JP3488453B2 - Transformer and transformer controller - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transformer device and a transformer control device capable of performing transformation with high transformation efficiency even when an input voltage or a load fluctuates.

[0002]

2. Description of the Related Art There are AC adapters that enable electric appliances to be used in a plurality of countries having different power supply voltages and frequencies. Such an AC adapter uses an electromagnetic transformer as a converter. The piezoelectric transformer has a unique resonance frequency determined by its length and shape. Mechanical vibration (resonance) is caused by the inverse piezoelectric effect by applying an AC voltage of its own resonance frequency to the primary side of such a piezoelectric transformer.
Cause On the secondary side, this mechanical vibration is converted into an electric signal again by the piezoelectric effect, and a voltage is generated. The resonance frequency of the piezoelectric transformer includes a λ / 2 mode in which the displacement is minimum in the center of the element, a λ mode in which there are two positions in which the displacement is minimum, or a higher-order 3 / 2λ mode. In addition, depending on the shape of the element, there are a plurality of vibration modes such as lateral, width, thickness slip, and disk spreading, and each vibration mode has its own resonance frequency. Piezoelectric transformers generally have the highest transformation ratio and conversion efficiency near the resonance point. As shown in FIG. 4, the piezoelectric transformer converter controls the output voltage by controlling the frequency by utilizing the characteristic of the piezoelectric transformer that the output voltage is changed according to the frequency. Piezoelectric transformers have the advantages of higher energy density, higher frequency and smaller size, and less electromagnetic noise than electromagnetic transformers, and have recently attracted attention as new converter materials. At present, one that has been put into practical use is an inverter for a cold cathode fluorescent lamp of a liquid crystal backlight.

[0003]

However, since the piezoelectric transformer has a plurality of resonance points as shown in FIG. 4, when it is used for an AC adapter or the like in which the input voltage and the load fluctuate, the frequency control is performed. There is a problem that it becomes difficult to perform efficient conversion by increasing the width and straddling the next resonance point, making it impossible to control the output to be constant, and moving away from the resonance point. In FIG. 4, the horizontal axis represents the frequency f (k) of the AC voltage input to the piezoelectric transformer.
Hz), and the vertical axis represents the amplitude (V) of the AC voltage output from the piezoelectric transformer. This is because the piezoelectric transformer has the highest input / output gain and conversion efficiency in the vicinity of the resonance frequency, and the input / output gain and conversion efficiency decrease as it deviates from the resonance frequency. Also, if the input voltage to the piezoelectric transformer becomes higher in the same frequency, the output voltage will also become higher.Therefore, it is necessary to change the frequency to keep the output voltage constant. There is a problem in that the voltage conversion efficiency may decrease.

The present invention has been made in view of the above-mentioned prior art, and an object of the present invention is to provide a transformer device and a transformer control device capable of performing transformation with high transformation efficiency even when the input voltage or the load fluctuates.

[0005]

In order to solve the above-mentioned problems of the prior art and achieve the above-mentioned object, the transformer device of the first invention is different according to the frequency of the input AC voltage.
Transform the AC voltage with a transformer circuit having the following transformation characteristics
A transformer device having a resonance frequency of the transformer circuit or
Is a switching circuit that switches a DC voltage based on an oscillation signal having a frequency near the resonance frequency to generate a first AC voltage, and outputs a second AC voltage by filtering the first AC voltage. A filter circuit having an impedance that increases / decreases according to an increase / decrease in the frequency of the first AC voltage; a transformer circuit that transforms the second AC voltage to output a third AC voltage; and the third AC voltage. Frequency control circuit that controls the frequency of the oscillation signal so as to suppress the fluctuation of the oscillation signal, and ON / OFF the operation of generating the oscillation signal so that the fluctuation of the third AC voltage is suppressed. a burst control circuit for burst control of the load detecting circuit for detecting the magnitude of the load which operates in response to the third ac voltage, based on the detection result of the load detection circuit, said load test
When the load detected by the output circuit is greater than the specified threshold
To select the frequency control by the frequency control circuit,
By the burst control circuit when the threshold value or less
And a control selection circuit for selecting the burst control .

