TW201208464A - Direct-driving light-emitting diode (LED) driver - Google Patents

Abstract

A direct-driving light-emitting diode (LED) driver is provided. The LED driver employs an isolation circuit coupled to an output of an LED string and a constant current controller to automatically adjust its output voltage according to the operating voltage of the LED string for driving LED strings each having different operating voltage. The LED driver omits an error amplifier circuit in a feedback loop to increase loop stability and loop bandwidth to be able to continuously perform pulse-width modulation (PWM) dimming from 1% to 100%. The LED driver employs the characteristic that the current through the LED string is zero when the operating voltage of the LED string is less than the cut-in voltage of the LED string to reduce the difference between the output voltage during an enable period and the output voltage during a disable period to reduce voltage ripple and electromagnetic interference.

Description

201208464 VI. Description of the Invention: [Technical Field] The present invention relates to a Light-Emitting Diode (LED) driver, and particularly relates to a direct drive that is directly driven by an AC power source. LED driver. [Prior Art] Fig. 1 is a circuit block diagram of a conventional direct drive type LED driver directly driven by an alternating current power source, and its output voltage is controlled by segmentation. Referring to the figure, the LED string 11 is composed of a plurality of LE:Ds coupled in series and has an input end and an output end. The direct drive led driver 2 is for receiving an AC power supply Vac and a dimming signal DIM to drive the LED string Π. The direct drive LED driver 2 includes an input rectification filter 21, an isolated DC to DC converter 22, a constant current controller 23, a dimming circuit 24, and a feedback circuit 25. The input rectification filter 21 includes a bridge rectifier 211 and a capacitor 212, wherein the bridge rectifier 211 converts the received AC power yac into a pulsating DC voltage, which is then filtered by the capacitor 212 into a stable DC voltage Vdc. The isolated DC-to-DC converter 22 includes a high frequency converter 221, an isolation transformer 222, and an output rectification filter 223, wherein the high frequency converter 221 converts the DC voltage Vdc into a first high by switching high frequency switching according to the feedback signal FB. The frequency AC voltage Vacl, the isolation driver 222 receives the first high-frequency AC voltage Vaci on its primary side and the second high-frequency AC voltage Vac2 on its secondary side, and the second high-frequency AC voltage Vac2 passes through the output rectifier filter. The 223 is rectified and filtered to output a stable output voltage v〇ut to the input end of the LED string 11. The high frequency converter 221 is, for example, a pulse width modulation converter, a semi-resonant converter, or a resonant converter. The output rectification filter 223 includes, for example, a diode 224 and a capacitor 225, wherein the diode 224 rectifies the second high-frequency AC voltage Vac2 into a pulsating DC voltage, and the pulsating DC voltage is filtered by the capacitor 201208464 into a stable output voltage Vout. The constant current control ϋ 23 is lightly connected between the output end of the LED string 11 and the ground terminal for controlling the current lQut flowing through the LED material 11. The dimming circuit 24 controls the L*£D string u according to the received dimming signal DIM through the constant current controller 23 to turn on the L light) to turn off (dark) 'Using the human eye to stay temporarily so that the human eye does not feel it : The next is dark and the eight will feel X to a certain degree of freedom. This brightness is related to the ratio of light to dark time (ie, the ratio of the opening and closing time of the LED material η). This is the pulse width modulation (Pulse~Width). Modulation, referred to as pwm) dimming. The feedback circuit 25 includes an output detection circuit 26, a reference voltage source 27, a debt error amplification circuit 28, and an optical lighter 29, wherein the output detection circuit 26 includes resistors 261-263. The switch control circuit 264 and the switch 265' error-amplifying circuit 28 include a debug amplifier 28 capacitor 282 and a resistor nano, and the optical chuck 29 includes a light-light diode and an optical transistor 292. The output detection circuit 26 samples the output voltage v〇ut to generate a corresponding detection voltage Vdet. The reference voltage source 27 is biased by the reference voltage. The Vref error amplifying circuit 28 amplifies the voltage difference based on the detected voltage and the reference voltage and outputs it to the cathode terminal of the pure diode 291. The light-light diode 291 is connected to a DC voltage Vbias. When the light-emitting diode 291 is turned on, the corresponding current is generated according to the light difference of the anode end of the anode end, and accordingly, the phase is generated, and the light is re-detected and the corresponding light is generated and the corresponding feedback is output to the south. Frequency conversion H 221. Therefore 'return signal FB and detection voltage

