KR101229733B1 - Switching mode power supply for light emitting diode - Google Patents

Abstract

PURPOSE: A switching mode power supply for a light emitting diode capable of eliminating a flicker effect is provided to include a ceramic capacitor capable of backing up, thereby increasing the life of the switching mode power supply. CONSTITUTION: A first rectifier(200) rectifies AC(Alternating Current) power applied from the outside to DC(Direct Current) power. A second rectifier(300) rectifies the DC power firstly rectified by the first rectifier for the second time. A constant current circuit includes a buck converter, a ripple attenuation element, and a static electricity prevention circuit. A feedback circuit(500) gives feedback to the secondly rectified DC power outputted from the second rectifier. A power factor correction circuit(600) controls the first rectifier according to the comparing value given by the feedback from the feedback circuit. [Reference numerals] (100) Noise filter; (200) First rectifier; (300) Second rectifier; (410) First constant current circuit; (420) Second constant current circuit; (500) Feedback circuit; (600) Power factor correction circuit; (AA) AC input; (B1) Output A; (B2) Output B

Description

Switching mode power supply for light emitting diodes {SWITCHING MODE POWER SUPPLY FOR LIGHT EMITTING DIODE}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching mode power supply for a light emitting diode, and in particular, for a light emitting diode having a constant voltage / constant current conversion circuit that performs constant voltage rectification and power factor compensation simultaneously in one stage and eliminates low frequency ripple and also reduces high frequency ripple. A switch mode power supply.

Switching mode power supplies are modular power supplies that convert alternating currents supplied from commercial power sources to suit a variety of devices. The switching mode power supply uses a high-speed power semiconductor to control intermittently at a high frequency and obtain stable DC voltages through rectification and smoothing circuits. In addition, switching mode power supplies are generally used as power for various electronic devices, and in particular, may be used for light emitting diodes as in the present invention.

The power supply for driving a light emitting diode is a constant voltage, and the driving circuit is complicated because the light emitting diode is driven with a constant current. However, lighting fixtures must be inexpensive, so the construction of power supplies at low cost must be simplified. Accordingly, a power supply for driving a conventional light emitting diode has used many single stages. However, this single stage power supply generates flickering 100 times (100Hz) or 120 times (120Hz) per second. This flicker phenomenon is not detected by the human eye, but the line is recognized when shooting a video using a camera or a camcorder. In addition, there is a case that a large recall situation has recently occurred in Japan because it is recognized as having an effect on the human body. However, this flicker phenomenon does not really affect the human body. However, since the consumer is often anxious to avoid using it, there is a need for a power supply capable of removing it.

Of course, this flicker phenomenon can be solved by using the conventional three-stage power supply, but the three-stage power supply consisting of the rectifier circuit-power factor correction circuit-switching constant voltage circuit-constant current circuit-light emitting diode is flickered. In order to eliminate the phenomenon, the circuit is complicated, and there is a problem in that it cannot be inexpensively supplied to the consumer due to an excessive number of stages configured such as a separate power factor correction circuit.

An object of the present invention is to provide a switching mode power supply for a light emitting diode that can eliminate the flicker phenomenon.

Another object of the present invention is to provide a switching mode power supply for a light emitting diode which can simplify the circuit configuration and reduce the manufacturing cost.

In order to achieve the above object, the present invention provides a rectifier for rectifying AC power applied from the outside into a DC power supply, and a second rectifier for receiving and rectifying the DC power rectified by the first rectifier by a transformer. A constant current circuit for stepping down and outputting the DC power output from the second rectifier, a feedback circuit comparing the DC power output from the second rectifier with a reference voltage and feeding back a current value according to the difference value; And a power factor correction circuit for switching the DC power applied to the transformer in the first rectifier according to the current value fed back from the feedback circuit.

The first rectifier includes a bridge diode for rectifying the externally applied AC power and converting it into a DC power source, a smoothing capacitor for smoothing the DC power output from the bridge diode, and a DC power output from the capacitor. A transformer is applied to the two rectifiers, and a second diode for switching the transformers. The second rectifier includes a bridge circuit for rectifying the DC power applied through the transformer and a capacitor for smoothly rectifying the DC power output from the bridge circuit.

The feedback circuit includes a reference voltage generator for generating a reference voltage, an operational amplifier for comparing the DC power output from the second rectifier with the reference voltage, and a current according to a difference value compared with the operational amplifier. It includes a photocoupler applied to.

