JP2000341939A - Piezo transformer converter - Google Patents

Abstract

(57) [Problem] To provide a piezoelectric transformer converter capable of operating in a wide input voltage range by using a chopper on an input side. SOLUTION: An input filter for rectifying and smoothing an input power supply, a switching circuit for switching an output DC voltage by two switch elements alternately conducting and converting the AC voltage to an AC, and insulating and transforming the AC output. A rectifying and smoothing circuit for rectifying and smoothing the output to output a DC voltage, and a frequency at which the DC voltage is controlled to a predetermined voltage, which is controlled by a comparison result between the DC voltage and a reference voltage. And a voltage frequency converter (VCO) driven by a chopper circuit interposed between the input filter and the switching circuit to control a DC voltage applied to the switching circuit. I do.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric transformer converter capable of operating in a wide input voltage range.

[0002]

2. Description of the Related Art Generally, output voltage control of a converter using a piezoelectric transformer is performed only by frequency control, and this frequency control copes with both input voltage fluctuation and fluctuation of circuit voltage drop due to load fluctuation. ing. FIG.
FIG. 1 shows a configuration of a conventional piezoelectric transformer converter based on frequency control. The input voltage 10 is rectified and smoothed by the input filter 20 and converted into a DC voltage. This DC voltage is converted to a high-frequency AC voltage by switching by a semiconductor switch of the switching circuit 40, insulated and transformed by the piezoelectric transformer 50, and then converted to a constant-voltage DC by the rectifying and smoothing circuit and supplied to the load 70. Is done.

Here, the constant voltage control is performed by a voltage frequency converter (VCO) 100 operated by comparison with a reference voltage 80.
This is performed by controlling the operating frequency of the switching circuit 40 according to the output frequency. FIG. 5 shows the relationship between the operating frequency of the piezoelectric transformer 50 and the output voltage. In this figure, the frequency f0 is the fundamental resonance frequency of the piezoelectric transformer 50, and in a region higher than f0, a region in which the voltage decreases as the frequency increases (frequency controllable range) f
Voltage control is performed using 0 to f1.

[0004]

However, as shown in FIG. 5, the frequency characteristic of the piezoelectric transformer has a high-order mode resonance point f0 'and the frequency range f1 to f0' cannot be used. There is a problem that the range is limited, and it is difficult to cope with load fluctuation and widening of AC input by only frequency control.

The present invention has been made under such a background, and an object of the present invention is to provide a piezoelectric transformer converter capable of operating in a wide input voltage range by using a chopper on an input side.

[0006]

According to the first aspect of the present invention, switching is performed by an input filter for rectifying and smoothing an input power supply and two switch elements for alternately conducting a DC voltage output from the filter. A switching circuit for converting the output to AC, a piezoelectric transformer for insulating and transforming the AC output of the switching circuit, a rectifying and smoothing circuit for rectifying and smoothing the output of the piezoelectric transformer and outputting a DC voltage,
An output voltage detection / comparison circuit that amplifies and outputs a result of comparison between the DC voltage and the reference voltage; and an output that is controlled by an output of the output voltage detection / comparison circuit, and drives the switching circuit at a frequency at which the DC voltage becomes a predetermined voltage. And a voltage frequency converter (VCO) that controls the DC voltage applied to the switching circuit by interposing a chopper circuit between the input filter and the switching circuit. Provide a transformer converter.

According to a second aspect of the present invention, in the piezoelectric transformer converter according to the first aspect, the chopper circuit is a step-down (buck) chopper for extracting a voltage lower than an input voltage.

[0008] The invention described in claim 3 is the first invention.
In the piezoelectric transformer converter described above, the chopper circuit is a step-up (boost type) chopper that extracts a voltage higher than an input voltage.

As described above, a chopper circuit is provided at the input of a converter using a piezoelectric transformer, and all input voltage fluctuations are absorbed by the chopper circuit, thereby enabling the piezoelectric converter circuit to support a wide input voltage. Features.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a piezoelectric transformer converter according to one embodiment of the present invention. In this figure, an input voltage 10 is rectified and smoothed by an input filter 20 and converted into a DC voltage. The converted DC voltage is voltage-controlled by the chopper circuit 30 by pulse width control (PWM), and is stepped down or stepped up to a predetermined voltage.

This voltage is converted into a high-frequency AC voltage by switching of a switching circuit 40 by a semiconductor switch, is insulated and transformed by a piezoelectric transformer 50, is converted into a constant-voltage DC by a rectifying and smoothing circuit, and is converted into a constant voltage DC. Supplied to The output voltage supplied to the load 70 is controlled based on the result of comparison between the output voltage and the reference voltage 80 by the error amplifier 90.
By controlling the CO) 100 and controlling the driving frequency of the switching circuit 40, the constant voltage is maintained.

