Anybody tried one of these 5v transient suppressing regulators?

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Shafto

Senior Member
I imagine this should be perfect for using the picaxe in my car, I just wanted to share with others and maybe hear from some people who have used it.. before hitting this though the 12-14.5v from the car will go through a 9v reg.. then into the 5.

http://www.national.com/ds/LM/LM2931.pdf

"The LM2931 positive voltage regulator features a very low
quiescent current of 1mA or less when supplying 10mA loads.
This unique characteristic and the extremely low input-output
differential required for proper regulation (0.2V for output currents
of 10mA) make the LM2931 the ideal regulator for
standby power systems. Applications include memory standby
circuits, CMOS and other low power processor power
supplies as well as systems demanding as much as 100mA
of output current.
Designed originally for automotive applications, the LM2931
and all regulated circuitry are protected from reverse battery
installations or 2 battery jumps. During line transients, such
as a load dump (60V) when the input voltage to the regulator
can momentarily exceed the specified maximum operating
voltage, the regulator will automatically shut down to protect
both internal circuits and the load. The LM2931 cannot be
harmed by temporary mirror-image insertion. Familiar regulator
features such as short circuit and thermal overload protection
are also provided."
 
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BCJKiwi

Senior Member
Used the LM2940 variant with success.
Watch the specs on the output capacitor - best to use Tantalum as ESR is critical. A Tantalum of nominally half the value of the Electrolytic specified can be used. There is more detail about this on the LM2940 Data sheet than there is on the LM2931 sheet.
 
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Tom2000

Senior Member
I've used the LM2931AZ-5 in a few projects with no problems. I place a 100 uF electrolytic on the output, per the data sheet recommendations.

Although I'm aware that it handles input transients well (again, from the data sheet), I've never installed one in an automobile or otherwise noisy environment. I use them for their "low dropoutness." :)

Tom
 
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Shafto

Senior Member
Excellent, thanks for the information.. it says it was designed for the automobile environment, so I'm pretty confident it'll work well, and it should be easier getting it's source from a 9volt reg.

I was reading into the capacitor and planned to go with the tantalum that has the right ESR value, 47uF is what the datasheet says for tantalum.. but what voltage should I use? just anything over 5? or should I go higher?
 
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Dippy

Moderator
Looks a good spec. But it's NOT transient suppressing is it, it's transient resistant up to a certain point.

I've only ever used the LM2950 and LM2936 where Nat Sem claim "LM2936 is ideally suited for automotive and other battery operated systems."

However, I would certainly include LCR and transient suppressor for the belt and braces method of protection. It costs pennies and could prevent shrieks of agony.

BTW: you say you are running through a 9V reg first before the LM2931 - is the 9V reg equally transient protected in automotive apps? If it isn't then there may be a weak link in the chain.

I have never 'scoped a car supply. I'm going to do it now.
 
hippy

hippy

Technical Support
Staff member
I don't agree with running the vehicle's supply through a 9V regulator first as you've then put a far weaker device in front of the LM2931 and it is this regulator which is at risk of damage. You lose all the advantages you would gain from using an LM2931.

The spec says the regulator will shutdown in adverse situations which is not what's always wanted, especially if you have a vehicle which has a lot of transients. It's undoubtedly a lot better than a 7805 but I would still use a coil, blocking diode, clamping zener and other supression components before the regulator to take out the worst of the nastiness.

The most important thing you can put before the regulator is a fuse of appropriate type and rating.

As to capacitor rating; the rule of thumb is twice the voltage it will have across it.

Added : All-in, what Dippy typed quicker than me :)
 
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Dippy

Moderator
Re: Capacitors.

Or lower depending on Iout - read futher on in Data Sheet.

Voltage rating? 6.3V is usually a standard spc. But from what I have read (never tested) the endurance is greater if you choose a slightly higher voltage e.g. 10V. This also has the side effect of a lower ESR.

I've just loooked at graph of output ESR on page 11 where it appears that you'll need an ESR of < 1 Ohm for complete stability.
I've only got Multicomp and AVX Tantalum cap Data Sheets.
A Multicomp 47uF 16V cap has an ESR of 1.5ohms
An AVX 47uF /16V = 1.3 ohms.

