KR20090132253A - Light emitting diode driver having single stage - Google Patents

Abstract

PURPOSE: A single-ended LED driver is provided to reduce waste of components needed for an LED driver circuit by forming the circuit simply. CONSTITUTION: A bridge rectifying(112) rectifies input current. An EMI(Electromagnetic Interference) filter(110) removes noise. A transformer(120) transforms output of the bridge rectifying circuit. A transformer magnetic flux detection unit(152) detects a magnetic flux of the transformer.

Description

LIGHT EMITTING DIODE DRIVER HAVING SINGLE STAGE}

The present invention relates to a light emitting diode (LED) driver, and more particularly, to a light emitting diode driver for driving a light emitting diode by providing a constant current in a single stage.

Light emitting diodes, which have been selected for lighting, are becoming more and more popular and, in many applications, are replacing existing lighting devices. For example, light emitting diodes are widely used in traffic lights, backlight units of liquid crystal displays, and the like, and are attracting attention for street lamps. It may be desirable for the light emitting diode to be able to control the light output according to the needs of the user. Since the brightness of the light emitting diode is proportional to the current flowing through the light emitting diode, the current of the light emitting diode should be controlled.

In general, since the source power source for driving the light emitting diode is AC, there may be a phase mismatch between the input voltage and the input current. In the presence of such a phase mismatch, the power delivered from the power supply to the load decreases in a uniform fashion, but if the voltage and current are in phase, the power loss is reduced. This technique is known as power factor correction (PFC).

In the circuit used for illumination, such a power factor correction circuit is almost essential, and the circuit for driving the light emitting diode described above is no exception.

FIG. 1 is a block diagram illustrating an example of a conventional LED driver. Referring to FIG. 1, a conventional LED driver 10 includes three stages, that is, a power factor correction circuit 12 and a DC-DC converter. 14 and a constant current supply 16.

The power factor correction circuit 12 receives an AC power source AC to perform a step-up function to perform power factor correction. This power factor correction circuit 12 stage has a power factor of approximately 0.9. The DC-DC converter 14 is a main power converter, and also performs an isolation function to protect the constant current supply unit 16 and the light emitting diodes 18. The DC-DC converter 14 stage has an efficiency of approximately 0.8. The constant current supply unit 16 is a stage for supplying a constant current for driving the light emitting diodes 18 by receiving the output of the DC-DC converter 14. The constant current supply 16 stage has an efficiency of approximately 0.8.

In the conventional light emitting diode driver, since it is configured in three stages as illustrated, the circuit configuration is very complicated, and the elements required for the circuit configuration are many, thus increasing the cost of implementing the light emitting diode driver. There is this. In addition, there is a problem that the power conversion efficiency is also lowered due to the multi-stage configuration.

Therefore, the present invention is a single stage that can solve the problem that the configuration of the circuit is complicated because the conventional light emitting diode driver is composed of multiple stages as described above, and the consumption of elements required for the circuit configuration is increased and the cost increases. An object of the present invention is to provide a light emitting diode driver.

It is also an object of the present invention to provide a single stage light emitting diode driver that can improve the problem of low power conversion efficiency.

A single stage light emitting diode driver for driving a light emitting diode for achieving the above object includes a bridge rectifying circuit for rectifying an input current; An electronic interference filter disposed in front of the bridge rectifier circuit to remove noise; A starting current supply unit for supplying a predetermined starting current by receiving the output of the bridge rectifier circuit; A transformer for transforming an output of the bridge rectifier circuit; A rectifier circuit for rectifying the output of the transformer; A smoothing circuit for outputting a DC current to be used for driving the light emitting diodes by smoothing the output of the rectifying circuit; A transformer magnetic flux detector coupled to the transformer for providing an operating current and detecting magnetic flux of the transformer; A comparator for comparing a voltage applied to a resistor connected to an input terminal of the light emitting diode with a first reference voltage; An optocoupler for adjusting a duty ratio of a pulse width modulated signal by increasing or decreasing a detection current according to a comparison result of the comparison unit; A switching TR unit controlled by a pulse width modulation signal to adjust a primary current of the transformer; A current detector for detecting a current flowing in the switching TR section; And start by receiving the predetermined starting current from the starting current supply unit, and operating by receiving the operating current from the transformer magnetic flux detecting unit, the current detected by the optocoupler, the current output from the current detecting unit, and the A control unit controlling the switching TR unit by adjusting a duty ratio of the pulse width modulated signal depending on the magnetic flux detected by a transformer magnetic flux detector; It includes.