FIG. 2 is a diagram showing a concrete circuit example in which a step-down (buck) chopper circuit 31 is inserted as a chopper circuit. FIG. 3 shows a step-up (boost) chopper circuit 32 inserted as a chopper circuit. FIG. 9 is a diagram showing a specific circuit example in the case. The step-down (buck) chopper circuit 31 and the step-up (boost) chopper circuit 32 perform pulse width modulation such that the output voltage of each chopper circuit becomes a predetermined voltage (usually a constant voltage) regardless of input voltage fluctuation. (PWM).

FIG. 5 shows the relationship between the operating frequency of the piezoelectric transformer 50 and the output voltage. In this figure, the frequency f0 is the fundamental resonance frequency of the piezoelectric transformer 50, and the voltage is controlled by using a region (frequency controllable range) f0 to f1 in which the voltage decreases as the frequency increases in a region higher than f0. I do. Generally, when the frequency of a converter using a piezoelectric transformer is controlled, the resonance characteristic of the piezoelectric transformer is used as shown in FIG. When the input voltage is high, the switching frequency is shifted to a higher frequency side.

However, since the piezoelectric transformer has a high-order mode resonance point f1, the range of frequency control is limited. For this reason, it is difficult to control the output voltage over a wide input voltage range from 100 Vac to 240 Vac as in the case of a wide range of AC input. Therefore, as described above, the chopper circuit 30 (the step-down chopper 31 or the step-up chopper 32) is inserted between the input filter and the switching circuit, the input voltage fluctuation is made constant by this chopper circuit, and the switching circuit always has a constant voltage. DC voltage is applied. As a result, the frequency control of the converter using the piezoelectric transformer only needs to cope with the load fluctuation, so that the load is greatly reduced.

Assuming that the input DC voltage of the chopper circuit is Vi, the duty ratio (on time / period) of switching of the chopper circuit is D, and the output DC voltage of the chopper circuit is Vo (chop), the case of the back type: Vo (chop) ) = DVi (1) In case of boost type: Vo (chop) = Vi / (1−D) (2) In both equations (1) and (2), PWM
By changing D with respect to the input fluctuation by control, Vo (cho
p) That is, the input voltage of the switching circuit can be made constant.

The operation of one embodiment of the present invention has been described above in detail with reference to the drawings. However, the present invention is not limited to this embodiment, and a design change or the like may be made without departing from the gist of the present invention. The present invention is also included in the present invention. For example, the input power source is not limited to AC, but may be DC input. Further, the output of the chopper circuit is not limited to the one controlled to a constant voltage, but may be controlled to output a high voltage under heavy load.

[0017]

As described above, according to the present invention, even if the input voltage fluctuates, the input voltage of the switching circuit is made constant by the chopper circuit,
The effect that it can respond to a wide input voltage is obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a piezoelectric transformer converter according to an embodiment of the present invention.

FIG. 2 is a circuit configuration diagram of a piezoelectric transformer converter using a step-down (buck) chopper.

FIG. 3 is a circuit configuration diagram of a piezoelectric transformer converter using a boost type (boost type) chopper.

FIG. 4 is a block diagram showing a configuration of a conventional piezoelectric transformer converter.

FIG. 5 is a diagram showing a relationship between an operating frequency of a piezoelectric transformer and an output voltage.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... AC input power supply 20 ... Input filter 21 ... Bridge diode 22 ... Capacitor 30 ... Chopper circuit 31 ... Buck type (buck type) chopper circuit 32 ... Boost type (boost type) chopper circuit 33 ... Pulse width control part (PWM) 34 ... switch 35 ... diode 36 ... inductor 37 ... capacitor 40 ... switching circuit 41, 42 ... switch 43 ... inductor 50 ... piezoelectric transformer 51 ... equivalent capacitor 52 ... equivalent inductor 53 ... equivalent capacitor 54 ... equivalent transformer 55 ... equivalent capacitor 60 ... rectification Smoothing circuit 61 Bridge diode 62 Capacitor 70 Load 80 Reference voltage 90 Error amplifier 100 Voltage frequency converter (VCO) 101 Oscillator (OSC) 102 Capacitors 103 and 104 Resistor 105 Transistors Ta

Claims (3)

[Claims] 1. An input filter for rectifying and smoothing an input power supply, and alternately conducting a DC voltage output from the filter.
A switching circuit for switching by a plurality of switch elements to convert to AC, a piezoelectric transformer for insulating and transforming an AC output of the switching circuit, and a rectifying and smoothing circuit for rectifying and smoothing the output of the piezoelectric transformer to output a DC voltage An output voltage detection / comparison circuit that amplifies and outputs a result of comparison between the DC voltage and the reference voltage; and a frequency controlled by an output of the output voltage detection / comparison circuit, wherein the switching circuit controls the frequency at which the DC voltage becomes a predetermined voltage. And a voltage frequency converter (VCO) driven by a chopper circuit interposed between the input filter and the switching circuit to control a DC voltage applied to the switching circuit. Piezo transformer converter. 2. The piezoelectric transformer converter according to claim 1, wherein said chopper circuit is a step-down (buck) chopper for extracting a voltage lower than an input voltage. 3. The piezoelectric transformer converter according to claim 1, wherein the chopper circuit is a step-up (boost) chopper that extracts a voltage higher than an input voltage.