May be fine in Real World or you may have to play with mixing cap types.
Phew, I'm exhausted.
 
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Dippy

Moderator
Blimey Tom, long thread it is!
Tell you what, fiddling with new cars could be a dangerous nightmare with electronic parking brakes and electronic steering etc. And Audis that can pop their brake pistons out while changing discs if you don't press a button first (so I've been told).
You could turn Fly-By-Wire into Breakdown-by-wire.
And DIY is turning into DDIY.

Right let's dig out Mr Tektronix.
 
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Shafto

Senior Member
Hmm, I thought that running the 9V reg first would just smooth out the power more ...and help it run cooler as well because it would be dropping less voltage, how could it possibly be worse? The 9V regs there are anyway for other reasons.. so I thought I'd just tap it there, but I don't have to..

I suppose I was just looking for some all in one package that would be perfect to power the picaxe in the car, I don't really know how to choose or implement a coil or a zener diode, though I was going to use a blocking diode... more reading needed.
 
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BeanieBots

Moderator
Don't forget, it's not just the power supply that you need to protect.
I've no idea what your application does, but unless it's just an LED to indicate 12v is present, it will need other leads comming into or going out of your "black box". Those leads can also pick up noise and pass it down to the circuit. Especially if they go anywhere near the engine compartment.

@Dippy.
If you do get that Tecktronics on a car supply, any chance you could publish pictures.
I'm sure your car is new enough to have electronic regulation rather than the old spark-gap type so shouldn't be riddled with kV spikes but I'd still expect 30v or so for about 20mS when full-beam is switched off. Rear window heater should also cause some serious overshoot.
If you've got a mechanical distributor, remove the suppression cap. (the points should be OK for a few minutes without it). That should add some solid 100V+ spikes.
Then run a "sensor" lead past the coil HT lead. 10k to 0v to simulate thermistor or similar sensor. Should be able to get at least 1500V on that one.
 
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Dippy

Moderator
Yes, it would run cooler as you're dropping volts across 2 devices obv.
The point I (and hippy) were trying to make was that if your 9V device wasn't transient resistant then THAT reg may get damaged and then your 5V reg would be irrelevant. Weak link in chain yes/no?

Read up on suppression, a blocking diode won't do much in that respect. It's a piece of cake. You can get fat zeners of say 15V which will dissipate transients. You can put a capacitor accross it to absorb (some use a cap and low value Res in series).

For the record I've just 'scoped my car at the cigar/ette lighter and started engine.
There were 600mV transients (duration 1 microsecondish) proportional to RPM - you'll remember that Sun/Krypton Engine diagnostic machines / MOT test machines have a cigar lighter plug in here for measuring RPM.
I then set the 'scope to trigger at any transient above 700mV (0.7V).
None after 5 mins even with me pressing everything (lights/brakes/honker/window heater) and Aircon on/off.
General noise was about +/-75mV.
Based on that (and on that particular car) I would use simple Zener and RC suppression just before my regulator. And a fuse.
This , of course, will vary depending on where you tap off for power on the car's loom. I couldn't be arsed to start pulling panels off sorry.

@BB: Sorry, didn't see your post 'til I'd posted. Sunlight was a bit bright to get a good photo. But there were NO transients above 700mV even down at 200nS duartion.
The 'ignition' pulses were of about 1uS duration and were resonanty in shape -like the resonance of a bell decaying. That indicates to me that the power has come through an LC filter or similar.
Car: my old faithfull MGZT190 2004. (2.5litre V6 and gives over 30mpg)
 
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BeanieBots

Moderator
I wouldn't be surprised if a modern car has built in suppression on the cigarette socket. Especially with all the new toys that now plug into them.
If you can, well worth doing same tests around relay box under bonnet.

Crossed again!
Interesting results. Ringing could well be indicative of my suggestion above if it's done with inductance.
 
