JPH0687656B2 - converter - Google Patents

Description

TECHNICAL FIELD The present invention relates to a converter used as a so-called switching power supply device.

[Conventional technology]

A switching power supply is a power supply system with excellent characteristics such as low loss, in which the DC input is switched at a specific frequency to convert it to AC, and the output voltage is adjusted according to the switching process by controlling the switching frequency and switching duty. In the past, it has been widely used in various electronic devices such as video tape recorders. However, along with the weight reduction and downsizing of electronic devices by the use of ICs, the volume ratio and weight ratio of switching power supply devices in electronic devices have increased, and there is a demand for downsizing and weight reduction.

Since the weight and volume of the switching power supply device are determined by the lowest switching frequency, in order to increase the size of the switching power supply without lowering the conversion efficiency, it is necessary to increase the switching frequency. It is necessary to plan.

[Problems to be Solved by the Invention]

By the way, in a switching power supply device that adjusts the output voltage by changing the switching frequency even when the switching frequency is increased, the controllability of the switching frequency has a limit in increasing the switching frequency. This hinders weight reduction and size reduction.

2. Description of the Related Art Conventionally, there has been proposed a resonant converter in which a high-frequency switching frequency is fixed and a resonant frequency is changed by using a variable capacitance circuit or a variable inductance circuit to adjust a voltage. Resonant converter has low switching loss,
It has characteristics such as low noise and has favorable characteristics as a power source for electronic devices, but conventional ones cannot achieve weight reduction and downsizing due to the large number of parts and complicated circuits. It was

Therefore, an object of the present invention is to provide a converter that has a high switching frequency, a reduced number of parts, and a simplified circuit, thereby achieving weight reduction, downsizing, and high efficiency.

[Means for Solving the Problems]

As illustrated in FIG. 1, the converter of the present invention is provided with a DC power supply that generates an input voltage to be converted and a DC power supply that is connected in parallel and that has a control input terminal and has a capacitance that changes according to the control voltage. Connected in series between the first and second variable capacitance capacitors made of variable capacitance multilayer ceramic capacitors, and the control voltage is connected between the control input terminals of the first and second variable capacitance capacitors. A control power source applied between them, a series connection of first and second transistors connected in parallel with the series connection of the first and second variable capacitors, and the first and second transistors individually. A switching pulse generating means for applying a switching pulse to alternately switch the first or second transistor; An inductor and an inductor that are connected between a connection point of series connection of a second transistor and a connection point of series connection of the first and second variable capacitors and form a resonance circuit with the first and second capacitors. A series connection with a transformer that is connected in series with the resonance circuit to extract an AC output, and a DC regenerating unit that rectifies the AC output extracted from the transformer to extract a DC output and supplies the DC output to a load. And comparing the output voltage taken out by the DC regenerating means with a reference voltage, taking out a comparison output representing the magnitude relation, and comparing means for controlling the control voltage generated by the control power supply from the comparison output. It is characterized by

[Work]

In the converter according to the present invention, the variable capacitor can have a capacity corresponding to the control voltage. Therefore, when the control voltage is changed, the charge amount according to the capacity obtained by the control voltage is accumulated. Therefore, when a DC input is applied to a variable capacitor whose capacitance is set by the control voltage, the amount of charge is accumulated by the DC input, and the amount of charge is proportional to the DC input and is a function of the control voltage. Becomes

When a resonance circuit is configured with such a variable capacitance capacitor and an inductor having a specific inductance and a switching element installed between the variable capacitance capacitor and the inductor is subjected to high frequency switching, when the switching element is in the cutoff state, When the variable capacitance is charged by the DC input and the switching element is in the conductive state, the electric charge of the variable capacitance is supplied to the inductor.

When the resonance frequency of the resonance circuit is set higher than the switching frequency of the switching element, when the switching element becomes conductive, electric charge is transferred between the variable capacitor and the inductor in the resonance circuit to cause the vibration phenomenon. Which results in a sinusoidal alternating current. Such a resonance operation is performed in each conduction section of the switching element because the variable capacitor is charged in the interruption section of the switching element.

Further, the AC output obtained by the resonance circuit is rectified by the DC regeneration circuit and taken out as a DC regeneration output, supplied to the load, and added to the capacity control circuit. Then, in the capacitance control circuit, a control voltage is formed based on the direct current reproduction output, and thus the capacitance of the variable capacitance capacitor is controlled by this control voltage.