Preferably, the single stage light emitting diode driver is connected between the bridge rectifying circuit and the switching TR section in parallel with a primary circuit of the transformer to provide a snap circuit for protecting the switching TR section. It may further include.

Preferably, the comparator may further compare the input voltage and the second reference voltage of the light emitting diode.

In addition, as a result of the comparison in the comparison unit, when the voltage at the first input terminal of the light emitting diode is smaller than the first reference voltage, the resistance value of the optocoupler is increased and the duty ratio of the pulse width modulation signal is increased. When the voltage at the first input terminal of the light emitting diode is greater than the first reference voltage, the resistance value of the optocoupler may decrease and the duty ratio of the pulse width modulation signal may be reduced.

Further, as a result of the comparison in the comparison unit, when the divided voltage of the input voltage of the light emitting diode is smaller than the second reference voltage, the resistance value of the optocoupler is increased, and the duty ratio of the pulse width modulation signal is increased. When the divided voltage of the input voltage of the light emitting diode is greater than the second reference voltage, the resistance value of the optocoupler may decrease and the duty ratio of the pulse width modulation signal may be reduced.

Preferably, a fuse for protecting the LED driver circuit of the circuit may be interposed between the AC power source and the electromagnetic interference filter unit.

As described above, the present invention provides a single stage light emitting diode driver, so that the circuit configuration is very simple compared to the light emitting diode driver conventionally configured in multiple stages, thereby reducing the consumption of elements required for the configuration of the light emitting diode driver circuit. Has the effect.

In addition, the present invention can implement a complete power factor correction operation by providing a single stage light emitting diode driver, implements a constant current operation for driving the light emitting diode, and has an effect of improving power conversion efficiency.

Hereinafter, with reference to the accompanying drawings, it will be described in detail preferred embodiments of the present invention. DETAILED DESCRIPTION The detailed description and the accompanying drawings are intended to be to those skilled in the art to assist in the understanding of the present invention, and are only intended to limit the scope of the present invention.

2 is a block diagram illustrating a single stage light emitting diode driver according to the present invention. Compared with the conventional three-stage light emitting diode shown in FIG. 1, the light emitting diode driver according to the present invention provides a constant current to the single-stage light emitting diode driver 100 to drive the light emitting diode 180. The specific configuration of such a single stage LED driver 100 is illustrated in the block diagram of FIG.

That is, Figure 3 is a block diagram showing an example of a single stage light emitting diode driver 100 according to the present invention. Referring to FIG. 3, the LED driver 100 according to the present invention includes an electromagnetic interference (EMI) filter 110, a bridge rectifier circuit 112, a starting current supply unit 114, and a transformer T ₁ , 120. ), Transformer magnetic flux detector 152, comparator 160, optocoupler 170, switching TR 140, current detector 150, rectifier circuit 122, smoothing circuit 124 and controller 130. It includes. Reference is also made to FIG. 4 which will be described later for better understanding.

The electromagnetic interference filter 110 is disposed at the front end of the bridge rectifying circuit 112 to remove noise carried on the power line. The electromagnetic interference filter 110 is generated at the front end or the rear end of the electromagnetic interference filter 110, that is, externally or internally. Filter impulsive noise.

The bridge rectifier circuit 112 is a part for rectifying the AC input AC, and the AC input AC is full-wave rectified through the bridge rectifier circuit 112.

The starting current supply unit 114 is a part for supplying a predetermined starting current to the control unit 130 by receiving the rectified output provided from the bridge rectifying circuit 112 to enable the control unit 130 to start.

The transformers T ₁ and 120 receive the rectified output from the bridge rectifier circuit 112 and transform the transformer T ₁ and 120 to operate in conjunction with the switching TR unit 140.

The rectifier circuit 122 is a circuit for rectifying the output of the transformer 120, and the smoothing circuit 124 smoothes the output of the rectifier circuit 122 to generate a direct current (DC) to be used for driving the light emitting diodes 180. Output The signal rectified and smoothed by the rectifying circuit 122 and the smoothing circuit 124 can be viewed as a direct current since the value of the capacitor (see C _{7 in} FIG. 4) used in the smoothing circuit 124 is very large. . Therefore, for convenience of description, this is referred to simply as direct current or direct current.