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Dippy

Moderator
BB:"..Ringing could well be indicative of my suggestion above if it's done with inductance."
Me: "That indicates to me that the power has come through an LC filter or similar."

Exactement.

So, people would be advised to get wiring diagram of car if poss. to check all this stuff.
The level of protection/suppression will depend on connection point.

HEALTH WARNING: Reading, yes reading, may be required before connecting PICAXE to car.
 
hippy

hippy

Technical Support
Staff member
Shafto said:
Hmm, I thought that running the 9V reg first would just smooth out the power more ...and help it run cooler as well because it would be dropping less voltage, how could it possibly be worse?
Click to expand...
Sure, you'll get a much nicer, cleaner, smoother supply for the 5V regulator which will run cooler, but you will be using a 9V regulator which isn't designed for automotive use and could likely fail. As the purpose of using the LMxxxx in the first place is to prevent your unit being broken by adverse electrical conditions you don't gain anything by using something in front of it which can itself be destroyed.

Like using steel chain instead of rope when towing for extra reliability you gain nothing if you tie the chain using a rope which remains the weakest link.

If you can find an automotive rated 9V regulator that will be fine, and you can use almost any normally rated regulator after it. It's the first line of defence which needs to be most robust.
 
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BCJKiwi

Senior Member
LM2940 to the rescue!
These are available in a range of fixed values (5, 8, 9, 10, 12, 15).

Please correct me if I'm wrong but these regulators operate at very high speeds internally and the output is effectively smoothed with the appropriate capacitors on both input and output.

Accordingly I don't really understand why 2 are better than one. Sure you will reduce the heat loss from each one but not the total heat loss. So aren't the additional regulator(s) and their capacitors are really just an expensive way to avoid using the right heatsink on the 5V unit?
 
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Shafto

Senior Member
Well the 9V regs are already there to regulate voltage to the LEDs, they are robust enough to be connected right to the +12~14.5v. The only thing I'm worred about as far as transients and noise are concerned is the picaxe. Each 9V reg has a 0.33 Cap on the input and a 0.1 on the ouput, that along with the 47uF on the output of the LM2938 I imagine will be enough.. But I'll look into figuring how how to choose a zener diode. A quick wikipedia read tells me that you place one in parallel across the supply ... so do I put one before my voltage regulator or afterwards? if I used a 15V zener before the regulator then it just sits there doing nothing but when there's a transient it quickly breaks down over 15v and the extra power is just grounded through the zener? seems easy enough... but I can't figure out why the resistor is needed or what value to make it.. or how much power the zener needs to be able to handle.. hmm.
 
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BCJKiwi

Senior Member
But are the 9V regs rated for automotive use? If so then you could use a second regulator of any sort (eg 7805). If Not then you should replace the 9V regulator(s) with Automotive rated types. The additional protection is then a PICAXE safety issue, not a regulator issue.
 
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hax

New Member
Can I just say that if you want a clean power signal from your car's wiring, you can use a relatively cheap mobile phone charger. My Nokia charger is rated at 4.7V and inside there is a switchmode chip and transformer. So the output is isolated from the input. Obviously not a "neat" solution for something that will be built into a car, but for most "plug in" car projects it is a great way around having to build hefty and complicated power conditioning circuits.
 
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Shafto

Senior Member
The 9 volt regulators aren't for removing transients or super power conditioning.. they're just high quality low loss regulators and they work very well in a car for powering LEDs.. That's not the concern here.. I'm concentrating on the 5V supply to the picaxe which I want to be clean... The car charger is a good idea.. but it adds a lot more money to the project when I can figure out how to do it myself for a lot less..

I'd like some more information on how to pair the proper resistor with the zener diode, I can't seem to find this information well explained anywhere.. I'd much appreciate that.

..I suppose I'll just run the 5v reg right off the line... maybe I'll try to find a high voltage drop blocking diode.. or run more than 1 diode in series?... and then I can just use a 5.6v zener which is the most efficient one from what I've read... to drop the voltage to a perfect input for the low loss 5v reg and into the picaxe.. that along with the proper cap on the reg and I should be good I imagine.

