OPTOELECTRONICS


The critical role of LED drivers in lighting applications


By Rolf Horn, applications engineer at DigiKey I


ncandescent and other older bulbs use electricity to heat a fi lament or gas, which then glows to emit light. A light-emitting diode (LED), on the other hand, is made of a special semiconductor material that directly converts electricity passed through it into light, a phenomenon known as electroluminescence.


Each LED material emits light in a narrow frequency range when supplied with a specifi c voltage and current. Deviations from these values can cause the LED to stop producing light or change its colour intensity. Designers typically rely on either constant current reduction (CCR) or pulse width modulation (PWM) to control LED intensity. Both aim to adjust the light output, but operate in fundamentally different ways, each with its own set of design trade-offs: CCR, often referred to as analogue dimming, works by reducing the current fl owing to the LED. It’s a straightforward and low-noise approach that doesn’t introduce fl icker, making it suitable for basic applications. However, reducing the current can slightly shift an LED’s colour and limit the dimming range, especially at very low light levels.


PWM dims LEDs by rapidly switching them on and off while maintaining a constant current during each pulse. This technique preserves colour consistency and enables a much wider dimming range, often down to less than one per cent. This makes it ideal for tuneable lighting or displays. The trade-off is that PWM can introduce electromagnetic interference (EMI) and visible fl icker if the switching frequency isn’t high enough. Designers must carefully balance these


factors.


PWM may require more complex drivers and attention to EMI fi ltering, while CCR may fall short in applications demanding colour precision or ultra-low dimming. In some cases, a hybrid approach combining CCR and PWM offers the best of both worlds.


Design considerations


Designers can overcome the limitations of either CCR or PWM dimming through smart design choices. For CCR, designers can select LEDs with stable colour performance across a wide current range and apply gamma correction or logarithmic dimming curves to adjust the dimming response to match how humans perceive changes in brightness. This results in smoother and more natural transitions. Careful driver selection and thermal management can also aid in maintaining colour stability and extending dimming performance without the need for additional circuitry.


For PWM dimming, the key challenges are


fl icker, EMI and design complexity. These can be overcome by using high PWM frequencies, typically above 20 kHz to 25 kHz, to avoid visible fl icker and minimise interference with audio or camera systems. EMI can be effectively controlled by carefully designing the circuit board, utilising fi lters and selecting


36 FEBRUARY 2026 | ELECTRONICS FOR ENGINEERS


When choosing the PWM route Applications that require multi-channel control, colour consistency and automotive reliability benefi t from the PWM approach. A good example is the AL5887Q Advanced 36-Channel Automotive LED Driver from Diodes Inc., which offers dual-


LED drivers that provide features such as adjustable signal rates. Drivers that incorporate built-in PWM capabilities simplify the process by generating signals internally, eliminating the need for precise timing management outside the driver. CCR may be preferred for applications that demand minimal EMI, such as healthcare settings, laboratories, or environments with sensitive electronics. This option provides reliably smooth and fl icker-free dimming over a limited range and its relative simplicity also lends itself to general illumination in homes, restaurants and large venues, particularly when simplicity and cost are top priorities.


PWM is often preferred for high colour consistency and a wide dimming range, such as for stage lighting or environments requiring very subtle lighting control. PWM drivers with integrated signal sources further simplify the design process by handling timing internally, reducing design complexity.


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