The transformer magnetic flux detector 152 is coupled to the transformer 120 to detect the magnetic flux of the transformer 120. Thus, the transformer magnetic flux detector 152 determines the set time point of the pulse width modulated signal for controlling the switching TR unit 140. In addition, the current provided from the output terminal of the transformer 120 to which the transformer magnetic flux detecting unit 152 is rectified provides an operating current to the controller 130.

Since it is connected in parallel between the output terminal of the transformer 120 and the control unit 130, it will be described below as part of the transformer magnetic flux detection unit 152 for providing such an operation current.

The node in which the operating current is provided from the transformer flux detection unit 152 to the control unit 130 and the node in which the starting current is provided from the starting current supply unit 114 to the control unit 130 are commonly connected to one pin of the control unit 130. do. Therefore, the starting current is provided at the start of the control unit 130, and the operating current is continuously supplied thereafter.

The comparator 160 is for controlling the current flowing through the input terminal of the light emitting diode 180, and the comparator 160 is the output terminal (N ₄ of FIG. 4) of the light emitting diode driver 100 and the input terminal of the light emitting diode 180 (Fig. This is a part for comparing the voltage applied to the resistor (R ₁₃ of FIG. 4) connected between OUT _{2 of} 4 and a predetermined reference voltage (V _ref1 of FIG. 4). In addition, the comparator 160 may further compare the input voltage of the light emitting diode 180 with the second reference voltage (V _ref2 of FIG. 4). Therefore, it is possible to prevent the overvoltage from being applied to both ends of the input terminal of the light emitting diode 180 when the light emitting diode 180 is opened.

The optocoupler 170 adjusts the duty ratio of the pulse width modulated signal by increasing or decreasing the current flowing in R ₂ of FIG. 4 according to the comparison result of the comparator 160. One end of the transistor constituting the optocoupler 170 is connected together to a node provided with an operating current, and changes the current flowing in R ₂ of FIG. Form a path for changing the voltage.

The switching TR unit 140 is controlled by the pulse width modulation signal to adjust the primary side current of the transformer 120.

The current detector 150 is a part for detecting a current flowing through the switching TR unit 140. That is, the current detector 150 detects a current flowing through the switching TR unit 140, and determines the reset point of the pulse width modulation signal in the control unit 130.

The control unit 130 is operated by receiving a predetermined starting current from the starting current supplying unit 114, operating by receiving an operating current from the transformer magnetic flux detecting unit 152, and detecting the current and current detected by the optocoupler 170. The switching TR unit 140 is controlled by adjusting the duty ratio of the pulse width modulated signal depending on the current output from the detector 150 and the magnetic flux detected by the transformer magnetic flux detector 152. For example, the control unit 130 is L6560, L6561, L6562, L6563 from NST1 Electronics, NCP1606, NCP1601 from ON Semiconductor, UC3852, UC3853, UC3854, UC28019, UCC28060 from Texas Instruments, ML4810, ML4812, ML4821, and Fairchild. SG6980 and the like, but is not particularly limited thereto.

Furthermore, the single stage LED driver 100 may further include a snubber circuit (see R ₁₀ , C ₄ , and D ₂ of FIG. 4) for protecting the switching TR unit 140. The snubber circuit is connected in series and in parallel with the primary circuit of the transformer 120 between the bridge rectifier circuit 112 and the switching TR unit 140.

For example, referring to the operation of the LED driver 100 based on the voltage comparison in the comparison unit 160, the voltage at the first input terminal OUT ₂ of the LED 180 is the first reference voltage. When smaller than V _ref1 , the resistance value of the optocoupler 170 increases and the duty ratio of the pulse width modulated signal output from the controller 130 to control the switching TR unit 140 increases. As a result, the output of the LED driver 100 is increased.

On the contrary, in the voltage comparison in the comparison unit 160, when the voltage of the first input terminal OUT ₂ of the light emitting diode 180 is greater than the first reference voltage V _ref1 , the resistance value of the optocoupler 170 is As a result, the duty ratio of the pulse width modulated signal output from the controller 130 is reduced, and as a result, the output of the LED driver 100 is reduced.

