KR100431058B1 - DC/DC inverter using PZT - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC / DC inverter circuit using a piezoelectric transformer, and in particular, a simple sensing of an open load state of a cold cathode tube when designing an inverter for a cold cathode tube (CCFL) using a piezoelectric transformer applied to a notebook PC. The present invention relates to a DC / DC inverter circuit using a piezoelectric transformer that controls the driving circuit and shuts down when the load is opened.

Description

DC / DC inverter using piezoelectric transformer {DC / DC inverter using PZT}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC / DC inverter circuit using a piezoelectric transformer, and in particular, a simple sensing of an open load state of a cold cathode tube when designing an inverter for a cold cathode tube (CCFL) using a piezoelectric transformer applied to a notebook PC. The present invention relates to a DC / DC inverter circuit using a piezoelectric transformer that controls the driving circuit and shuts down when the load is opened.

In general, a power supply device, which is an inverter that generates an output voltage by inducing an input voltage by using a transformer formed of a piezoelectric piezoelectric (PZT), has an output voltage of the piezoelectric transformer due to the variable drive frequency. To be controlled.

1 is a circuit diagram of a DC / DC inverter using a piezoelectric transformer according to the prior art. Referring to a schematic configuration of a DC / DC inverter using a piezoelectric transformer according to the prior art, the magnitude of the input voltage is compared with a preset reference voltage. When the signal output from the comparator 3 outputting the comparison value is input, the voltage adjusting oscillator 4 for controlling the pulse width and the input voltage switched by the output of the voltage adjusting oscillator 4 are applied accordingly. Adjustment of the piezoelectric body PZT set corresponding to the change of the voltage as the driving unit 1 is applied to the piezoelectric body PZT used as a transformer and the voltage switched by the driving unit 1 is caught by the piezoelectric body PZT. A cold cathode tube (CCFL) that emits light by a voltage that is transformed to a predetermined voltage by a gain and receives a voltage that is conducted to the ground side through the cold cathode tube (CCFL) The rectifying unit 2 rectifies the DC voltage and provides it to the comparing unit 3 and the voltage applied to the ground side via the cold cathode tube CCFL, and senses the voltage applied to the cold cathode tube. It consists of the shutdown control part 5 which shuts down the said drive part 1 after the predetermined time passes using the set timer or counter.

Briefly referring to the operation of the DC / DC inverter using the piezoelectric transformer configured as described above, the drive unit 1 composed of switching means by the pulse width modulated signal output from the voltage adjusting oscillator 4 is operated and Accordingly, a voltage having a constant resonant frequency is applied to the input side of the piezoelectric body PZT, and thus the output voltage transformed from the piezoelectric body PZT by a constant ratio is used as the driving voltage of the cold cathode tube CCFL.

At this time, the state of the voltage applied to the cold cathode tube (CCFL) is connected to the inverting terminal (-) of the comparator 3 through the rectifying unit 2 and compared with the reference voltage connected to the non-inverting terminal (+). Accordingly, the voltage adjusting oscillator 4 recognizes the state of the driving voltage applied to the cold cathode tube CCFL and modulates the width of the pulse signal applied to the driving unit 1 according to the recognition degree.

In addition, the shutdown control unit 5 receives the voltage conducting to the ground side via the cold cathode tube CCFL and continuously senses the voltage applied to the cold cathode tube while open load in the cold cathode tube CCFL. Is generated, that is, if the current for the cold cathode tube is not detected even after elapse of a predetermined time using a preset timer or counter, it is determined that the drive unit 1 is shut down.

At this time, the shutdown reference determination time, which is usually set using a timer or counter, is set very short in consideration of the stability of the system.

In the DC / DC inverter circuit using the piezoelectric transformer operating as described above, no problem occurs in the analog dimming mode. However, when the PWM dimming operation is performed, the driving circuit continues to match the PWM frequency during PWM dimming. In case of ON / OFF, malfunction is often occurred because it is not possible to distinguish between PWM dimming off period or open load.

In addition, the counter or timer implementing the shutdown control unit 5 has to be used as a very sophisticated device because it causes a rise in production cost has also been presented as a significant problem.