[0006] for the work of the first aspect of the invention is as follows.
In the switching circuit, the resonance frequency of the transformer circuit
There is a first AC voltage by switching a DC voltage based on the oscillation signal of a frequency near the resonant frequency is generated.
Then, the first alternating voltage is filtered by the filter circuit and the second alternating voltage is output. Then, the second AC voltage is transformed by the transformer circuit to output the third AC voltage. Further, the load detection circuit detects the size of the load operating according to the third AC voltage . Then, by the control selection circuit,
Based on the detection result of the load detection circuit , the load detection circuit
If the load detected by the
The frequency control by the frequency control circuit is selected,
If the burst control circuit is below the threshold,
Burst control is selected.

Further, in the transformer device of the first invention, preferably, the control selection circuit makes the selection under the condition that the magnitude of the detected load becomes equal to or less than a first threshold value. The control is switched from the frequency control to the burst control, and the selected control is performed on the condition that the magnitude of the detected load is equal to or more than a second threshold value larger than the first threshold value. The burst control is switched to the frequency control.

In the transformer device according to the first aspect of the present invention, it is preferable that the frequency control is possible or whether the transformer circuit has a desired transformer efficiency.
Determine the first threshold and the second threshold. In the transformer device of the first invention, preferably, the transformer circuit is a piezoelectric transformer.

The voltage transformation control device of the second invention is input
It has different transformation characteristics depending on the frequency of the AC voltage
A transformer control device for controlling a transformer circuit for transforming an AC voltage , comprising the resonance frequency of the transformer circuit or the resonance frequency.
A switching circuit that switches a DC voltage to generate a first AC voltage based on an oscillation signal having a frequency near the wave number; and a second AC voltage that filters the first AC voltage and supplies a second AC voltage to the transformer circuit. and a filter circuit having an impedance which increases or decreases according to the increase or decrease of the frequency of said first alternating voltage, so as to suppress the variation of the third AC voltage output from the variable pressure circuit, the frequency of the oscillation signal
A frequency control circuit for controlling a frequency for performing control, and a control circuit for controlling the oscillation signal so as to suppress the fluctuation of the third AC voltage .
A burst control circuit that performs burst control for turning on / off the generation operation , a load detection circuit that detects the magnitude of a load that operates according to the third AC voltage, and a detection result of the load detection circuit, If the load detected by the load detection circuit is
If the frequency control circuit is larger than a predetermined threshold,
When the frequency control is selected by
And a control selection circuit for selecting the burst control by the burst control circuit .

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is an overall configuration diagram of an AC adapter 1 according to an embodiment of the present invention. As shown in FIG. 1, the AC adapter 1 includes, for example, a rectifier circuit 12,
Drive circuit 13, switch elements Q1 and Q2, filter circuit 14, piezoelectric transformer 15, rectifier circuit 16, frequency control circuit 17, burst control circuit 18, load detection circuit 19, control switching circuit 20, input voltage detection circuit 21, and oscillation. It has a circuit 22. Here, the switch elements Q1 and Q2 correspond to the switching circuit of the present invention, the filter circuit 14 corresponds to the filter circuit of the present invention, the piezoelectric transformer 15 corresponds to the transformer circuit of the present invention, and the frequency control circuit 17 is the main. The burst control circuit 18 corresponds to the burst control circuit of the present invention, and the control switching circuit corresponds to the control selection circuit of the present invention.

The power supply 11 generates an AC voltage Vin having a predetermined amplitude and frequency. The rectifier circuit 12 is, for example, a bridge full-wave rectifier circuit, receives an AC voltage Vin having a predetermined amplitude and frequency from the power source 11, rectifies the AC voltage Vin,
The DC voltage V1 (DC voltage of the present invention) smoothed by the capacitor C00 is supplied between the drain of the switch element Q1 and the source of the switch element Q2.

The drive circuit 13 switches the switch elements Q1 and Q in accordance with the frequency of the oscillation signal input from the oscillation circuit 22.
Turn gate 2 on / off.

The switch elements Q1 and Q2 form a half bridge, and alternately, the drain and source are turned on / off by the control of the drive circuit 13, and the rectangular wave voltage V2 ( The first AC voltage of the present invention) is generated at the intersection point Q. The rectangular wave voltage V2 is
A rectangular wave corresponding to the voltage obtained by rectifying the DC voltage V1 is obtained.

