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Linear LED Driver Board Design

Published Date
Author Cadence PCB Solutions

Key Takeaways

  • LED drivers are specially designed voltage conversion devices that allow LEDs to work normally by supplying the required voltage. 

  • LED drivers can save LED lights from voltage and current fluctuations. 

  • There are two main types of LED drivers: constant current LED drivers and constant voltage  LED drivers.

 LED driver

LED driver board design aims to prevent thermal runaway problems in LED systems

Thermal runaway is a significant concern in LED lighting systems. With the increase in temperature, the forward voltage of the LED decreases and draws more current. The excessive flow of current heats up the LED and can ultimately burn out the light. LED driver boards are self-contained power supplies that are designed to an output voltage that matches the electrical characteristics of the LED. The LED driver board design aims to prevent thermal runaway problems in LED systems.  

The Importance of LED Drivers

LEDs are innovative lighting systems used extensively due to their long life and energy-saving properties. LEDs are designed to operate at low DC voltage, in the range of 12-24 V. However, the universal voltage range is between 85-264 V AC, operating at 50 Hz and 60 Hz frequency. It is necessary to convert the alternating current to a low DC voltage suitable for LEDs.

LED drivers are specially designed voltage conversion devices that allow LEDs to work normally by supplying the required voltage. LED drivers are specialized power supplies that perform the AC to DC conversion. They deliver the required output to the LED and ensure the light source functions smoothly.

LEDs are rated for a certain range of current, and any deviation from that range affects the LED light brightness. The variation in light output from current fluctuations can degrade the LED due to heat generation. Increased heat generation leads to the decreased forward voltage of the LED. If the power supply continues to provide the rated forward voltage at high temperatures, it can cause LED failure. The increased heat generation in LEDs can cause detrimental effects and permanent damage. LED drivers can save LED lights from voltage and current fluctuations. LED drivers regulate the LED circuit current and voltage for long battery life, LED service life, and optimum brightness. LED drivers are significant in maintaining the voltage and current in the LED circuit within the rated level.   

Constant Current and Constant Voltage LED Drivers

LED drivers can be internally or externally included in LED lighting systems. There are two main types of LED drivers:

  1. Constant current LED drivers: Constant current LED drivers deliver a fixed output over a range of output voltages. A constant current LED driver regulates the current and prevents the LED current overdrive above the rated value. The regulation provided by constant current LED drivers prevents thermal runaway and premature burnout as well as extends the lifespan of the LED. 

  2. Constant voltage LED drivers: A constant voltage LED driver outputs a constant voltage of 12 Vdc or 24 Vdc with a maximum output current. Constant voltage LED drivers maintain constant voltage irrespective of the load current as long as the current stays below the maximum value.

Linear LED Driver Board Design

Linear LED drivers are innovations in solid-state lighting technology and offer advantages such as:

  1. Low cost

  2. Scalability of output channels

  3. No magnetics required

  4. Ripple suppression

  5. Better electromagnetic compatibility

Several linear LED driver ICs are available. Let's look at the 24 V, 100mA LED driver board design using IC BCR430U. The schematic diagram is presented below. 

LED driver board schematic

Linear LED driver circuit

The LED current can be increased up to 100mA by changing the resistor value (Rset) connected to pin Rs. The resistor value Rset can be varied for a current range of 20mA to 100 mA. The Rset value range is 120kΩ to 6.2kΩ, keeping the default value to 12kΩ for 50mA LED current. The LED driver board is capable of driving 8 LEDs in series.

The supply DC voltage can be from 6 V to 42 V. The electrolytic capacitor C1 can suppress the ripples in the power supply voltage. The RC combination R1 and C3 is the high-frequency noise filter for the power supply. The capacitor C2 reduces the oscillations at the LED pin and is preferably connected nearer to the LED pin. The pad Rph is the slot for the soldering of a variable resistor, which can be left unassembled as well. The LED+ and LED- are the connections for assembling external LEDs other than the 8 onboard LEDs. 

Extend the Lifespan of LEDs With LED Driver Boards

In modern lighting systems, LED driver board design is used for extending the lifespan of LEDs. You can use constant current or constant voltage LED drivers, depending on the application. Cadence PCB design software can be used to design LED driver boards. Cadence’s suite of PCB design software can help engineers design LED driver circuits for domestic, industrial, automotive, and street lighting applications.

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