Question regarding diodes

daftpunker · 05-26-2012, 02:28 PM

Hi guys,

I have a problem finding the right diode for my application. I need to put 2 power supplies (different types) in series and need to protect each of them from reverse currents using diodes. I believe that they already have diodes built in, but I want to take precautions.
So my problem is that I am not sure which diodes to order.
One power supply is 52V, 30 Amp and the other one is 30 V, 20 Amp. the circuit will be powered at 72 V and current could increase up to 12.5 Amp.
Since I am not experienced with diodes I am wondering which ones to choose.
I have the following diodes (1N5402), but I believe the current rating does not match.
http://www.diodes.com/datasheets/ds28007.pdf

I found these: http://www.digikey.com/product-detai...ICT-ND/2242770

Do you think they will be appropriate?

Thanks so much

budm · 05-26-2012, 07:19 PM

If you are going to have 12.5A or more flowing through the Diode, the Vf at that current will be about 1V or more, so at 12.5A, the Diode must be able to dissipate at least 12.5Watts of power. You should get the Diode that can handle at least 25Watts which more likely that it will have to be mounted on the heat sink.

PeteS in CA · 05-26-2012, 11:07 PM

Maybe I'm missing something, but I think you could use a 60V Schottky, maybe a 20A or 25A rated part (30A or 40A would be even better, but the package might be TO-247 instead of TO-220). That would bring your V(f) down to .6V or .7V, dissipating significantly less power. However you do it, you will need to be able to dissipate a fair amount of power, and heatsinks are not tiny or light.

daftpunker · 05-27-2012, 10:24 AM

Thanks for the help.
I would like to avoid the use of heatsinks.
Couldn`t I use multiple diodes in parallel? Let`s say 4 diodes rated to 3 A in parallel.
Do you see any problem with this solution?

budm · 05-27-2012, 04:40 PM

You need room for safety margin, usually x2.

ben7 · 05-27-2012, 07:16 PM

Quote:

Originally Posted by daftpunker

Thanks for the help.
I would like to avoid the use of heatsinks.
Couldn`t I use multiple diodes in parallel? Let`s say 4 diodes rated to 3 A in parallel.
Do you see any problem with this solution?

Well, one might have a lower forward voltage drop than the others, even if it is minuscule, it might make the diode fail (short circuit from over-current) after a while.

budm · 05-27-2012, 07:19 PM

It is not good to parallel the Diode either unless you use resistors to balance them out or match the Vf really well, the Diode with the lowest Vf will conduct, the one with higher Vf may not conduct at all.

999999999 · 05-27-2012, 10:26 PM

This is a bad design, something is bound to go wrong. Two PSU, different currents, etc.

Can you electrically make something work? Often. Does that make it a good idea? The simplest solution is usually the best one. I may be wrong, you might be stranded on a deserted island with no way to communicate with the outside word or order parts. Otherwise, I hope nothing goes wrong but predict something will, sooner or later...

I'm kidding a little, but not entirely.

Evil Lurker · 05-28-2012, 01:13 AM

Your looking at three terminal diode type devices, probably one or more STPR1620 ultrafast or BYW series.

05-26-2012, 02:28 PM	#1
daftpunker New Member Join Date: Dec 2010 Posts: 5	Question regarding diodes Hi guys, I have a problem finding the right diode for my application. I need to put 2 power supplies (different types) in series and need to protect each of them from reverse currents using diodes. I believe that they already have diodes built in, but I want to take precautions. So my problem is that I am not sure which diodes to order. One power supply is 52V, 30 Amp and the other one is 30 V, 20 Amp. the circuit will be powered at 72 V and current could increase up to 12.5 Amp. Since I am not experienced with diodes I am wondering which ones to choose. I have the following diodes (1N5402), but I believe the current rating does not match. http://www.diodes.com/datasheets/ds28007.pdf I found these: http://www.digikey.com/product-detai...ICT-ND/2242770 Do you think they will be appropriate? Thanks so much

