# voltage regulator for automotive use

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#### MrDEB

##### Well-Known Member
awhile back someone posted a site that deals with voltage regulators for electronic circuits.
the standard 78XX series I understand is not stable due to the fact that an automotive electrical system changes value of voltage.
Some company makes special regulators just for automotive use??

#### smanches

##### New Member
Simple lame answer, but just go to Welcome to STMicroelectronics and search their site. They make (almost exclusively) components for the automotive world.

#### MikeMl

##### Well-Known Member
awhile back someone posted a site that deals with voltage regulators for electronic circuits.
the standard 78XX series I understand is not stable due to the fact that an automotive electrical system changes value of voltage.
Some company makes special regulators just for automotive use??
The concern is high voltage spikes on the input side, and possible reverse polarity if some dummy jumps the car backwards.

#### tcmtech

##### Banned
I have never had problems with any properly designed 78xx regulator on automotive, farm equipment, or industrial applications.
I just use a small in line resistor and a good capacitor on the input. It stops any serious voltage spikes and does the job of any snubber or bypass filter.
All regulator circuits require this, its a standard design requirement with all regulator IC's.

#### picbits

##### Well-Known Member
Look at the LM293x and LM2940 from ST electronics. They have been designed for the spikes/load dump/reverse polarity etc and are very similar to the 78xx range.

Do however pay special attention to the fact it needs a low ESR output capacitor or you'll end up spending a lot of time trying to work out why your regulator is oscillating.

#### 3v0

##### Coop Build Coordinator
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The devices designed for automotive use are not expensive. The auto market is huge and it drives the price down. Why not use parts designed to do the job.

3v0

#### MrDEB

##### Well-Known Member
contacted STM

the L4995 looks good but they list a bunch of different units.
the first schematic shows the chip connected to a MCU like it needs it to control voltage??
contacted tech dept with description of needs.
Just a 5v stable supply that needs at max 100ma.if I use the LM386 amp in my design.

#### eng1

##### New Member
LM2937 500 mA LDO regulator

Ideally suited for automotive applications, the LM2937 will
protect itself and any load circuitry from reverse battery connections,
two-battery jumps and up to +60V/−50V load dump
transients. Familiar regulator features such as short circuit
and thermal shutdown protection are also built in.

#### livehho

##### New Member
LM2937 500 mA LDO regulator

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I go here Welcome to STMicroelectronics and then type LM2937 on the 'Search Keyword' or 'Search Part #' and system returns zero results..

any direct link maybe? sorry, I'm slow

#### Hero999

##### Banned
There are plenty of cheap ways to give a decent level of overvoltage protection.

The easiest is to just add a 33V zener in parallel with the supply.

A crowbar is also another good idea but it does have the disadvantage of taking out a fuse whenever there's a spike.

A zener and crowbar with a low pass filter and possibly using a poly fuse instead of a one shot fuse provides pretty tough overvoltage protection.

I'll post a schematic tomorrow if you don't understand what I'm saying.

##### Banned
Hero, have you tried 'polyfuses' the reseting type? They might perform well enough.

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#### slutty22

##### New Member
Im actually looking for an automotive application as well, somthing a cap to make headlights and interior lights dim after usage.

#### livehho

##### New Member
Newark has them for about $2. Linear Regulators | Newark.com thanks.. these two look exactly the same and yet the price is so different: LM2937IMP-5.0$1.74 Termination:SMD
LM2937ET-5.0 \$0.330 Termination:Through Hole

Do you think there is another difference than their termination?

thanks

#### 3v0

##### Coop Build Coordinator
Forum Supporter
It is a good idea to check when you see a price spread like this but it does happen. It is more common when two chip makers source the same part. Possibly because the reseller has purchased one item in bulk but not the other.

Both parts share a single datasheet so I expect them to be the same.

The less expensive part has a P code
Promotional Price: A discounted price as a result of a Newark product promotion.
If you look at the cost per unit breakdown you will see they are selling a single unit at the 10,000 unit price. Stock up before they change their mind.

#### livehho

##### New Member
It is a good idea to check when you see a price spread like this but it does happen. It is more common when two chip makers source the same part. Possibly because the reseller has purchased one item in bulk but not the other.

Both parts share a single datasheet so I expect them to be the same.

The less expensive part has a P code
If you look at the cost per unit breakdown you will see they are selling a single unit at the 10,000 unit price. Stock up before they change their mind.
thanks.. I'll go for it

In the data sheet of LM2937 (http://www.electro-tech-online.com/custompdfs/2009/05/LM2937.pdf) it says:

The LM2937 is a positive voltage regulator capable of supplying
up to 500 mA of load current. However, this current can be supplied only when the input to
output voltage differential is greater than 3V.

How many current would you think this regulator would supply if the input voltage is 14V and output voltage is 12V (less than 3V).. would it be sufficient to power a 12V LED?

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#### 3v0

##### Coop Build Coordinator
Forum Supporter

With
a load current of 500 mAthe minimum input to output voltage
differential required for the output to remain in regulation is
typically 0.5V (1V guaranteed maximum over the full operating
temperature range).
And this

Special circuitry has been incorporated
to minimize the quiescent current to typically only
10 mA with a full 500 mA load current when the input to
output voltage differential is greater than 3V
talkes about quiescent current ... the first is what you are interested in.

So yes if you have 1 volt about 12V you can regulate to 12V.

#### livehho

##### New Member
talkes about quiescent current ... the first is what you are interested in.

so the LM2937 and a low ESR capacitor (below
3Ω) is all I need ?

sorry if the question sounds stupid.. I'm new to this

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