The power factor correction circuit includes a power factor correction IC for receiving a current applied from the photocoupler and a first transistor for controlling a gate duty of the power factor correction IC to switch a current applied to the second rectifier by the transformer. Include. The constant current circuit includes at least one constant current circuit. The constant current circuit is provided with a step-down converter for stepping down the DC power output from the second rectifier, a ripple reducing element provided between the step-down converter and the output stage to reduce the ripple of the DC power source, and between the step-down converter and the output terminal. And an electrostatic protection circuit to prevent static electricity. In this case, the step-down converter includes a buck converter. The ripple reduction element also includes a capacitor connected in parallel between the output stages. The static electricity protection circuit includes a zener diode connected between one end of the ripple reduction element and the output terminal, a diode connected in parallel with the zener diode, and one end connected in parallel between the zener diode and the diode and the other end of the zener diode. And a resistor connected to the other end of the ripple reduction element.

In addition, the present invention may further include a ceramic capacitor for backing up the smoothing capacitor which is an electrolytic capacitor.

The present invention can provide a switching mode power supply for a light emitting diode capable of simultaneously performing constant voltage and power factor compensation in one-stage, eliminating low frequency ripple and reducing high frequency ripple simultaneously with constant current rectification in two-stage.

In addition, the present invention can provide a switching mode power supply for a light emitting diode that can be manufactured in a two-stage structure to reduce the manufacturing cost.

In addition, the present invention can provide a switching mode power supply for a light emitting diode having a ceramic capacitor that can be backed up even if the smoothing capacitor, which is an electrolytic capacitor, in a constant voltage circuit reaches its end of life.

1 is a block diagram of a switched mode power supply for a light emitting diode according to the present invention.
2 is a circuit diagram of a switched mode power supply for a light emitting diode according to the present invention.
3 is a step-down converter block diagram of a switched mode power supply for a light emitting diode according to the present invention.

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

It will be apparent to those skilled in the art that the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, It is provided to let you know. Like reference numerals refer to like elements throughout.

1 is a block diagram of a switched mode power supply for a light emitting diode according to the present invention.

As shown in FIG. 1, a switching mode power supply for a light emitting diode according to the present invention includes a noise filter 100 for removing noise of an AC power applied from the outside and an AC power applied from the noise filter 100. The first rectifier 200 rectified by the power source, the second rectifier 300 receives the DC power rectified by the first rectifier 200 by the transformer, and the second rectified by the second rectifier 300 A feedback circuit 500 for feeding back a secondary rectified DC power output from the second rectifier 300, a constant current circuit 400 that receives a DC power supply, removes ripple, and outputs the result to the light emitting diode, and a feedback. The power factor correction circuit 600 controls the first rectifier 100 according to the comparison value fed back from the circuit 500.

2 is a circuit diagram of a switching mode power supply for a light emitting diode according to the present invention.

The noise filter 100 is for removing EMI (Electro Magnetic Interference) noise before externally applied AC power is applied to the first rectifier 200. As shown in FIG. 2, the resistor, the inductor, and the capacitor are shown in FIG. Using high frequency noise and low frequency noise can be removed. Of course, as shown in FIG. 2, the noise is removed using an inductor, a capacitor, a resistor, and the like, but the circuit configuration may vary. In addition, the noise filter 100 may be omitted. In this case, the AC power applied from the outside is directly applied to the first rectifier 200.

The first rectifier 200 is for first rectifying the external AC power applied from the noise filter 100 and converting the DC power to DC power. The first rectifier 200 rectifies and rectifies the AC power applied from the noise filter 100 to a bridge diode to supply DC power. Convert to To this end, the first rectifier 200 applies the DC power output from the first and second bridge diodes BD1 and BD2 and the first and second bridge diodes BD1 and BD2 to the second rectifier 300. A transformer T1, a second diode D2 and a first transistor Q1 for switching the transformer T1 are included. In this case, the second diode D2 is for switching during the initial driving of the switching mode power supply for the light emitting diode according to the present invention, and the first transistor Q1 is for switching after the initial driving.

The second rectifier 300 is for re-rectifying the DC power applied from the first rectifier 200 through the transformer T1, and the bridge circuits D3A, D3, D4A, D4, and capacitors C15, C12, C13, C40, C25, C42, C26). At this time, the bridge circuits D3A, D3, D4A, and D4 rectify the DC current sheared through the transformer T1 using the third and third A diodes and the fourth and fourth A diodes. In addition, the DC power rectified through the bridge circuits D3A, D3, D4A, and D4 may include the 24th resistor, the 15th capacitor, the 12th capacitor, the 13th capacitor, the 25th resistor, the 40th capacitor, the 25th capacitor, and the 42nd. Through the capacitor, the 26 th capacitor is again wave rectified.