The filter circuit 14 includes, for example, a coil Li.
The rectangular wave voltage V2 is filtered to generate a pulsating current voltage V3 (second AC voltage of the present invention) including a sine wave component and is supplied to the piezoelectric transformer 15. The pulsating current voltage V3 is the coil Lin and the piezoelectric transformer 15
Due to resonance with the parasitic capacitance C01, a sine wave is generated. The impedance of the filter circuit 14 increases / decreases as the frequency of the rectangular wave voltage V2 increases / decreases. With the AC adapter 1,
Even if the frequency of the oscillation signal from the oscillation circuit 22 slightly changes, the filter circuit 14 has almost no effect. However, if the frequency is rapidly increased, the impedance of the coil Lin increases, and conversely, the input impedance of the piezoelectric transformer 15 increases. Will be lower. That is, by rapidly changing the frequency of the oscillation signal, the pulsating current voltage V input to the piezoelectric transformer 15 is increased.
The amplitude of the sine wave component of 3 can be controlled. Therefore, even if the AC voltage Vin changes, the amplitude of the sinusoidal component of the pulsating current voltage V3 input to the piezoelectric transformer 15 is adjusted by controlling the frequency of the oscillation signal output from the oscillation circuit 22. It is possible to keep the output V4 of V.sub.4 constant. In the present embodiment, by utilizing this fact, the pulsating current voltage V
Control is performed to keep the amplitude of the sine wave component of 3 at an optimum value.

As described above with reference to FIG. 4, the piezoelectric transformer 15 outputs the AC voltage V4 (the third embodiment of the present invention) within the frequency within the predetermined range of the sine wave component of the input pulsating current voltage V3. There are several resonance frequencies that resonate the AC voltage). Further, the AC voltage V4 has a plurality of characteristics in which the value of the AC voltage V4 at the resonance frequency is different from each other according to the frequency of the sine wave component of the input pulsating current voltage V3. Piezoelectric transformer 15
The equivalent circuit of is shown in FIG.

The rectifier circuit 16 rectifies the AC voltage V4 output from the piezoelectric transformer 15 and outputs a DC voltage V5. The DC voltage V5 is smoothed by the capacitor C10 and supplied to the load 30.

The frequency control circuit 17 controls the frequency of the oscillation signal output from the oscillation circuit 22 via the control switching circuit 20 so as to suppress the fluctuation of the DC voltage V5. Specifically, the frequency control circuit 17 controls the load 30 and the AC voltage Vi.
When the voltage value of n changes, control is performed so that the frequency of the oscillation signal output from the oscillation circuit 22 follows so as to keep the DC voltage V5 constant.

The burst control circuit 18 performs burst control for turning on / off the operation of generating an oscillation signal in the oscillation circuit 22 via the control switching circuit 20 so as to suppress the fluctuation of the DC voltage V5.

The load detection circuit 19 detects the current from the load 30 to detect the power consumption of the load 30, for example. The control switching circuit 20 selects one of the frequency control circuit 17 and the burst control circuit 18 based on the power consumption detected by the load detection circuit 19, and causes the selected circuit to control the oscillation circuit 22. Specifically, the control switching circuit 20 selects the frequency control circuit 17 when the power consumption detected by the load detection circuit 19 is larger than a predetermined threshold value, and selects the frequency control circuit 17 when the power consumption is lower than the threshold value. 18
Select. In addition, as shown in FIG. 2A, the control switching circuit 20 switches the frequency control circuit 17 to the burst control circuit 18 based on the power consumption detected by the load detection circuit 19 based on the threshold value A1. The burst control circuit 18 is switched to the frequency control circuit 17 by the threshold value B.
Based on 1. That is, the threshold has hysteresis. As a result, even if the power consumption of the load 30 fluctuates at a certain value, it is possible to prevent the control between the frequency control circuit 17 and the burst control circuit 18 from being frequently switched, and to ensure stable operation of the AC adapter 1. Can be done.

The input voltage detection circuit 21 detects the voltage value of the DC voltage V1 and outputs it to the oscillation circuit 22.

The oscillation circuit 22 selects a predetermined resonance frequency based on the voltage value input from the input voltage detection circuit 21 from the plurality of resonance frequencies of the piezoelectric transformer 15 described with reference to FIG. An oscillation signal having the selected resonance frequency or a frequency near the resonance frequency is generated and output to the drive circuit 13. At this time, the oscillation circuit 22 divides the voltage value input from the input voltage detection circuit 21 into several stages within the range of AC80 to 264V, and selects the resonance frequency suitable for the stage to which the voltage value belongs.

