What is the most indestructible voltage regulator?

Other Hardware General Electronics
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I am extremely worried about my voltage regulator failing short and frying my electronics see: AMS1117 short circuit protection not working

Some context: I'm a beginner at electronics I want to power a handful of 5V electronics - some passive infra red sensors which draw only 100-200 uA each, as well as some active radars which may draw around 100mA each.

Maximum current draw will be less than 300mA.

The datasheet on my PIR sensors say that a stabilized power supply is needed so I think I do need a voltage regulator to regulate the already-regulated output of my wall wart. Now I'm wondering which voltage regulator I should get and whether I should get a 6V or 7.5V wall wart.

The advantage of the 6V wall wart is that even if the voltage regulator fails short, it won't fry my components (which can tolerate up to 6V), whereas if voltage regulator fails short with the 7.5V power supply then the 7.5V input may fry my sensors.

But the advantage of the 7.5V power supply is that it allows me to chain two voltage regulators - maybe one LDO to step it down from 7.5V to 6V, and then another LDO to step it down from 6V to 5V? That sounds more complicated but it should result in a less noisy power supply? And also, having two voltage regulators provides some redundancy in case one of them fails short?

Originally I was thinking of using an Arduino Uno for powering my electronics but I've read many reports of the AMS1117 failing short so now I'm worried about buying an Arduino Uno since the Arduino Uno internally uses one of those AMS1117 voltage regulators and if that fails then my precious electronic components will be fried.

My next thought was to buy a breadboard power supply like the DFRobot DFR0140 but I saw that one also has a reputation for failing short and internally it also uses the AMS1117 voltage regulator.

I've seen many people online saying that the 7805 voltage regulator will not fail short but some other people have said that it is possible that even the 7805 can also fail short.

Other people have said that the OFFICIAL AMS1117 should have built-in over-current protection and thermal shutdown and thus all of those online horror stories are due to people using Chinese AMS1117s. But aren't most electronic components made in China now? And DFRobot is a reputable company, it presumably uses properly sourced components including the AMS1117 - surely DFRobot is not using the fake AMS1117s. Plus, there have been reports of the Arduino's voltage regulator failing too - surely not all of the failed Arduinos were also using the fake AMS1117s??

I see many people online saying that the 7805 is "bulletproof" and "indestructible" but it has quite a large voltage dropout - 2 volts - compared to modern LDO voltage regulators which means it has to dissipate a lot of heat, so I'm worried that it will overheat with 300mA from 7.5V voltage (2.5V * 0.3A = 0.75W which is quite a lot).

If I instead buy a 6V wall wart and then use a low dropout voltage regulator then the voltage regulator won't have to dissipate as much heat (1V * 0.3A = 0.3W which is much less) so maybe I won't need a heat sink in that case?

But I have only seen online comments about the 7805 and how bulletproof and indestructible it is. I can't find online comments about the modern low dropout voltage regulators so I don't know how reliable these are. Are they as bulletproof and indestructible as the 7805/LM340A?

I also thought of buying some automotive-grade voltage regulators. Reading the datasheets, it sounds like those should be even more indestructible than the 7805, but those have so many pins and look really complicated to wire up. Also I couldn't find online comments about the reliability of those things either.

What is the most indestructible voltage regulator that I can get so that I won't have to worry about it failing short and frying my electronics? And should I get a 7.5V or 6V wall wart?

Thanks a lot!

2

You could look at a CROWBAR CIRCUIT which will short the power rail if it goes over voltage, if you include a fuse then this will blow the fuse rather than let the high voltage go to your electronics.

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3

A voltage regulator failing short will not fry your electronics. It can't.

A short on the output could clear the fuse (or PTC et al.) at its input or over-burden things "upstream" as it were.

4

That depends what you mean by "failing short". It could be taken to mean that the input voltage is shorted to the output. I have known (fake) ams1117 to do that and zap the circuit with 12V.

Does that not strike you as a strange thing to want/need? Why not get a 5V wall wart? You can fit a fast-blow fuse in your circuit if you want.

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Yes, in fact initially I did plan to buy 5V wall warts, but I looked at the datasheet for the 5V wall wart and saw that noise was 50mV and the line regulation was 0.5% which I thought would not be good enough for my electronics.

In the datasheet for my PIR sensor it says that noise can cause errors.