The constant current circuit 400 is applied to the light emitting diode by removing the ripple by receiving the second rectified DC power from the second rectifier 300, the present embodiment is the first constant current circuit 410 and the second constant current circuit 420.

The first constant current circuit 410 is for applying a DC power supply to a first light emitting diode (not shown), and reduces the first ripple provided between the first step-down converter IC5 and the first step-down converter IC5 and the output terminal. Element C33 and first static electricity protection circuits D9, D10, and R42.

3 is a block diagram of a step-down converter of a switching mode power supply for a light emitting diode according to the present invention.

The first step-down converter IC5 is for converting a constant voltage into a constant current by stepping down the DC power applied from the second rectifier 300 and includes a buck converter. In this case, as shown in FIG. 3, the AP8802 includes a PWM / DC controller, a voltage regulator, a sensing block, and a comparator therein as a first step-down converter IC5. In addition, the AP8802 can eliminate low frequency ripple and reduce high frequency ripple.

The first ripple reduction element C33 is to reduce the ripple of the DC power source stepped down by the first step-down converter IC5 and includes a thirty-third capacitor C33. At this time, the thirty-third capacitor C33 is connected in parallel to the output terminal.

The first static electricity protection circuits D9, D10, and R42 are for protecting the output stage from static electricity, and are a zener diode, a ninth diode D9 connected between one end of the first ripple reduction element C33 and the output stage, A tenth diode D10 connected in parallel with the ninth diode D9, and one end thereof is connected in parallel between the ninth diode D9 and the tenth diode D10, and the other end of the first ripple reduction element C33 is closed. And a 42nd resistor R42 connected to the other end.

The second constant current circuit 420 is for applying DC power to a second light emitting diode (not shown), and reduces the second ripple provided between the second step-down converter IC4 and the second step-down converter IC4 and the output terminal. Element C32 and second static electricity protection circuits D7, D8, and R41. In this case, the second step-down converter IC4, the second ripple reduction element C32, and the second static electricity protection circuits D7, D8, and R41 are the first step-down converter IC5 and the first ripple reduction element C33 described above. Since the configuration and the function are the same as those of the first static electricity protection circuits D9, D10, and R42, description thereof will be omitted.

The feedback circuit is for feeding back the secondary rectified DC power output from the second rectifier, and includes a reference voltage generator IC3, an operational amplifier op-amp IC2, and a photocoupler PC1. do.

The reference voltage generator is for generating a reference voltage, and this embodiment illustrates TL431.

The operational amplifier IC2 may include the twentieth resistor R20 and the twelfth resistor R20 to which the voltage of the twenty-second resistor R22 to which the reference voltage generated by the reference voltage generator IC3 is applied and the voltage output from the second rectifier 300 are applied. The magnitude of the current applied to the photocoupler PC1 is adjusted by comparing the voltages of the 21st resistor R21 and the 26th resistor R26. That is, when the voltage of the second rectifier 300 is lower than the reference voltage generated by the reference voltage generator IC3, the magnitude of the current applied to the photocoupler PC1 is increased, and the voltage of the second rectifier 300 is referred to. When the voltage is higher than the reference voltage generated by the voltage generator IC3, the amount of current applied to the photocoupler PC1 is reduced. Of course, the magnitude of the current increased or decreased here preferably corresponds to the difference between the voltage of the second rectifier 300 and the reference voltage.

The photocoupler PC1 is for applying the current value adjusted through the operational amplifier IC2 to the power factor correction IC IC1, and the light emitting diode therein emits light by the current applied from the operational amplifier IC2. As a result, the transistor inside thereof is conducted from the fourth to the third. At this time, the magnitude of the current conducted in the internal transistor is correspondingly changed according to the current value adjusted through the operational amplifier IC2, and the changed current value is applied to the power factor correction IC IC1.

The power factor correction circuit 600 is for controlling the first rectifier 200 according to the comparison value fed back from the feedback circuit. The power factor correction circuit 600 controls the gate duty by the power factor correction IC IC1 and the power factor correction IC IC1. One transistor Q1 is included. At this time, the power factor is compensated simultaneously with the constant voltage by the first transistor Q1 whose gate duty is adjusted by the power factor correction IC IC1.

On the other hand, the present invention may further include a ceramic capacitor for backing up the electrolytic capacitor.

