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To introduce On semicoductor’s Constant Current Regulators and its applications

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- 1. Constant Current Regulator for Driving LEDs <ul><li>Source: On Semiconductor </li></ul>
- 2. Introduction <ul><li>Purpose </li></ul><ul><ul><li>To introduce On semicoductor’s Constant Current Regulators and its applications </li></ul></ul><ul><li>Outline </li></ul><ul><ul><li>LED drivers basics </li></ul></ul><ul><ul><li>CCRs Basics </li></ul></ul><ul><ul><li>Key features </li></ul></ul><ul><ul><li>Application circuits of CCRs </li></ul></ul><ul><ul><li>CCR selection </li></ul></ul><ul><li>Content </li></ul><ul><ul><li>22 pages </li></ul></ul>
- 3. LED Basics <ul><li>LEDs are still a diode – once they turn on they have a high positive forward current to forward voltage coefficient. </li></ul><ul><li>Increasing the LED drive current, increasing the forward voltage, increasing the power dissipated. </li></ul><ul><li>LEDs have a negative forward voltage to temperature coefficient. </li></ul><ul><ul><li>LED warms up -> V f drops -> V R increases -> I f increases -> power increases -> temperature increases -> V f drops…. </li></ul></ul><ul><ul><li>It leads thermal runaway. </li></ul></ul>R LED2 LED1 GND V IN
- 4. Temperature Influence <ul><li>LEDs have a negative light output to temperature coefficient. </li></ul><ul><li>As LEDs warm up they output less light. </li></ul><ul><li>LEDs change color based on temperature and current. </li></ul>Ambient Temperature vs. Chromaticity Coordinate Forward Current vs. Chromaticity Coordinate
- 5. LED Driver Basics <ul><li>To obtain the longest life and highest reliability it is very desirable to drive LEDs with a constant current and keep the temperature stable. </li></ul><ul><li>The main function of a driver is to limit the current regardless of input and output conditions across a range of operating conditions. </li></ul>
- 6. LED Current Regulation Solutions Improved efficiency but higher complexity & cost Resistors Linear Regulators Switching Regulators Vin R Set Point Vin Rset PWM L C Vin R Rset <ul><li>Advantages </li></ul><ul><ul><li>Low cost </li></ul></ul><ul><ul><li>Easy to design-in </li></ul></ul><ul><ul><li>No EMI issues </li></ul></ul><ul><li>Advantages </li></ul><ul><ul><li>Easy to design-in </li></ul></ul><ul><ul><li>Current regulation & fold back </li></ul></ul><ul><ul><li>External current set point </li></ul></ul><ul><ul><li>No EMI issues </li></ul></ul><ul><li>Advantages </li></ul><ul><ul><li>High efficiency </li></ul></ul><ul><ul><li>Voltage independent </li></ul></ul><ul><ul><li>Brightness control </li></ul></ul><ul><li>Disadvantage </li></ul><ul><ul><li>Battery voltage dependent </li></ul></ul><ul><ul><li>Requires binning of LED </li></ul></ul><ul><ul><li>Large inventory of resistors </li></ul></ul><ul><ul><li>Low efficiency </li></ul></ul><ul><li>Disadvantage </li></ul><ul><ul><li>Power dissipation </li></ul></ul><ul><ul><li>Moderate cost </li></ul></ul><ul><ul><li>Low efficiency </li></ul></ul><ul><li>Disadvantage </li></ul><ul><ul><li>High cost </li></ul></ul><ul><ul><li>Complexity </li></ul></ul><ul><ul><li>EMI </li></ul></ul>