Therefore, the comparison control unit 160 achieves a current control loop that can increase or decrease the driving current of the light emitting diode 180 within a predetermined range.

In addition, when comparing voltages in the comparison unit 160, when the divided voltage of the input voltage of the light emitting diode 180 (the voltage applied to R ₁₂ in FIG. 4) is smaller than the second reference voltage V _ref2 , the optocoupler 170. ), The resistance value increases, and the duty ratio of the pulse width modulated signal output from the controller 130 to control the switching TR unit 140 increases. As a result, the voltage at the output terminal of the light emitting diode driver 100 is increased.

On the contrary, in the voltage comparison in the comparison unit 160, when the divided voltage of the input voltage of the light emitting diode 180 is greater than the second reference voltage, the resistance value of the optocoupler 170 decreases and the pulse width modulation signal As a result of the reduced duty ratio, the voltage at the output terminal of the light emitting diode driver 100 is reduced.

In this way, a voltage control loop for adjusting the voltage at the output terminal of the LED driver 100 is formed through the comparison in the comparison unit 160, so that the LED driver 100 has no opening or disconnection when the LED 180 is opened. If this occurs, the risk of excessive output voltage of the LED driver 100 may be reduced.

4 is a circuit diagram of a single stage light emitting diode driver according to an embodiment of the present invention. A single stage light emitting diode driver according to an embodiment of the present invention will be described in detail below with reference to FIGS. 3 and 4. For ease of understanding, the following description has given the same reference numerals for corresponding components in FIGS. 3 and 4.

First, the electromagnetic interference filter 102 includes capacitors C ₁₁ , C ₁₂ , C ₁₃ , C ₁₄ and an inductor L ₁ . A fuse F ₁ may be further interposed between the AC power source and the electromagnetic interference filter 102 to protect the LED driver 100.

Capacitors C ₁₂ and C ₁₃ secure the ground voltage and remove impulsive noise from the outside. Capacitors C ₁₁ , C ₁₄ and inductor L ₁ form a low pass filter (LPF). In particular, the inductor L ₁ is wound so that the primary side and the secondary side have the same phase to remove the in-phase component.

The output of the electromagnetic interference filter 102 is rectified by the bridge rectifying circuit BR. The bridge rectifying circuit BR may be composed of four diodes as shown, and the bridge rectifying circuit BR full-wave rectifies the output of the electromagnetic interference filter 102. The full wave rectified voltage is supplied to the rear end in the form of a pulse wave. The high frequency component induced at the full-wave rectified voltage, that is, the voltage at the N ₁ node (hereinafter referred to as “input voltage” for convenience) is removed by the capacitor C ₁ . Capacitor C ₁ is preferably a small capacitance film capacitor (also referred to as a "film capacitor"), the size of which may be about 1 μF, but is not particularly limited.

First, referring to the resistor (R ₆ ) and the capacitor (C ₅ ) constituting the starting current supply unit 114, when the input voltage (voltage of the N ₁ node) is supplied, to the capacitor (C ₅ ) through the resistor (R ₆ ) The charge is charged and the voltage of the node N ₅ , that is, the voltage applied to the eighth pin of the controller 130 increases. When the voltage applied to pin 8 of the controller 130 continues to rise and rises to a voltage sufficient to start the controller 130, the operation of the controller 130 is started.

When the control unit 130 operates to output the pulse width modulation signal PWM to pin 7 as an output terminal, the switching TR unit 140 is turned on. That is, as shown, the switching TR unit 140 may include a resistor R ₇ and a switching transistor Q ₁ , and the pulse width modulation signal output to pin 7 which is an output terminal of the controller 130 may be The switching transistor Q ₁ is turned on through the resistor R ₇ . The switching transistor Q ₁ is preferably a MOSFET.

Then, the main current is the source of the transformer node connected to the primary winding (120a) of _{(T 1, 120) (N} 1, N 6), a switching transistor (Q ₁₎ a drain terminal, a switching transistor (Q ₁₎ of the terminal, It flows through the path of the resistor R ₉ . This current induces the output voltage to the secondary winding 120b of the transformers T ₁ and 120. The output induced on the secondary winding 120b side is rectified by the rectifier circuits D ₄ and 122. The rectifier circuits D4 and 122 may be formed of one diode D ₄ , as shown.