6 off' is related to the output voltage V〇ut, and can be fed back to the high crying 221 to adjust its switching high frequency switching, and then adjust the output voltage _. "Replacement H Because the electric valley stealer 282 and the resistor 283 are connected in series between the negative and output terminals of the error-detecting amplifier 281 to form a negative feedback architecture, the error-sensing amplifier 281 has a negative input and outputs a scale. When Vdet f is turned off, the output voltage VoutW〇ut^=x〇+Ri=, rr 5 201208464 and when the switch 265 is turned on, the output voltage v〇ut is v〇ut h=Vrefx , (1+R1/ (R2| | R3)) ' R2| | R3 = (R2XR3) / (R2 + R3), where R1, R2, and R3 are the resistance values of the resistors 261, 262, and 263, respectively. As the LED light string 11 is turned off, the brightness perceived by the human eye is lowered, and the operating voltage Vcc of the constant current controller is increased. When the switch control circuit 264 detects that the operating voltage Vcc of the constant current controller is high to some extent and the operating voltage Vied of the LE:D string n is insufficient, the switch control circuit 264 controls the switch 265 to be turned on to increase the output voltage V〇. Ut is Vout,h; when the switch control circuit 264 detects that the operating voltage Vcc of the constant current controller does not cause the operating voltage vied of the LED string 11 to be insufficient, the switch control circuit 264 controls the switch 265 to be turned off to control the output voltage. V〇u1: Lu is Vout, h is direct drive type; D drive 2 output voltage VoM is controlled by segmentation. After the design of the LED string 11 is completed, the resistor value of the resistor = 263 is a fixed value, so that the output voltage v〇ut is not V〇ut, and h is v〇ut' i, can only be applied to the same working voltage as the LED string n = LED string 'has low compatibility. In addition, the 'direct drive LED driver 2 uses a negative j error amplifier circuit 28'. If the loop bandwidth is high, the loop stability is poor. If it is back, the stability is good __ wide and low, and Peng’s servant is unable to hide it. PWM dimming is performed continuously without interruption in the dimming range of 〇%, and the dimming cannot be smoothed.鲁 [Summary of the Invention] The object of the present invention is to propose a direct-drive (10) shaft that can be turned over in a variety of = same working power _ LED material and a high hybrid, and fine high back _ width and stability can be 1% PwM dimming is performed without interruption in the 100% dimming range. Another purpose of Ming is to propose a direct-drive LED driver that can reduce the differential, ripple and electromagnetic interference of TM II, the transmission voltage, and the ban. - know the main skin 6 201208464

V v % 'The present invention proposes a direct drive LED driver for receiving AC power and tuning the tiger to drive the LED string 'where the LED string has an input end and a wheel end, and the dimming signal includes enabling each cycle Period and period of inactivity. The LED string can be used for backlighting of liquid crystal displays, LCD TVs or LCD PCs. The straight-type driver includes an input rectification filter, an isolated DC-to-DC converter, a constant current control (4), an isolation circuit, a voltage clamping circuit, and a dimming circuit. Input rectification, the wave of the device converts the alternating current into a DC. The isolated money-to-dc converter is used to convert the direct current to the output voltage to the output of the string Φ according to the feedback signal. The 疋 current controller is coupled between the output end of the LED lamp and the ground end for controlling the current flowing through the LED string. The isolation circuit is configured to output a feedback signal based on the voltage difference between the voltage at the output of the LED string and the reference voltage. The voltage clamp circuit is connected between the input terminal and the output terminal of the LED string for the operating voltage of the (10) string. The dimming circuit is used to turn on the ED string via the constant current controller and/or the voltage clamp circuit according to the dimming signal during the enable period and to turn off during the disable period. In a practical example, the dimming circuit controls the operating voltage of the LED string during the enable period (CUt in V〇ltage), and during the disable period is less than the cut-in voltage of the LED string and greater than zero. . The above and other objects, features, and advantages of the present invention will be apparent from the appended claims appended claims [Embodiment] FIG. 2 is a timing chart showing the circuit control of the direct drive type LED driver shown in FIG. 2 according to the circuit of the first embodiment of the direct drive type (10). 1_string 11 is composed of a plurality of leds of a series of chicks and has one