An object of the present invention for solving the conventional problems as described above relates to a DC / DC inverter circuit using a piezoelectric transformer, in particular, in the design of a cold cathode tube (CCFL) inverter using a piezoelectric transformer applied to a notebook PC In order to provide a DC / DC inverter circuit using a piezoelectric transformer that simply senses the open load state and controls the driving circuit to shut down when the load is opened. have.

1 is an exemplary circuit diagram of a DC / DC inverter according to the prior art.

2 is an inverter frequency control circuit in a DC / DC inverter using a piezoelectric transformer according to the present invention.

Features of the DC / DC inverter circuit using a piezoelectric transformer according to the present invention for achieving the above object, the comparison unit for comparing the magnitude of the input voltage with a predetermined reference voltage and outputs the comparison value; A voltage adjusting oscillator for controlling a pulse width when a signal output from the comparator is input; A driving unit which converts a voltage of an input DC component applied by being switched by an output of the voltage adjusting oscillator into an AC component; A piezoelectric transformer which receives a variation of the voltage converted and output from the driver and converts the voltage to a predetermined voltage by an adjustment gain set corresponding to the variation of the voltage and outputs it through a plurality of output terminals; A cold cathode tube connected to an output terminal of the piezoelectric transformer and emitting light according to the output voltage of the piezoelectric transformer; A rectifier for receiving a voltage conducting to the ground side through the cold cathode tube, rectifying a DC voltage, providing the comparator to the comparator, and outputting a signal inversely proportional to the magnitude of the rectified voltage signal to an A output terminal; And a voltage signal output from the A output terminal of the rectifying unit is divided by the second and third resistors when the voltage conducting to the ground side through the cold cathode tube is not detected and applied to the base terminal to apply the voltage above the limit voltage. In this case, the transistor is turned on and the charge charged during the turn-on operation of the transistor is discharged.

The above object and various advantages of the present invention will become more apparent from the preferred embodiments of the present invention described below with reference to the accompanying drawings by those skilled in the art.

First, briefly looking at the technical concept applied to the present invention, the operation of the conventional shutdown control unit detects the current or voltage flowing in the cold cathode ray tube to detect whether the cold cathode ray tube is open and if the current or voltage is not detected within a certain time, Since the cold cathode ray tube is judged to be in an open state, the driving unit is stopped. Therefore, the above-mentioned function is considered to be possible by the combination of the charging charge time of the capacitor and the switching element.

Hereinafter, with reference to the accompanying drawings, preferred embodiments of the present invention will be described in detail.

2 is a diagram illustrating the configuration of an inverter frequency control circuit in a DC / DC inverter using a piezoelectric transformer according to the present invention. Referring to the schematic configuration of the DC / DC inverter using a piezoelectric transformer according to the present invention, The voltage adjusting oscillator 4 and the voltage adjusting oscillator 4 for controlling the pulse width accordingly when a signal output from the comparing unit 3 which compares the magnitude of the voltage with a preset reference voltage and outputs the comparison value is input. The driving unit 1 which applies the input voltage switched and applied to the piezoelectric body PZT to be used as a transformer by the output of the voltage, and the voltage switched by the driving unit 1 is caught by the piezoelectric body PZT. Via the cold cathode tube CCFL and the cold cathode tube CCFL, which emit light by the voltage outputted after being converted to a constant voltage by the adjustment gain of the piezoelectric body PZT set corresponding to the variation. The rectifying unit 2a for receiving a voltage conducting to the ground side and rectifying the DC voltage to provide the comparison unit 3 and outputting a signal inversely proportional to the magnitude of the rectified voltage signal to the A output terminal, and the cold cathode tube (CCFL). When the voltage conducting to the ground side is not detected through the input voltage), the voltage signal output from the A output terminal of the rectifier 2a is input and divided by the second and third resistors R2 and R3 and applied to the base terminal. When a threshold voltage or more is applied, the transistor Q1 is turned on and the charge charged during the turn-on operation of the transistor Q1 is composed of a capacitor C1 for discharging.

