Reverse Polarity Protection 1N5817 or 1N4001

[POTL]

I have some SMD 5817 diodes that I use, give me a second and I'll find the part number for you. They absolutely exist.

Try out the SM5817 or B5817. Same thing as 1N5817, SMD package.

https://www.mouser.com/ProductDetail/Micro-Commercial-Components-MCC/SM5817PL-TP?qs=sGAEpiMZZMtQ8nqTKtFS%2FEo19YTfnJP1ysRBdx90Swg%3D

Hi, thanks, I know that 1N5817 exists in the form of smd.
I just wanted to use a more compact body, not that it is an urgent need, but sometimes it can be useful 
I looked for possible replacements and found 2 models from the same series, they look good, but I'm afraid I can miss something in their specifications.

[vigilante397]

Hi, thanks, I know that 1N5817 exists in the form of smd.
I just wanted to use a more compact body, not that it is an urgent need, but sometimes it can be useful 
I looked for possible replacements and found 2 models from the same series, they look good, but I'm afraid I can miss something in their specifications.

Ah, gotcha. Just took a quick look at the datasheets, either of those diodes should work fine as a replacement for 1N5817.

[POTL]

Hi, thanks, I know that 1N5817 exists in the form of smd.
I just wanted to use a more compact body, not that it is an urgent need, but sometimes it can be useful 
I looked for possible replacements and found 2 models from the same series, they look good, but I'm afraid I can miss something in their specifications.

Ah, gotcha. Just took a quick look at the datasheets, either of those diodes should work fine as a replacement for 1N5817.

thank
As for the datasheet, I was afraid that there are pitfalls in the spirit of heat dissipation and other things. thanks again)
P.S. 1N5817 is sold in my country only as a DO-213AB, it is still big.

[merlinb]

P.S. 1N5817 is sold in my country only as a DO-213AB, it is still big.

Do you even need a 1A diode? A BAT54 is rated for 200mA... And you can use a BAT54A and connect the two devices in parallel for lower drop.

[POTL]

No, just 5817 proved to be a good solution, MBR130LSFT1 & MBR120VLSFT1
look no worse, and the voltage drop is even smaller.
I was just looking for the closest-in-band analogue in the smd package and the minimum voltage drop, that's all.

[Fancy Lime]

I don't suppose anyone ever took a DMM to the "parallel diodes" hypothesis?

Andy

[PRR]

> I don't suppose anyone ever took a DMM to the "parallel diodes" hypothesis?

Not for this application; but general theory suggests ~20mV less drop. (Which is probably not worth a second part, but Merlin cites a dual-diode so it is just one added connection.)

[Groovenut]

I think Merlin's suggestion was to increase the current handling of the device by paralleling the two in the package. This would bring the total current limit to 400mA. The slight Vf drop is just a beneficial side effect.

[POTL]

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.

I decided to re-read this topic.
Did I understand correctly that mosfet polarity protection devices are unsuitable for pedalboard work?
If I want to power different effects from one power supply and there will be at least one pedal with a stack of protection among them, can there be problems?
What is the point?

[bushidov]

I use TO92 P MOSFET reverse polarity all the time. Works great for me.

[vigilante397]

It's correct if you're using N-channel MOSFETs and low-side switching, as there is no such thing as an RDS-on of 0, so there will be a ground offset between devices, potentially making things wonky. Granted if you used a P-channel MOSFET and did high-side switching it would be fine.

Personally I like using schottkey bridge rectifiers for polarity protection. Low input voltage drop, and it not only won't be damaged by the wrong polarity, there is no wrong polarity so it can work with anything

[POTL]

It's correct if you're using N-channel MOSFETs and low-side switching, as there is no such thing as an RDS-on of 0, so there will be a ground offset between devices, potentially making things wonky. Granted if you used a P-channel MOSFET and did high-side switching it would be fine.

Personally I like using schottkey bridge rectifiers for polarity protection. Low input voltage drop, and it not only won't be damaged by the wrong polarity, there is no wrong polarity so it can work with anything

Problem only with N-channel mosfets?
I thought everyone uses only p-channel mosfets.
Ok p-channel = no ploblems
thank

[bushidov]

https://youtu.be/IrB-FPcv1Dc
Good reference video. Note the end about the RDS on.

[POTL]

Yes, I am aware of RDS.
It is good that this protection does not create problems for use with other pedals.
In my store now available bsp250 and irfr9024 at a price of a little less than $ 0.5, I'll definitely try.

[Wenander]

Hey hey new member....

Hope it´s ok to do this, posting a question in a half-dead thread. 

I somehow seems to have given my RAT a dose of juice with the wrong polarity.  The little resistor closest to 9v in on the card has blown, a load of gunk had shot out around it and it´s pretty much charcoal now !!...I first thought it was a diode but thats just next to and it is ok...tested with multimeter. 

I read somewhere, electrosmash maybe, that it will be fine with any resistor up to 100 0hm .. can anyone confirm this ??

Everything else seems to be fine but im no expert...anything i should check out in perticular.

Sorry if this post is not ok...

// M Wenander

[antonis]

Hi & Welcome..

That resistor forms a Low Pass Filter with 100μF capacitor and also serves as a "fuse" (like in your case)..
Original is (was) 47R but any value up to 100R should be fine..
Actually, the bigger resistor the better LP filtering, as long as you can afford the extra voltage drop..
(which drop is resistor value times circuit total current draw..)

[Wenander]

Hi & Welcome..

That resistor forms a Low Pass Filter with 100μF capacitor and also serves as a "fuse" (like in your case)..
Original is (was) 47R but any value up to 100R should be fine..
Actually, the bigger resistor the better LP filtering, as long as you can afford the extra voltage drop..
(which drop is resistor value times circuit total current draw..)

Thank you.

47R   whats the R  

i found a 102 ohm resistor .. the closest match i have found. 

Are there any risks involved with trying to use it ??  or is the only risk that nothing happends ?? 

I´m thinking with a battery it should be safe ??  or doesnt it matter if i use a pedalpower thingy ?? 

(and off-topic .,.. how do know that someone has answered ??  i had to go search for the thread and manually look here to find this?!?)

[Gandalf_Sr]

47R is just a common way of writing 47 Ohms.  R is also sometimes used as the decimal point so 4R7 means 4.7 Ohms.

Antonis suggested a 100 Ohm resistor but 102 Ohms is fine as a substitute for your purposes.

[duck_arse]

......

(and off-topic .,.. how do know that someone has answered ??  i had to go search for the thread and manually look here to find this?!?)

also welcome. at the top of each page, under your username, is two links - one of which is:

Show new replies to your posts.

clik that and it shows all the topics you have posted in that have had any activity since.

and - at the top and bottom of each thread page is a bar of buttons, thusly [but horizontal]

REPLY
ADD POLL
NOTIFY
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I don't use it, but I imagine the "notify" button, when clicked will, well, notify you of a reply or something.