- 7. Constant Current Regulators (CCR) Solution Improved efficiency but higher complexity & cost Resistors Linear Regulators Switching Regulators CCR <ul><li>CCR is a simper and lower cost solution to linear & switching regulators; </li></ul><ul><li>Significantly improves performance over resistors. </li></ul>Vin R Set Point Vin Rset PWM L C Vin R Rset <ul><li>Advantages </li></ul><ul><ul><li>Low cost </li></ul></ul><ul><ul><li>Easy to design-in </li></ul></ul><ul><ul><li>No EMI issues </li></ul></ul><ul><li>Advantages </li></ul><ul><ul><li>Easy to design-in </li></ul></ul><ul><ul><li>Current regulation & fold back </li></ul></ul><ul><ul><li>External current set point </li></ul></ul><ul><ul><li>No EMI issues </li></ul></ul><ul><li>Advantages </li></ul><ul><ul><li>High efficiency </li></ul></ul><ul><ul><li>Voltage independent </li></ul></ul><ul><ul><li>Brightness control </li></ul></ul><ul><li>Disadvantage </li></ul><ul><ul><li>Battery voltage dependent </li></ul></ul><ul><ul><li>Requires binning of LED </li></ul></ul><ul><ul><li>Large inventory of resistors </li></ul></ul><ul><ul><li>Low efficiency </li></ul></ul><ul><li>Disadvantage </li></ul><ul><ul><li>Power dissipation </li></ul></ul><ul><ul><li>Moderate cost </li></ul></ul><ul><ul><li>Low efficiency </li></ul></ul><ul><li>Disadvantage </li></ul><ul><ul><li>High cost </li></ul></ul><ul><ul><li>Complexity </li></ul></ul><ul><ul><li>EMI </li></ul></ul>
- 8. Constant Current Regulators - Overview <ul><li>Developing a portfolio of constant current regulators in 2-terminal, 3-terminal to provide a simple & cost effective solution for regulating current in LEDs </li></ul><ul><ul><li>CCRs are self biased circuits </li></ul></ul>2-Terminal Fixed Output 10mA – 350mA VAK = 50V 3-Terminal Adjustable Output 20mA – 160mA VAK = 50V
- 9. CCR Low Turn On Voltage V / I plot crosses through zero The CCR turns on fast immediatedly the voltage goes positive With 0.5V input the current is already at 5mA - 25% ON
- 10. CCR Surge Test Measure 2V 2V 2V 12 V 50 V 1 ms Pulse
- 11. <ul><li>Comparing a resistor bias circuit to a CCR biased circuit </li></ul><ul><li>The resistor circuit has </li></ul><ul><ul><li>Low brightness LEDs at low voltages </li></ul></ul><ul><ul><li>LED brightness changes as voltage increase </li></ul></ul><ul><ul><li>Very brightness changes as voltage increase </li></ul></ul><ul><li>The CCR provided a </li></ul><ul><ul><li>A constant current over a wide voltage range </li></ul></ul><ul><ul><li>Brighter LEDs at low voltages </li></ul></ul><ul><ul><li>Protection for the LEDs at high voltages </li></ul></ul>CCR – Value Proposition Brighter at low voltage Constant brightness over Critical Operating Region Resistor CCR Vin Ireg Protection at High Voltage Vin R ±10% I LED ± 50% I LED
- 12. Current Regulation of CCR vs. Temperature 20mA CCR SOD-123 Package 30mA CCR SOT-223 Package <ul><li>Regulated current over V AK voltage and temperature </li></ul><ul><li>Negative temperature coefficient protects LEDs from overheating as voltage or temperature increases </li></ul><ul><li>Power packages have tighter regulation over voltage and temperature </li></ul>
- 13. CCRs from ON Semiconductor Parameters NSI450XXT1G SOD-123 (2-terminal) NSI450XXZT1G SOT-223 (2-Terminal) NSI500XXDZT1G SOT-223 (3-Terminal) NSI500XXDDT1G D-PAK (2-Terminal) Max Anode to Cathode Voltage (V AK ) 45V 45V 50V 50V Voltage Overhead 1.8 V 1.8 V 1.8 V 1.8 V Constant Current Ireg @ Vak = 7.5V 10, 20, 25 & 30 mA 25 & 30 mA 20 - 40 mA ADJ 35 - 70 mA ADJ 60 – 100 mA ADJ 90 – 160 mA ADJ Current Tolerance over Voltage ± 15%, ±10% ± 15%, ±10% ± 15%, ±10% ± 15%, ±10% Ambient Operating Temp Range -55 to 85 o C -55 to 85 o C -55 to 85 o C -55 to 85 o C Max Junction Temperature 150 o C 150 o C 150 o C 150 o C Power Dissipation ( 25 o C; 500mm 2 ) 463 mW 1389 mW 1389 mW 2400 mW Power Dissipation ( 85 o C; 500mm 2 ) 230 mW 750 mW 750 mW 1270 mW ESD Rating: HBM – 1C > 1kV > 1kV > 2kV > 2kV