I really appreciate all the help... I can't wait to show everyone what I wouldn't be able to create without it.
 
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Dippy

Moderator
Shafto, there is no reason why you can't do Plan A: Vcar---9VREG---5VREG or have them as separate REGs from Vcar.

I didn't know that the 5.6 zener (usu marked 5v6) is the most efficient one?

Suppresion:
In som cases a cap+100R in series are used as a suppressor - but this is only for little H/F sparklies. This is commonly used across switches etc. but will also work across the loads. This method will absorb some noise. The Res is the 'absorber' Example: http://www.farnell.com/datasheets/92109.pdf
You obviously know how to calculate the impedance of a capacitor at various frequencies?
You will see how the capacitor impedance reduces as f increases. Therefore it becomes a shorter-circuit as f increases. Sadly, caps aren't perfect and have an L-R component so cannot 'absorb' perfectly.

When you've got big honkers coming down the line you need something a bit more manly. This is where, for light duty stuff, a small Zener is fine. Again, if seriesed with an R (though I've never seen n example of it myself), the R absorbs - though it will, by default, affect the Zener performance.
Here is some bed time reading: (1Mb note): http://www.onsemi.com/pub/Collateral/HBD854-D.PDF

Then we have Voltage Dependent Resistors or Varistors (or maybe som other names too). Bung them across the power connections. These maintain a high res at their rated voltage but quickly become low res at higher voltages. You WILL NEED TO READ the Data Sheets to choose your device. http://www.farnell.com/datasheets/89344.pdf


In the Real World you may have to buy a couple of different values to get the setup right for you.
 
hippy

hippy

Technical Support
Staff member
Shafto said:
The 9 volt regulators aren't for removing transients or super power conditioning.. they're just high quality low loss regulators and they work very well in a car for powering LEDs.. That's not the concern here.. I
Click to expand...
What we're saying is that it should be a concern. Those transients and glitches ( regardless of what gets through the regulator ) are likely to send the regulator itself off to meet its maker, and in the process can damage other parts of your circuit.

Unless you have an automotive spec for the regulator you could well find that one day you have no power, a small cloud of black smoke, a regulator with legs but no body and all other manner of nasty things. If it's tough enough to hang on in there, it may just sit their smirking to itself while smouldering before finally torching the car.

It's not how well the regulator can do its job of regulating and smoothing voltage out, it's how well the regulator can stand up to the crud which is on the vehicle power-supply.
 
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BeanieBots

Moderator
I'm so pleased you found that Dippy.:D
Now we can refer to it every month that this comes up!

I'll be honest, I had no idea that load dumps could be that bad.
125v for 400mS OUCH! That would EXPLODE a 7805 regulator.:eek:

15kv for 50nS is actually not too frightening. A bead and cap will sort that but INSTANT death without them.

I think the examples are here Dippy!
http://www.picaxeforum.co.uk/showthread.php?t=7986&page=2
 
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Dippy

Moderator
Ah, yes, the "I remember when my ____ caught fire." reminiscing thread.

I was walking barefoot in the dark through the house the other night and stubbed my toe. Blooming hurt. Guess what I'd stubbed my toe on? Yup, my steel toe-cap safety boots. Now that's irony. (And untidiness).

Back to the plot.
This really is not rocket science and with care and reading and calculation, a little suppressor could easily be made for a couple of quid that could easily withstand those scenarios. No dramas, no fires, no panic.
 
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BeanieBots

Moderator
Quite right Dippy. But with nothing, the pictures on the link tell it all!
1mH and a few thousand uF should keep the load dump surges at bay.
Ferrite bead and 100nF will catch the 15kV.
Transorb would help too. (especially fast zener with high joule rating)
IMHO, ordinary zener would do nothing. They are too slow and would probably just pop if they could react quick enough.
 
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evanh

Senior Member
It is similar to designing for mains (Except for electrocution safety), spikes are identical but the surges are more relative to the supply voltage. So, they are saying to have spike arrestors for absorbing 15kV and surge handling for 10x the rated supply voltage.

