High Power Rgb Led Driver Supports Color Lighting Design - Electronics Industry

The next generation of architectural and decorative lighting through the appropriate

combination of red, green, blue LED The output can be more comprehensive color. In such high-brightness, multi-LED series applications, the typical turn-drop may reach 22V to 36V, 1A to absorb current 2A. Figure 1 shows the LED driver can provide multiple modules in series 2A LED drive current, forward voltage up to 36V. The circuit driver RGBLED only one color, driving in three colors need to triple this drive. As the LED intensity produced by conduction currents and their non-linear relationship, select by PWM (rather than the LED current amplitude) control the brightness level of each LED by pulse modulation of the fixed current control light intensity. IC Using average current mode controller provides LED drivers require minimal external components.

Works To provide current drive efficiency, LED Driver with continuous conduction mode (CCM) of the boost topology, using average current mode control boost converter input voltage, constant current driver for the LED load. Single Chip (MAX16821B) work in the 300kHz, control the boost converter work. As the boost converter topology in the conversion between input and output provides a direct channel, to ensure that the minimum turn-series LED input voltage greater than Power supply The maximum voltage. LED load through the MOSFET (Q1) and the sense resistor (R13) cross-connected to the boost converter output, PWMON LED current during the Q1 turn, PWMOFF is disconnected during the current channel. Detect the voltage across R13 (on behalf of current through the LED) when, IC can suppress common mode noise and DIFF pin provides for reference of the output gain of 6V / V. Galvanometer amplifier output signal and the internal 0.6V reference voltage error amplifier comparison, the differential galvanometer amplifier 6V / V gain can make current detection reference point from 0.6V down to 0.1V, the rated load current, the pressure of R13 difference is only 0.1V, help to improve efficiency. The boost converter with average current control mode, by two LED current control feedback loop. Outer Ring Road test LED current, and compared with the reference voltage, in EAOUT (17 pin) produced amplified error signal. Detected within the loop error amplifier output voltage, corresponding to control flow through the inductor (L1) of the current. Error amplifier output also decided to R13 set the LED drive current required when the inductor current, LED rated current in the R13 produces a voltage drop to 0.1V.

Second sense resistor (R15) return channel for setting the inductor current. U2 internal differential current sense amplifier provides 34.5V / V gain. Current error amplifier output voltage and the voltage error amplifier compares the output to produce an average current control loop within the error signal. The amplified error signal and the internal Oscillator Ramp comparison, the resulting PWM signal (at DL 3-pin) to drive MOSFETQ2. Current error amplifier's high gain makes the circuit to the requirements of the voltage loop to produce an inductor current (in the range of permissible restrictions), a very low error. The specified input voltage and LED forward voltage (ignore the switch, diode, sense resistor and other components of the pressure) under, boost converter CCM PWM switch mode determines the duty cycle, fixed duty cycle and required by the corresponding LED current, thus determine the required inductor current. Voltage loop control current loop produces the average inductor current, thus providing the required LED current. Control loop should be provided two separate compensation to ensure stability.

Converter Converter parameter requirements are as follows:

Input voltage range: 9V to 15V

LED maximum forward voltage: 33V LED current: 2A Switching Frequency: 300kHz (low frequency filter will increase the cost of higher frequency will reduce efficiency and EMI. Based on these factors, the optimal switching frequency in 300kHz).

Be calculated using the ON duty cycle of Q2:

Type of VLEDMAX as the biggest turn-on voltage of LED (should include MOSFETQ1 the pressure drop and the voltage drop across sense resistor R13), VD is Rectifiers The voltage across D1, VINMIN is the minimum input voltage, VFET ON, the average voltage during the MOSFETQ2. The circuit: DMAX = 0.74.

Select inductor (L1), we must consider the inductance and peak current rating, using the following formula for calculating the maximum average inductor current (ILAVG):

Determine inductor peak current (ILPEAK), they should pay attention to flow through the inductor ripple current, and inductor values and switching frequency. Suppose the maximum peak to peak inductor current ripple (ILPP) of 20%. As the average inductor current ILAVG ILPP 20%, then:

On the type of substitution known parameters are: ILAVG = 7.7A, ILPEAK = 9.24A.

by:gaga

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