- 14. Example of CCR Circuits 1 Driving Multiple LED Strings <ul><li>Circuit A </li></ul><ul><li>LEDs forward voltage must be match </li></ul><ul><li>High power dissipation in one package </li></ul><ul><li>High current in other strings if one fails </li></ul><ul><li>CCR can be high or low side </li></ul>10 V 10 V <ul><li>Circuit B </li></ul><ul><li>LEDs need not be matched </li></ul><ul><li>Power dissipated multiple packages </li></ul><ul><li>No impact if one string fails </li></ul><ul><li>CCR can be high or low side </li></ul>2V 2V 2V 2V 2V 2V 2V 2V 2V 2V 2V 2V 2V 2V 2V 2V 2V 2V
- 15. Example of CCR Circuits 2 CCRs in parallel driving higher current LED string <ul><li>Higher current can be achieved by connecting multiple CCRs in parallel </li></ul><ul><ul><li>20 + 30 = 50 mA </li></ul></ul><ul><li>The LEDs are cross connected to help with power sharing </li></ul>24 V 3.4V 3.4V 3.4V 3.4V 3.4V 3.4V 3.4V 3.4V 3.4V 20 mA 30 mA 50 mA 3.4V 3.4V 3.4V 3.4V 3.4V 3.4V 3.4V 3.4V 3.4V
- 16. Example of CCR Circuits 3 Dimming with external BJT <ul><li>Typical PWM frequency for LED dimming is 0.1 – 3 kHz </li></ul><ul><li>Color does not shift since LED is always “ON” at optimum current </li></ul>2V 2V 2V
- 17. Example of CCR Circuits 4 SW1 close – LED Dim Vibrator runs at 50% duty cycle SW2 close – LED Full Vibrator stops Select RC constant for 5 mS Dimming with external BJT Vibrator 2V 2V 2V 2V 2V 2V 2V 2V 2V SW2 SW1
- 18. Direct A/C Line LED circuit with CCR A/C 110 V RMS 3.52V 3.52V 3.52V 3.52V 3.52V 3.52V 30 LEDs 25 mA 100 Ω TP 1 TP 2 Current Loop TP 1 - 156 V P-P TP2 - LEDs 108 V, 52% On Current probe 25 mA
- 19. Direct A/C Line LED circuit with CCR -10% +10% 110 V RMS, TP1 - 156 V P-P TP2 - LEDs 108 V, 52% On Current probe 25 mA 100 V RMS, TP1 - 142 V P-P TP2 - LEDs 108 V, 47% On Current probe 25 mA 120 V RMS, TP1 - 170 V P-P TP2 - LEDs 108 V, 56% On Current probe 25 mA
- 20. Selecting the Right CCR <ul><li>Power disspation vs. Package size & cost </li></ul><ul><ul><li>SOD-123: low cost, lower power dissipation </li></ul></ul><ul><ul><ul><li>May be able to use a larger copper pad to dissipate heat </li></ul></ul></ul><ul><ul><li>SOT-223: higher cost, higher power dissipation </li></ul></ul><ul><ul><ul><li>May be able to use a smaller copper pad to dissipate heat </li></ul></ul></ul>SOT-123 Package SOT-223 Package
- 21. Summary Features Benefits Regulated current <ul><li>Constant brightness over wide voltage range </li></ul><ul><li>Protects LEDs from over drive at higher input voltage </li></ul><ul><li>Brighter LEDs at lower input voltage </li></ul><ul><li>Reduces or eliminates LED binning inventory </li></ul><ul><li>Lower overall solution cost </li></ul>50V max operating voltage <ul><li>Withstands battery load dump </li></ul>Power packages (SOD123/SOT223/DPAK) <ul><li>Operates in harsh thermal environment (85 o C still air) </li></ul>Negative temperature coefficient <ul><li>Protects devices & LED </li></ul>Simple design/NO EMI generation <ul><li>Less complexity </li></ul>
- 22. Additional Resource <ul><li>For ordering NSI CCRs, please click the part list or </li></ul><ul><li>Call our sales hotline </li></ul><ul><li>For more product information go to </li></ul><ul><ul><li>NSI CCR </li></ul></ul><ul><li>Visit Element 14 to post your question </li></ul><ul><ul><li> www.element-14.com </li></ul></ul><ul><li>For additional inquires contact our technical service hotline or even use our “Live Technical Chat” online facility </li></ul>Newark Farnell

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