I've seen many a voltage regulator that has gone short-circuit because a surge of 2 or 3 times the rated voltage came out of the transformer.

Common linear voltage regulators don't like that. They are good at handling over-current and thermal shutdown but reverse voltage and over-voltage causes them to go short from IN to OUT which in turn over-voltages the regulated side of the circuit. Smoke and flames ensue.

One way to handle surges, if you know they are only freaks, is to use clamping components that will pop the circuit breaker.
 
hippy

hippy

Technical Support
Staff member
evanh said:
One way to handle surges, if you know they are only freaks, is to use clamping components that will pop the circuit breaker.
Click to expand...
I'd say that should be a last line of defence. I've seen over-current take out master breakers before individual ring breakers. Losing all power when travelling at high speed is not a good thing. This is what pushes all automotive circuits into a grey area of; do all vehicle powered circuits become safety critical components ?

For unexpected component failure or unexpected levels of surge it's probably acceptable to blow out the fuses but for expected surges a circuit should be designed to shrug them off to start with.
 
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Dippy

Moderator
Yes, I wouldn't want to lose power when driving, though are we wandering of into the subject of mains AC stuff now?

Look at those crummy old car radios from the 70s/80s. An in-linefuse + inductor* and a few caps (caps+Rs maybe) for suppressors and that was it. Add a blocking diode and transorb type thing and I reckon you'd have a healthy transient suppressor. If the inline fuse was 1 amp I can't really see a main big fuse/cb popping before that?

A bit of care/thought/etc and job done.

*Didn't the old fellahs call them 'chokes' ?
 
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BeanieBots

Moderator
Yes Dippy, we called them chokes;)
and they are as effective today as they were then.
Car radios of the 70's had to cope with MORE than they do today.
Early car regulation was done with coils and contacts. Much like an electric bell. This worked for both current limit and voltage.
At a specific current, the contact would break, drop the current and then re-make. As course and noisy as you could possibly get. You could always tell when a car went by, there would be lots of white dots on each of the 415 lines that made up telly picture.
Build a circuit like a 70's radio power input and it'll be fine in today's cars.
 
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Dippy

Moderator
Sorry BB, didn't mean to imply.... you sound so young :)

Well that's that's then. Job done. Next please.

Or will we have some more tales of doom....
 
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Dippy

Moderator
BB, if you were doing this, would you put a res accross input inductor as a damper?
I've done this with S/mode PS o/p filters but never on a suppressor circuit.
 
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davyjoneslocker

New Member
A few months ago, I built a user configurable engine management system called Megasquirt.

Naturally, as the Megasquirt is microprocessor based, this needs good immunisation, as people are using this to fuel inject anything from a Briggs and Stratton lawnmower engine to V12 Jags.

You can have a look at the schematic for the Megasquirt power conditioning circuit on page 4 of the PDF document here-

http://www.bgsoflex.com/v22/megasquirt_ShemV2.2.pdf

Andy
 
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BeanieBots

Moderator
Dippy said:
BB, if you were doing this, would you put a res accross input inductor as a damper?
I've done this with S/mode PS o/p filters but never on a suppressor circuit.
Click to expand...
No I wouldn't. In a SMPS, there is continuous ripple which (may) require damping. In a linear PSU application, the inductor needs to 'absorb' the (single) surge and release it at its leasure. The driving impedance will be low because it is the alternator putting out too much (for up to 400mS acording your link). The large electrolytic on the regulator input will also be low impedance so there should not be any ringing problem. In this insatnce, the inductor (sorry, choke) is acting more like a current regulator.
I would however, put the ferrite first and use something with a higher rating than 1N4001 for the blocking diode. I'd also put a low value resistor in series with the first stage capacitive filtering to save the cap from high current caused by the HV spikes.
 
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Shafto

Senior Member
You built megasquirt? wow.. that's an accomplishment, I've heard much about it.... I drive a DSM, many have switched to the megasquirt over DSM-Link... I haven't tried either yet myself.
 
