Boost converter with short circuit protection is aceptable for Car light?

[Flyback]

Hello, the following is a 40W boost converter with latch-OFF short circuit protection.
The short circuit protection is needed because as you know, the boost converter lacks intrinsic short circuit protection unlike the Flyback, Sepic and buckboost converter.
Would this be an acceptable solution as an Automotive power supply to supply a Daytime running light on a car?
The boost converter has..
Vin=10V
Vout = 48V
Power output = just over 40W.
The load is several Buck LED drivers.
F(sw) = 138KHz.
schematic and LTspice simulation is attached.

 

[ronsimpson]

Flyback, you know what I am going to say. Too many parts by 3x.

 

[alec_t]

Would this be an acceptable solution as an Automotive power supply to supply a Daytime running light on a car?

Depends who you ask . I can't see the bean-counters agreeing.
Are Underwriters Labs/ Insurers happy with this?
Does it meet all vehicle/accessory manufacturing regs in whatever country you propose selling it?
Is the whole caboodle really cheaper than a length of wire for feeding a 12V filament bulb?

 

[Flyback]

it would go on a million pound sports car..cost isn't much of an issue

 

[alec_t]

Oh well, in that case you're missing some 'essentials'. For starters, how about individual temperature sensors monitoring all susceptible components (semiconductors etc) and controlling converter performance accordingly?

 

[ronsimpson]

it would go on a million pound sports car..cost isn't much of an issue

You have not worked for a car maker.

I will build a 20% lower cost item and knock you out of the market. (less parts)
Then production will get moved to some rat hole in a 3 world country and another -20%. (cost of labor)
Then someone will change to 'questionable' parts and -10%. (so it will only work for 1/4 as long but who cares) (get a smaller LED and over drive it)
Then engineering gets moved to the same rat hole and an engineering what makes very little is in charge. One day he is a rice farmer and the next he is a R&D engineer.

I have been down this road too many times.

 

[ronsimpson]

Oh well, in that case you're missing some 'essentials'. For starters, how about individual temperature sensors monitoring all susceptible components (semiconductors etc) and controlling converter performance accordingly?

Yes. Even some flashlights have a temperature sensor on the LEDs. We had a competitor that had 2x the light output from the same LED. They over drove the LED by 2x until it got hot then backed down. And on cold nights you got 2x the light. So I figured out how to get the same effect for less money.

 

[Flyback]

The point is that it is really difficult to get effective active latching short circuit protection that's low in component count and yet still solves the following problems...

1....Mustn't trip on transients or inrush currents.
2.....If the power is cycled on and off repeatedly in quick succession, then each time it comes back on , the latching short circuit protection must be available.....the latch mustn't still be "latched" when the power is brought back on.
3....The protection must be able to act if the lamp is turned on into a short circuit.
4.....If, due to high wiring resistance, the short causes the voltage at the lamp to be extremely low, (due to ohmic voltage dropping) then the latching short circuit protection must still work, in spite of the low supply voltage available to it.
5....The current sensing method must not be very dissipative in normal operation...it must only dissipate around 200mW or less.

The problem with doing active latching short circuit protection with alternateive topologies like buckboost, flyback and sepic is that they don't draw much current when their output is short circuited, but they still draw enough current (during output short circuit) to flatten the battery quickly, so it is even more difficult to do active latching short circuit protection for those topologies. Also, a fuse won't trip when a flyback/sepic/buckboost suffers a shorted output, because no large current surge happens from the input to these type of converters.
At least with the boost converter, the input fuse to the lamp would blow due to the current surge.

All the above assumes that no microcontrollers are allowed in the solution, just analog circuitry.

the following ltspice is an update of the active latching short circuit protection

 

[ronsimpson]

What about buckboost, flyback or sepic and add a simple circuit that latches off if the output voltage does not come up in 1 second. It should power up in 1mS.

 

[Flyback]

yes that's a good idea,
though ...
the flyback needs a transformer and an rcd clamp
the sepic needs a big series capacitor
the buckboost needs two fets if its output is to be referenced to ground.

also, the boost has less rms input current ,than those three topologies.
-shame it cant be done any simpler with the boost

 

[ronsimpson]

the buckboost needs two fets if its output is to be referenced to ground.

Remember, if you are driving a LED, neither lead needs to be on ground.

What I have done; the PWM is inside the light bulb. There is really no need for short protection. There are no wires to get shorted out.

 

[Flyback]

yes but in automotive use the led pcb enclosure could get condensation creeping into it, which could short it.

 

[ronsimpson]

That's what potting materiel is for. A auto light bulb should work under water.

 

[Flyback]

potting is expensive, as you know.

 

[ronsimpson]

Failure is expensive, Water corrosion is expensive.

1) Water at 12V is not very conductive.
2) If you add 2x more parts, so there will be no excess current with water, why will the current limit circuit work with water on it.

 

[Flyback]

ok maybe the psu can be potted, but for obvious reasons, the led pcbs cannot be potted.

 

[ronsimpson]

Here is a bulb that does work under water. It should not be used under water it just works.

Input voltage 2V to 10V. If I remember they worked well at 15V but we did not want them used on cars so they say 10V max.
Picture taken on my lap top.
The inductor (and cap) is on the other side of the PCB.
You can see why I can't have many parts.

 

[Flyback]

This is a 40W buckboost that does output short circuit protection by simply turning off when it detects the output voltage has gone to zero volts...a monostable circuit ensures this protection does not kick in immediately the power is turned on otherwise the buckboost would never get started in the first place.
Can you think of a way to do this with less components?

LTspice simulation and pdf schematic attached

 

[ronsimpson]

Here is a power supply that should be safe if the LED shorts.
Current regulation is not good. The current changes with Vin just like a incandescent bulb. If I add a couple of parts I can hold the current very tight but then it does not act like an incandescent bulb.
I have done this in several designs. There are LED driver ICs that use this type of current regulation.

 

[Flyback]

thanks, that's interesting, subharmonic oscillation, but why not, doesnt affect the light