and the ground GND1. The capacity of the second capacitor C2 is sufficiently larger than that of the first capacitor C1.

On the output circuit side, a series circuit of the secondary coil N2 of the transformer T1 and the third capacitor C3 is connected between both ends of the third diode D3, and furthermore, both ends of the third diode D3. An LC formed between a series circuit of the second inductor L2 and the fourth capacitor C4
The smoothing circuit 10 is connected. The output side of the LC smoothing circuit 10 is connected between both ends of the fourth capacitor C4, that is, the output terminal V _OUT of the output circuit and the output side ground GND2.
A series circuit of resistors R1 and R2 is connected therebetween, the output voltage of the output circuit is divided by the resistors R1 and R2, and the detection voltage is applied to the control circuit 14.

FIG. 2 shows an example of a circuit configuration of the control circuit 14. As shown in FIG. The triangular wave generating circuit 3 shown in FIG.
A triangular wave is generated and output as shown in FIG. The triangular wave is provided with a reference voltage V _ref1 for producing a drive voltage of the first switch element Q1 and a reference voltage V _ref2 for producing a drive voltage of the second switch element Q2.
The drive voltage of the switch element Q2 is produced with a pulse width having a portion where the triangular wave is convex above the reference voltage V _ref2, and a width where the triangular wave is convex below the reference voltage V _ref1. The pulse width of the first switch element Q
One drive voltage is produced.

The control circuit 14 operates as follows. In FIG. 2, when the output voltage V _out of the output circuit increases, the current I ₁ flowing from the resistor R3 to the photocoupler PC1 increases, and the current I ₂ flowing from the resistor R4 to the photocoupler PC1 via the resistor R5. Increase. This increase in current causes the voltage V at the junction of resistors R4 and R5 to
_s decreases. This reduction in voltage V _s, the level of the triangular wave is reduced. Then, as a result, the width at which the convex portion above the triangular wave cuts off the reference voltage V _ref2 is reduced, so that the pulse width of the drive voltage of the switching element Q2 is reduced. On the other hand, the width of the portion that protrudes below the triangular wave cuts off the reference voltage _Vref1 , so that the pulse width of the drive voltage of the switch element Q1 increases.

Conversely, when the voltage _Vout on the output circuit side decreases, the level of the triangular wave increases, so that the pulse width of the drive voltage of the switch element Q2 increases, and the pulse width of the drive pulse of the switch element Q1 decreases. Narrows. As described above, the control circuit 14 variably controls the pulse width of the drive pulse of the switch elements Q1 and Q2 according to the increase and decrease of the output voltage.

This embodiment is configured as described above.
Next, the circuit operation will be described based on the equivalent circuit of FIG. 5 and the time chart of FIG. Note that this equivalent circuit assumes that the winding ratio of the primary coil N1 and the secondary coil N2 of the transformer T1 is N2 / N1 = 1, and that the second, third, and Fourth capacitors C2 and C
3 and C4 are assumed to be constant voltage sources in the steady state, and the voltage sources of the second, third and fourth capacitors C2, C3 and C4 and their respective voltages are denoted as VC2, VC3 and VC4. . Further, it is assumed that the inductance LN1 of the primary coil N1 of the transformer T1 is ∞. R0 is a load resistance.

In this equivalent circuit, in the initial state at t = t ₀ , the current flowing through the first inductor L 1 is zero, the first switch element Q 1 is turned on, and the second switch element Q 2
Is off. Further, the second and third capacitors C
VC2 and VC3 are applied to VC2 and VC3, respectively, so that VC2> VC3. In the period from t ₀ to t ₁ shown in FIG. 5A, the voltage sources VC2 and V
C3 causes a current IL1 to flow from the first inductor L1 in the direction of the first switch element Q1 (this direction is referred to as a negative direction), and this current increases in accordance with the linear slope of (VC2-VC3) / L1. The electromagnetic energy is stored in the inductor L1. On the LC smoothing circuit 10 side, a current ID3 flows from the third diode D3 toward the second inductor L2 due to the electromagnetic energy stored in the second inductor L2.

Next, in t = t _1, when the first switching element Q1 is turned off, for electromagnetic energy stored in the first inductor L1, the first inductor L1 and the second diode D2 go through the current IL1 flows sequentially to the input power supply V _in, in t ₁ ~t ₂ period this current IL1 is
It decreases with a linear gradient of _{(V in + VC3-VC2)} / L1. By turning on the second switch element Q2 while the IL1 is flowing, zero cross switching (zero voltage switching) is achieved.