After rectification by the rectification circuits D ₄ and 122, the smoothing circuits C ₇ and 124 are then smoothed to provide a direct current DC to the light emitting diodes 180.

Transformers T ₁ and 120 are primary winding 120a connected between node N ₁ and node N ₆ , and secondary winding 120b connected between node N ₉ and node N ₄ . And further, further comprises an auxiliary winding (120c) connected between the node (N ₈ ) and node (N ₂ ).

Therefore, when the switching transistor Q ₁ is turned on and current flows through the drain terminal and the source terminal thereof, the voltage is induced in the auxiliary winding 120c of the transformers T ₁ and 120. The voltage induced by the auxiliary winding 120c is rectified by the diode D3, and is supplied to the node N ₅ connected to the eighth pin of the controller 130, and the power supply voltage (generally V _CC as the operating voltage of the controller 130). Will be supplied. The power supply voltage V _CC is applied to the node N ₅ , and in this case, the current input to the eighth pin of the controller 130 has been expressed as an operating current.

The resistor R ₂₇ is a component for detecting the magnetic flux of the transformers T ₁ and 120 through the output induced by the auxiliary winding 120c and generates a zero current of the transformers T ₁ and 120. It detects and reflects to the pulse width modulation signal for control of the switching transistor Q1.

In FIG. 3, the transformer magnetic flux detector 152 for providing the operating current to the controller 130 and detecting the magnetic flux of the transformers T ₁ and 120, as described in FIG. 3, has a resistance R as shown in FIG. 4. ₂₇ ), and may be seen to include a diode D ₃ and a capacitor C ₅ .

When the power supply voltage V _CC is applied to the node N ₅ by the series of operations as described above, the supply of the starting current to the controller 130 by the starting current supply unit 114 is stopped. That is, substantially no current flows through the resistor R ₆ of the starting current supply unit 114.

The resistor R ₁₀ , the capacitor C ₄ , and the diode D ₂ constitute a snubber circuit. The snubber circuit is connected in parallel to the primary winding 120a of the transformers T ₁ and 120 between the node N ₁ and the node N ₆ . This switch naebeo circuit, transformer, switching transistor (Q ₁₎ a circuit for suppressing this, when the excess spike voltage exceeding the rating of the switching transistor (Q ₁₎ by a leakage magnetic flux caused in the (T _1, 120) Function to protect

The current detector 150 including the resistor R ₈ and the resistor R ₉ is a portion for detecting a current flowing through the switching transistor Q ₁ and applying it to the fourth pin of the controller 130. That is, the current detector 150 is a voltage applied to the fourth pin of the controller 130 through the resistor R ₈ by the resistor R ₈ and the resistor R ₉ , and is applied to the resistor R ₉ . Detects whether the flowing current is a predesigned current.

The resistor R ₁ and the resistor R ₅ are portions for dividing an input voltage, that is, a voltage rectified by the bridge rectifying circuit BR, and providing the divided voltage to the controller 130. The capacitor C ₂ connected in parallel to the resistor R ₁ is a small capacitor for noise reduction. In addition, the resistor R ₄ and the capacitor C ₃ are stabilizing elements for preventing oscillation of the components in the controller 130.

The comparator 160 may compare the voltage of the output terminal (the input terminal of the light emitting diode 180) OUT ₂ of the driver 100 with the predetermined reference voltage V _ref1 , and further, the input voltage of the light emitting diode 180. (Actually, the voltage divided by the resistor R ₁₁ and the resistor R ₁₂ ) and the second reference voltage V _ref2 may be further compared.

In the former case, the voltage of the input terminal OUT ₂ of the light emitting diode 180 and the reference voltage V _ref1 are compared by the first comparator COM ₁ of the comparator. In the latter case, the input of the light emitting diode 180 is input. The divided voltage of the voltages (voltages across OUT ₁ and OUT ₂ ) and the reference voltage Vref ₂ are compared by the second comparator COM ₂ of the comparator. The second reference voltage Vref _{2 is} provided from the reference voltage generator 164, and the first reference voltage V _ref1 is the second reference voltage V _ref2 by the resistor R ₁₅ and the resistor R ₁₆ . Is the partial pressure of. The reference voltage generator 164 receives a voltage of the input terminal OUT ₁ of the light emitting diode 180 to provide a precise reference voltage to the comparator 160.

