How about taillight brightness?
I'm not sure if this has gotten better in recent years, but there are a bunch of high-end vehicles (looking at you AUDI) with extremely bright red LED taillights that are just painful to sit behind at a red light.
I'm not sure if this has gotten better in recent years, but there are a bunch of high-end vehicles (looking at you AUDI) with extremely bright red LED taillights that are just painful to sit behind at a red light.
But maybe it's possible, if you just want to fix your LEDs at a specific brightness which never changes, that you could find exactly the right current level...?
You might ask why not connect them in series and get the voltage difference as small as possible. But the “forward voltages” of LEDs are highly temperature dependent and car battery voltage is (somewhat) engine rpm dependent (might swing between 12 and 13.8V between no rpm and some rpm. It’s kept flat at 13.8V)
Your classic LM317 linear regulator can do it pretty easily, with a potentiometer instead of a fixed resistor to set the output current. Section 9.3.3[1] of the datasheet describes the circuit, though in practice you might add a couple of capacitors for stability.
There are also a number of discrete-transistor circuits. A current mirror with a rheostat is probably the simplest, though not generally ideal performance.
[1]https://www.ti.com/lit/ds/symlink/lm317.pdf?ts=1734395381792...
One that I think would work well in cars is a fixed-current linear regulator like the AMC7135. There's no need to do anything fancy to control it; put a 7135 in the circuit and the LED gets 350mA. Two in parallel and it gets 700mA, and so on. More fancy is a linear regulator with variable current output.
Linear regulators are a low-end option for flashlights, with switched-mode power supplies being preferred for their superior efficiency. A car has a lot more energy to work with and more mass with which to sink and radiate heat.
I first noticed slow PWM in factory tail lights on Cadillacs somewhere around the turn of the century. I pointed it out to my dad one night when we were out for a walk, and told him how to see it on a car that was disappearing down the road.
It took a few seconds for him to understand and to observe it himself, and then he said "I can accept that you're annoyed by that, but maybe they just build them that way because they think it looks cool."
Ever since that night, I have always assumed that slow PWM was used as a deliberate visual effect: After all, General Motors isn't really trying to squeeze a few pennies out of a new Cadillac [that's what Chevrolet is for!].
(I also think it's a dick move on the manufacturer's part, whether it is to save forty-seven cents, or if it is to look cool, or even if it is both.)
https://electronics.stackexchange.com/questions/164078/why-i...
Or they could use a variable linear regulator with no flickering at all.
There's nothing I'm aware of relating to the electronics that drive them that would place such a low bound on frequency that the resulting pulses would be visibly distinct.
MOSFETs are generally good for > tens-of-KHz frequencies, and so are the hardware PWM channels in every-day MCUs.
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.
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.
I've never seen a strobing tail light. The most "strobing" I've seen are some brake/tail lights that flash for 1-2 seconds right after they're turned on (to alert drivers better? still annoying imo).
But I think the poster is complaining about the higher frequency flickering that's supposed to be imperceptible... if you don't perceive it, that's better for you. Unfortunately, I regularly see it especially when moving my heads or eyes and find it pretty distracting. There's circuit design techniques to reduce the flickering, but saving pennies here and there adds up, so there you go.
(This could be as simple as a filter that turns the duty cycle into a current target. This feature is nearly ubiquitous in off-the-shelf “dimmable constant current” line-voltage-input LED drivers from basically every supplier (e.g. Mean Well). The tricky bit would be to get the thing to turn on quickly enough without annoying brightness swings, so some actual care in the filter design and frequency selection would be required. Or one could use 0-10V control (also ubiquitous) or have just two states plus off or have digital control… there’s no shortage of perfectly fine solutions.)
Also: https://standards.ieee.org/ieee/1789/4479/
For me, it's the sudden sensation of being mashed in a Berlin disco. While driving!