How to add reverse polarity protection to LED drivers that doesn't have that.

Erilaz

Newly Enlightened
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Dec 9, 2019
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A quick, effective and easy fix is to add a Schottky diode in series between the LED driver and the battery . It will then block current if the battery or batteries is installed the wrong way.
I think that it should be on the positive side of the driver.

The diode must be rated at the LEDs maximum current, so for a Cree XHP70.2 that is rated 4.8 Amps at 6volt or 2.4 Amps at 12 volts you need to choose a diode that has a rating that is "rounded up" and close to the maximum current. 5 Amperes will be just fine for a Cree XHP70.2 .

A diodes forward voltage refers to the voltage drop that occurs when an electrical current passes through a diode in an electrical circuit. It is generally independent of the amount of current passing through the diode, and will be the same for a given family of diodes. For silicon diodes, which are generally the most common, the diode forward voltage drop is about 0.7 volts (V).
This voltage drop generates thermal heat.
The wattage generated when current is flowing is caused by the voltage drop over the diode.
It's calculated with this formula: Wattage= Volts x amperes. A example: 0.67 x 5 = 3.35 W.

Some diodes:
https://www.mouser.co.uk/ProductDet...=sGAEpiMZZMtQ8nqTKtFS/DWQDSFdwJ2R21CS8inKhwI=
Generates 3.3W in use. It has a voltage drop of around 0.6 volts.
Two of these in parallel handles 10Amps.

These below will need cooling, and the cooling flange or pad under it must be electrically insulated from the heat sink or mounting surface.
https://www.digikey.com/product-detail/en/rohm-semiconductor/SCS310APC9/SCS310APC9-ND/6166614
Voltage - Forward (Vf) (Max) @ If 1.5V @ 10A
Thats 15W thermal power generated in use.

https://www.digikey.com/product-detail/en/rohm-semiconductor/SCS210KGC/SCS210KGC-ND/3902856
Voltage - Forward (Vf) (Max) @ If 1.6V @ 10A
Thats 16W thermal power generated in use.

They use the TO-220AC package,so dimensions are the last one on this page:
http://www.vishay.com/docs/95180/to220abc.pdf


I don't know how many drivers that doesn't have reverse polarity protection, but the LD-B4HV 2-12Amp 2S/4S led driver is one of them.

It's my opinion that all drivers should have this built in.

Sent fra min ONEPLUS A6013 via Tapatalk
 
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An example where is will not work is a Malkoff MDC 1AA. Loss would be probably be 1/ 2 volts. Correct me if I am wrong.

Bill
 
An example where is will not work is a Malkoff MDC 1AA. Loss would be probably be 1/ 2 volts. Correct me if I am wrong.

Bill
As long as it's possible to get to the internal parts and solder it should not be a issue. It's a common trick to protect against wrong polarity with a Schottky diode. A FET can also be used:

https://m.youtube.com/watch?v=IrB-FPcv1Dc

Sent fra min ONEPLUS A6013 via Tapatalk
 
I was meanig to say, that the loss of 1/2 volt is not good for a one cell AA light.

Bill
 
I was meanig to say, that the loss of 1/2 volt is not good for a one cell AA light.

Bill
Well, 0.35 volts at 4 Amps is what I will call acceptable. But, that's a SMD mounted component. Those are not that easy to solder.
https://www.mouser.co.uk/ProductDet...Q8nqTKtFS/L6ueELhqahQw9jcJw9dDQcYZwDGFKaeQw==

And there is of course the FET circuit that is better, it's mentioned here:
https://youtu.be/IrB-FPcv1Dc

https://www.infineon.com/dgdl/Rever...2.pdf?fileId=db3a304412b407950112b41887722615
 
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