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Control circuit and control method for piezoelectric transformer

A technology for controlling circuits and transformers, applied in electric light sources, electrical components, output power conversion devices, etc., and can solve problems such as low conversion efficiency

Inactive Publication Date: 2003-08-20
TAIHEIYO CEMENT CORP
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

Therefore, although this control circuit has the desired function of maintaining the load current at a predetermined value even when the input voltage Vi changes, the driving frequency of the piezoelectric transformer changes due to the change in the input voltage Vi, resulting in lower conversion efficiencies

Method used

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  • Control circuit and control method for piezoelectric transformer
  • Control circuit and control method for piezoelectric transformer
  • Control circuit and control method for piezoelectric transformer

Examples

Experimental program
Comparison scheme
Effect test

no. 1 example 〕

[0095] 4 is a block diagram of the piezoelectric transformer control circuit of the first embodiment of the present invention.

[0096] In Figure 4, reference number 1 represents a piezoelectric transformer; 2 is a load, such as a cold cathode fluorescent lamp connected to the output terminal of the piezoelectric transformer 1, and 3 is a detection resistor Rdet to detect the flow through The current of the load; 4 is a rectifier circuit, used to convert the AC voltage generated in the detection resistor 3 into a DC voltage; 5 is an error amplifier, used to convert the output voltage from the rectifier circuit 4 (load current detection voltage) Vri Compare with a reference voltage Vref1 and amplify its difference; 7 is a drive circuit with and figure 2 The configuration described in the same; 8a and 8b are detection resistors, used to detect the size of the driving voltage delivered to the piezoelectric transformer 1; 9 is a rectifier circuit, used to detect the AC generated in t...

no. 2 example

[0106] The second embodiment will be described below in which the driving circuit 7 is a so-called half-bridge or full-bridge type using switching transistors. Since the configuration of the half-bridge or full-bridge circuit is generally known, its detailed description will be omitted. Figures 7 and 8 schematically show the drive circuit.

[0107] Fig. 7 is a diagram showing the internal configuration of the half-bridge drive circuit of the second embodiment of the present invention.

[0108]In the driving circuit 7A, transistors 7a and 7b, such as FETs (field effect transistors; in this second embodiment, transistors 7a and 7b are p-type and n-type, respectively), are used to form a half-bridge type, such as Shown in Figure 7. Two types of oscillating signals are respectively output from the voltage control oscillation circuit 11A (described later) to the high side and the low side to alternately turn on / off the transistors 7a and 7b. By the switching operation of the driving ci...

no. 3 example

[0129] This third embodiment will be taken as an example of a case where the wide-range brightness control function of the cold cathode fluorescent lamp used as load 2 is added to the piezoelectric transformer control circuit described in the first embodiment.

[0130] Fig. 15 is a block diagram of a piezoelectric transformer control circuit according to a third embodiment of the present invention. In FIG. 15, the same reference numerals as the control circuit in FIG. 4 described in the first embodiment are used to represent the same parts, and the description thereof will be omitted here.

[0131] In FIG. 15, reference number 13 represents a pulse power supply circuit, which can generate a pulse type power supply voltage (hereinafter referred to as pulse voltage) from the input voltage Vi, supply it to the driving circuit 7, and control the pulse voltage The pulse width or period length.

[0132] The driving circuit 7 can output a driving voltage from the pulse voltage of the pul...

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Abstract

When an input voltage rises, (the amplitude of) a sine-wave voltage for driving a piezoelectric transformer (1) increases, so that a detection voltage (Vti) rectified by a rectifying circuit (9) also increases. An output voltage from an error amplifier (10) for comparing the detection voltage (Vti) with a reference voltage (Vref2) rises. If the output voltage from the error amplifier (10) rises, a voltage-controlled oscillation circuit (11) decreases the duty ratio of an oscillation signal to be output. In a driving circuit (7), as the duty ratio of the oscillation signal decreases, the amplitude of a fundamental wave contained in a rectangular wave to be output decreases to be a small driving voltage to the piezoelectric transformer (1).

Description

Background of the invention [0001] Invention category [0002] The present invention relates to a control circuit and a control method of a piezoelectric transformer suitable for use in a cold cathode fluorescent lamp (CCFL) driving device. Background technique [0003] Recently, liquid crystal display devices are widely used as displays for portable notebook personal computers, for example. These liquid crystal display devices are equipped with cold cathode fluorescent lamps as a so-called backlight for illuminating a liquid crystal display panel from the back. When turning on this kind of cold cathode fluorescent lamp, it needs an inverter (Inverter) for converting the low DC voltage of the battery or the like into the high AC voltage of 1,000Vrms or higher in the initial lighting state and High AC voltage of about 500Vrms in stable lighting state. Usually, a winding transformer is used as the step-up transformer for this inverter. However, in recent years, piezoelectric transf...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): C02F1/32H02M7/538H05B41/282H05B41/392
CPCH02M7/538H05B41/3925C02F1/32H05B41/2822H02M5/44
Inventor 藤村健石川胜之外山正明
Owner TAIHEIYO CEMENT CORP
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