Next, in t = t _2, the current IL1 becomes zero, this time the input power source V _in the second switching element Q2, the first inductor L1, the direction (which go through the second inductor L2 Current starts flowing in the positive direction).
current IL1 in t ₂ ~t ₃ period, (V _in + VC3-V
C2) It increases according to the linear slope of / LI. Also, L
Since the current flowing through the second inductor L2 of the C smoothing circuit 10 is substantially constant in the steady state as shown in FIG. 4G, the current ID3 flowing from the third diode D3 to the second inductor L2 is As described above, the current is reduced by the amount of current flowing from the first inductor L1 to the second inductor L2.

Next, in t = t _3, the current ID3 becomes zero, the second switching element Q2 from the input power source V _in, the first inductor L1, current IL1 in a direction passing through the second inductor L2 flows, t ₃ ~t ₄ current flowing through the second inductor L2 during _{period, (V in + VC3-VC2} -V
C4) / increases slightly according to the linear slope of (L1 + L2). The t ₃ ~t ₄ respectively electromagnetic energy by the current IL1 from the first inductor L1 to the second inductor L2 during the period is stored.

Next, in t = t _4, when the second switching element Q2 is turned off, the electromagnetic energy stored in the first inductor L1, a first diode D1
From the current IL1 flows in the first inductor L1 direction, the current IL1 is during t ₄ ~t ₅ period, (VC2-
VC3) / L1. IL
The current ID3 flows from the third diode D3 toward the second inductor L2 due to the energy stored in the second inductor L2 on the side of the LC smoothing circuit 10 by an amount corresponding to the decrease of 1.

By turning on the first switch element Q1 while the current IL1 is flowing from the first diode D1 to the first inductor L1, the switch element Q1 is turned on.
Is achieved.

When the current IL1 decreases and becomes zero, the circuit returns to the initial state, and the circuit operation is continued by repeating the operations (a) to (e) in FIG.

According to the circuit of this embodiment, when the voltage V _{OUT of the} output circuit decreases, the control circuit 14
The pulse width of the drive voltage of the switching elements Q1 and Q2 is controlled so that the ON period of the switching element Q2 is made longer and the ON period of the first switching element Q1 is made shorter. As described above, when the ON period of the second switch element Q2 is controlled to be longer,
Since the period during which the electromagnetic energy is accumulated in the second inductor L2 becomes longer, the output voltage is controlled to increase,
The drop in the output voltage is compensated for, and the output voltage is stabilized.

Conversely, when the output voltage V _OUT of the output circuit increases, the control circuit 14 causes the second switch element Q2
The pulse width of the drive voltage of the switching elements Q1 and Q2 is controlled such that the ON period of the first switching element Q1 is shortened and the ON period of the first switching element Q1 is lengthened. With this pulse width control,
Since the period during which the electromagnetic energy is stored in the second inductor L2 decreases, the output voltage is controlled to decrease,
As a result, the rise of the output voltage is subtracted,
The output voltage is controlled to be constant.

In this embodiment, by utilizing these phenomena, the pulse width control of the switching elements Q1 and Q2 can be realized at a fixed frequency, and the zero-voltage switching operation of the switching elements Q1 and Q2 becomes possible. As a result, switching loss is reduced and switching noise hardly occurs. Further, since the first switching element Q1 series circuit of the second switching element Q2 is interposed between the input power supply V _in the input ground GND1, switching element Q1,
Without voltage higher than the input power supply V _in is applied to the Q2, it can be relatively small breakdown voltage of the switching elements Q1, Q2. Therefore, even if the switch elements Q1 and Q2 are constituted by MOS FETs, the on-resistance can be reduced, and the switch elements Q1 and Q2 can be reduced.
In combination with the zero-voltage switching of 2, the circuit efficiency can be significantly increased.

Further, in this embodiment, since the transformer T1 is incorporated between the input circuit and the output circuit, AC insulation is achieved between the input circuit and the output circuit.

FIG. 6 shows a second embodiment of the present invention. This embodiment has a configuration in which a first inductor L1 is connected in series to a secondary coil N2 of a transformer T1, and other configurations are the same as those of the first embodiment. The circuit of this embodiment also performs a circuit operation similar to that of the first embodiment, and can provide the same effects as those of the first embodiment.

