Why are car rear/brake LED lights done with linear LED drivers?

[Flyback]

Car Rear/Brakelights are only 4W each.
Why do people do them with linear regulators?
4W doesn't sound much but with the rear light being non-ventilated, that heat is trapped, and so can overheat.
Why can't an SMPS led driver be done as below.......?
This is a DCM Boost preceeded by a current clamp to prevent high current oscillations in the LC EMI filter if the driver "stutters" on and off repeatedly with the brake pedal.
From the moment the brake pedal is pressed, the output is in regulation just 1.3ms later......that ain't that much worse than a linear regulator....and it runs a whole lot cooler.

 

[large_ghostman]

apparently our old landy has 55W bulbs in (according to dad) and that copes fine with the heat! man i thought i had a thing about Leds!!

 

[ronsimpson]

 

[jpanhalt]

Please delete

 

[JimB]

apparently our old landy has 55W bulbs

In the headlamps, yes, but not the brake lights.
Brake lights and flashers 21W, sidelights - cant remember.

Jimb

 

[large_ghostman]

In the headlamps, yes, but not the brake lights.
Brake lights and flashers 21W, sidelights - cant remember.

Jimb

sorry for the miss information, point is tho its still way higher than 4W and cars have managed like that for a long time

 

[4pyros]

Its ether government regulations, reliability, complexity, cost, or any combination of any of them.

 

[Flyback]

The TPS61161 looks good but isn't in any of the docs revealed to be for automotive use. I cant see why it shouldn't be....but it isn't revealed as such.
To be honest I reckon two tps61161 type supplys gives redundancy and I would say is more robust than any linear regulator solution, even if multiple linear regs are used.

 

[audioguru]

I hope no truck (Land Rover or lorry) with 55W stop lights is not ahead of me at a stop light. It would burn my eyes out.
A Lincoln SUV truck thing was ahead of me yesterday with EXTREMELY bright tail lights. When driving along the LEDs flickered with PWM. I blocked the brake lights with my sun visor.

 

[ronsimpson]

Why are car rear/brake LED lights done with linear LED drivers?

$$$$$$$$$$$$$

 

[Flyback]

I take your point....but I reckon switcher driven leds will last longer (the lamp will last longer).....and anyway, people who buy bentleys can afford a bit extra on the led drive. It seems a shame to have the 4W worth of leds on a huge heatsink, and then go and dump in an extra 4W of dissipation due to a linear led drive.

 

[ronsimpson]

NXP just sent me an email. They have a new automotive LED driver. ASL1002,4,7,10
I would look at LM3421,3,4,9 and LM3401,02,06 Down load LM3402. I can/have put this inside a bulb and no one will know.

I have two large trucks. I must have clearance light all around the top. If one bulb is out, any where, I can get a ticket. I am willing to pay extra for a long lasting bulb. Extra for a brighter bulb. Every 5 miles I burn a gallon of fuel. Four watts is nothing.

 

[large_ghostman]

NXP just sent me an email. They have a new automotive LED driver. ASL1002,4,7,10
I would look at LM3421,3,4,9 and LM3401,02,06 Down load LM3402. I can/have put this inside a bulb and no one will know.

I have two large trucks. I must have clearance light all around the top. If one bulb is out, any where, I can get a ticket. I am willing to pay extra for a long lasting bulb. Extra for a brighter bulb. Every 5 miles I burn a gallon of fuel. Four watts is nothing.

in the uk you would be bankrupt with that kind of fuel use what kind of trucks are they? and what size engine?? (i like engines )

 

[Flyback]

i do like the LM3421.....its the only constant off time controller that ive ever seen that has an internal error amplifier....it says it uses 'predictive off time' control, but from what i can see, the off time is just how long it takes the RCT cap to charge up to VIN/25.
It looks like you can connect the timing resistor to the drain or the vin.....but if its a boost converter, then connecting to the drain will make the off time longer.
The high side dimming drive blew my mind a bit , but i suppose it is the easiest way, even though it has shedloads of external components.

 

[tcmtech]

LED lights for vehicle brakes have to draw a minimum amount of power or the blinker system thinks it has a bulb burned out and thusly does not work right. That's why they have to draw at least 4 watts per unit.

 

[Flyback]

is that only for retrofit led lamps?

 

[tcmtech]

It's for any vehicle that came with incandescent bulbs from the factory. Without the correct current draw at minimum the blinker device will not blink properly.

One little side or front bulb goes out on my wifes car or my pickup and the blinker slows from ~2 flashs a second to maybe 1 every 10 seconds.
One large rear bulb goes out and they don't blink at all.

 

[audioguru]

in the uk you would be bankrupt with that kind of fuel use

Most cars in Canada use gasoline (petrol) and are not diesel. Most trucks (lorries) use diesel.
Some oil comes out of the ground in Canadian Oil Sands but it is thick, cold and full of sand so it is difficult to clean it and transport it. Most oil in Canada comes from The Middle East and Venezuela.

31% of the price of Gasoline in my part of Canada is taxes. Today one litre costs $1.29 which is 0.75 British pounds Sterling.
I think your taxes are much higher causing your petrol to cost twice as much or more.

 

[Nigel Goodwin]

31% of the price of Gasoline in my part of Canada is taxes. Today one litre costs $1.29 which is 0.75 British pounds Sterling.
I think your taxes are much higher causing your petrol to cost twice as much or more.

Yes, much higher taxes - and then 20% VAT (Value Added Tax) added on top, costs about £1.29 per litre at the moment.

 

[Flyback]

Never mind the petrol prices.......at least the houses are cheap over here in UK......take this typical , bargain 2-bed-terrace in Cambridge for just £325,000

https://www.rightmove.co.uk/property-for-sale/property-37970479.html

...there's nowhere to park anywhere near it so you won't need to use petrol (the on street parking doesn't quite work out because each house is less length than a car....so only room for one car outside every 2 houses)