TW201618597A - LED dimming driving method and circuit thereof - Google Patents

Abstract

An LED dimming driving method and its circuit are disclosed. A receiver, a current source and a controller are installed in a dimming module. After a dimming signal is received by the receiver, the current source is driven to output a current whose amount corresponds to the dimming signal. Then the controller converts the current into a voltage level through a terminal resistor before adjusting the driving current of the LED according to the voltage level to realize the improvement of linear dimming accuracy.

Description

LED dimming driving method and circuit thereof

The invention belongs to the technical field of controlling the light intensity of a lighting device, in particular to an LED (Light Emitting Diode) dimming driving method and a circuit thereof for controlling brightness by using a current signal to pass through a non-PWM (Pulse Width Modulation). , pulse width modulation) signal control brightness to improve circuit efficiency and dimming accuracy.

It is generally known that the dimming circuit used in LED lamps mostly uses phase-controlled switching elements such as SCR (Silicon Controlled Rectifier) or TRIAC (Tri-Electrode AC Switch) to change the input power. The voltage phase changes the driving voltage outputted by the overall driving circuit by changing the phase conduction angle, thereby adjusting the driving current flowing into the LED light source to realize the dimming effect. However, although such a dimming setting has the advantages of simple control and easy installation, the input power supply voltage waveform is easily in a distorted state, causing problems such as PF drop and voltage harmonic increase. Moreover, according to the current/voltage (I/V) characteristic curve of the LED, the LED and the nonlinear component, that is, the ratio of the voltage to the current is not proportional, therefore, the dimming method will change the driving voltage and the driving current. Inconsistent, making the dimming effect inaccurate and causing virtual power consumption. Therefore, the conventional driving circuit often connects the LEDs to a transistor and a sensing resistor to adjust the duty ratio of the Pulse Width Modulation (PWM) signal after detecting the LED current by using the sensing resistor. In this way, by controlling the on or off of the transistor through the PWM signal, the driving voltage of the output can be adjusted to maintain the LED current in a constant state.

However, although the above-mentioned driving circuit is suitable for 80-260V commercial power and is convenient to use, it is affected by the component characteristics of the TRIAC, and the voltage of the PWM signal is too low to make the electricity flowing through the TRIAC. When the current is insufficient for the required operating current, the TRIAC will repeatedly switch to the working state, causing the driving current to be discontinuous and causing the LED to flicker. Otherwise, when the PWM signal is too high, the high and low voltages of the signal itself will be used. The level change is too fast and the noise interference is formed, which causes the LED to work abnormally and reduces the practicability. To solve this problem, a PWM driving circuit 1 having a dimmer 10 can be additionally provided with a compensation circuit 12, which is mainly provided by a reference voltage generator, as shown in FIG. 120, a voltage sampler 121, a comparator 122 and a control switch 123, the comparator 122 compares a reference voltage generated by the reference voltage generator 120 with a sample voltage formed by the voltage sampler 121 And outputting a control voltage to the control switch 123 when the sampling voltage is lower than the reference voltage, so that the compensation circuit 12 and the control circuit 11 form a loop through the control switch 123 to provide a holding current to the control circuit 11, It can ensure the stability of the operation of the dimmer 10 and avoid problems such as stroboscopic LEDs. The additional compensation circuit 12 can ensure the quality of the dimmer 10, but at the same time, it has a certain power loss and seriously affects the overall efficiency of the system. Moreover, the TRIAC output voltage signal is used for adjustment. The way of light will affect the dimming accuracy due to the loss of signal transmission in the line.

Deeply aware of this, how to improve the dimming mechanism and component architecture of the LED driver circuit to ensure the working efficiency of the whole circuit, the working stability of the lamp and the accuracy of dimming is the subject of the invention.

In view of the problems of the prior art, the object of the present invention is to provide an LED dimming driving method and a circuit thereof, which use a current signal to control the LED current to perform dimming, so that no current voltage signal is generated during transmission. The situation that affects the accuracy of dimming occurs.

According to the purpose of the present invention, the LED dimming driving method uses a dimming module disposed in an LED dimming driving circuit to adjust the brightness of the plurality of LED strings, and the dimming module adjusts the LEDs by using a current signal. The driving current of the string is used to achieve the effect of improving the linear dimming accuracy, and the dimming module receives the dimming signal and drives the internal A current source outputs a current amount corresponding to the dimming signal, and then is converted into a voltage level by using a terminating resistor to adjust the driving current according to the voltage level to affect the brightness of the LED string.

