Have any of you compared the sonic differences between GaAs Schottky Diodes, regular Schottky Diodes, FREDs, and HiPerFRED Epitaxial Diodes? Would one type be better for rectifying a power supply?
(such as those at http://www.ixys.com/appasp/newparts.asp )
Also, I see data that shows the HiPerFRED Epitaxial Diodes turn on at 30 to35 nS. Are the Schottky's as fast (I don't seem to see speeds typically listed for them)?
Thanks, Robert
(such as those at http://www.ixys.com/appasp/newparts.asp )
Also, I see data that shows the HiPerFRED Epitaxial Diodes turn on at 30 to35 nS. Are the Schottky's as fast (I don't seem to see speeds typically listed for them)?
Thanks, Robert
I came across data on the Vishay web site that indicated their Schottky diodes had speeds of 5ns as compared to typical HiPerFREDs wtih 30 to 40ns.
I have no idea whether speed is any issue; but I am curious as to the sonic differences among the various types of devices.
Another related question is, are snubber circuits necessary for these 'soft recovery' types as compared to standard silicon diodes?
I have no idea whether speed is any issue; but I am curious as to the sonic differences among the various types of devices.
Another related question is, are snubber circuits necessary for these 'soft recovery' types as compared to standard silicon diodes?
FACE VALUE ONLY.
Hi,
Your general assumption that Schottky diodes are superior to Freds and hexFreds seems correct to me.
Generally speaking, I think speed always is an issue.
One reason I stick with vacuum state devices is their inherent speed.
Considering only the forward fed signal I wouldn't care about that too much, you can make them dissapear easily.
Howerver, if you care about what is thrown back into the mains (and you should) , snubbers are a godsend.
So to answer your question, I would put them in.
Ciao,
Hi,
Your general assumption that Schottky diodes are superior to Freds and hexFreds seems correct to me.
Generally speaking, I think speed always is an issue.
One reason I stick with vacuum state devices is their inherent speed.
Considering only the forward fed signal I wouldn't care about that too much, you can make them dissapear easily.
Howerver, if you care about what is thrown back into the mains (and you should) , snubbers are a godsend.
So to answer your question, I would put them in.
Ciao,
Next question, if snubbers are a good idea, a capacitor or an RC style snubber for soft recovery types?
Another piece of data I'm noticing from the spec sheets are junction capacitance. Most of the Schottkys are 40-50V seem to have about 115pF; many of the FREDs (like BYV32 have about 45pF); the GaAS Schottky from IXYS has 22pF for the 15A/180V device. So, is this capacitance significant? (Please excuse my ignorance; I'm not EE educated.)
Thanks, Robert
Another piece of data I'm noticing from the spec sheets are junction capacitance. Most of the Schottkys are 40-50V seem to have about 115pF; many of the FREDs (like BYV32 have about 45pF); the GaAS Schottky from IXYS has 22pF for the 15A/180V device. So, is this capacitance significant? (Please excuse my ignorance; I'm not EE educated.)
Thanks, Robert
About Shottky diodes......
The reason that they do not have the reverse recovery problem is that they do not use any minority carriers. There are lots of other ways semicon makers come up with to shorten the lifetime of the charge held by the minority carriers.
Comparing capacitance figures between Shottky diodes and soft-recovery types might not be a fair comparison.
Jocko
The reason that they do not have the reverse recovery problem is that they do not use any minority carriers. There are lots of other ways semicon makers come up with to shorten the lifetime of the charge held by the minority carriers.
Comparing capacitance figures between Shottky diodes and soft-recovery types might not be a fair comparison.
Jocko
high speed diode data
Some more info on high speed diodes. These are written from the standpoint of switching power supplies but the use of snubbers is relevant to reduction of RF noise in 60 Hz power supplies.
http://www.e-insite.net/ednmag/archives/1997/020397/03DI_03.htm
http://www.maxim-ic.com/appnotes.cfm/appnote_number/849/ln/en
Some more info on high speed diodes. These are written from the standpoint of switching power supplies but the use of snubbers is relevant to reduction of RF noise in 60 Hz power supplies.
http://www.e-insite.net/ednmag/archives/1997/020397/03DI_03.htm
http://www.maxim-ic.com/appnotes.cfm/appnote_number/849/ln/en
rtjones
Are you talking about the DGS20 series rated at 17A? Has anyone any thougths on the newer higher voltage parts? What is the consensus on the dual unit diodes and bridges as compared to the discreet single units, is there any benefit to having the parts on the same silicon as opposed to matching them? Will the heat be an issue in a typical Class A application with sufficient heatsinking?
stating the obvious
Go to http://www.ixys.com/Appasp/pdpgsd01.asp and look at the data sheets. The part he is talking about is there. If one of you would actually give an actual part number this wouldn't be confusing.