Further, as shown in FIG. 2B, the oscillation circuit 22 switches from the first resonance frequency to the second resonance frequency based on the voltage value input from the input voltage detection circuit 21. Based on the threshold value A2, switching from the second resonance frequency to the first resonance frequency is performed based on the threshold value B2. That is, the threshold has hysteresis. As a result, even when the DC voltage V1 fluctuates at a certain value, it is possible to prevent the resonance frequency selected by the oscillation circuit 22 from being frequently switched, and to make the AC adapter 1 perform a stable operation.

An operation example of the AC adapter 1 shown in FIG. 1 will be described below. [First Operation Example] In the operation example, the power consumption of the load 30 is sufficiently large, and the control switching circuit 20 causes the frequency control circuit 1 to operate.
An operation example when the control of No. 7 is selected will be described. The AC adapter 1 is applied to a predetermined power plug, and the AC voltage Vin having a predetermined amplitude and frequency is supplied from the power supply 11 to the rectifier circuit 12.
Is supplied to. Then, in the rectifying circuit 12, the AC voltage Vin is rectified and smoothed by the capacitor C00 to become the DC voltage V1. The DC voltage V1 is supplied to the drain of the switch element Q1 and the source of the switch element Q2.

Further, the oscillation circuit 22 selects, for example, the resonance frequency F1 from the plurality of resonance frequencies of the piezoelectric transformer 15 described with reference to FIG. 4 based on the voltage value detected by the input voltage detection circuit 21. Then, an oscillation signal having the selected resonance frequency F1 or a frequency near the resonance frequency F1 is generated and output to the drive circuit 13. As a result, the drive circuit 13 causes the resonance frequency F1 of the oscillation signal
Accordingly, the gates of the switching elements Q1 and Q2 are turned on / off to generate the rectangular wave voltage V2 having the resonance frequency F1 at the intersection Q. The rectangular wave voltage V2 is filtered in the filter circuit 14 to become a pulsating current voltage V3 including a sine wave component, which is supplied to the piezoelectric transformer 15.

Then, in the piezoelectric transformer 15, only the sine wave component of the input pulsating current voltage V3 is converted into an AC voltage V4 which is an output voltage according to the input / output ratio of the frequency that the piezoelectric transformer 15 has, and the rectifier circuit. 16 is output. Then, in the rectifying circuit 16, the AC voltage V4 is rectified into a DC voltage V5, which is supplied to the load 30.

In the load detection circuit 19, the load 3
The amount of power consumption of the load 30 is detected based on the current from 0. Then, the control switching circuit 20 determines that the power consumption detected by the load detection circuit 19 is larger than a predetermined threshold value, selects the frequency control circuit 17, and the frequency control circuit 17 controls the oscillation circuit 22. As a result, the frequency control circuit 17 controls the frequency of the oscillation signal output from the oscillation circuit 22 so as to keep the DC voltage V5 constant when the load or the AC voltage Vin changes. As described above, in the first operation example, since the power consumption of the load 30 is sufficiently large, the frequency control circuit 17 performs frequency control.

[Second Operation Example] In this operation example, the load 3
An operation example when the power consumption of 0 is small and the control switching circuit 20 selects the control of the burst control circuit 18 will be described.
Similar to the first operation example, for example, an oscillation signal is generated with the resonance frequency F1 as a reference, and the load detection circuit 19 detects the power consumption of the load 30 based on the current from the load 30. Then, the control switching circuit 20 determines that the power consumption detected by the load detection circuit 19 is less than or equal to a predetermined threshold value, selects the burst control circuit 18, and the burst control circuit 18 controls the oscillation circuit 22. . That is, the oscillation circuit 2 is controlled by the burst control circuit 18 so as to suppress the fluctuation of the DC voltage V5.
Burst control for turning on / off the operation of generating the oscillation signal in 2 is performed.

As described above, according to the second operation example, when the power consumption of the load 30 is small, the resonance frequency F1 is used instead of the frequency deviating from the resonance frequency F1 to generate the oscillation signal. Turn on / off the DC voltage V5
Adjust. Therefore, the piezoelectric transformer 15 can be operated with high transformation efficiency.

As described above, according to the AC adapter 1, the frequency of the sine wave component of the pulsating current voltage V3 input to the piezoelectric transformer 15 is set to the resonance frequency regardless of the power consumption of the load 30. The efficiency of the transformation of the piezoelectric transformer 15 can be improved.

