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Electrical Supplier Help needed!

RV8iator

Well Known Member
Benefactor
Folks, I know what I need is out there but I need help finding it.

I need a Schottky type diode with a .2 volt flow through rating. (or real close). I’ll admit up front I’m electrically challenged but figuring out the right one has my eyes watering. Seems not many places pit the flow through, or voltage drop in their ads.

I’m keeping my standby battery charged through a diode to keep current from backflowing but I’ve got a diode that has a .6 to .7 volt drop and that's too much to keep my earthX from keeping a proper charge. A buddy has one that’s labeled 6A05 0950 but I can’t find any.

Can someone point me to a site or supplier that I can find what I need?
 
I got mine from Perihelion Designs some years ago. https://periheliondesign.com/
They don't appear on the site now but if no one else has a source you might try contacting them. Digikey or Mouser should have them. There's normally always a spec sheet that would show the voltage drop.
 
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Here's your buddy's diode https://www.digikey.com/en/products/detail/micro-commercial-co/6A05/261592 It's not going to work for your application. Depending on a whole bunch of specs, you will need a Shottky diode.

I have used the V30100S https://www.digikey.com/en/products...nductor-diodes-division/V30100S-E3-4W/2048215

You'll need to tradeoff forward voltage, operating current, reverse voltage and reverse leakage current. There are hundreds of types available on Digikey.

Here is where I use it: http://www.vx-aviation.com/sprocket/photos/panel_elec/schematics-2/IGN.pdf

VV
 
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Schottky Diode

Diodes typically spec their forward voltage at their rated current, but you will want to pick a diode with a rated current higher than what you will actually run though.

At lower currents, the forward voltage will be lower (not linearly, though). Forward voltage also drops as temperature increases.

A special category called "Schottky Diodes" have lower forward voltage than "Regular" silicon diodes, with some drawbacks that you probably don't care about (like lower maximum reverse max voltage and increased reverse leakage current).

You mention you need 0.2V, but not at what typical current. I doubt you will find anything with 0.2V forward drop with currents much higher than a few milliamps. (at least not anything in an easy-to-handle package).

With that mini lecture out of the way, take a look at the 1N5820G. Available at Digikey. The maximum (i.e., guaranteed) forward voltage at 3A is 475 mV.

However, if you are trickle-charging the battery, the current is going to be lower than that. If you look at Figure 7, the typical forward voltage at 25*C is 300 mV with a 500mA current, and 250mV at about 200mA and it will get better as the temperature goes up.

If you need to get better than this, you're going to need something more complicated than just a diode. Definitely possible, though...

EDIT: I see Vern likes the V30100S. Its forward voltage behavior below 2A is pretty similar, but with a much higher reverse voltage and maximum current rating. I like it, too!
 

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It is unlikely that you will find one better than this:
https://www.digikey.com/en/products/detail/ixys/DSS2X121-0045B/416786
Looking at the forward voltage drop chart, at 3 amps, the voltage drop will be 0.3 volts across one diode.
Connect the two diodes in parallel. Less current per diode will drop less voltage.
Small lithium backup batteries need a series diode to limit charging current.
Without a diode, the battery will accept all of the current that the alternator is capable of putting out.
 

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Jerry,

If you go to Digi-Key or Mouser and search for Schottky diode. There will be a million that come up, but you can filter based upon Vf or the forward voltage drop. Look for the parts that meet your Vf = 0.2Volts or less. That should give you a group of parts to choose from. The problem is Vf typically varies with current so the more current you put through a diode the voltage will increase. So you need to find a part the has the Vf voltage that you want at your required current. The thing is as your battery charges up it will draw less current and as a result the diode voltage drop will go down.
 
Unlike resistors, if you connect two identical diodes in parallel, you don't get half the current going into each one.

When you have two diodes in parallel, one of them will turn on at a slightly lower voltage the the other one (even if that voltage difference is a few millivolts), and it will conduct most of the current, leaving the other diode to sit around and take only a small percentage of the total current.
 
It is unlikely that you will find one better than this:
https://www.digikey.com/en/products/detail/ixys/DSS2X121-0045B/416786
Looking at the forward voltage drop chart, at 3 amps, the voltage drop will be 0.3 volts across one diode.
Connect the two diodes in parallel. Less current per diode will drop less voltage.
Small lithium backup batteries need a series diode to limit charging current.
Without a diode, the battery will accept all of the current that the alternator is capable of putting out.

Nice device, except for the breakdown voltage, which in aircraft operations should be around 100V. Spikes are real, I've seen them on my oscilloscope in flight.

VV
 
Here's your buddy's diode https://www.digikey.com/en/products/detail/micro-commercial-co/6A05/261592 It's not going to work for your application. Depending on a whole bunch of specs, you will need a Shottky diode.

I have used the V30100S https://www.digikey.com/en/products...nductor-diodes-division/V30100S-E3-4W/2048215

You'll need to tradeoff forward voltage, operating current, reverse voltage and reverse leakage current. There are hundreds of types available on Digikey.

Here is where I use it: http://www.vx-aviation.com/sprocket/photos/panel_elec/schematics-2/IGN.pdf

VV

Thanks Vern,
What type of batteries do you have?
 
Breakdown voltage

Nice device, except for the breakdown voltage, which in aircraft operations should be around 100V. Spikes are real, I've seen them on my oscilloscope in flight.

VV

I believe the breakdown voltage is just preventing the protected bus from getting pulled down by a main bus fault, you should only need enough to stop the reverse flow, nothing more. those 100V spikes from the main bus will find their way straight through the diode.

If you want to beat down voltage spikes maybe try a TVS diode.

This is the diode I use to isolate my critical bus:
https://octopart.com/search?q=STPS24045TV&currency=USD&specs=0

Bill
Monkworkz.com
 
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Breakdown Voltage

I don't see "breakdown voltage" in the datasheet. Is that the same as maximum reverse blocking voltage?
If that voltage is exceeded for a few milliseconds, what harm is done in the OP's application?
Bob Nuckolls uses 1N5400 diodes in many of his drawings. The 1N5400 has a Maximum DC blocking voltage of 50V.
Eric M. Jones (PerihelionDesign.com) wrote,"For several years I have sold: IXYS DSSX61-0045A with a heatsinks,
mounting hardware, shipping and manual. It's a good choice." http://forums.matronics.com/viewtopic.php?p=416389
The DSS2x121-0045B and the DSSX61-0045A have the same 45 reverse voltage limit.
 
Eyes still bleeding,

But, you guys are educating me and that's a feat! Thanks for the info and insight.
I’ve ordered a couple DSS2x121-0045B diodes and will see if they can fix my problem. I’ll let you know.
I used to think Vf was a speed!
See. Old dog, new tricks.
 
Follow up

Well, thanks for steering me in the right direction. I installed a DSS2x121-0045B and with engine running and everything on the voltage drop was .3 volts. Perfect for me.
My old diode was a DSS2X061-0045A, but it had a lot of resistance when I checked it, so was failing.
You guys helped a bunch.

Thx
 
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