Diode assistance

[saabluster]

I need to buy some diodes that match the ones used on the DX plain 7135 driver boards. Just need them for reverse polarity protection. If anyone knows of a higher quality version that would be nice as well. I am somewhat electronically challenged. :o Thanks guys.

 

[kramer5150]

DX sometimes ships out batches of those boards with black / gray diodes. I have seen www pics of them before, although I do not know if they are any better than the round/copper colored ones that seem to be more typical. I'll try and dig that up for you.

I assume you're looking for low loss diodes?... ones with lower V-drop through them? They are common in DIY audio circles when component/circuit slew rates are critical, and losses must be kept at a minimum.

http://en.wikipedia.org/wiki/Schottky_diode

 

[saabluster]

DX sometimes ships out batches of those boards with black / gray diodes. I have seen www pics of them before, although I do not know if they are any better than the round/copper colored ones that seem to be more typical. I'll try and dig that up for you.

I assume you're looking for low loss diodes?... ones with lower V-drop through them? They are common in DIY audio circles when component/circuit slew rates are critical, and losses must be kept at a minimum.

http://en.wikipedia.org/wiki/Schottky_diode

Well like I said I am electronically challenged but it does seem logical to use a low loss diode. The drivers are only running on one cell so the more I can reduce voltage drop across it the better. Thank you kindly sir for helping me out.:thumbsup:

 

[kramer5150]

Well like I said I am electronically challenged but it does seem logical to use a low loss diode. The drivers are only running on one cell so the more I can reduce voltage drop across it the better. Thank you kindly sir for helping me out.:thumbsup:

I always just wire jump bypass them, so its just the 7135 chips in parallel by themselves regulating current. Its about as bare bones simple a PCB layout as there is.... Personally I have no need for reverse polarity protection, and I have had the copper diodes fail before. So I just get rid of them.

 

[kramer5150]

here you go....
http://www.candlepowerforums.com/vb/showpost.php?p=2540954&postcount=2

 

[saabluster]

I always just wire jump bypass them, so its just the 7135 chips in parallel by themselves regulating current. Its about as bare bones simple a PCB layout as there is.... Personally I have no need for reverse polarity protection, and I have had the copper diodes fail before. So I just get rid of them.

Jumping past it would be fine for a light made for myself but these are lights I want to sell to others.;) Better safe than sorry.

here you go....
http://www.candlepowerforums.com/vb/showpost.php?p=2540954&postcount=2

I hope I'm not trying your patience but I'm unsure what I am supposed to be looking at at that link. I was hoping for some guidance on how to pick a specific diode to use in the circuit. I am actually removing all the 7135s off their boards and using my own setup. Each light will use two 7135s but each board of four chips(1400mA version) only comes with one diode. That means if I want to use all my chips I need to buy more diodes. Seems to me like one of those things where probably a thousand different types would do the job but I really don't know. I like to buy from Mouser since they are only about 50 miles from me. Will just any old diode do? Thanks again.

 

[HKJ]

That means if I want to use all my chips I need to buy more diodes. Seems to me like one of those things where probably a thousand different types would do the job but I really don't know. I like to buy from Mouser since they are only about 50 miles from me. Will just any old diode do? Thanks again.

Use the parametric search and select Schottky diodes.
Select a diode that can take at least 2A "Forward Continuous Current" (You can mark 2 to 4 amps to get a range).

"Peak Reverse Voltage" must be above you battery voltage, select 10 to 30 volt.

"Forward Voltage Drop", you want this as low as possible, select from lowest value to 0.4 volt.

Press "Apply filter" and press the sorting in "Forward Voltage Drop".

Select a diode.

 

[HarryN]

PM Sent.

 

[Illum]

those certainly do not resemble Schottky barrier diodes...if any they resemble more of zeners or signal diodes:candle:

the odd part of these drivers is the complete lack of caps on either end for stability..

 

[HKJ]

PM Sent.

I wonder who you send it to, it was not me.

those certainly do not resemble Schottky barrier diodes...if any they resemble more of zeners or signal diodes:candle:

That is true, but if they are in series with the battery they must be schottky diodes.

the odd part of these drivers is the complete lack of caps on either end for stability..

I do not believe that it need any capacitor.

 

[uk_caver]

That is true, but if they are in series with the battery they must be schottky diodes.

I don't think that the 7135 boards I have use schottky diodes - the forward voltage seems to be about 0.6V.

