The Tech Blog

We looked into PWM dimming last time. Analog dimming, unlike its digital counterpart, involves manipulating the continuous current flowing through LEDs to adjust their brightness. While PWM dimming regulates the on-off cycles of LEDs, analog dimming offers a seamless, gradual, and continuous adjustment. The main benefit of analog dimming is the fact that it offers flicker-free LEDs, this is why it’s one more preferred approach for photography applications. You don’t have the hassle of shutter speed sync as in PWM dimming.

Analog dimming is supported by certain LED drivers where you have a dedicated pin that is driven by an analog voltage from a microcontroller or a DC source. These drivers usually have a linear range of operation wherein increasing the voltage on the control pin will increase the current through the LEDs. At the extremities of the linear region you may have sharp jumps in brightness, so always take care of the region of operation if you want a constant light output. BTW if you don’t have variable DAC output to drive the analog pin, you can generate a PWM signal and pass that through a low pass filter whose average output can then be fed to the Control pin.

Since these drivers need to be driven by small analog values, it’s usually recommended to have the driver relatively near to the microcontroller generating the voltage to avoid losses in transmission, esp. in the cases that LEDs are placed in a separate board and you are connecting them with long wires. One main disadvantage of analog dimming is its lower dimming ratio and also the colour shift in the light output because the current is getting changed. So if you want the colour temperature to be constant through its range, this would not be the right topology for you. Choose wisely.

LED dimming is a fundamental aspect of modern lighting systems. Rarely do you see LED systems just doing ON and OFF these days. Mood lighting, custom fades and ambiance is all a rage now. It’s all about achieving the desired brightness for a particular application. The key reason why dimming is essential is that it increases energy efficiency and also keeps extending its lifespan by not driving it at its full brightness.

There are different kinds of dimming drives possible for LEDs. Before we get into that, it’s important to understand what dimming ratio is. This is a ratio number you see in most LED driver datasheets. The dimming ratio in LEDs refers to the ratio between the maximum brightness (luminance) of the LED at full power and its minimum brightness when dimmed. It essentially measures how effectively an LED can be dimmed. A higher dimming ratio indicates a better performance in terms of achieving lower brightness levels when dimmed. For instance, a dimming ratio of 1000:1 means the LED can dim down to 1/1000th of its full brightness.

It also corresponds to the dimming resolution of an LED driver which refers to the number of distinguishable steps or levels at which an LED light can be dimmed. It represents the granularity of control over the brightness levels. Meaning, that even if you have a high dimming ratio and low dimming resolution, you may be able to get to the lowest dimming ratio but the gradation from low to high may not be smooth and your eye might be able to pick it up when you go from high to low. The higher dimming resolution allows for finer adjustments to the light output. Some LED types of drives can achieve only some range of dimming ratios. We will look into those in detail next time.