The dimming module uses a current mirror to intercept the driving current to obtain a brightness value, and compares the voltage level with the brightness value, and then adjusts the driving current through the current mirror to achieve a linear dimming effect. Moreover, the LED dimming driving method further comprises the steps of: detecting a driving current of the LED string and obtaining a minimum driving voltage, comparing and adjusting an on-period of a period switch of the LED dimming driving circuit, To adjust the total output of the output voltage, to ensure that the total output voltage is greater than the forward bias of the LED strings.

According to another aspect of the present invention, the LED dimming driving circuit has a conversion module, an energy distribution module, and a dimming module, and the energy distribution module is electrically connected to the conversion module and the plurality of The LED string is electrically connected to the dimming module. The conversion module has a built-in transformer for sensing an input voltage to form an output voltage, and outputting the LED string to the LED distribution module through the energy distribution module. a driving current is generated on each of the LED strings, wherein the dimming module is provided with a receiver, a current source and a controller, and the controller is provided with a terminating resistor and electrically connected to the LED groups. And the current source is electrically connected to the receiver; the receiver receives a dimming signal, and drives the current source to output a current corresponding to the dimming signal for the controller to utilize the terminating resistor The driving current is adjusted by converting to a voltage level.

The controller is mainly composed of an operational amplifier, a current mirror and the terminating resistor. The current mirror is coupled to the LED string at one end and coupled to the output terminal and the negative input terminal of the operational amplifier at the other end, and The positive input terminal of the operational amplifier is coupled to the terminal resistor and the current source; after the current mirror intercepts the driving current to obtain a brightness value, the operational amplifier compares the voltage level with the brightness value and adjusts the current value by using the current mirror The magnitude of the drive current is such that a linear dimming effect is achieved.

Moreover, the energy distribution module is provided with a minimum voltage detector, an error amplifier, a comparator and a period switch, and the lowest voltage detector is coupled to the LED string and the positive input of the error amplifier. And the negative input terminal of the error amplifier receives a reference value and the output end The output of the comparator is coupled to the periodic switch, and the two ends of the periodic switch are respectively electrically connected to the transformer and the LED string; the lowest voltage detector detects the Waiting for the driving current of the LED string to obtain a minimum driving voltage for the error amplifier to determine the lowest driving voltage and the reference value to obtain an error value, and the comparator uses the triangular wave to compare the error value and then adjust the periodic switch. The conduction period adjusts the total output of the output voltage to ensure that the total output voltage is greater than the forward bias of the LED strings.

In summary, the present invention does not perform dimming in such a manner that the output period of the output voltage is adjusted by controlling the phase angle of the input voltage by the TRIAC, that is, the LED light intensity is not adjusted by the PWM signal without significant dimming. Problems such as delay and dimming misalignment occur.

Conventional technology

1‧‧‧PWM drive circuit

10‧‧‧Dimmer

11‧‧‧Control circuit

12‧‧‧Compensation circuit

120‧‧‧reference voltage generator

121‧‧‧Voltage Sampler

122‧‧‧ comparator

123‧‧‧Control switch

this invention

2‧‧‧LED dimming drive circuit

20‧‧‧Rectifier Module

21‧‧‧Transition module

210‧‧‧Transformer

211‧‧‧Transition controller

2110‧‧‧current transistor

2111‧‧‧current resistance

2112‧‧‧Transformation Control Wafer

212‧‧‧ storage capacitor

22‧‧‧ energy distribution module

220‧‧‧ Lowest Voltage Detector

221‧‧‧Error amplifier

222‧‧‧ comparator

223‧‧‧ triangle wave generator

224‧‧‧cycle switch

23‧‧‧ Dimming module

230‧‧‧ Receiver

231‧‧‧current source

232‧‧‧ Controller

2320‧‧‧Operational Amplifier

2321‧‧‧current mirror

2322‧‧‧Terminal resistance

2323‧‧‧First regulator

2324‧‧‧Second regulator

3‧‧‧LED string

S1~S6‧‧‧ process steps

Figure 1 is a circuit diagram of a conventional PWM drive circuit.