Vac and two outlets. The direct drive LED driver 3 is configured to receive an AC power source and a shame DIM to drive (10) a string of lights, wherein the dimming signal surface is as shown in FIG. 3 201208464 = two = ΤΤ during the enable period and during the disable period, for example, the first period τ ==:==Tff Two weeks _ _ LED driver 3 includes input rectification ^ _ gambling 2. Direct drive 22, constant current controller 23, regulating circuit ° 21, _ type DC to DC converter changed to seven red life π 〃 尤 ^ 34 34 and feedback circuit 35, which is not limited to The apparatus of the present invention will not be described here, and the circuit is lightly swayed by 29 mesh and the barrier in the feedback path shown in Fig. 2 - an isolation circuit such as an isolation transformer can be used instead.

VaC II, t, __ _ is used to output the FB according to the output of the LED string 11 of the lion. Miscellaneous _ secret 36 is connected between the H-end and the round-out end of the 丨 string. The work for the LED string 11 is used to control the light string U through the constant current controller. The opening string is closed. Therefore, the brightness of the LED string 11 is determined by the dimming signal DIM determining the ratio of the LED ΓΕ=ΓΓΓ, for example: = degree map. The third cycle T shown in Fig. 3 includes two sets of control loops, one of which is voltage controlled back to ',' and is a neon k control loop. The voltage control loop is output by the secondary side of the isolation transformer 222 8 201208464 «, via the output rectification filter 223, the load of the external LED string 11, the optocoupler diode 291 of the optocoupler 29 and the reference voltage source 27 to The ground terminal on the secondary side is output from the optocoupler transistor 292 of the optocoupler 29 to the high frequency converter 221 to return to the primary side of the isolation transformer 222 to complete voltage control. The constant current control loop is outputted by the secondary side of the isolation transformer 222, passes through the output rectification filter 223, the load of the external LED string 11, and the ground current controller 23 to the ground of the secondary side returns to the isolation transformer 222. The stage side output completes the constant current control. Referring to Figure 3, when the operating voltage Vd of a single LED is greater than the cut-in voltage of the LED, the LED is turned on and emits light because the current is not zero. When the operating voltage Vd of the single LED is less than the cut-in voltage of the LED, the LED is turned off and the current is zero. Does not shine. The direct-drive LED driver 3 of the present invention controls the operating voltage Vied of the LE:D string 11 when the operating voltage Vd of a single Lf:D is less than that of the LED, and the LED is turned off and the current is zero. The energy period (e.g., Toni) is greater than the cut-in voltage Vr of the LED string 11 (i.e., Vled>Vr), at which time the LED string 11 is turned on and the current I〇ut is not zero to emit light, and the operation of the LE:D string 11 is controlled. The voltage Vled is less than the cut-in voltage Vr of the led string 11 and greater than zero (ie, Vr > vled > 〇) during the disable period, at which time (4) the light string 11 faces and the current lout is zero without emitting ' The cut-in voltage Vr of the LED string ^ is the sum of the cut-in voltages of all series-coupled LE:D in the LE:D string 11. Since the output voltage Vout is the sum of the operating voltage of the LED string U and the constant current controller 23 6 working voltage Vcc, and the constant current controller 23 ❾ operating voltage Vcc is determined after the direct drive LED driver H 3 is designed. The value (which will be explained later), the timing waveform of the working dragon system of the non-LED lamp φ 11 is similar to the hard voltage: therefore, the PWM dimming driving method of the invention can reduce the voltage Vout during the dimming period during the enabling period. (such as TQnl) and during the disable period (such as the electrical difference between T〇f(1)' to reduce voltage chopping and electromagnetic interference. The first feature of the direct-drive LED driver of the present invention is that [S] 9 201208464 The LED string is highly shared. As shown in Fig. 2, the operating voltage Vcc of the constant current controller 23 is the sum of the reference voltage Vref and the operating voltage Vpcd of the optocoupler diode 291. The output voltage Vout of the direct drive LED driver 3 is The sum of the operating voltage Vied of the LED string 11 and the operating voltage Vcc of the constant current controller 23 is expressed mathematically as follows:

Vcc=Yref+Vpcd (1)

