voltage regulator

Depends where in the automotive environment you are.

If you are behind some of the switched power systems, you won't have to worry about load dump _too_ much. If you're on the battery side, you have to take that (and a lot of other things) very seriously. (Things like E-marking, for instance).

All the usual suspects make supposedly 'load-dump protected' regulators, but I have my doubts.

I don't have a list handy (not currently at the office) but for a parametric search use a minimum of 30V Vin (a 24V vehicle has a typical run voltage of about 27.5V). If it's rated higher, all the better.

Input protection can be pretty simple if you get a 40V device; use a 32

- 36V transorb (or one designed for automotive load dump such as the SM8S series), an electrolytic for energy storage (rated at 63V should be fine behind a protector) and a ceramic or two for high frequency noise.

The only extra component I see there is the input protector - hardly a 'plethora' of protection components.

Cheers

PeteS

Seems simple enough, LM317 and 2 resistors drawing power off the accessory circuit.

Luhan

Would it were only that simple. The market is littered with the remains of devices that used such without extensive protection. I have considered the LM317HV but the protection required is relatively costly and quite tight as Vin max is (from memory) only about 60V for the HV and 40V for the standard part.

Thanks for the response. The problem is with a single SAD , say a 5KW device, with a nominal clamping voltage of 33V, a classIII surge will limit at around 80V. A

30V part is *very* close to the limits for a 24V automotive system and may not be within accepted limit extremes. Two or three parallel 1K5W devices could keep this down to ~60V. I am trying to avoid an inductor varistor resistor transorb capacitor diode 60V regulator set up as I am running out of volts at the 12V end! 35 to 40V devices are fine in 12v systems with straightforward protection. Problem is in 24V systems, which are 'harsher' than 2x 12v systems, 70 to 80V devices would be necessary for similar protection to be adequate. Such dedicated auto devices were once available, typically with 100V input, reverse, and load dump protection, but they now seem no more - or at least I cant find one. Everyone uses switchers but this app cannot do so at this time.

It is an 'e' product: there is no 'E' applicable

Use a hash choke and a Transzorb. THat's any ol' choke that'll carry your current, and a Transzorb is a transient voltage suppressor:

I used to use the 1.5KE series, but I'm sure they have even better ones nowadays. Just pick one whose minimum threshold is above the system voltage, and you should be good to go.

I do have qualms about the headroom on the LM317, however.

Good Luck! Rich

I saw a similar design for an aircraft device (12-28 volts) that used an active clamp before a simple LDO reg. It used an ON NCP346 voltage sensor/clamp that can be set very accurately, to turn on a hi-current FET, IIRC it was one of the Infineon SmartFETs or ProFETS.

Might be more complex than you want though.

Barry Lennox

If I were doing something like this, I would use a LM317HV (Vin

Thanks for that. I had come to a similar conclusion but using two 1.5KE - 33's in parallel. What was the nature of your problem with the choke ?