The above embodiment is an example of the present invention, and the present invention is not limited to the above embodiment. For example,
In the above-described embodiment, the case where the resonance frequency F1 is selectively used from among the plurality of resonance frequencies shown in FIG. 4 regardless of the magnitude of the power consumption of the load to perform control has been described. The frequency may be fixedly used.

In the present invention, the piezoelectric transformer 15 is exemplified as the transformer circuit, but it has a plurality of resonance frequencies.
Other devices may be used as long as they have different characteristics depending on the frequency of the input AC voltage and perform transformation. Further, as shown in FIG.
A configuration excluding the configuration for controlling the oscillation signal based on the input voltage detection circuit 21 in FIG. 1 may be adopted.

[0032]

As described above, according to the present invention,
It is possible to provide a transformer and a transformer control device that can perform transformation with high transformation efficiency even when the input voltage or load changes.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an AC adapter according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining switching timings of an oscillation circuit and a control switching circuit shown in FIG.

FIG. 3 is a diagram for explaining a modified example of the AC adapter of the embodiment of the present invention shown in FIG.

FIG. 4 is a diagram for explaining characteristics of a piezoelectric transformer.

[Explanation of symbols]

12 ... Rectifier circuit, 13 ... Drive circuit, 14 ... Filter circuit, 15 ... Piezoelectric transformer, 16 ... Rectifier circuit, 17 ... Frequency control circuit, 18 ... Burst control circuit, 19 ... Load detection circuit, 20 ... Control switching circuit, 21 ... Input voltage detection circuit,
22 ... Oscillation circuit

Claims (5)

(57) [Claims] 1. The voltage varies depending on the frequency of the input AC voltage.
Transform the AC voltage with a transformer circuit having the following transformation characteristics
A transformer device which is at or near the resonance frequency of the transformer circuit.
A switching circuit for generating a first AC voltage by switching a DC voltage based on an oscillating signal having a frequency of , and outputting a second AC voltage by filtering the first AC voltage to output the first AC voltage. A filter circuit having an impedance that increases / decreases according to an increase / decrease in voltage frequency, a transformer circuit that transforms the second AC voltage and outputs a third AC voltage, and suppresses fluctuations in the third AC voltage. So that the oscillation
A frequency control circuit for performing frequency control signal, so as to suppress the fluctuation of the third alternating voltage, the oscillation
A burst control circuit that performs burst control that turns on / off a signal generation operation, a load detection circuit that detects the magnitude of a load that operates in accordance with the third AC voltage, and a detection result of the load detection circuit And the load detection circuit
If the load detected by the
Select the frequency control by the frequency control circuit,
If the burst control circuit outputs
A transformer device having a control selection circuit for selecting a first control. 2. The control selection circuit, on the condition that the magnitude of the detected load is equal to or less than a first threshold value,
Switching control of the selected <br/> your on the burst system from said frequency control, that the magnitude of the detected load is equal to or greater than larger second threshold value than the first threshold value The transformer device according to claim 1, wherein the selected control is switched from the burst control to the frequency control according to a condition. 3. Whether or not the frequency control is possible, or
The transformer device according to claim 2, wherein the transformer circuit determines the first threshold value and the second threshold value based on whether or not the transformer efficiency has a desired value. 4. The transformer device according to claim 1, wherein the transformer circuit is a piezoelectric transformer. 5. The voltage varies depending on the frequency of the input AC voltage.
Has a transformer characteristic that controls the transformer circuit that transforms the AC voltage.
A transformer control device for controlling the resonance frequency of the transformer circuit or in the vicinity of the resonance frequency.
A switching circuit that switches a DC voltage to generate a first AC voltage based on an oscillation signal of a frequency of, and supplies a second AC voltage to the transformer circuit by filtering the first AC voltage, a filter circuit having an impedance which increases or decreases according to the increase or decrease of the frequency of said first alternating voltage, so as to suppress the variation of the third AC voltage output from the variable pressure circuit, the frequency control of the oscillator signal a frequency control circuit for controlling the frequency of performing, so as to suppress the fluctuation of the third alternating voltage, the oscillation
A burst control circuit that performs burst control for turning on / off a signal generation operation , a load detection circuit that detects the magnitude of a load that operates according to the third AC voltage, and a detection result of the load detection circuit And the load detection circuit
If the load detected by the
Select the frequency control by the frequency control circuit,
If the burst control circuit outputs
A voltage conversion control device having a control selection circuit for selecting a first control.