Figure 2 is a block diagram of a preferred embodiment of the present invention.

Figure 3 is a flow chart of a preferred embodiment of the present invention.

Figure 4 is a circuit diagram of a preferred embodiment of the present invention.

In order for your review board to have a clear understanding of the contents of the present invention, please refer to the following description for matching drawings.

Please refer to FIG. 2 to FIG. 4 for a block diagram, a flow chart and a circuit diagram of a preferred embodiment of the present invention. As shown in the figure, the LED dimming driving circuit 2 can be used to connect a plurality of LED strings 3 to a device such as a liquid crystal display, a television or an LED lamp, and is provided with a rectifying module 20 and a conversion module 21, An energy distribution module 22 and a dimming module 23, the energy distribution module 22 is electrically connected to the conversion module 21 and the LED string 3, and the LED strings 3 are electrically connected to the dimming mode. Group 23. The rectifier module 20 is a bridge rectifier circuit coupled to an external power source (not shown) and the conversion module 21, and the conversion module 21 can adopt, for example, a flyback type, a forward direction, a full bridge type, and a half. Bridge or push-pull switching, or LLC series resonant, etc. The power conversion circuit of the combined coil is used as a main structure and is provided with a transformer 210 and a conversion controller 211.

For example, the conversion module 21 that controls the flyback power conversion circuit architecture on the primary side has a primary side coil (N ₁ ), a secondary side coil (N ₂ ), and an auxiliary coil (N _A ). The conversion controller 211 is provided with a current transistor 2110, a current resistor 2111 and a conversion control chip 2112. The primary side coil is coupled to the current transistor 2110 and the current resistor 2111 and coupled to the conversion control wafer 2112. The energy distribution module 22 is provided with a minimum voltage detector 220, an error amplifier 221, a comparator 222, a triangular wave generator 223, and a period switch 224. The lowest voltage detector 220 is coupled to the LED string. 3 and the positive input terminal of the error amplifier 221, and the negative input terminal of the error amplifier 221 receives a reference value (V _ref ) and the output terminal is coupled to the negative input terminal of the comparator 222. The positive input end of the comparator 222 is coupled to the triangular wave generator 223 to receive a triangular wave, the output end of which is coupled to the periodic switch 224, and the two ends of the periodic switch 224 are electrically connected to the secondary side coil and the LEDs String 3. The dimming module 23 is provided with a receiver 230, a current source 231 and a controller 232. The controller 232 can be mainly composed of an operational amplifier 2320, a current mirror 2321 and a terminating resistor 2322. One end of the current mirror 2321 is coupled to the LED group 3 through a plurality of first regulators 2323 and the other end is coupled to the output terminal and the negative input terminal of the operational amplifier 2320 through a second regulator 2324, and the operational amplifier 2320 The positive input terminal is coupled to the terminating resistor 2322 and the current source 231, and the current source 231 is electrically connected to the receiver 230.

In this manner, when the LED dimming driving circuit 2 is in step S1, the bridge rectifier rectifies the alternating voltage of the external power source to form one variable DC input voltage, and step S2: the input voltage is charged and discharged through a storage capacitor 212. The primary side coil is stored to form a primary side current, and the secondary side coil senses the fluctuation of the primary side current to form an output voltage. Incidentally, the switching control chip 2112 immediately detects and adjusts the current value of the primary current through the current transistor 2110 to control the output voltage to exhibit a stable voltage state.

Next, in step S3, the energy distribution module 22 rotates the output voltage to the LED string 3 to cause a driving current to flow on each of the LED strings 3, and step S4: The minimum voltage detector 220 detects the driving current of the LED string 3 to obtain a minimum driving voltage for the error amplifier 221 to determine the lowest driving voltage and the reference value to obtain an error value, and the comparator 222, using the triangular wave to compare the error value, adjusting the on-period of the periodic switch 224 to adjust the total output of the output voltage, so as to ensure that the total output voltage is greater than the forward bias of the LED string 3, and at the same time, stabilize the The driving current is a constant value.