05-26-2012, 07:19 PM	#2
budm Badcaps Veteran Join Date: Feb 2010 City & State: S.F. Bay area My Country: USA Line Voltage: 120V 60Hz I'm a: Knowledge Seeker Posts: 6,992	Re: Question regarding diodes If you are going to have 12.5A or more flowing through the Diode, the Vf at that current will be about 1V or more, so at 12.5A, the Diode must be able to dissipate at least 12.5Watts of power. You should get the Diode that can handle at least 25Watts which more likely that it will have to be mounted on the heat sink. __________________ Never stop learning or per Greek Pro "when you will update your ID from Knowledge Seeker to a Pro (in 10 years) , then I will take you more seriously, for now you are just a kid playing with it keyboard" Baisc LCD TV and Monitor troubleshooting guides. http://www.badcaps.net/forum/showthr...956#post305956 Voltage Regulator (LDO) testing: http://www.badcaps.net/forum/showthr...999#post300999 Inverter testing using old CFL: http://www.badcaps.net/forum/showthr...er+testing+cfl Tear down pictures : Hit the ">" Show Albums and stories" on the left side http://s807.photobucket.com/user/budm/library/ TV Factory reset codes listing: http://www.badcaps.net/forum/showthread.php?t=24809

05-26-2012, 11:07 PM	#3
PeteS in CA Badcaps Veteran Join Date: Aug 2005 City & State: San Jose, CA My Country: USA, Unsure of Planet Line Voltage: 120VAC, 60Hz & 115VAC, 400Hz I'm a: Professional Tech Posts: 1,576	Re: Question regarding diodes Maybe I'm missing something, but I think you could use a 60V Schottky, maybe a 20A or 25A rated part (30A or 40A would be even better, but the package might be TO-247 instead of TO-220). That would bring your V(f) down to .6V or .7V, dissipating significantly less power. However you do it, you will need to be able to dissipate a fair amount of power, and heatsinks are not tiny or light. __________________ PeteS in CA Republican Operative discussion forums Where might is right There is no right. - Sophocles in "Antigone" ************************** All that is gold does not glitter, Not all those who wander are lost; - J.R.R. Tolkien, The Fellowship of the Ring ************************** To kill personal responsibility, initiative or success, punish it by taxing it. To encourage irresponsibility, improvidence, dependence and failure, reward it by subsidizing it.

05-27-2012, 10:24 AM	#4
daftpunker New Member Join Date: Dec 2010 Posts: 5	Re: Question regarding diodes Thanks for the help. I would like to avoid the use of heatsinks. Couldn`t I use multiple diodes in parallel? Let`s say 4 diodes rated to 3 A in parallel. Do you see any problem with this solution?

05-27-2012, 04:40 PM	#5
budm Badcaps Veteran Join Date: Feb 2010 City & State: S.F. Bay area My Country: USA Line Voltage: 120V 60Hz I'm a: Knowledge Seeker Posts: 6,992	Re: Question regarding diodes You need room for safety margin, usually x2.

05-27-2012, 07:19 PM	#7
budm Badcaps Veteran Join Date: Feb 2010 City & State: S.F. Bay area My Country: USA Line Voltage: 120V 60Hz I'm a: Knowledge Seeker Posts: 6,992	Re: Question regarding diodes It is not good to parallel the Diode either unless you use resistors to balance them out or match the Vf really well, the Diode with the lowest Vf will conduct, the one with higher Vf may not conduct at all.

05-27-2012, 10:26 PM	#8
999999999 Badcaps Veteran Join Date: Sep 2006 City & State: Near Cincinnati, OH My Country: USA Line Voltage: 120VAC 60Hz Posts: 704	Re: Question regarding diodes This is a bad design, something is bound to go wrong. Two PSU, different currents, etc. Can you electrically make something work? Often. Does that make it a good idea? The simplest solution is usually the best one. I may be wrong, you might be stranded on a deserted island with no way to communicate with the outside word or order parts. Otherwise, I hope nothing goes wrong but predict something will, sooner or later... I'm kidding a little, but not entirely. Last edited by 999999999; 05-27-2012 at 10:30 PM..

05-28-2012, 01:13 AM	#9
Evil Lurker Warranty Voider Join Date: Feb 2011 City & State: West Tennessee, USA Posts: 430	Re: Question regarding diodes Your looking at three terminal diode type devices, probably one or more STPR1620 ultrafast or BYW series.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode