Reverse Polarity Protection 1N5817 or 1N4001

[POTL]

Hello
Earlier I asked about the power filter, and I was given a magnificent response with detailed information that helped a lot.
I decided to ask more details about the protection against reverse polarity.
There are a variety of ways, but in stoppboxes the most popular are 2 ways (the diagrams below).



These schemes are used both in DIY projects, and in boutique manufacturers and even from large manufacturers (BOSS / EHX / MXR).
The method using 1N4001 + resistor 10-100 ohm allows to protect the scheme circuit from reverse polarity. Its main advantage is that it does not lower the voltage and the effect gets as much as the power supply gives, but at the same time, judging by the feedback from the forums, it has a number of drawbacks:
1) In case of polarity error - the resistor burns out
2) There is a risk of burning the power source
3) If the diode dies before the resistor, then the probability of destroying full effect.

The scheme using 1N5817 is considered (again on forums) more advanced and reliable.
But has the following drawback - reduces the voltage by 0.45V.
When working with germanium fuzz and AIAB, it seemed to me that when the battery was sitting down (it was more than 8v, but I do not know how much exactly), problems were noticed
1) Oscillation of fuzz (Hello Fuzz Factory)
2) The amplifiers in the box sounded less convincing.
In the near future, I want to start studying the modulation, some circuits require a small power offset, for example 5V in Phase 90

So I'm not sure that the effects will work stably (although the site Madbean has now transferred its projects to 1N5817, although previously actively used 1N4001).

In general, I appeal to local gurus and experienced users with questions:
1) What method do you use?
2) Is there a way to improve reliability when working with 1N4001
3) Please tell us more about the principle of 1N5817 - its advantages and disadvantages, is it really reliable.
4) there may be good Schottky diodes that eat less than 0.45 volts (the power requirements I indicated below).

P.S.
1) The effects with which I work have negative earth, power from 9 to 18 volts, consume no more than 100mA
2) Yes, I heard about 2 circuits R G Keen using mosfet or 2 bipolar transistors. The circuit with bipolar transistors is very large and it is inconvenient when working with small pcb and a lot of details. MOSFET BS250P is very expensive, maybe it has the appropriate analogs, which cost not $ 3.

[Phoenix]

I was sure I already answered these same questions in your other thread, but here we go again.

1) What method do you use?

I use a modified version of RG's Cheap but Good circuit.

2) Is there a way to improve reliability when working with 1N4001

For low current applications like effects pedals, there is no way to improve the reliability of reverse-biased diode polarity protection. It provides adequate protection against momentary reverse polarity from a battery (with it's high source impedance relative to a power supply) accidentally connected backwards briefly, but that is all. Relying on a resistor to burn out is a bad idea, too slow, and will create a mess and damage anything else nearby. Fusing at low currents is tricky and unreliable, and low current fuses have high resistance, which given your insistence on absolute minimum voltage drop, will cause higher voltage drops than a series schottky.

3) Please tell us more about the principle of 1N5817 - its advantages and disadvantages, is it really reliable.

Series diode provides essentially perfect protection. It will only fail if the Vrrm (reverse voltage) is exceeded (20V for 1N5817). If you require higher reverse voltage protection, then the 1N5818 (30V) or 1N5819 (40V) are available, as are many other types. A 1N5817 has a forward voltage drop of around 0.18V at 10mA (some pedals will draw more, many will draw less), it'll only start dropping 0.45V around 1.5A! So don't know where you got that idea from.
So yes, it is really, really reliable. It's about as foolproof as you can get.

4) there may be good Schottky diodes that eat less than 0.45 volts (the power requirements I indicated below).

Yes, there are plenty of other schottky's out there, many with lower forward voltage at whatever current than the 1N581* series. They can all have different current/voltage curves, so you can't really make generalisations about which one will always have the lowest forward voltage, as that will be dependent on the current (and how much you want to spend).

Hopefully this answers your questions.

[R.G.]

What he said.

New info. There is a variation of the MOSFET protection scheme that uses some active circuitry to make the forward drop of the MOSFET very low indeed. In fact, there are some  chips now that are intended solely to do this task (a) for a single series MOSFET, and (b) a long ago idea of mine that I got nowhere with, a full wave bridge of MOSFETs to make a pedal power supply be polarity-agnostic.