Select a diode that can take at least 2A "Forward Continuous Current" (You can mark 2 to 4 amps to get a range).

For the 7135 boards, the protection diodes are only passing the current needed to turn the 7135s on, which is tiny (~200uA).

 

[HKJ]

I don't think that the 7135 boards I have use schottky diodes - the forward voltage seems to be about 0.6V.

For the 7135 boards, the protection diodes are only passing the current needed to turn the 7135s on, which is tiny (~200uA).

In that case it is completely different, nearly any signal diode can be used, and there are no worries about losses in the diode!

Then I would select the diode (General purpose) and use the following filter settings:
Configuration: Single
Forward Continuous Current: everything below 0.3A
Maximum Power Dissipation: everything below 0.3W

Look at price and package and select one.

The current and power settings are not critical and could be larger values.

 

[HarryN]

HKJ - thanks - I was pm'ing saabluster. We talked today about diodes.

I might be reading it incorrectly, but at least in my simple interpretation of the 7135 component, putting a diode at that point is of limited value. It keeps the 7135 from activating, but AFAIK, it still will blow the 7135, or at least exceed the max values of the part.

How do you interpret the data sheet on those parts?

 

[saabluster]

HKJ - thanks - I was pm'ing saabluster. We talked today about diodes.

I might be reading it incorrectly, but at least in my simple interpretation of the 7135 component, putting a diode at that point is of limited value. It keeps the 7135 from activating, but AFAIK, it still will blow the 7135, or at least exceed the max values of the part.

How do you interpret the data sheet on those parts?

I appreciated your call Harry. Enjoyed talking with someone else about the nuts and bolts of flashlights that understands. When I get all excited about a new design or idea and show my wife I just get an unhuh yeah...thats so wonderful.:rolleyes: Thanks to everyone else that has contributed as well. I think I know what I need now but I am curious to hear some responses on whether or not the chip needs more protection than just on the +pin for the chip. Just so noone needs to dig for it here is the datasheet for the 7135.

 

[HKJ]

I might be reading it incorrectly, but at least in my simple interpretation of the 7135 component, putting a diode at that point is of limited value. It keeps the 7135 from activating, but AFAIK, it still will blow the 7135, or at least exceed the max values of the part.

How do you interpret the data sheet on those parts?

This is a bit tricky, according to the data sheet the chip must not have more than -0.3 volt on either VDD or OUT with reference to GND.
Using a (small) diode on the VDD pin will protect that pin from reverse polarity, but not the OUT pin.
BUT the output is already connected to a diode (Light Emitting Diode), that is usual rated for 5 volt reverse voltage, i.e. it is also protected.

I.e. the diode on VDD will provide reverse battery protection on single LiIon batteries.

 

[uk_caver]

...BUT the output is already connected to a diode (Light Emitting Diode), that is usual rated for 5 volt reverse voltage, i.e. it is also protected.

I.e. the diode on VDD will provide reverse battery protection on single LiIon batteries.

It could depend on the LED used.

While old Luxeons Is and IIIs and Cree XR-E/XP-E/XP-Gs seem happy to block low reverse voltages, Seoul P4s have a built-in diode which will conduct at ~0.6V.

 

[Illum]

I do not believe that it need any capacitor.

I have yet to find a datasheet that says otherwise:thinking:

~200uA? well gee...grab any 1N914/1N4148 diode and it'll work, they are widely available :)

 

[HKJ]

I have yet to find a datasheet that says otherwise:thinking:

AMC7135 Datasheet, top of page one, features: "No external component required"

 

[HarryN]

This is a bit tricky, according to the data sheet the chip must not have more than -0.3 volt on either VDD or OUT with reference to GND.
Using a (small) diode on the VDD pin will protect that pin from reverse polarity, but not the OUT pin.
BUT the output is already connected to a diode (Light Emitting Diode), that is usual rated for 5 volt reverse voltage, i.e. it is also protected.

I.e. the diode on VDD will provide reverse battery protection on single LiIon batteries.

Hi, I was confused by the same point. The rebels I tend to use are not rated for reverse bias at all, AFAIK. Which LEDs have such a high (5 volt) reverse voltage bias rating?

 

[HarryN]

I appreciated your call Harry. Enjoyed talking with someone else about the nuts and bolts of flashlights that understands. When I get all excited about a new design or idea and show my wife I just get an unhuh yeah...thats so wonderful.:rolleyes: [/URL] for the 7135.

Feel free to call anytime, I have the same challenge. Harry