Briefly referring to the operation of the DC / DC inverter using the piezoelectric transformer configured as described above, the drive unit 1 composed of switching means by the pulse width modulated signal output from the voltage adjusting oscillator 4 is operated and Accordingly, a voltage having a constant resonant frequency is applied to the input side of the piezoelectric body PZT, and thus the output voltage transformed from the piezoelectric body PZT by a constant ratio is driven by the output terminal of the cold cathode tube CCFL. to provide.

After that, the rectifying unit 2a rectifies and outputs the voltage flowing through the cold cathode tube CCFL, and the magnitude of the voltage rectified and output is input to the inverting terminal (-) of the comparator 3.

In addition, the rectifier 2a outputs a voltage signal inversely proportional to the magnitude of the voltage applied to the first resistor R1 through an output terminal referred to by reference number A. For example, the rectifier 2a is applied to the first resistor R1. If the magnitude of the voltage is high, the low-state signal is output through an output terminal referred to by reference number A. If the magnitude of the voltage applied to the first resistor R1 is low, the high-state signal is referred to as reference number A. It is output through the output stage.

Therefore, the output signal of the output terminal A of the rectifier 2a is divided by the second resistor R2 and the third resistor R3, and the divided voltage is applied to the base terminal of the transistor Q1. .

The transistor Q1 is turned on when the voltage applied to the base terminal is greater than or equal to the threshold voltage, that is, 0.7 V, thereby discharging the electric charges charged in the capacitor C1 connected to the collector terminal and the emitter terminal. It will provide a path to it.

At this time, since the voltage applied to the enable terminal of the driving unit 1 is applied to the capacitor C1, it is always occupied. When the transistor Q1 is turned on, the charged charge is charged in the transistor Q1. Through the collector terminal, the electric charge charged to the ground connected to the emitter terminal is discharged.

That is, when the voltage passing through the cold cathode tube is a low voltage, the output signal of the output terminal A of the rectifying unit 2a becomes a high signal, thereby discharging the charges charged in the capacitor C1.

At this time, if the voltage adjusting oscillator 4 operates in the PWM dimming mode, the output signal of the output terminal A of the rectifier 2a at any time before the charges charged in the capacitor C1 are completely discharged. Becomes a low signal, which causes the transistor Q1 to turn off and thereby the discharge path of the capacitor C1 is blocked.

If the turn-on operation of the transistor Q1 is maintained continuously, the charges charged in the capacitor C1 are completely discharged, and thus the enable terminal of the driving unit 1 drops to a low voltage and thus the driving unit (1) stops the operation.

While the invention has been shown and described in connection with specific embodiments thereof, it is well known in the art that various modifications and changes can be made without departing from the spirit and scope of the invention as indicated by the claims. Anyone who owns it can easily find out.

Providing the DC / DC inverter circuit using the piezoelectric transformer according to the present invention as described above can solve the problems caused by using the conventional shutdown control, there is an effect that can reduce the production cost.

Claims (1)

A comparison unit for comparing the magnitude of the input voltage with a preset reference voltage and outputting the comparison value, and switching by the output of the voltage adjusting oscillator and the voltage adjusting oscillator controlling the pulse width accordingly when a signal output from the comparator is input. The driving unit converts the voltage of the input DC component applied to the AC component and the variation of the voltage converted and output from the driving unit, and is converted to a predetermined voltage by the adjustment gain set corresponding to the variation of the voltage. It is connected to the output terminal of the piezoelectric transformer and the piezoelectric transformer to output through the cold cathode tube and the voltage applied to the ground side via the cold cathode tube to emit light according to the output voltage of the piezoelectric transformer to rectify the DC voltage Pressure including rectifier provided to the part In the DC / DC inverter using a transformer, The rectifier outputs a signal inversely proportional to the magnitude of the rectified voltage signal to the A output terminal, and receives a voltage signal output from the A output terminal of the rectifier when the voltage conducting to the ground side is not detected through the cold cathode tube. And a voltage dividing voltage through a third resistor, and the transistor is turned on when the voltage is applied to the base terminal, and the charge charged during the turn-on operation of the transistor is discharged. DC / DC inverter using a piezoelectric transformer, characterized in that for controlling the drive by separating the open load.