KR19990019087A - Piezoelectric Transformer Inverter - Google Patents

Abstract

According to the present invention, a piezoelectric transformer can be applied with a wide range of input voltage, and at the same time, the contrast of the screen is adjusted, and the first switching unit to which the input voltage is switched to improve efficiency, and the output of the first switching unit is smoothed. And a distribution unit connected in parallel to the output of the smoothing unit to distribute an output voltage, a second switching unit switching the output of the smoothing unit to be pulse width modulated by a second control unit, and switching in the second switching unit. A piezoelectric transformer in which the input voltage is input, a cold cathode tube to which the output of the piezoelectric transformer is applied and lit, a detector in which the output of the cold cathode tube is rectified and smoothed, a comparison unit in which the output of the detector is compared, and the Comparing the output of the comparator, the voltage divided by the distribution unit is applied to the first control unit to control the first switching unit pulse width modulation. It is made.

Description

Piezoelectric Transformer Inverter

The present invention relates to a piezoelectric transformer inverter, and more particularly, to a piezoelectric transformer inverter is provided with a constant voltage circuit so that the input of the piezoelectric transformer is constantly applied.

Inverters that generate an output voltage by inducing an input voltage using a transformer made of a piezoelectric transformer (PZT) generally include a cold cathode tube (CCFL) used for screen brightness of a notebook computer. As a power supply for driving, the frequency of the input voltage input to the piezoelectric transformer is controlled so that the output voltage of the piezoelectric transformer is controlled. Excessive fluctuations in the input voltage affect the output voltage. The stability of the input voltage applied to the piezoelectric transformer is a major problem of the inverter because it causes damage.

1 is an inverter circuit diagram according to the prior art.

The inverter circuit according to the related art has a control unit 10 through which the output of the comparator 50 is input through the variable resistor R1, a driver 20a to which the output of the controller 10 is applied, and an output of the driver 20a. The output of the switching unit Q1, the piezoelectric transformer 30 to which the voltage Vcc switched by the switching unit Q1 is input, and the output of the piezoelectric transformer 30 are cold cathode tubes CCFL. The comparator 40b rectified and smoothed through the 40a and the output voltage Vo of the detector 40b are input to the inverting stage, and the reference unit Vref is input to the non-inverting stage to be compared. 50).

In the inverter according to the related art configured as described above, when the current flowing in the cold cathode tube 40a is small due to the voltage output from the piezoelectric transformer 30, the output voltage Vo decreases, so that the comparator 50 The voltage applied to the inverting terminal (-) of N) becomes small. Therefore, the output of the comparator 50 becomes high and controlled by the variable resistor R1 of the controller 10 so that the frequency applied to the piezoelectric transformer 30 is decreased, and the voltage is increased by the reduced frequency. The ratio becomes large and thus the output voltage Vo becomes large.

In addition, if the current flowing in the cold cathode tube 40a is large due to the voltage output from the piezoelectric transformer 30, the output of the comparator 50 becomes low, so that the current in the cold cathode tube 40a is small. It becomes small compared with the case where it flows. Therefore, the frequency applied to the piezoelectric transformer 30 is controlled by the variable resistor R1 of the controller 10 so that the boosting ratio is decreased by the increased frequency, so that the output voltage Vo becomes small. do.

In addition, the pulse width modulated signal of the controller 10 has a frequency, and thus the voltage of the output signal and the reference voltage Vref are compared in the comparator 50 so that the controller 10 can be controlled through the variable resistor R _T. ), The driving frequency of the piezoelectric transformer 30 is changed to control the output voltage of the piezoelectric transformer 30.

However, the inverter according to the prior art as described above, if the overvoltage is applied to the cold cathode tube due to the high input voltage, out of the resonant frequency range of the piezoelectric transformer, the efficiency of the inverter is reduced, the piezoelectric transformer is damaged by heat generation, etc. There is a problem.

Therefore, the present invention has been made to solve the conventional problems as described above, the main object of the invention is that the piezoelectric transformer can be applied to a wide range of input voltage, at the same time dimming the screen (Dimming), the efficiency is improved To provide a piezoelectric transformer inverter.

A feature of the present invention for achieving the above object is a first switching unit for switching the input voltage, a smoothing unit for smoothing the output of the first switching unit, the output voltage is distributed in parallel to the output of the smoothing unit A second switching unit for switching the distribution, the output of the smoothing unit to be pulse-width modulated by a second control unit, a piezoelectric transformer for inputting the voltage switched by the second switching unit, and an output of the piezoelectric transformer The cold cathode tube to be lit, the output of the cold cathode tube is rectified and smoothed, the comparison unit to which the output of the detection unit is compared, the output of the comparison unit is applied, and the voltage distributed by the distribution unit is applied. 1st control part is comprised by the 1st control part which controls a pulse width modulation.

1 is an inverter circuit diagram according to the prior art,

2 is a piezoelectric transformer inverter circuit diagram according to the present invention.

* Explanation of symbols for main parts of the drawings

5: smoothing part 10: distribution part

30: piezoelectric transformer 40a: cold cathode tube

40b: detection unit 50: comparison unit

60: first control unit 70: second control unit

Hereinafter, a preferred embodiment of a piezoelectric transformer inverter according to the present invention will be described in detail with reference to the accompanying drawings.

