T
treez
Guest
Hello,
My question is why is anybody using High Frequency Switched Mode LED drivers to power LED streetlights?
As the attached LTspice simulation and schematic shows, simple ‘Switched Linear Regulator’ based LED streetlights are very good and have admirable efficiencies...
They also need no electrolytic capacitors. Also, they are far easier to protect from mains transients (the biggest streetlight ‘killer’ out there) than High Frequency Switched Mode LED drivers. ‘Switched Linear Regulator’ based LED streetlights are easier to protect from mains transients than High Frequency Switched Mode LED drivers because the FETs can be very high voltage rated, without this badly affecting the efficiency. If a High Frequency Switched Mode LED driver uses a high voltage FET with a low enough Rds(on), then its switching losses become excessive. Therefore, a High Frequency Switched Mode LED driver based LED streetlight will use a lower voltage rated FET and be more susceptible to mains transient related failure.
Also, the ‘Switched Linear Regulator based LED streetlight’ needs no custom wound transformer and uses few different components.
The only disadvantage is the larger number of LEDs that are needed to make the ‘Switched Linear Regulator’ based LED streetlight. However, the cost of this is totally offset by the reduction in susceptibility to mains transients…..which means a dramatically lower failure rate and massively less replacement costs.
The power factor of the “Switched Linear Regulator based LED streetlight”, is not as good as the High Frequency Switched Mode LED drivers can be, however, it is good enough to pass regulations. After all, streetlights have only low Power Factor and Mains Harmonic regulatory requirements because they are only on at night, when the electricity grid is under-utilised, and so power factor does not matter anywhere near so much.
So why on Earth is anybody using High Frequency Switched Mode LED drivers for LED streetlighting?
The attached is a Streetlight with 63.5W of LED power. It is 76% efficient. It uses only switched Linear current regulators (which at certain times are “swamped” and have little dissipation during those times).
The linear regulators are switched ON/OFF at around the twice mains frequency.
The efficiency actually varies with the mains input level, and in fact at 265VAC input, it is actually 84% efficient, and gives 77.5W of LED power.
If you wanted to add a microcontroller and change the reference voltage of the linear regulators as the mains input voltage changed, then you could make it >84% efficient over the whole 206 to 265 VAC range. It wouldn’t be workable over the full 100-265VAC mains range however.
Attached is the LTspice simulation, pdf schematic and mains input voltage and current waveform scope shot.
So indeed, why on Earth is anybody using High Frequency Switched Mode LED drivers for LED streetlighting?
My question is why is anybody using High Frequency Switched Mode LED drivers to power LED streetlights?
As the attached LTspice simulation and schematic shows, simple ‘Switched Linear Regulator’ based LED streetlights are very good and have admirable efficiencies...
They also need no electrolytic capacitors. Also, they are far easier to protect from mains transients (the biggest streetlight ‘killer’ out there) than High Frequency Switched Mode LED drivers. ‘Switched Linear Regulator’ based LED streetlights are easier to protect from mains transients than High Frequency Switched Mode LED drivers because the FETs can be very high voltage rated, without this badly affecting the efficiency. If a High Frequency Switched Mode LED driver uses a high voltage FET with a low enough Rds(on), then its switching losses become excessive. Therefore, a High Frequency Switched Mode LED driver based LED streetlight will use a lower voltage rated FET and be more susceptible to mains transient related failure.
Also, the ‘Switched Linear Regulator based LED streetlight’ needs no custom wound transformer and uses few different components.
The only disadvantage is the larger number of LEDs that are needed to make the ‘Switched Linear Regulator’ based LED streetlight. However, the cost of this is totally offset by the reduction in susceptibility to mains transients…..which means a dramatically lower failure rate and massively less replacement costs.
The power factor of the “Switched Linear Regulator based LED streetlight”, is not as good as the High Frequency Switched Mode LED drivers can be, however, it is good enough to pass regulations. After all, streetlights have only low Power Factor and Mains Harmonic regulatory requirements because they are only on at night, when the electricity grid is under-utilised, and so power factor does not matter anywhere near so much.
So why on Earth is anybody using High Frequency Switched Mode LED drivers for LED streetlighting?
The attached is a Streetlight with 63.5W of LED power. It is 76% efficient. It uses only switched Linear current regulators (which at certain times are “swamped” and have little dissipation during those times).
The linear regulators are switched ON/OFF at around the twice mains frequency.
The efficiency actually varies with the mains input level, and in fact at 265VAC input, it is actually 84% efficient, and gives 77.5W of LED power.
If you wanted to add a microcontroller and change the reference voltage of the linear regulators as the mains input voltage changed, then you could make it >84% efficient over the whole 206 to 265 VAC range. It wouldn’t be workable over the full 100-265VAC mains range however.
Attached is the LTspice simulation, pdf schematic and mains input voltage and current waveform scope shot.
So indeed, why on Earth is anybody using High Frequency Switched Mode LED drivers for LED streetlighting?