Next, the transforming unit secondary winding (120b) In operation after the output voltage, namely (voltage between OUT ₁ end OUT ₂ stage) the light emitting diode 180, the input voltage of (T _1, 120) has a resistance (R ₁₁₎ and a resistor (R is divided by ₁₂₎ the second comparator (is applied to the inverting input of COM _2), the second comparator (second supplied from the non-inverting input, the reference voltage generating unit 164 of the COM ₂₎ The reference voltage V _ref2 is applied.

First, in the first comparator COM ₁ , the voltage of the input terminal OUT ₂ of the light emitting diode 180, which is a voltage detected by the resistor R ₁₃ and proportional to the output current, and the first reference voltage V _ref1 . In comparison, when the voltage of the input terminal OUT ₂ is lower than the first reference voltage V _ref1 , the voltage of the output terminal OP ₂ of the first comparator COM ₁ is increased. When the voltage at the output terminal OP ₂ increases, the current flowing to the outputs of the resistor R ₁₄ , the output terminal OP ₁ , the output terminal OP ₂ , and the first comparator COM ₁ decreases, thereby causing the optocoupler. The LED of ISO ₁ darkens and flows to the transistor-side current of the optocoupler ISO ₁ (i.e., node N ₅ , the transistor of optocoupler ISO ₁ , resistor R ₂ and node N ₂ ). The current) decreases to lower the voltage across the resistor R ₂ . As a result, the voltage input to pin 1 of the controller 130 is lowered, thereby increasing the duty ratio of the pulse width modulated signal output to pin 7, thereby increasing the output voltage of the driver.

On the contrary, when the voltage of the input terminal OUT ₂ of the light emitting diode 180 is compared with the first reference voltage V _ref1 , and the voltage of the input terminal OUT ₂ is higher than the first reference voltage V _ref1 , the first comparator The voltage at the output terminal OP ₂ of (COM ₁ ) is lowered. When the voltage at the output terminal OP ₂ decreases, the current flowing to the output of the resistor R ₁₄ , the output terminal OP ₁ , the output terminal OP ₂ , and the first comparator COM ₁ increases, thereby causing the optocoupler. The LED of ISO ₁ becomes brighter, and the current at the transistor side of the optocoupler ISO ₁ increases, thereby increasing the voltage across the resistor R ₂ . As a result, the voltage input to pin 1 of the controller 130 is increased, thereby reducing the duty ratio of the pulse width modulated signal output to pin 7, thereby lowering the output voltage of the driver.

As such, a current control loop is formed to control the current input to the light emitting diode 180. Here, the reference voltage V _ref2 generated by the reference voltage generator 164 is directly controlled by the first comparator COM _1. The voltage is divided by using the resistors R ₁₅ and R ₁₆ instead of being applied to the inverting input of the power source. The reason is that when the reference voltage is large, the output terminal of the driver 100, that is, the input terminal OUT ₂ of the Since the voltage applied to the resistor (R ₁₃ ) for the current detection must be large, the resistance (R ₁₃ ) must be large, and the resulting power loss increases, so as to prevent this.

Thus, since the LED driver 100 according to the present invention intends to drive the constant current driving of the LED 180, the constant current setting value for driving the LED 180 (actually, the first comparator COM ₁ ) It is set through the reference voltage applied to the non-inverting input terminal of the) can be controlled to the constant current flow by setting the driving current of the light emitting diode.

Next, in a second comparator _{(COM. 2),} if the resistors (R _11, R ₁₂₎ compares the partial pressure and the second reference voltage (V _ref2) of, if the partial pressure is lower than the second reference voltage (V _ref2) the 2 The voltage at the output terminal OP ₂ of the comparator COM ₂ is increased. When the voltage at the output terminal OP ₂ increases, the current flowing to the outputs of the resistor R ₁₄ , the output terminal OP ₁ , the output terminal OP ₂ , and the second comparator COM ₂ decreases, thereby causing the optocoupler. The LED of ISO ₁ darkens and flows to the transistor-side current of the optocoupler ISO ₁ (i.e., node N ₅ , the transistor of optocoupler ISO ₁ , resistor R ₂ and node N ₂ ). The current) decreases to lower the voltage across the resistor R ₂ . As a result, the voltage input to pin 1 of the controller 130 is lowered, thereby increasing the duty ratio of the pulse width modulated signal output to pin 7, thereby increasing the output voltage of the driver.