2 is a circuit diagram of a piezoelectric transformer inverter according to the present invention.

The piezoelectric transformer inverter circuit according to the present invention includes a first switching unit Q1 for switching an input voltage Vcc, a smoothing unit 5 for smoothing an output of the first switching unit Q1, and the smoothing unit ( The distribution unit 10 is connected in parallel to the output of 5) and the output voltage is distributed, and the second switching unit Q2 is switched so that the output of the smoothing unit 5 is pulse width modulated by the second control unit 70 ), A piezoelectric transformer 30 into which the voltage switched by the second switching unit Q2 is input, a cold cathode tube 40a which is turned on by the output of the piezoelectric transformer 30, and the cold cathode tube A detector 40b in which the output of 40a is rectified and smoothed, a comparator 50 whose output of the detector 40b is compared with a comparison voltage Vref, and an output of the comparator 50 are applied The first control unit 60 controls the first switching unit Q1 to be pulse-width modulated by applying the voltage divided by the distribution unit 10. It is.

The smoothing unit 5 is connected to the diode D1 connected in parallel to prevent the input power from flowing in reverse, the coil L1 connected in series to the input power, and the output of the coil L1 in parallel. It consists of a capacitor C1.

In the distribution unit 10, a first resistor R1a connected in series and a second resistor R1b which is a variable resistor are connected in parallel to the smoothing unit 5, and the first resistor R1a and the second resistor are connected in parallel. The voltage divided between the resistors R1b is output.

The following describes the operating state of the present invention configured as described above.

The voltage divided between the first resistor R1a of the distribution unit 10 and the second resistor R1b, which is a variable resistor, is detected by the input voltage Vcc. In the first switching unit Q1, which is a channel field effect transistor, when the voltage detected by the distribution unit 10 is large, the rate of application is small, and when the voltage detected by the distribution unit 10 is small, the rate of application is large. Since the voltage variation detected by the distribution unit 10 is reduced because it is controlled to modulate the pulse width, the second control unit in which the pulse width modulation, that is, the ratio of the ratio, is set by the time constant capacitor CT and the time constant variable resistor RT. The output of the piezoelectric transformer 30 required by 70 is applied to the piezoelectric transformer 30 by switching of the second switching unit Q2, which is a field effect transistor, which is pulse width modulated to a value set to generate the output.

In addition, the output of the piezoelectric transformer 30 is applied with a voltage to the cold cathode tube 40a for the back light of the notebook computer, so that the cold cathode tube 40a is turned on, and the cold cathode tube 40a is turned on. The output is rectified in the detector 40b, smoothed and applied to the inverting terminal (-) of the comparator 50, and compared with the comparison voltage Vref connected to the non-inverting terminal (+), and thus the comparator 50 ) Is applied to the first control unit 60. Therefore, depending on the state of the output, that is, when the output is increased, the first control unit 60 controls the output rate to be reduced by reducing the rate of fertilization of the first switching unit Q1, and when the output is reduced, the first control unit ( 60 controls the output of the piezoelectric transformer 40a by increasing the rate of fertilization of the first switching unit Q1 so that the voltage applied to the piezoelectric transformer 40a becomes stable.

In addition, the magnitude of the voltage applied to the piezoelectric transformer 30 is controlled by the variable of the second resistor R1b, which is the variable resistor of the distribution unit 10, and thus the brightness of the cold cathode tube 40a is controlled. Therefore, the contrast can be adjusted.

The first switching unit Q1, the smoothing unit 5, the distribution unit 10, and the first control unit 60 configured in the input circuit are reduced from the input voltage Vcc to the piezoelectric transformer 30. Since the inverter operates stably by the applied power source, the efficiency of the inverter is enhanced.

As described in detail above, the piezoelectric transformer inverter according to the present invention operates stably even when the piezoelectric transformer is applied with a wide range of input voltages, adjusts the contrast of the notebook computer screen, and improves efficiency.

The present invention is not limited to the above embodiments, and it is apparent that many modifications are possible by those skilled in the art within the technical spirit of the present invention.

Claims (5)

A first switching unit to which an input voltage is switched; A smoothing unit for smoothing an output of the first switching unit; A distribution unit connected in parallel with the output of the smoothing unit to distribute an output voltage; A second switching unit for switching the output of the smoothing unit to be pulse width modulated by a second control unit; A piezoelectric transformer configured to receive a voltage switched by the second switching unit; A cold cathode tube which is lit when the output of the piezoelectric transformer is applied; A detector configured to rectify and smooth the output of the cold cathode tube; A comparison unit to which the output of the detection unit is compared; And a first controller configured to control the first switch to be pulse-width modulated by applying the output of the comparator and applying the voltage divided by the distribution. The display apparatus of claim 1, wherein the smoothing unit comprises: diodes connected in parallel to prevent input power from flowing in reverse; A coil connected in series with the input power source; And a condenser connected in parallel to the output of the coil. The apparatus of claim 1, wherein the distribution unit comprises: a first resistor connected in parallel to the smoothing unit output; And a second resistor connected in series with the first resistor. The piezoelectric transformer inverter of claim 1, wherein the first switching unit is a P-channel field effect transistor. 4. The piezoelectric transformer inverter of claim 3, wherein the second resistor is a variable resistor.