FIG. 7 shows a third embodiment of the present invention. The difference between this embodiment and the first embodiment is that the winding direction of the secondary coil N2 of the transformer T1 is reversed, and the other configuration is the same as that of the first embodiment. In this embodiment, the period when the electromagnetic energy is stored in the second inductor L2 is the second switch element Q2.
, The ON period of the first switch element Q1. Further, the waveform of the current flowing through the first inductor L1 is also positive / negative symmetric with the case of the first embodiment, but the principle of the circuit operation is almost the same as that of the first embodiment. In the case of the configuration of the third embodiment, if the on-period of the first switch element Q1 is controlled to be longer and the on-period of the second switch element Q2 is shortened, the output voltage becomes higher. On the contrary, the output voltage is lowered by controlling the on-period of the first switch element Q1 to be shorter and the on-period of the second switch element Q2 to be longer.

The present invention is not limited to the above embodiments, but can take various embodiments. For example, in the above embodiments, the switch elements Q1 and Q2 are configured using MOS FETs, but may be configured using other switch elements such as bipolar transistors, for example.

Although the first capacitor C1 is configured using external circuit components, the first capacitor C1 is different from the first capacitor C1 when the switching elements Q1 and Q2 are configured by MOS FETs.
Since the OSFET itself has an output capacitance, this output capacitance may be used as the first capacitor C1.
In this case, on an equivalent circuit, the output capacitance C1 is a circuit connected in parallel with the switch element Q1.

Further, in each of the above embodiments, the inductor L1
Is constituted by external components, but may be constituted by using only the leakage inductance of the transformer T1. In this case, on the equivalent circuit, an inductor L1 having leakage inductance is connected in series with the primary coil N1 and the secondary coil N2 of the transformer T1.

Further, in the above embodiment, the series circuit of the first inductor L1, the primary coil of the transformer T1, and the second capacitor C2 is connected to the ground GND1 and the connection between the first and second switch elements Q1, Q2. was connected between the input supply V _in the first, it may be connected between the connection portion of the second switching element Q1, Q2.

Further, in the above embodiment, the first inductor L1 is connected in series on an equivalent circuit to one side of the primary coil N1 or the secondary coil N2 of the transformer T1, but the first inductor L1 is connected in series with the secondary coil N2. An inductor may be connected to both in series on an equivalent circuit.

[0036]

According to the circuit of the present invention, since both the first switch element and the second switch element can perform zero voltage switching, the switching power loss is reduced, the circuit efficiency is increased, and the switching efficiency is improved. No noise is generated. Further, the pulse width of the first and second switch elements can be controlled at a fixed frequency. Further, since the first and second switch elements are connected in series and provided between the input power supply and the ground, the peak voltage applied to each switch element is the voltage of the input power supply, and therefore, the switch elements are relatively relatively switched. In particular, when the switching element is configured using a MOS FET, the on-resistance is reduced by the reduced withstand voltage, and the zero-voltage switching of the switching element becomes possible. Together with this, the efficiency of the circuit operation can be significantly improved.

Further, since a transformer is interposed between the input circuit and the output circuit, the AC circuit on the input circuit side and the output circuit side
Insulation is achieved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a first embodiment of the voltage resonance converter of the present invention.

FIG. 2 is an explanatory diagram of a switch control circuit used in the voltage resonance converter of the present embodiment.

FIG. 3 is a time chart showing operation waveforms of the switch control circuit.

FIG. 4 is a time chart of waveforms of respective parts showing an operation state of the voltage resonance converter in the embodiment.

FIG. 5 is an explanatory diagram showing each circuit operation of the embodiment using an equivalent circuit.

FIG. 6 is a circuit diagram showing a second embodiment of the present invention.

FIG. 7 is a circuit diagram showing a third embodiment of the present invention.

FIG. 8 is a circuit diagram showing a conventional voltage resonance converter.

[Explanation of symbols]

 10 LC smoothing circuit Q1 First switch element Q2 Second switch element T1 Transformer D1 First diode D2 Second diode D3 Third diode C1 First capacitor C2 Second capacitor L1 First inductor

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02M 3/335 H02M 3/28 H02M 7/48

Claims (1)

(57) [Scope of request for utility model registration] 1. A primary side of a transformer is an input circuit, a secondary side of the transformer is an output circuit, and a series circuit of a first switch element and a second switch element is interposed between an input power supply of the input circuit and ground. A first diode is connected to the first switch element, a second diode is connected to the second switch element in reverse parallel, and the first diode is connected to the first switch element.
A first capacitor is connected in parallel on the equivalent circuit to the switch element, and the primary coil of the transformer is connected between one of the ground and the input power supply and the connection between the first and second switch elements. And a series circuit of a second capacitor is connected. On the output circuit side, a series circuit of the secondary coil of the transformer and the third capacitor is connected to both ends of a third diode. LC
A voltage resonance converter to which a smoothing circuit is connected and a first inductor is connected in series on an equivalent circuit to at least one of the primary coil and the secondary coil of the transformer.