Clean (semi-)regulated power from car

[Doktor Jones]

Hi, I'm looking to build a small power supply for some LED lighting in my pickup. My main concern is making sure the power stays at or below +12V (if it sags to ~10.5-11V I'm not worried about that) and spikes/noise/etc endemic to automotive power are filtered out.

Would it be sufficient to have a 15V zener across the input along with a couple filter caps (1000μF/50V + 0.33μF/50V), running into an LM7812CT (TO-220) with a 0.1μF/50V bypass cap on the output? Would it be beneficial to add a third mid-range capacitor (~100-220μF) in the filter cap set? The power draw will not exceed 1A, so with the 15V zener, the 7812 should never have to dissipate more than 3W.

I know I could use a LDO regulator to reduce sags when running directly off the battery (~12.8V), but I've tested the LEDs on a 10V power supply and they work just fine, and I have a bucketful of LM7812s on hand already so I figure I'd make use of them if possible.

Thanks!

 

[Nigel Goodwin]

For simply lighting LED's I would suggest there's no need for any precautions at all - the environment in a car isn't as bad as you might think, and LED's are sturdy things anyway. A 7812 is no use in a car anyway, you don't have enough voltage for it to work.

 

[Doktor Jones]

Well looking closer at the module, I'm wondering if maybe it has a buck (or buck/boost?) converter built-in. Can someone confirm whether this is the case? If so, how resilient do you figure it will be in an automotive installation? I'd like it to last for years -- ideally the life of the truck -- which is why I was looking at filtering the input, so there'd be less work for the onboard electronics to do (and thus less heat generated and a longer lifespan).

 

[KeepItSimpleStupid]

LT has introduced a surge protection device: https://www.linear.com/product/LT4356-1_-2

Bourns has introduced the TBU: https://www.bourns.com/RoHS.aspx?name=rohs_transient_blocking_units

Minimally, I like a 18V TVS diode and an 1n2004 reverse biased diode on the inputs.

In your pic there is a coil and some IC looking thing. Any numbering on that?

 

[Doktor Jones]

The coil has "470" on it
the six small black bits (diodes?) have a vertical line marking followed by "S4"
the resistor above the IC-type thing says "R500" (500Ω resistor?)
the IC itself looks like it says "EQC3G"

 

[Diver300]

4 of the diodes are so that the lamp works either way round in the fitting.

It looks like a buck regulator that controls the current in the LED. The inductor is almost certainly 47 μH. The resistor is 0.5 Ω and will be the current sense resistor. I guess the IC is a dedicated LED driver.