3 ms·

Linear regulators waste a lot of power and generate a lot of heat, so that's why they don't use them. Switching regulators can be used without having PWM on th

Linear regulators waste a lot of power and generate a lot of heat, so that's why they don't use them. Switching regulators can be used without having PWM on the LEDs though. LED flashlights use constant current sources, I don't know if that's infeasible or not for some reason on high-power car headlights. Personally I wouldn't be surprised if it's just to save the 47c. The car industry is competitive.

Zak 2y ago
A series of web searches found one of the driver boards often used in LED tail lights: the Valeo b003809. Some images of it show an identifiable TLE4242 linear driver IC. I was starting to suspect that would be the case after reading the explanation about slow PWM and a short duty cycle resulting in greater perceived brightness from cheap LEDs that aren't rated for much power. Direct drive from the car's electrical system wouldn't result in the constant brightness seen in LED tail lights because the voltage is lower at idle, so there has to be some kind of regulation. There would be little reason to use a more efficient, more expensive switched-mode power supply, though an aftermarket replacement for the Valeo board does use one. Even an inefficient LED design will be far more efficient than an incandescent bulb, and the power requirement of any taillight is trivial relative to a modern car's electrical system. Linear makes the most sense for the application. Linear regulators aren't rare in LED flashlights nor is direct drive with PWM on a FET for low modes. Neither is good in flashlights, but that only matters to the manufacturer if their customers know the difference. Most customers don't; lights marketed to discerning customers use a switched-mode power supply.
- neuralRiot 2y ago
  The problem could be the LED driver itself rather than the vehicle driver output. Most LED lights use some kind of PWM or multplexing, but people only notice the bad or rather the slow) ones. It’s easy to find out, just take a few videos at different frame rates an you’ll see.

Zak 2y ago

A series of web searches found one of the driver boards often used in LED tail lights: the Valeo b003809. Some images of it show an identifiable TLE4242 linear driver IC. I was starting to suspect that would be the case after reading the explanation about slow PWM and a short duty cycle resulting in greater perceived brightness from cheap LEDs that aren't rated for much power. Direct drive from the car's electrical system wouldn't result in the constant brightness seen in LED tail lights because the voltage is lower at idle, so there has to be some kind of regulation. There would be little reason to use a more efficient, more expensive switched-mode power supply, though an aftermarket replacement for the Valeo board does use one. Even an inefficient LED design will be far more efficient than an incandescent bulb, and the power requirement of any taillight is trivial relative to a modern car's electrical system. Linear makes the most sense for the application. Linear regulators aren't rare in LED flashlights nor is direct drive with PWM on a FET for low modes. Neither is good in flashlights, but that only matters to the manufacturer if their customers know the difference. Most customers don't; lights marketed to discerning customers use a switched-mode power supply.

neuralRiot 2y ago
The problem could be the LED driver itself rather than the vehicle driver output. Most LED lights use some kind of PWM or multplexing, but people only notice the bad or rather the slow) ones. It’s easy to find out, just take a few videos at different frame rates an you’ll see.