As shown in FIG. 2, the present invention includes a seventh capacitor C7, which is a smoothing capacitor for smoothing the current rectified by the direct current from the first and second bridge diodes BD1 and BD2. In this case, the seventh capacitor C7 is an electrolytic capacitor, and heat is generated when the switching mode power supply for the light emitting diode according to the present invention is operated. In addition, in this manner, when heat is generated, the temperature of the seventh capacitor C7 is increased to degrade the electrolyte in the interior, thereby rapidly decreasing performance. Therefore, the seventh capacitor C7 cannot perform its role, and thus the life of the switching mode power supply for the light emitting diode ends.

However, the present invention includes the eighth capacitor C8, the ninth capacitor C9, and the tenth capacitor C10, which are ceramic capacitors that back up the seventh capacitor C7, and thus the seventh capacitor C7 has reached its end of life. Even so, switching-mode power supplies for light-emitting diodes remain available. That is, even if the life of the seventh capacitor C7, which is a large capacity smoothing capacitor, ends, the eighth capacitor C8, the ninth capacitor C9, and the tenth capacitor C10 connected in parallel are the seventh capacitor C7. It will play the role of. Of course, the eighth capacitor C8, the ninth capacitor C9, and the tenth capacitor C10 have smaller capacities than the seventh capacitor C7, but there is no problem for the light emitting diode switching mode power supply to operate.

As described above, the present invention provides a switching mode power supply for a light emitting diode capable of simultaneously performing constant voltage and power factor correction in one-stage, eliminating low frequency ripple and reducing high frequency ripple simultaneously with constant current rectification in two-stage. can do. In addition, the present invention can provide a switching mode power supply for a light emitting diode that can be manufactured in a two-stage structure to reduce the manufacturing cost. In addition, the present invention can provide a switching mode power supply for a light emitting diode having a ceramic capacitor that can be backed up even if the smoothing capacitor, which is an electrolytic capacitor, in a constant voltage circuit reaches its end of life.

100: noise filter 200: first rectifier
300: second rectifier 400: constant current circuit
410: first constant current circuit 420: second constant current circuit
500: feedback circuit 600: power factor correction circuit

Claims (11)

A first rectifier for rectifying the AC power applied from the outside into a DC power supply;
A second rectifier for receiving and rectifying the DC power rectified by the first rectifier by a transformer;
A step-down converter for stepping down the DC power output from the second rectifier, a ripple reducing element provided between the step-down converter and the output terminal to reduce the ripple of the DC power, and provided between the step-down converter and the output terminal to prevent static electricity At least one constant current circuit composed of an electrostatic protection circuit,
A feedback circuit comparing the DC power output from the second rectifier with a reference voltage and feeding back a current value according to the difference value;
In the switching mode power supply for a light emitting diode comprising a power factor correction circuit for switching the DC power applied to the transformer in the first rectifier according to the current value fed back from the feedback circuit,
The static electricity protection circuit,
A zener diode connected between one end of the ripple reduction element and the output end;
A diode connected in parallel with the zener diode, and
And a resistor connected at one end thereof in parallel between the zener diode and the diode and at the other end thereof connected to the other end of the ripple reduction element. The method of claim 1,
The first rectifier,
A bridge diode which rectifies and rectifies the AC power applied from the outside into a DC power source;
A smoothing capacitor for smoothing the DC power output from the bridge diode;
A transformer for applying the DC power output from the capacitor to the second rectifier;
A switching mode power supply for a light emitting diode comprising a second diode for switching the transformer. The method of claim 2,
The smoothing capacitor is an electrolytic capacitor,
The switching mode power supply for a light emitting diode further comprises a ceramic capacitor for backing up the electrolytic capacitor. The method of claim 2,
The second rectifier,
A bridge circuit for re-rectifying the DC power applied through the transformer,
And a capacitor for smoothly rectifying the DC power output from the bridge circuit. The method of claim 1,
Wherein the feedback circuit comprises:
A reference voltage generator for generating a reference voltage,
An operational amplifier comparing the DC power output from the second rectifier with the reference voltage;
And a photocoupler for applying a current according to the difference value compared in the operational amplifier to the power factor correction circuit. The method of claim 5,
The power factor correction circuit,
A power factor correction IC receiving the current applied from the photocoupler;
And a first transistor whose gate duty is controlled by the power factor correction IC to switch a current applied by the transformer to the second rectifier. delete delete The method of claim 1,
The step-down converter comprises a buck converter switching mode power supply for a light emitting diode. The method of claim 1,
And the ripple reduction element comprises a capacitor connected in parallel between the output stages. delete

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