There are some gotchas on this front, but there's good news here for pedal power protection.

However, neither is a single diode. Sorry.

[POTL]

I was sure I already answered these same questions in your other thread, but here we go again.

1) What method do you use?

I use a modified version of RG's Cheap but Good circuit.

2) Is there a way to improve reliability when working with 1N4001

For low current applications like effects pedals, there is no way to improve the reliability of reverse-biased diode polarity protection. It provides adequate protection against momentary reverse polarity from a battery (with it's high source impedance relative to a power supply) accidentally connected backwards briefly, but that is all. Relying on a resistor to burn out is a bad idea, too slow, and will create a mess and damage anything else nearby. Fusing at low currents is tricky and unreliable, and low current fuses have high resistance, which given your insistence on absolute minimum voltage drop, will cause higher voltage drops than a series schottky.

3) Please tell us more about the principle of 1N5817 - its advantages and disadvantages, is it really reliable.

Series diode provides essentially perfect protection. It will only fail if the Vrrm (reverse voltage) is exceeded (20V for 1N5817). If you require higher reverse voltage protection, then the 1N5818 (30V) or 1N5819 (40V) are available, as are many other types. A 1N5817 has a forward voltage drop of around 0.18V at 10mA (some pedals will draw more, many will draw less), it'll only start dropping 0.45V around 1.5A! So don't know where you got that idea from.
So yes, it is really, really reliable. It's about as foolproof as you can get.

4) there may be good Schottky diodes that eat less than 0.45 volts (the power requirements I indicated below).

Yes, there are plenty of other schottky's out there, many with lower forward voltage at whatever current than the 1N581* series. They can all have different current/voltage curves, so you can't really make generalisations about which one will always have the lowest forward voltage, as that will be dependent on the current (and how much you want to spend).

Hopefully this answers your questions.

Hi again
I was advised to create a separate topic so that it does not intertwine with the power filter.
In fact, in that topic everything was perfectly stipulated (regarding the power filters) and it can come in handy for a beginner in the future as an FAQ, because there is a lot of useful links =)
Regarding the information on the voltage drop of 0.18V - it's fine (much better than 0.45) I could not test today, but I'll try to do it tomorrow =)
Please tell me about the shortcomings and pros in more.
In the case of destruction of the diode, what is the probability that an ok passes through its stakes.
Is there a problem with the burnout of the power supply (as when using 1N4001).

I'm more interested in working with a power adapter than using a battery.
Thank you! =)

[Fancy Lime]

Hi POTL,

reverse polarity protection is basically a part of power supply filtering and what type of power supply filtering is best really depends on the pedal you need the power for.

The parallel diode method (because the diode is parallel to the power supply), as in your schematic with the 1N4001, is only really useful for very short term protection. The kind that happens when the poles of a battery quickly touch the wrong contacts. When using an external power supply, I would not do it like this.

The series diode method (low-drop diode such as 1N5817 in series with power supply) is essentially perfect except for the voltage drop you seem very worried about. But the fact of the matter is, that the 0.2-0.4V or so are rather small compared to the actual voltage difference between different supplies. When you buy a "9V" supply, that may actually put out 10V or 8.5V. And the voltage will change depending on how much current your circuit consumes and how linear the voltage output of the supply is. And batteries can drop to even lower voltages. So when you really need 9.00V at all times to feed your circuit, you need to do a whole lot more. It is possible but I cannot think of any instance where this would be remotely useful for a circuit that otherwise fits on a tiny PCB. Chances are, if your circuit is small, its probably a fuzz, booster, distortion or something of that nature. Those circuits are totally fine with quite a range of different input voltages. Sound will change a little bit but that can easily be compensated elsewhere in the circuit. In fact many fuzzes often sound better at lower voltages.

If you need 9.00V or some other precise voltage for some reason (some digital circuits may need that), I would use a series diode reverse polarity protection or better yet a bridge recifier, followed by a simple 5V voltage regulator, followed by a charge-pump, followed by noise filtering, followed by an adjustable precision voltage regulator set to 9.00V. But again, this is complicated and bulky and offers no benefit over the simple series Schottky diode for all but very, very few exotic effects.

