High-power LED lighting dynamic change controller design

LED light source has the characteristics of long life, high luminous efficiency and low energy consumption. At the same time, the color saturation and purity of LED light source are unmatched by traditional light sources. In the mid-1990s, the breakthrough of G aN-based blue and green LEDs made LEDs a complete luminescence system of red, green and blue. By controlling the current levels of the red, green, and blue LEDs, continuous changes in brightness, grayscale, and color can be achieved, allowing illumination to extend from white light in the usual sense to light of multiple colors. Therefore, people can choose different lighting effects at different times according to individual requirements and scene conditions. The scene lighting system that reflects many characteristics of LED is bound to be one of the important development directions of LED application. Its most important feature is the use of LED to realize the regulation, preset and selection of scene illumination.

This design uses three Boost Chopper circuits to drive red, blue and green LED lights. The current closed loop algorithm and DDS principle are used to dynamically change the LED current, and different intensity LED lights (RGB) are combined to achieve the color change effect.

1 program design

2 A。 The LED lamp rated operating voltage is 30 V, the rated current is 1. 2 A. In the LED lighting controller design, the 3-way Boost Chopper circuit is used to change the red, green, and blue LED lamp voltages according to predetermined requirements. Since the current of the LED lamp increases exponentially with the increase of the voltage, the current control is more accurate and stable than the voltage control, so the current control mode is adopted.

The controller samples the LED lamp current and uses the dsPIC30F2023 processor from Microsoft Corporation to perform closed-loop control of the output current. At the same time, the output voltage is detected to prevent the voltage across the LED lamp from being too high and damaging the LED lamp. In order to make the serial communication anti-interference ability and transmission distance far, the SP491E chip of Max im company is used to convert the asynchronous serial port signal of the processor into RS422 differential signal. On the PC side, the RS422RS232 converter is used to convert the signal into RS232 signal. When docked with a PC, the user can read and set the current of the three-color lamp on the PC. The system structure diagram is shown in Figure 1. The inside of the dotted line is the controller part.

1. 1 dsPIC30F2023 Introduction

The dsPIC30F2023 is a 16-bit fixed-point digital signal controller DSC for power control in the US microchip (Miccroch ip). It uses a high-performance modified Harvard R ISC CPU core that allows for a variety of peripherals and internal interrupts. It integrates a DSP operation engine and supports multiple addressing modes and single-cycle multiply-accumulate instructions. I / O pin drive capability; integrated peripherals powerful, including three 16-bit timers; integrated SPI interface, I2C bus interface, UART serial interface, 12-channel 10-bit A / D converter and power control PWM Module, dedicated to power control. It also has multiple modes of operation, capable of operating in a low power mode, reducing system power; operating voltage range of 3.3 V and 5 V, excellent interference immunity.

1. 2 Boost Chopper circuit design

In this scheme, the input voltage of the Boost Chopper circuit is 12V, and the output voltage value changes with the turn-on and turn-off law of the fully-controlled device. Since the rated voltage of the LED is 30 V, the designed output voltage range of the Boost Chopper circuit is 15~ 40 V.

(1) Selection of fully controlled devices. The power MOSFET has the advantages of low on-resistance and large load current.

This solution uses International Rectifier's MOSFET device IRF540, which can withstand a drain-source voltage of 100 V, an on-resistance of 44 m, and a source-drain current of up to 33 A. In practice, the MOSFET device has an operating temperature of 70 ∃ and a large peak current. The MOSFET power transistor can operate reliably with the LED lamp power not higher than 40 W and heat dissipation.

(2) Selection of power diodes.

The diode in the Boost boost circuit is subjected to a reverse voltage of 28 V and a current of 1.5 A. In the power diodes that meet the requirements, in order to save energy, the on-resistance is as small as possible, and in the actual process, the operating frequency is high and the current spike is large. Therefore, IR company's MBR20100 dual-parallel Schottky Fast Recovery Diode is selected, its overcurrent is 20 A, the reverse voltage is 100 V, and the on-resistance is 0.77. The reverse recovery time is short. Design needs.

(3) Determination of inductance parameters and chopping frequency.

The high-power boost converter should work in the continuous current mode. The size of the inductor is closely related to the chopping frequency. Since the boost ratio in the design is at most 2.5, considering the design margin, the boost ratio is higher. 3, at the same time can not saturate the magnetic material of the inductor. When the requirements are met, the inductance should be reduced as much as possible to reduce the area of ​​the controller. 。 According to the test results, in the case of a chopping frequency of 480 kH z, the inductance is 1. 2 H.

1. 3 drive circuit design

The gate capacitance of the MOSFET is relatively large. The capacitor is charged before being turned on. When the capacitor voltage exceeds the threshold voltage, it starts to conduct. Therefore, the load capacity of the gate driver must be large enough to ensure that the equivalent gate capacitance is charged within the time required by the system. At the same time, the turn-on voltage is greater than 10 V to make the MOSFET turn on reliably. 025V, up to 0. 025V, the output high voltage is lower than the power supply voltage of 0. 025V, the highest output voltage is 0. 025 V, the output high voltage is lower than the power supply voltage of the TC4426A 18 V. The controller uses two TC4426As that can drive four MOSFETs, one for expansion.

1. 4 current sampling and voltage sampling

A small resistance sampling method is adopted for the output current detection, and the voltage drop of the small resistance is adjusted by the same direction operational amplifier circuit, and then transmitted to the dsPIC30F2023. The dsPIC30F2023's integrated 10-bit high-precision A/D converter module has a sampling rate of up to 2Mb / s and can sample the current of the LED lamp in real time for current closed-loop operation. The power consumption of the resistor is less than 0. 5W, and the power consumption of the resistor is less than 0. 5W, which satisfies the power consumption of the resistor. Actual requirements.

During the sampling of the output voltage, the comparator circuit is used. When the voltage of the LED lamp exceeds 36 V, the MOSFET power tube is turned off immediately, and the voltage across the LED lamp is reduced to the input voltage.