I heard that linear voltage regulators have little noise and good line regulation but they require a voltage drop. The LM340A needs a voltage drop of 2V so that's why I need 7.5V power supply to get a regulated 5V.

If I use a LDO voltage regulator then I can use a 6V wall wart instead of 7.5V.

6

Yes, of course. But how much noise? No circuit will ever be 100% noise free. 50mV/0.5% does not sound too bad to me. That's probably worst-case figure. As long as you are not drawing close to the maximum current the wall wart can supply, it will probably be lower than that.

7

Your concern over your DC supply should also apply to the mains AC voltage being applied to your power source! It is NOT regulated at all and has many excursions both low and high!

8

TRACO Power for one, makes a number of 'switching' regulators or (dc to dc power supplies) that include protection for over voltage and current. The TRACO TSR 1 line has the same footprint as the linear regulators. They are a bit pricey but they work very well. They are extremely efficient and effectively eliminates the heat wasted with linear types.

9

If it's truly such a grave concern then source from reputable, industry-trusted manufacturers.
Or don't.

10

I never had a regulator fail unless something that it was connected to failed.
So maybe you should be worring about whatever is connected to the regulator.

11

I think what the answers in this thread are saying boils down to 'don't worry about it'

One of the problems with getting information online is knowing who knows what they're talking about and who doesn't. And unfortunately there is lots of misinformation flying around and it gets repeated until everyone parrots it back.

A voltage regulator is unlikely to fail unless it's stressed. Better quality ones are likely to fail in predictable ways, but in the end you should avoid running any component near its limits and not stress it in the first place. If you are really that concerned (and you really shouldn't be), then purchase a specified component from an official distributor such as Digi-Key so you know that it's most likely not a knock-off and the supply chain is secure back to the source.

But I think you are worrying about something not worth worrying about.

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Hi, @1f604

I agree, modern regulators have temperature and overload protection.
Good physical and electronic design of the circuit they will be supplying will help ensure protection.

If you are that worried, install crowbar protection.

What will you be using as the main power supply for your regulators?

Thanks.. Tom.. :grinning: :+1: :coffee: :australia:

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I will be using a probably 7.5V wall wart connected directly to mains power.

Actually I am thinking of using 9V wall wart so that I can put a diode in series to protect against reverse polarity...but I am worried that the diode might add extra voltage noise to the circuit, since the voltage drop across the diode will vary with the load...

I will probably need to put some extra resistor in front of the voltage regulator to drop the voltage too...but the voltage drop across the diode might vary from 1V to 1.6V...and I am not sure if the 25nA reverse leakage current might damage my components...maybe I should just forget about connecting the diode in series.

14

The things you talk about make very little sense.
Use a 5volt cellphone charger to power you Arduino on the USB socket, and get on with life.
Leo..

15

You might need to make sure that you get "genuine" parts that have all the over-current, over-temp, etc features that actually work, rather than some clone that "mostly behaves the same as long as things go well."

I've seen the LM2940 mentioned as a particularly robust regulator - it's designed for automotive environments. (that does mean that it's designed to behave well during failure conditions that you're not likely to see, operating off of wall warts.)

Watch your "dropout" specifications. Operating a 5V regulator off of a 6V input is pretty ... edgy. (OTOH, a 6V "unregulated" wall wart output will tend to be higher than 6V at low loads.)

On the third hand, why are you bothering with a 5V regulator at all? These days you can get "USB charger" wall-warts with highly regulated 5V outputs for pretty cheap (although beware "really cheap" versions here, as well.)

16

You can do this on the input to your voltage regulator, putting on on the wall wart will not provide any protection.

but I am worried that the diode might add extra voltage noise to the circuit, since the voltage >drop across the diode will vary with the load...

No it won't your regulator will take care of any input voltage variations, that is one of its jobs.

I will probably need to put some extra resistor in front of the voltage regulator to drop the >voltage too
No that is what the voltage REGULATOR does.

.and I am not sure if the 25nA reverse leakage current might damage my components

No it won't.

Can I suggest you stop thinking and do some research.

Goolge;

how to use a voltage regulator

Tom... :grinning: :+1: :coffee: :australia:

17

Addressing the regulator only, I would suggest you look (and purchase) from Digikey. They sell genuine parts and I've never had any issues with the products they supply.

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