Andy

[antonis]

a full wave bridge of MOSFETs to make a pedal power supply be polarity-agnostic.

More info, plzzzz ... 

[Fancy Lime]

Oh, another thing that came to my mind: With a suitably sized precision rectifier you should be able to get exactly the input voltage but with always the correct polarity, no matter what polarity you feed it with. However, I have no idea what to watch out for in terms of design when they are being fed DC instead of AC. R.G. and PRR are the experts on that sort of thing, if I'm not mistaken. But this method too seems like a lot of unnecessary hassle.

Andy

[Fancy Lime]

@ antonis

This here explains that quite well:
https://en.wikipedia.org/wiki/Diode_bridge

But with that you have of course twice the voltage loss because you always have 2 series diodes. May or may not be a problem.

[Phoenix]

Oh, another thing that came to my mind: With a suitably sized precision rectifier you should be able to get exactly the input voltage but with always the correct polarity, no matter what polarity you feed it with. However, I have no idea what to watch out for in terms of design when they are being fed DC instead of AC. R.G. and PRR are the experts on that sort of thing, if I'm not mistaken. But this method too seems like a lot of unnecessary hassle.

Andy

You'd also need a supply voltage for the precision rectifier, so how are we going to do polarity protection for that?
And it's voltage rails would need to be higher than the input voltage to be rectified, etc, etc. Sounds good at first suggestion, but quickly falls apart.

[antonis]

@ antonis

This here explains that quite well:
https://en.wikipedia.org/wiki/Diode_bridge

But with that you have of course twice the voltage loss because you always have 2 series diodes. May or may not be a problem.

Thanks Andy but my concern is focused specifically on MosFets and more specifically on polarity-agnostic supply.. 

[Phoenix]

Thanks Andy but my concern is focused specifically on MosFets and more specifically on polarity-agnostic supply.. 

Here you go Antonis, sorry about the ugly schematic!

[antonis]

PMos...!!! 

[Phoenix]

PMos...!!! 

And that's not the only downside unfortunately, you also can't power more than one device with the wall-wart/power adapter if this mosbridge is used, as there is a ground offset voltage. Even if all the devices powered all use the same mosbridge with the same mosfets and draw the same current, device tolerance means that the ground offset voltage will always be different between devices, and will cause serious ground-loop issues. Nice concept, in practice though, not really practical at all.

[antonis]

Even if all the devices powered all use the same mosbridge with the same mosfets and draw the same current, device tolerance means that the ground offset voltage will always be different between devices, and will cause serious ground-loop issues.

Maybe not such a problem when deal with "foating" loads but we diverge from topic.. 

[Fancy Lime]

You'd also need a supply voltage for the precision rectifier, so how are we going to do polarity protection for that?
And it's voltage rails would need to be higher than the input voltage to be rectified, etc, etc. Sounds good at first suggestion, but quickly falls apart.

Hi Greg,
right... I had not thought of that. But you're totally right, we'd need a second power supply, rendering the whole exercise ever more useless than I thought it was. So everybody please just forget what I said about the precision rectifier.

Andy

[Fancy Lime]

Thanks Andy but my concern is focused specifically on MosFets and more specifically on polarity-agnostic supply.

Hi Antonis,
sorry, I thought you meant the general principle of polarity agnosticism. Anyway, as you can see in Greg's schematic it basically works the same with MOSFETS as it does with diodes, if you replace each diode with a MOSFET-resistor pair like you would use in a simple series diode protection to MOSFET conversion.

To get back to the original topic:
I still don't quite get what the drawbacks of series diode protection with a 1N5817 are. Loosing 0.2V or so? Where would that be relevant, all things considered? I have used PMOS protection in the past but gave up on that because I could never tell any audible difference to a plain old diode. The OP lists "Oscillation of fuzz (Hello Fuzz Factory)" as a problem. I never experienced anything like that, can anyone explain how a series diode in the power line cause that? To me that sounds like a capacitor related problem. Or one that could be fixed by a capacitor to ground in the right place.

Andy

[antonis]

I still don't quite get what the drawbacks of series diode protection with a 1N5817 are. Loosing 0.2V or so?