Therefore, even if the DC reproduction output fluctuates due to the relationship with the load or other causes, the control voltage is formed so as to compensate for it, and the capacity of the variable capacitor is increased or decreased.
The resonance frequency is adjusted and a stable direct-current regeneration output is extracted.

Further, in the converter of the present invention, the first and second switching elements are installed corresponding to the first and second variable capacitors, and the first and second switching elements are alternately switched, so that the resonance The operation is alternately performed in the resonance circuit including the first and second variable capacitors and the inductor. In other words, in the commonly used inductor, the resonance operation is continuously performed between the inductor and the first or second variable capacitance capacitor regardless of the switching frequency, and the AC output is extracted. Therefore, in this converter, high efficiency is achieved.

And, in the present invention, by using the variable capacitance monolithic ceramic capacitor for the variable capacitance capacitor,
Capacitance corresponding to the control voltage can be obtained with high precision, and highly accurate regulation operation can be obtained by varying the capacitance.

〔Example〕

 FIG. 1 shows an embodiment of the converter of the present invention.

For example, a battery 4 is used as a DC voltage source at the input terminals 2A and 2B.
Are connected and an input voltage Ei is applied as a DC input.
This input voltage Ei is applied to the first and second variable capacitors 61 and 62 connected in series, and when the variable capacitors 61 and 62 are set to have a capacitance C, the DC voltage of the variable capacitors 61 and 62 is reduced. The bias voltage V _B becomes Ei / 2.

The variable capacitors 61 and 62 have the main electrodes 6a and 6b facing each other.
A capacitance control electrode 6c is provided between the capacitors, and a capacitor whose capacitance between the main electrodes 6a and 6b changes according to a control voltage V _C applied to the capacitance control electrode 6c is used.
A control voltage V _C is applied from the control voltage source 82 of the capacitance control circuit 8 between the capacitance control electrodes 6c of 1 and 62.

An inductor 10 having a specific inductance for forming a resonance circuit with each of the variable capacitors 61, 62 is installed, and an n-channel enhancement type is used as the first and second switching elements connected in series. MOS-FETs (hereinafter simply referred to as FETs) 121 and 122 are installed. In addition, the inductor 10 includes a primary coil 14 of a transformer 14 as a means for extracting an AC output obtained by a resonance circuit.
P is connected in series.

The switching pulse generation circuit 18 is connected to the gates of the FETs 121 and 122 through switching input terminals 16A and 16B. The switching pulse generation circuit 18 has
In order to realize high-frequency switching, a pulse oscillator that generates a high-frequency pulse and a rectangular wave pulse with a duty of 50% is used. One pulse output is inverted through an inverter. , B, the switching pulses S _A and S _B having mutually inverted phases are obtained.

Therefore, when the switching pulse S _A shown in A of FIG. 2 is applied to the switching input terminal 16A and the switching pulse S _B shown in B of FIG. 2 is applied to the switching input terminal 16B,
Each of the FETs 121 and 122 is conductive during the H level section of the switching pulses S _A and S _B , and is in the cutoff state during the L level section.
The FETs 121 and 122 alternately repeat the conductive state and the cutoff state.

When the FET 121 becomes conductive, as shown in FIG. 3A, the resonance circuit 21 is formed by the variable capacitors 61 and 62 and the inductor 10.
Since the FET 122 is in the cutoff state at this time, the battery 4 is connected to the variable capacitor 62 through the primary coil 14P of the transformer 14 and the inductor 10, and charging is performed by the input voltage Ei.

Further, when the FET 122 becomes conductive, as shown in FIG. 3B, the resonance circuit 22 is constituted by the variable capacitors 61 and 62 and the inductor 10. At this time, the FET 121 is in the cut-off state, so that it is variable. The battery 4 is connected to the capacitive capacitor 61 through the primary coil 14P of the transformer 14 and the inductor 10, and is charged by the input voltage Ei. That is, when the resonance circuit 21 is established, the accumulated charge of the variable capacitor 61 accumulated when the resonance circuit 22 is established is discharged through the inductor 10, and when the resonance circuit 22 is established, the resonance circuit 22 is formed. The accumulated charge of the variable capacitor 62 accumulated when the condition 21 is satisfied is released through the inductor 10.

By the way, for the capacitance C of the variable capacitors 61 and 62,
When the inductance of the inductor 10 is L, the resonance frequency f _R is Becomes

Then, assuming that the resonance frequencies f _R of the resonance circuits 21 and 22 are set to be higher than the switching frequencies f _S of the FETs 121 and 122, the variable capacitance capacitor 61 and the variable capacitance capacitors 61 and 122 during each conduction time of the FETs 121 and 122. 62 and inductor 10
A vibration phenomenon occurs due to the exchange of electric charges between and. As a result, the FET 121 has an alternating current I _AC1 corresponding to the H level section of the switching pulse S _A as shown in C of FIG. 2, and the FET 122 has a switching current of _AC as shown in D of FIG. pulse S AC current I _AC2 corresponding to H level section of the _B flows. The combined current I _AC (= I _AC1 + I _AC2 ) flows through the inductor 10 and the primary coil 14P of the transformer 14.
When the capacitance C of the variable capacitors 61 and 62 is changed, the waveform changes as indicated by a dotted line in C and D of FIG. 2, and the peak value of the alternating current I _AC changes as indicated by E of FIG. To do. Along with this, the peak value of the voltage applied to the primary coil 14P of the transformer 14 changes. From the secondary coil 14S, a continuous AC voltage E _AC corresponding to the transformation ratio 1: n is obtained. In addition,
The peak value of this AC voltage E _AC depends on the ratio between the switching frequency f _S and the resonant circuit frequency f _R. This AC voltage E _AC is applied to the bridge rectifier circuit 240 of the DC regenerating circuit 24 to perform full-wave rectification. This full-wave rectified output is added to the smoothing capacitor 242, the pulsating component in the rectified output is removed by the smoothing capacitor 24, and the smoothing capacitor
A stable DC regenerative output voltage E _O is obtained between the terminals of 242. This output voltage E _O is applied to the output terminals 26A and 26B.
And is supplied to the load 28.

Further, the output voltage E _O is applied to the error amplifier 84 installed in the capacitance control circuit 8, and the reference voltage E _REF from the reference voltage source 86 is added.
Compared to. In the error amplifier 84, the output voltage E _O is compared with the reference voltage E _REF, and the error voltage Er representing the difference voltage between the output voltage E _O and the reference voltage E _REF is obtained together with the polarity according to the magnitude relationship. This error voltage Er is used as an adjustment input of the control voltage V _C of the control voltage source 82 by superimposing the DC bias voltage E _BIAS by the voltage source 88 installed on the output side of the error amplifier 84.

By the way, it is assumed that variable capacitance monolithic ceramic capacitors are used for the variable capacitance capacitors 61 and 62, and for example
As shown in the figure, when the voltage V _B is applied to the main electrodes 6a and 6b through the main electrode terminals 7A and 7B and the control voltage V _C is applied to the capacitance control electrode 6c through the control input terminal 7C, the experimental results are Shown in the figure. In FIG. 5, L ₁ shows V _B = 0 and L ₂ shows V _B = 20 V, but in any case, the control voltage V _C can continuously change the capacitance C.

Therefore, when the control voltage V _C is adjusted by the error voltage Er, the control voltage V _C
Set capacitance C in accordance with the results in the accumulation of charge corresponding to the capacitance C is performed, the control voltage AC output corresponding to V _C is applied to the DC restorer circuit 24, an output corresponding to the control voltage V _C The voltage E _O is obtained. That is, the output voltage E _O, since it is adjusted by the ratio between the switching frequency f _S and the resonance frequency f _R, by changing the capacitance C of the variable capacitor 61, the adjustment of the output voltage E _O lines It will be stabilized.

In the embodiment, with respect to the two variable capacitors 61 and 62,
Since the FETs 121 and 122 are installed as two switching elements, by alternately switching the FETs 121 and 122, the inductor 10 has a continuous variable capacitor 61,
By exchanging the electric charge with 62, a resonance operation is performed, and the output voltage E _O can be taken out with high efficiency. Needless to say, the output voltage can be adjusted in the same manner even if a single variable capacitance capacitor is used to perform a switching operation separately from the embodiment.

Then, the capacitance control circuit 8 as the capacitance control feedback circuit is disconnected, and the variable capacitance multilayer ceramic capacitors are used for the variable capacitance capacitors 61 and 62, and the switching frequency f _{S is set} to 10
Fig. 6 shows the experimental results when the input voltage Ei was set to 40V at 0KHz. In this case, the turns ratio n of the transformer 14
Is set to n = 1, and in FIG. 6, L ₁ is
V _C = 20V, L ₂ shows the case where V _C = 60V, −20V, L ₃ shows the case where V _C = 100 V, −60V, and I ₀ represents the load current flowing through the load 28.

