Low Cost LED Drivers for General Lighting
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To introduce Infineon’s low cost linear mode constant-current LED drivers
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Low Cost LED Drivers for General Lighting
- 4. LED Drivers are Required to Operate LEDs! Strong brightness variation in case of voltage variation LED current reacts exponentially to supply voltage variations Degradation or destruction of LED’s due to thermal runaway Positive thermal coefficient of LED current Inhomogenous light output of different LED branches & shorter lifetime of some LED strings Big variety of LED forward voltages leads to different current consumption in LED strings
- 6. LED Drivers for Low and Medium Power LEDs Product Description Package Vcc, max [V] Current range** VOverhead [V] Ptot [mW] Id, typ [mA] Id, max [mA] LED drivers for low power LEDs BCR401W LED driver with output current up to 60mA SOT-343 18 10 60 1,2 500 BCR402W LED driver with output current up to 60mA SOT-343 18 20 60 1,2 500 BCR401U LED driver with output current for high power dissipation up to 65mA SC-74 40 10 65 1,4 750 BCR402U LED driver with output current for high power dissipation up to 65mA SC-74 40 20 65 1,4 750 BCR405U LED driver with output current for high power dissipation up to 65mA SC-74 40 50 65 1,4 750 LED drivers for 0.5W LEDs BCR320U LED driver for currents up to 250mA SC-74 24* 10 250 1,4 1000 BCR321U LED driver for currents up to 250mA with µ-controller interface SC-74 24* 10 250 1,4 1000 BCR420U LED driver for currents up to 150mA SC-74 40* 10 150 1,4 1000 BCR421U LED driver for currents up to 150mA with µ-controller interface SC-74 40* 10 150 1,4 1000
- 8. BCR40x as Stand Alone Current Source
Editor's Notes
- Welcome to the training module on Infineon Technologies Low Cost LED Drivers for General Lighting.
- This presentation will cover the trend of the LED market as the future of lighting. Next, the factors that lead to the growing trend will be described, along with the reasons that differentiate LEDs drivers from traditional sources of lighting. Finally, you will gain an insight into Infineon’s range of solutions across the various applications that use LED driver technology.
- The Solid State Lighting (SSL) market has experienced significant growth in the past decade, due to rapid advancements in LED technology. Higher light output levels, improved packaging, improvements in efficiency / efficacy and decreasing cost per lumen of light output, as well as long lifetimes and physical robustness, have helped drive LED-based light fixtures into niches formerly occupied by more traditional light sources. As of 2007, LEDs are the most energy-efficient sources of colored light available for nearly the entire visible light spectrum. The long lifetime, physical robustness and rapidly improving efficiency / efficacy of LED based light sources makes a compelling argument for their use in a wider range of applications. Here we list some applications with their requirements.
- LEDs and LED displays suffer form varying illumination levels as a result of changes in power supply voltages. This is true for displays used in automotive applications, battery-operated handheld devices, or fixed (architectural) installations. To keep LED brightness constant, it is necessary to stabilize the LED’s current over the anticipated power supply voltage variation range. Therefore, LED drivers are required to operate LEDs properly.
- Often a resistor in series with the LED(s) is used to stabilize current. However, this method has some serious drawbacks. To achieve good LED current stability over the varying supply voltage range, the resistor must take on a large value (infinite resistance, in the ideal case) to make the power supply plus series resistor combination approach the traits of an ideal constant current source having infinite output impedance. A Linear discrete solution is another low-cost method to drive LEDs. But it also has disadvantages, like high part count leading to increased assembly cost, reliability issues due to more solder points, more PCB space needed, and the high risk of mismatch between diodes and transistor leading to wrong LED current. Infineon Technologies’ low-cost linear-mode LED driver family offers several advantages over using resistors to bias and stabilize LED arrays. It has high output impedance, low voltage drop, and negative temperature coefficient (NTC).
- Here lists Linear Technologies’ linear LED driver portfolio. All LED drivers may have the output current adjusted upwards from a minimum value by the addition of a single external resistor. If used at minimum current, no external resistor is required. For example, BCR401U output current is 10 mA nominal with no external resistor; current may be adjusted upwards to any desired value up to 60 mA maximum limit with addition of 1 external resistor.
- Here we show a generic block diagram and application circuit of the BCR401 / 402 / 405 series LED drivers. When the LED driver is used at its nominal output current (e.g. 20 mA for BCR402U, 10 mA for BCR401R, 50 mA for BCR405U) no external current adjust resistor is needed; if the current needs to be increased upwards from the nominal value to any value up to the device's maximum rating, an external current adjust resistor is placed externally, in parallel to the BCR40xx's internal resistor.
- BCR40x serves as an easy to use constant current source for LEDs. In a stand alone application an external resistor can be connected to adjust the current from 10 mA to 65 mA. Rext can be determined by using the diagram 'Output current versus external resistor', or by refering to diagram 'Reference voltage versus output current'. Look for your desired output current on the x axis and read out the corresponding Vdrop.
- The BCR32xU/BCR42xU provide a low-cost solution for driving 0.5W LEDs with a typical LED current I LED of 150mA to 250mA. The BCR32xU/BCR42xU serve as an easy to use constant current sources for LEDs. In stand alone application an external resistor can be connected to adjust the current. Rext (pin 6) can be determined by using the diagram 'Output current versus external resistor'. A digital input pin (BCR321U/BCR421U) allows dimming via a Microcontroller with frequencies of up to 10 kHz.
- Infineon’s linear-mode constant-current LED drivers offer the LED lighting system designer a flexible, versatile and cost-efficient solution for his or her drive circuit designs. These drivers maintain constant current over temperature and supply voltage variation, while having low voltage drops (1.2 to 1.5 V), thereby maximizing system energy efficiency as compared to designs using resistors for current control. The high output impedance of these driver ICs make LED current less sensitive to statistical variations in LED parameters, and may enable the end user to reduce or relax 'binning' requirements on LED forward voltage, reducing costs and simplifying logistics. The negative temperature coefficient (NTC) of these driver ICs helps to protect expensive LED arrays from thermal runaway. Drive current may be increased beyond the 60 / 65 mA level of the stand-alone driver IC by addition of a single external booster transistor, permitting light fixture designs with 1/2 W, 1 W and 2 Whigh power LEDs to be addressed.
- Thank you for taking the time to view this presentation on “ Low Cost LED Drivers for General Lighting ” . If you would like to learn more or go on to purchase some of these devices, you may either click on the part list link, or simply call our sales hotline. For more technical information you may either visit the Infineon Technologies site, or if you would prefer to speak to someone live, please call our hotline number, or even use our ‘live chat’ online facility. You may visit Element 14 e-community to post your questions.