Vout=Vled+Vcc (2) Since the reference voltage Vref and the operating voltage Vpcd of the optocoupler diode 291 are constant after the direct-drive LED driver 3 is not counted, the operation of the constant current controller 23 is known from the equation (1). The voltage Vcc is also constant. It can be seen from equation (2) that the output voltage Vout of the direct-drive LED actuator 3 will automatically change as the operating voltage Vled of the string 11 changes, so the direct drive L® The driver 3 is suitable for driving a plurality of LED light strings of different working voltages, for example, driving (6) light strings of four (10) series light connections can also drive 10 LE:!) LED light strings coupled in series. The second feature of the IJD driver is the constant current controller, and the constant current control is performed at a safe read voltage. (4) The working voltage vcc of the constant current operation and the benefit voltage is measured by the reference voltage Vref and the light-consuming diode: the sum of the voltage Vpcd is selected by selecting the reference voltage source 27 and the aperture diode 291; the current control (4) is determined. It can be completed under the extremely lying and safe working voltage, and the flow control task. Constant current control · 23 resident voltage is low, in addition to the drop, can be _ low-cost Laizi (four) crystal to replace the high cost of the cost of the efficiency of the transistor, but also save the need for a heat sink. The third feature of the direct-drive LED driver is that it can be dimmed without interruption from 1% to the dimming range of the brain, taking into account the high resilience. It can be seen that the light-emitting diode 291 of the optical consumer 29 outputs the feedback signal FB according to the voltage difference of the 201208464 voltage (ie, the operating voltage Vcc of the constant current controller 23) and the reference voltage Vref at the output end of the LED string ii. There is no debug amplifier circuit 28 as shown in Figure 1 in the feedback path, so the loop gain is 1 'so this improves loop stability and loop bandwidth' so it can be between 1% and 100%. P-side dimming is performed continuously without interruption in the dimming range. The fourth feature of the direct drive LED driver of the present invention is that the operating voltage of the LED string is less than the cut-in voltage of the LED string during the disable period, and the current of the LED string is zero, which can reduce the PWM dimming. The voltage difference between the output voltage during the enable period and during the disable period to reduce voltage ripple and electromagnetic interference. Figure 4 is a circuit block diagram of a second embodiment of a direct drive LED driver in accordance with the present invention. Referring to FIG. 4, the direct drive LED driver 4 is used to drive a plurality of LE) D strings 11 to 13. In contrast to the direct drive LED driver 3, the direct drive type del:d driver 4 is primarily such that the feedback circuit 45 further includes a feedback logic circuit 46. The output terminals of the LED strings 11 to 13 are coupled to the voltage clamping circuit 36 and the optocoupler to the optocoupler diode 29 via the feedback logic circuit 46. At this time, the optocoupler diode 291 of the optocoupler 29 is based on the feedback logic. The voltage difference between the voltage outputted by the circuit 46 and the reference voltage vref is illuminated, and the feedback signal FB is output by the optocoupler transistor 292. The voltage clamping circuit 36 is coupled to the input terminal of the LE:D string 11 and the feedback logic circuit 46. The output is used to clamp the operating voltage Vied of the LED string u. In addition, the constant current controller 43 requires a constant current controller that supports a plurality of strings. Knowing that the direct-drive LED driver of the present invention consumes an output of a LED string and a constant current controller by using an isolation circuit (such as an optical device), and its output voltage will change with the operating voltage of the LED string. And automatically change, can be applied to drive a variety of different working voltage LED materials, and improve the loop stability and loop weaving by eliminating the feedback of the road-to-error amplifier circuit, which can be uninterrupted at 1% to Cong Do PWM dimming's use of the LED string's operating voltage is less than the LED string's cut-in voltage, its current is zero characteristic' reduce the voltage difference between the output voltage during the simple dimming and the 201208464 period. To reduce voltage ripple and electromagnetic interference. The direct drive LED driver of the present invention therefore has extremely high stability, performance, compatibility and cost effectiveness. Although the present invention has been disclosed in the above preferred embodiments, it is not intended to limit the invention, and it is intended that the invention may be modified and modified without departing from the spirit and scope of the invention. The scope of the invention is defined by the scope of the appended claims. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a circuit block diagram of a conventional direct drive type LED driver directly driven by an alternating current power source. Figure 2 is a circuit block diagram of a first embodiment of a direct drive LED driver in accordance with the present invention. FIG. 3 is a timing diagram of the dimming control of the direct drive LED driver shown in FIG. 2. Figure 4 is a circuit block diagram of a second embodiment of a direct drive type LED driver in accordance with the present invention. [Main component symbol description] 11 to 13 : LED string 21 : Input rectification filter 212 = Capacitor 221 : High frequency converter 223 : Output rectification filter 225 : Capacitor 24 : Dimming circuit 2 : Existing direct drive LED Driver 211: Bridge rectifier 22: Isolated DC to DC converter 222: Isolation transformer 224: Diode 23: Constant current controller 25: Feedback circuit 12 201208464 26: Output detection circuit 264: Switch control circuit 27: Reference Voltage source 281: Detector amplifier 283: Resistor 291: Optocoupler diode 3: Direct drive LED driver 35 of the present invention: Feedback circuit 4: Direct drive LED driver 45 of the present invention: Feedback circuit