At the same time, in step S5, the receiver 230 determines whether to receive a dimming signal. If the receiver 230 receives a dimming signal in a wireless or wired manner, step S50: the receiver 230 drives the current source 231 to output a current amount corresponding to the dimming signal for the controller 232 to utilize the The terminal resistor 2322 is converted into a voltage level. At this time, in step S51, the current mirror 2321 obtains the driving current by using the second regulator 2324 to obtain a brightness value, and then proceeds to step S6: the operational amplifier 2320 compares the voltage level. Adjusting the operation state of the second regulator 2324 with the brightness value, and adjusting the on and off periods of the first regulators 2323 through the current mirror 2321 to affect the magnitude of the driving currents, thereby realizing a linear dimming effect.

The above description is only illustrative of preferred embodiments and not limiting. Any equivalent modifications or alterations to the spirit and scope of the invention are intended to be included in the scope of the appended claims.

2‧‧‧LED dimming drive circuit

20‧‧‧Rectifier Module

21‧‧‧Transition module

210‧‧‧Transformer

22‧‧‧ energy distribution module

23‧‧‧ Dimming module

230‧‧‧ Receiver

231‧‧‧current source

232‧‧‧ Controller

3‧‧‧LED string

Claims (6)

An LED dimming driving method uses a dimming module provided in an LED dimming driving circuit to adjust the brightness of a plurality of LED strings, and the dimming module uses a current signal to adjust the driving of the LED strings. The current magnitude is used to achieve the effect of improving the linear dimming accuracy, and the dimming module receives a dimming signal and drives one of the internal current sources to output a current amount corresponding to the dimming signal, and then uses one The terminating resistor is converted to a voltage level to adjust the driving current according to the voltage level to affect the brightness of the LED string. The LED dimming driving method according to claim 1, wherein the dimming module intercepts the driving current by using a current mirror to obtain a brightness value, and compares the voltage level with the brightness value. The linear dimming effect is achieved by adjusting the magnitude of the driving current through the current mirror. The LED dimming driving method according to claim 2, further comprising the steps of: detecting and detecting the driving current of the LED string to obtain a minimum driving voltage, comparing and adjusting the LED dimming driving circuit The on-period of the one-cycle switch adjusts the total output of the output voltage to ensure that the total output voltage is greater than the forward bias of the LED strings. An LED dimming driving circuit has a conversion module, an energy distribution module and a dimming module, wherein the energy distribution module is electrically connected to the conversion module and a plurality of LED strings, and the LED strings are Electrically connecting the dimming module, the conversion module has a built-in transformer for sensing an input voltage to form an output voltage, and then outputting the LED string to the LED array through the energy distribution module, so that each LED string has a driving current The current is characterized in that: the dimming module is provided with a receiver, a current source and a controller, the controller is provided with a terminating resistor and electrically connected to the LED string and the current source, and the current source Electrically connecting the receiver; the receiver receives a dimming signal, and drives the current source to output a current amount corresponding to the dimming signal, so that the controller uses the terminal resistor to convert to a voltage level to adjust the driving Current size. The LED dimming driving circuit of claim 4, wherein the controller is mainly composed of an operational amplifier, a current mirror and the terminating resistor, and the current mirror is coupled to the LED string at one end and the other One end is coupled to the output end and the negative input end of the operational amplifier, and the positive input end of the operational amplifier is coupled to the terminating resistor and the current source; the current mirror intercepts the driving current to obtain a brightness value, and the operational amplifier compares The voltage level and the brightness value are used to adjust the magnitude of the driving currents to achieve a linear dimming effect. The LED dimming driving circuit according to claim 5, wherein the energy distribution module is provided with a minimum voltage detector, an error amplifier, a comparator and a period switch, and the minimum voltage detector coupling The LED input string and the positive input end of the error amplifier are connected, and the negative input end of the error amplifier receives a reference value and the output end is coupled to the negative input end of the comparator, and the output end of the comparator is coupled to the cycle a switch, wherein the two ends of the periodic switch are electrically connected to the transformer and the LED strings; the lowest voltage detector detects the driving current of the LED strings to obtain a minimum driving voltage for the error amplifier to judge The minimum driving voltage and the reference value obtain an error value, and the comparator compares the error value by using a triangular wave, and then adjusts the on-period of the periodic switch to adjust the total output of the output voltage, so as to ensure the total output voltage. Greater than the forward bias of the LED strings.