A new white LED module driver circuit design (1)

0 introduction

Due to the current global warming and the energy crisis, makes it more and more attention to energy saving technologies.

LED lighting with energy-saving, long life and other advantages of LED lighting technology as the new green lighting technology, the increasing use of. LED white light illumination usually use blue, green, red RGB LED multi-chip modules, since this LED modules each LED chip in the aging characteristics of different color temperature over time and temperature changes, this white led has restrictions of use. This article provides an analysis of the white LED module-driven mode, introduced a new type of white LED module driver circuit design.

1 white LED driver module

For traditional light sources of the drive way, mostly in the form of a constant voltage, this makes the traditional light source drive is very simple.

Online sex, luminous intensity and the LED driving current and is proportional to the voltage drop, and as the temperature changes, this requires a constant current to drive the LED. In addition, white LED module has an important metric that is the color temperature. The color temperature to absolute temperature K, a source of light and dark color is the same as the absolute temperature of a black body at the time known as the light source color temperature. White LED color temperature depends on the light color components in three of the Constitution.

In order to adjust the white LED module light source color temperature, it will be necessary for white LED modules, in blue, green, red and 3 LEDs chips driving current control separately, you need three separate constant current driver circuit.

At present, the constant current driver circuit generally uses the switch-mode PWM controller, its driving current regulation is mainly divided into analog adjustment mode and PWM regulation.

Simulation of the regulation is to use PWM controller for driving current regulation, to stabilize the LED drive current, stable output light intensity.

Because usually PWM controller for feedback control signal is a voltage values, so the regulate is to use an analog measuring resistor on the output drive current sampling, and convert them to feedback voltage signal, through PWM controller for feedback voltage stability, so as to achieve stable output drive current, circuit schematic diagram shown in Figure 1.

Analog way regulated output current to regulate LED output light intensity methods exist for a very big problem: as the LED output wavelength increases as the LED drive current changes and changes, so that different output light intensity, white LED module color will change.

In order to overcome these shortcomings, it also developed on the PWM LED driving current adjustment mode.

2 PWM LED driving current adjustment mode

PWM regulation refers in 1 cycle using a specific duty of pulse driven waveform to drive the LED.

The average LED driving current depends on the pulse waveform of duty and LED driving current rating, in fixed LED driving current rating, by changing the dutyfactor, you can change the average LED driving current, thus changing the LED output light intensity. In order to avoid flicker effect, usually pulse waveform frequency greater than 2 Hz.

Linglier Inc's LED driver IC LT3474 is a rated output current adjustable LED constant current driver control chip, maximum driving current can be up to 1 A.

It offers 2 types of driving method: simulation of the adjustment mode and PWM regulation. In PWM modulation mode, use the PWM signal changes plus the dutyfactor, can achieve 400: 1 ratio of dimming. The PWM modulation modes of typical application circuit shown in Figure 2, plus a PWM control signal is exert PWM pin.

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