On the contrary, when the divided voltage is higher than the second reference voltage V _ref2 , the voltage of the output terminal OP ₂ of the second comparator COM ₂ is lowered. When the voltage at the output terminal OP ₂ is lowered, the LED of the optocoupler ISO ₁ becomes brighter, so that the transistor-side current of the optocoupler ISO ₁ increases to increase the voltage across the resistor R ₂ . As a result, the voltage input to pin 1 of the controller 130 is increased, thereby reducing the duty ratio of the pulse width modulated signal output to pin 7, thereby lowering the output voltage of the driver.

As such, the voltage control loop is formed. Here, since the second comparator COM ₂ is a circuit for safety, it is set slightly higher than the required voltage, so that the current control associated with the first comparator COM ₁ is normally operated. It is preferable to adjust the voltage setting value so that only the loop operates and such a voltage control loop is performed so that the output voltage does not excessively increase when the light emitting diode 180 is disconnected or the output is opened.

In order to simplify the circuit, the first comparator COM ₁ , the second comparator COM ₂ , and the reference voltage generator 164 constituting the comparator 160 may be an integrated circuit configured in one package.

The light emitting diode driver according to the present invention as described above is not limited to the above embodiments, and various modifications and applications can be made without departing from the basic principles of the present invention. It will be obvious to those who have knowledge.

1 is a block diagram showing an example of a conventional LED driver;

2 is a block diagram illustrating a single stage light emitting diode driver according to the present invention;

3 is a block diagram showing an example of a single stage light emitting diode driver according to the present invention; and

4 is a circuit diagram of a single stage light emitting diode driver according to an embodiment of the present invention.

Claims (5)

A bridge rectifier circuit for rectifying the input current; An electronic interference filter disposed in front of the bridge rectifier circuit to remove noise; A starting current supply unit for supplying a predetermined starting current by receiving the output of the bridge rectifier circuit; A transformer for transforming an output of the bridge rectifier circuit; A rectifier circuit for rectifying the output of the transformer; A smoothing circuit for smoothing the output of the rectifying circuit to output a DC current to be used for driving a light emitting diode; A transformer magnetic flux detector coupled to the transformer for providing an operating current and detecting magnetic flux of the transformer; A comparator for comparing a voltage applied to a resistor connected in series to an input terminal of the light emitting diode and a first reference voltage; An optocoupler for adjusting a duty ratio of a pulse width modulated signal by increasing or decreasing a current detected according to a comparison result in the comparison unit; A switching TR unit controlled by the pulse width modulation signal to adjust a primary current of the transformer; A current detector for detecting a current flowing in the switching TR section; And It operates by receiving the predetermined starting current from the starting current supply unit, and operates by receiving the operating current from the transformer magnetic flux detecting unit, the current detected by the optocoupler, the current output from the current detecting unit, and the transformer magnetic flux. A control unit controlling the switching TR unit by adjusting a duty ratio of the pulse width modulated signal depending on the magnetic flux detected by the detector; Single stage light emitting diode driver comprising a. The method according to claim 1, And a snapper circuit connected in parallel to the primary circuit of the transformer between the bridge rectifier circuit and the switching TR section to protect the switching TR section. The method according to claim 1 or 2, wherein the comparison unit, The LED driver of claim 1, further comprising comparing the input voltage of the light emitting diode with a second reference voltage. The method according to claim 1 or 2, When the voltage at the first input terminal of the light emitting diode is smaller than the first reference voltage, the resistance value of the optocoupler is increased, and the duty ratio of the pulse width modulation signal is increased. When the voltage at the first input terminal of the light emitting diode is greater than the first reference voltage, the resistance value of the optocoupler is decreased, and the duty ratio of the pulse width modulation signal is reduced. . The method according to claim 3, When the partial pressure of the input voltage of the light emitting diode is smaller than the second reference voltage, the resistance value of the optocoupler is increased, and the duty ratio of the pulse width modulation signal is increased. And when the partial pressure of the input voltage of the light emitting diode is greater than the second reference voltage, the resistance value of the optocoupler decreases and the duty ratio of the pulse width modulation signal decreases.

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