According to the experiment, a DC bias voltage V _B of Ei / 2 = 20V is applied to each of the variable capacitors 61 and 62, and the maximum value of the capacitance C of the variable capacitors 61 and 62 is the control voltage V _C = 20.
Obtained at V. Therefore, the load characteristics for two control voltages V _C that are positive and negative and are separated by the same amount around V _C = 20 V are the same, and almost no current flows in the DC control voltage group between each control input terminal 7C. Was confirmed. As a result, no power loss occurs in the DC control voltage loop.

As is clear from the results of this experiment, by using the laminated ceramic capacitor as the variable capacitor, the output voltage adjusting operation can be realized with high accuracy.

Although the variable capacitance multilayer ceramic capacitor has been described as an example of the variable capacitance capacitor in the embodiments, the converter can be configured by using a variable capacitance element other than the ceramic capacitor. It is not limited to the variable capacitance monolithic ceramic capacitor.

〔The invention's effect〕

As described above, according to the present invention, the switching frequency is increased and the resonance circuit is configured by using the variable capacitor, and the resonance frequency is controlled by the capacitance change of the variable capacitor. Can be reduced and the circuit can be simplified, and the weight and the size can be reduced.

Further, according to the present invention, for the first and second variable capacitors, a common inductor is used to form a resonance circuit, and the first and second switching elements perform a switching operation alternately. 1 and 2
Since the variable capacitors of are alternately charged and discharged,
By reducing the number of parts and simplifying the circuit, in addition to the reduction in weight and size, the conversion efficiency can be improved and high efficiency can be realized.

Further, according to the present invention, since the variable capacitance multilayer ceramic capacitor is used as the variable capacitance capacitor,
It is possible to realize a converter in which the capacitance can be changed with high precision by the control voltage and the output voltage can be adjusted with high precision using the variable capacitance.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a converter of the present invention,
2 is a diagram showing the operation of the converter shown in FIG. 1, FIG. 3 is a circuit diagram showing the operation of the converter shown in FIG. 1,
4 is a diagram showing a basic circuit of a variable capacitor in the converter shown in FIG. 1, FIG. 5 is a diagram showing an experimental result in the basic circuit of the variable capacitor shown in FIG. 4, and FIG. It is a figure which shows the experimental result in the converter shown in a figure. 4 …… Battery (DC power supply) 10 …… Inductor 14 …… Transformer 18 …… Switching pulse generation circuit 24 …… DC regeneration circuit (DC regeneration means) 61 …… First variable capacitor 62 …… Second variable Capacitor 82 …… Control voltage source 84 …… Comparator (comparing means) 121 …… MOS-FET (first transistor) 122 …… MOS-FET (second transistor)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Fumiyuki Fujiwara, 1-167, Higashi-Ome, Ome-shi, Tokyo Within Japan Chemi-Con, Inc. (72) Inventor, Haruhiko Matsushita, 1-167, Higashi-Ome, Ome, Tokyo Japan (56) References JP-A-63-77377 (JP, A) JP-A-57-46673 (JP, A) JP-A-56-35679 (JP, A) JP-A-59-44177 (JP , A) JP-A-63-128618 (JP, A)

Claims (1)

[Claims] 1. A first direct current power source for generating an input voltage to be converted, and a variable capacitance monolithic ceramic capacitor which is connected in parallel with the direct current power source and has a control input terminal and whose capacitance changes according to the control voltage. And a second variable capacitance capacitor connected in series; a control power supply connected between the control input terminals of the first and second variable capacitance capacitors to apply the control voltage between the control input terminals; And a series connection of the first and second transistors connected in parallel with the series connection of the second variable capacitance capacitor, and a switching pulse is applied to each of the first and second transistors to provide the first or second transistor. A switching pulse generating means for alternately switching the second transistor, and a series connection of the first and second transistors. An inductor that forms a resonance circuit with the first and second capacitors, and an inductor that is connected in series with the inductor and is connected between the connection point and a connection point of the series connection of the first and second variable capacitors; A series connection with a transformer for extracting an AC output to the resonance circuit, DC output means for rectifying the AC output output from this transformer to output a DC output and supplying the DC output to a load, and a DC output means for outputting the DC output. The output voltage and the reference voltage are compared, a comparison output indicating the magnitude relationship is taken out, and the comparison output controls the control voltage generated by the control power supply. .