Recently, there’s been a lot of buzz surrounding artificial intelligence, especially when it comes to robots taking over certain tasks. People often imagine a future where robots dominate and control everything, leading to a robotic world. While these ideas might sound exciting in science fiction, they’re mostly just sensationalist talk. Most machines, like those on assembly lines, operate strictly according to pre-programmed instructions and can’t adapt automatically to environmental changes. If the environment shifts slightly, their performance suffers, making them far from what we’d call “smart†devices. Our focus should be on using intelligent technology to solve real-world problems and improve our daily lives.
The heart of intelligent technology lies in adaptability. Technologies that adjust device operations optimally based on environmental changes are adaptive. By integrating adaptability, we can transform traditional methods and achieve remarkable outcomes.
One great example of this is the intelligent adaptive LED constant current source.
1. Classic Linear Constant Current Source
We know that power supplies generally fall into two categories: constant voltage and constant current. A constant voltage power supply maintains a steady output voltage regardless of fluctuations in input voltage or load. A constant current power supply, on the other hand, provides a fixed output current irrespective of input voltage or load changes. Since LEDs are semiconductor diodes with a negative temperature coefficient, they require a constant current supply to avoid overheating. There are two primary approaches to achieving this: switch-mode and linear-mode. Switch-mode offers high efficiency (around 90%) but comes with more components, lower reliability, larger size, and higher costs. Linear constant current sources are simpler with fewer components, higher reliability, smaller size, and lower costs. However, their efficiency is much lower, around 85%.
2. Efficiency of Linear Constant Current Sources
The efficiency of linear constant current sources drops as the input voltage increases. Here’s a typical efficiency curve:
At 220V mains voltage, the efficiency is only 85%. Lower input voltages yield higher efficiencies. Could we make this source highly efficient even at 220V?
To answer this, we need to delve deeper into the circuit composition and performance of linear constant current sources.
3. Linear Constant Current Source with Ordinary Constant Current Diodes
The simplest linear constant current source uses an ordinary constant current diode. Its circuit looks like this:
Here, CRD represents a constant current diode. Multiple CRDs can be connected in parallel to achieve the desired current value. There are various CRDs available with different current ratings, eliminating the need for parallel connections. Simply connect a suitable constant current diode and all LEDs in series to create a constant current supply for the LED. This makes the circuit very straightforward!
Its operation principle can be understood through its volt-ampere characteristics:
It maintains a constant current from Vk up to the input DC voltage range of the POV. The absolute value of Vk is less than 3V. Assuming the rectified DC voltage is 300V and the constant current value is 0.1A, the total power is 30W. If the total voltage of the LED string closely matches 300V, the constant current diode operates near Vk, consuming only 0.3W of power, resulting in an efficiency of (30-0.3)/30 = 99%.
However, as the input voltage increases, the constant current diode must handle excess voltages, shifting its operating point to the right and gradually increasing power consumption, leading to a drop in overall efficiency.
This low-efficiency characteristic is inherent to constant current diodes, requiring them to be housed in packages with large heat sinks, which seems unavoidable.
That’s what most textbooks say.
4. Improving Linear Constant Current Source Efficiency with Adaptive Methods
To enhance the efficiency of linear constant current sources, we need entirely new approaches.
Since our application involves powering LEDs, which serve as the load of the constant current source, the number of LEDs must match the rectified voltage output. For instance, if the rectified voltage is 300V and each LED has a forward voltage of 3V, then 100 LEDs must be connected in series. When the mains voltage rises, the rectified voltage also increases, but since the LED is powered by a constant current source, its forward voltage remains constant, leaving the excess voltage to be handled by the constant current diode. This naturally leads to a drop in overall efficiency.
Is there a way to prevent the constant current diode from bearing the extra voltage after rectification?
The best solution is to adaptively change the number of LEDs. When the mains voltage rises, add more LEDs. When it falls, reduce the number of LEDs. This can be easily achieved using an adaptive digital switching circuit. Here's how it works:
LEDs in the block can be adaptively connected to or disconnected from the main LED string based on input voltage changes. The number of connections or disconnections depends on the input voltage change. It senses voltage changes and adjusts the number of LEDs accordingly, making it adaptive and intelligent.
Shenzhen Effie has successfully developed such a chip capable of automatic switching, named AICS, standing for Adaptive-Intelligence-Current-Source.
5. Performance of Intelligent LED Constant Current Source
**5.1 Input Voltage Adaptability**
As mentioned earlier, with adaptive control, this constant current source can reach 99% efficiency. Moreover, this efficiency can be maintained across a wide range of input voltage variations. Below is the relationship between efficiency and input voltage:
The blue line represents the efficiency of the constant current source itself, while the red line shows the total efficiency including the rectifier. Within a mains voltage range of 175V-265V, the efficiency of the constant current source stays at 99%, with the total efficiency including the rectifier exceeding 98%.
**5.2 Temperature Adaptability**
When the ambient temperature changes, the power consumption of the constant current diode increases. For example, as the ambient temperature rises, the forward voltage of the LED decreases due to its negative temperature coefficient. This reduces the voltage drop across the constant current diode, increasing its power consumption. This intelligent constant current source counteracts this by increasing the number of LEDs in the string, keeping the total voltage matched to the rectified voltage, ensuring high efficiency:
From the graph, we see that as the ambient temperature rises from 35°C to 85°C, the overall efficiency remains nearly constant at over 98% (including rectifier losses).
**5.3 Adaptability to LEDs with Different Forward Voltages**
This intelligent LED constant current source also features adaptability to LEDs with varying forward voltages. Even when LEDs with different forward voltages are mixed in the same string, the adaptive intelligent LED constant current source can automatically adjust the number of LEDs to maintain 99% efficiency. This patent has been recently authorized by the US Patent Office.
**5.4 Changing the Number of LEDs Without Altering Luminous Flux**
Simply changing the number of LEDs would alter the total luminous flux because the constant current source's current remains constant. This issue is addressed in the design of the intelligent LED constant current source. The current value of the constant current source is adaptively adjusted along with the number of LEDs to keep the total power and luminous flux constant:
From the figures, we see that after adaptive adjustments, the input power, output luminous flux, and overall luminous efficiency remain largely unchanged across different input voltage ranges.
6. Integrated Photoelectric Light Engine
This intelligent LED constant current source completely overturns the conventional understanding of linear constant current sources found in textbooks, achieving 99% efficiency. Consequently, the constant current source and the light source can be placed on the same aluminum substrate to form an integrated photoelectric light engine. Due to its extremely low power consumption, placing it on the light source's aluminum substrate doesn’t raise the LED junction temperature. Shenzhen Effie has produced a series of light engines with different powers using this intelligent constant current source:
7. Conclusion
The efficiency of this intelligent LED constant current source reaches an impressive 99%, effectively making it a non-electricity-consuming constant current source. Typically, the efficiency of LED constant current sources is 85-90%, meaning that using this intelligent constant current source can save an additional 10-15% of energy. Its significance is immense!
China’s lighting accounts for 14.5% of total electricity consumption. In 2014, total electricity generation was 564.96 billion kWh, meaning lighting consumed 819.19 billion kWh. Using Effie’s light engines could save at least 10% of energy, equivalent to 81.92 billion kWh, which is close to the annual power generation of the Three Gorges Power Station (84.7 billion kWh). Globally, lighting accounts for 19% of total electricity consumption. In 2014, global electricity generation was 238.67 billion kWh, meaning lighting consumed 453 billion kWh. Using Effie’s light engines could save 453.5 billion kWh, equivalent to the power generation of 5.5 Three Gorges Power Stations!
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