That makes us - at least - two of a kind... 

[R.G.]

The issue of small ground offsets leading to noise and circulating DC currents is why I stopped developing the active bridge. What's different with the active drivers for the active bridge is that (a) they drive the MOSFETs HARD to give the lowest forward voltage possible, and (b) newer MOSFETs can achieve much lower forward resistances, so in combination the ground offsets ...can... be driven down into the millivolts. Will that be enough??? Who knows? Worse yet, there is the issue of "tolerance" on the tolerance of pedals for offsets. Today's pedal market, with literally tens of thousands of cottage pedal makers trying to sell on the pedal market ensures that some of them will be intolerant of even microscopic offsets in either voltage or resistance, and the protection mechanism or the power supply, not the IN-tolerant pedal will be blamed.

It's an insoluble problem, not because of the power supply technology, but because of the pedals.

As to whether losing a small amount of forward voltage is a problem, again the answer is a question: Which pedal are you talking about? Some will, some won't. Besides, losing a fraction of a volt is more of an issue when using batteries, where the voltage is certain to change over time, than when using active adapters, where the voltage will not change over time. As an "industry", where that's the term as used by anthopologists and archeologists, not techies, the pedal "industry" has moved to where batteries are a special purpose and slightly unusual answer, not what is the main-line answer to powering pedals. So losing a fraction of a volt is not as big an issue as it was when you forgot to change batteries and your 9V PP3s were down at 7.5V.

On the other hand, a PMOS transistor or a bipolar is good insurance for the issue of changing batteries; so is the single reverse-polarity diode.

What a reverse polarity diode is NOT good insurance for is someone with a giant pedalboard containing a L!ne & 9V>>AC<< pedal adapter connecting that adapter up to pedals with a reverse polarity diode. That scenario runs like: AC adapter overheats the diode, causes the diode to short; continuing high current burns the diode open; reverse polarity pulses now kill ICs; then they kill capacitor; then ....

The presence of AC-output adapters is the big issue. It doesn't get a lot of press, though. Only series protection - series diode, series transistor, etc. - can help you much with AC.  But then if you're not using batteries, you're not so worried.

This is one of those issues that isn't amenable to quick answers in a pedal forum. It needs some thought.

[amptramp]

It would really be nice to get away from 9 volt batteries and positive shell connections for power.  If you are building a unit for yourself, a 12 VDC or 15 VDC wall wart supply makes everything better.  You don't need a Schottky diode because you can permit several volts of drop, so a 1N400X in series will do.  Even if you are stuck with batteries, many circuits can tolerate 18 volts as a power supply and others may only need a simple change of capacitor voltages to permit use at 18 volts.  I don't know any other industry that has stayed with a legacy power requirement for more than five decades.

If you are using a wall wart because the current consumption precludes batteries, maybe a relay with a diode in series with the winding would be a good protection switch - the diode in series with the winding to ground only permits current flow in one direction.  The switch only turns on with the correct polarity.  You could make it so the wrong polarity turns it off, but if the voltage is in the wrong direction but not enough to pull the relay in, you still get reverse voltage.

[Fancy Lime]

@amptramp

I don't know any other industry that has stayed with a legacy power requirement for more than five decades.

I don't know many other industries that are as traditionalist as (rock) music. We still build fuzzes that are trying to sound "exactly like Jimi at Woodstock", for cryin out loud. No, no, "live at Monterey was waaaay better, that was the ultimate, never to be surpassed guitar sound!". And lets face it, the real money to be made in stompboxes, guitars and amps is in selling millions of teenagers (some of them are in their 60s, mind you) stuff with which they supposedly sound like their heroes. Thank goodness we don't HAVE to abide by the traditionalist rules in the DIY world but can choose if we want to. Damn it, I'm ranting, aren't I. So, yes, I agree, there are good reasons to move away from 9V for some pedals. For others, it doesn't really make a difference, so we keep what we have. Inertia is a powerful force.

BTW: Is there something about power supply filtering and polarity protection methods in the Wiki of FAQs? I'd be willing to write something about the basics if someone would be willing to read the thing and correct mistakes and such. Don't want to confuse novices with poorly written half-truths.

Andy