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Shafto

Senior Member
I've been looking at the design.. It helps a lot, and I can see how it works, unfortunately I'm not experienced enough to make my own from only that, the part selection kills me.. it's been the hugest holdup in this project. The 1uH coil for example, when I look on digikey for a 1uH coil I get 27pages of them, and I have no idea what to pick... same with the capacitors and diodes, which I've been reading about tonight... something I don't understand though, everything I read is saying that ceramic caps are the most common for bypass since they're cheap.. whaaaa? they're so expensive! cheapest 0.1uF ceramic bypass cap on digikey is $0.77 each! I can buy 0.1uF tantalum from them for $0.20 each, and they're supposed to be expensive.. what gives? The regular ceramic caps are cheap, but the bypass specific ones are a rip off... should I just use standard 0.1uFs? surely nobody is paying close to a dollar for ever little bypass cap in all their circuits.

Why do you have 2 Vout? 1 is for supply to the chip and the other is reference voltage for inputs?

..I don't suppose you have the actual parts you used written down somewhere?

..well I'll continue plugging away here, any help appreciated.
 
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Dippy

Moderator
It's difficult to povide an exact circuit for you shafto as we don't know what the rest ofthe circuit is.
Based on my 'scoping I would need very little suppression in my car.
Anyway, I will brave the criticism/smart-ass-corrections and post this simple thing.
The components were chosen simply on what is cheap and easily available in UK.
Apologies for tatty artwork, as I've only got a spare 5 mins.

You could replace/supplement the Varister with something like this.
http://www.farnell.com/datasheets/66097.pdf
But specific values are difficult to give.

So, the inductor (choke) forms a resistance/impedance to anything AC. This increases with F-up, you can do the calcs? Obv there is a DC resistance which will also affect the DC current rating, so read spcs.

The capacitors form a resistance/impedance which reduces as F goes up (to a certain point). You know the equation I'm sure.
Look at this> http://www.farnell.com/datasheets/75261.pdf

I honestly don't know whether ferrite beads would do anything, but they look good.
If my downstream circuit was <200mA I would have another inductor (or a 4R7 res) before regulator cicuit.

And finally, a 100nF to 1uF cap right next to PICAXE power pins - this bit is recommended for most circuits.

Sometimes this really is a case of try-it.
I will await the moans.....
 

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BeanieBots

Moderator
I think it would cover most "modern" car situations as shown.
To be a little safer, I would make the choke (inductor) 1mH minimum.
I would fit a ferrite bead between the blocking diode and inductor with 100nF+10R series to ground on line side of inductor.
I'd also put a large (4700uF) on the load side of the inductor.
1mH/4700uF to inhibit load-drop surges, ferrite/100nF to "catch" 15kV spikes.
If possible to source, transorb (24-36v) just after inductor.
Also worth considering inductor in ground line coupled to line inductor.
ie both wound on same core. Reduces unbalanced currents and helps prevent core saturation at high current.

As mentioned, the circuit shown will cover most eventualities but what happens if/when it doesn't? If the car crashes due to electrical failure and/or catches fire, who pays? Who is responsible?
If the circuit is fitted by the manufacturer, they are responsible and they will have taken adequate precautions against what what they know is the environment in their car.
Anything published on a forum such as this is available to be used & abused in inapropriate circumstances at the users risk.

Would it be OK in Dippy's car? Yes, if fitted to the cigarette socket.
Would it be OK in an S-type Hilman Imp. No. (the caps would pop within seconds of starting the engine).
 
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Dippy

Moderator
Yes, a common doo-dah choke would be good.

btw: I did use this circuit (sans transorb but v similar) in my first car which was my Mum's kernackered Hillman Imp which she gave me 20 years ago.
Worked fine. But in those days there wasn't so much glomm'n'doom.

So, did my Halford's tachometer which had a single choke and cap for suppression.

Sorry, don't believe for a second that the caps would pop especially if you used mains X2 (600VDC) type.

Fuse would blow years before it caught fire unless installed by an idiot.
Of course it can be improved or changed completely but I didn't see any volunteers to provide a drawing - so if nothing else I've got the ball rolling :)

"Who is responsible?"
You are. If you're not competant, don't do it.
 
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