Vac : AC power supply

Vacl: the first high frequency AC voltage

Vout: output voltage

Vied : Operating voltage of LED string

Vdet: detection voltage

Vpcd: operating voltage of the optocoupler diode lout: current flowing through the LED string FB: feedback signal

Toni, Ton2: enable period t: time axis 261~263: resistor 265: switch 28: debug amplifier circuit 282: capacitor 29: light 292: optocoupler transistor 34: dimming circuit 36: voltage clamp circuit 43: constant current controller 46: feedback logic circuit

Vdc, Vbias: DC voltage

Vac2: second high frequency AC voltage

Vd: operating voltage of a single LED

Vcc: operating voltage of constant current controller

Vref: reference voltage

Vr : cut-in voltage of LED string DIM : dimming signal T: period of dimming signal

Toffl, Toff2: Prohibition period [S] 13

Claims (1)

201208464 VII. Patent application scope: 1. A direct-drive LED driver for receiving an AC power supply and a dimming signal for driving a light-emitting diode string, the LED string having an input And the output end of the dimming signal includes a period of uniform energy and a period of inactivity. The direct-drive LED driver includes: an input rectifying chopper for converting the alternating current power into a direct current An isolated DC-to-DC converter for converting the DC voltage into an output voltage output to an input end of the LED string according to a feedback signal; a constant current controller coupled to the LED a current between the output end of the polar body string and a ground end for controlling current flowing through the light emitting diode string; an isolating circuit for voltage and a reference according to an output end of the light emitting diode string The voltage difference of the voltage is outputted to the feedback signal; a voltage clamping circuit is coupled between the input end and the output end of the light emitting diode string for hanging the work of the light emitting diode string Pressure; a dimming circuit, a circuit for controlling the light emitting diode string is opened and closed during the disabled during the enable dimming signal clamped by the constant current control and / or the voltage. 2. The direct drive type LED driver of claim 1, wherein the dimming circuit controls the operating voltage of the LED string to be greater than the LED during the enabling period. The cut-in voltage of the string is less than the cut-in voltage of the light-emitting diode string and greater than zero during the disable period. 3. The direct-drive LED driver as described in the scope of claim 2, wherein the isolated DC-to-DC converter II comprises - high-altitude H, _ isolation transformer 201208464 and an output rectifier filter 'the high The frequency converter is configured to convert the DC voltage into a first high-frequency AC voltage by switching the frequency-converted signal according to the feedback signal, and the isolation transformer is configured to receive the first high-frequency AC voltage on its primary side and in its secondary sense And outputting a second high frequency alternating voltage, the output rectifying filter for converting the second high frequency alternating current voltage into the output voltage. 4. The direct drive type LED driver according to the third aspect of the invention, wherein the frequency converter is a pulse width modulation converter, a half spectrum converter or a resonant converter Device. 5. The direct-drive light-emitting diode driver according to the above item (4), wherein the first coupling device comprises an illuminating crystal of an optocoupler diode and an optocoupler diode, and the crystal is used for Detecting the position of the direct-drive light-emitting diode driver, which makes the brain-body machine's backlit liquid crystal display, a liquid crystal TV or a liquid crystal. 7. As claimed in the patent scope - feedback logic circuit, The direct-drive light-emitting diode driver 'also includes the circuit lightly connected to the voltage ^ / light - the output end of the light string through the feedback logic to the feedback logic circuit: two circuits and the isolation circuit 'the isolation circuit For the root feedback signal, the voltage difference between the voltage of the electric power and the reference voltage is outputted and the feedback logic circuit=the circuit is lightly connected to the input end of the light-emitting diode string. The output of the road for clamping the LED string