Yes, I have thoughts on higher voltage parts.
Consensus on what about dual unit diodes and bridges? How are you matching diodes? What parameter are you matching them for? There tradeoffs in price and power dissipation for multiple diode packaging verses single diodes. Very few high current schottys and FREDs are available in bridges. They are designed for switching power supplies.
How is heat an issue with sufficient heatsinking? Doesn't the question contain the answer? I suppose you'll want to know what the four most important specs for choosing a diode are.......
As WC Fields used to say, "Go Away Kid You Bother Me"
nania said:
Go to http://www.ixys.com/Appasp/pdpgsd01.asp and look at the data sheets. The part he is talking about is there. If one of you would actually give an actual part number this wouldn't be confusing.
Yes, I have thoughts on higher voltage parts.
Consensus on what about dual unit diodes and bridges? How are you matching diodes? What parameter are you matching them for? There tradeoffs in price and power dissipation for multiple diode packaging verses single diodes. Very few high current schottys and FREDs are available in bridges. They are designed for switching power supplies.
How is heat an issue with sufficient heatsinking? Doesn't the question contain the answer? I suppose you'll want to know what the four most important specs for choosing a diode are.......
As WC Fields used to say, "Go Away Kid You Bother Me"
Attachments
as Fred here.Fred Dieckmann
Well, I suppose you could test the rectified voltage under changing loads in dual mono configurations, that would be one way. I don't have any experience with these diodes yet so I don't know anything about them except from what I read in the specs. I believe the ultrafast diodes from IXYS are already in a bridge package so it wasn't unreasonable to ask about the possibility of waiting for the same thing to happen in the GA line. Still stinging from the tongue lashing you got in the transformer thread Fred? Don't be bitter, I'm sure that you'll find something to pick on sooner or later but I don't think this is it
The point I was trying to bring out was the possibility of getting a better result from the aforementioned ultrafast bridge part than with the GA separates (part number DSGK40-018A and DGS20-018A for those not yet up to speed). So Fred has thoughts that he doesn't want to share yet. Well, considering how he takes every opportunity to jump down anyones throat who might sound like they're not up on the latest new knowledge, I suppose he has to be real careful about looking a fool lest he gets shot down by the waiting hordes of the previously insulted. I still love you Fred. I just try to think of you as the parapalegic that Mr. Rogers sang to:
It's you, I like...not your fancy chair...
Well, I suppose you could test the rectified voltage under changing loads in dual mono configurations, that would be one way. I don't have any experience with these diodes yet so I don't know anything about them except from what I read in the specs. I believe the ultrafast diodes from IXYS are already in a bridge package so it wasn't unreasonable to ask about the possibility of waiting for the same thing to happen in the GA line. Still stinging from the tongue lashing you got in the transformer thread Fred? Don't be bitter, I'm sure that you'll find something to pick on sooner or later but I don't think this is it
The point I was trying to bring out was the possibility of getting a better result from the aforementioned ultrafast bridge part than with the GA separates (part number DSGK40-018A and DGS20-018A for those not yet up to speed). So Fred has thoughts that he doesn't want to share yet. Well, considering how he takes every opportunity to jump down anyones throat who might sound like they're not up on the latest new knowledge, I suppose he has to be real careful about looking a fool lest he gets shot down by the waiting hordes of the previously insulted. I still love you Fred. I just try to think of you as the parapalegic that Mr. Rogers sang to:
It's you, I like...not your fancy chair...
SAY WHAT?
Hi,
Such as?
Nania, for the record: it's very hard to fault Fred in this department.
We had some minor e-mail exchange on this topic, which I still have to answer if needed.
Nonetheless it seems you're grasping at straws here...I haven't seen any inconsistencies in what Fred said in that thread other than my BW disagreement for power xformer duty.
Fred galantly explained that his major experience was with pulse xformers in digital circuits which happen to be way out of my territory.
Although after having read some docs, I'm learning and now see what he meant.
Why don't you guys read the pointers you're given rather than discussing things ad nauseum?
Invest in some books, read the damn things and make an effort instead of sucking on other people's knowledge for a change.
Cheers,
Hi,
Such as?
Nania, for the record: it's very hard to fault Fred in this department.
We had some minor e-mail exchange on this topic, which I still have to answer if needed.
Nonetheless it seems you're grasping at straws here...I haven't seen any inconsistencies in what Fred said in that thread other than my BW disagreement for power xformer duty.
Fred galantly explained that his major experience was with pulse xformers in digital circuits which happen to be way out of my territory.
Although after having read some docs, I'm learning and now see what he meant.
Why don't you guys read the pointers you're given rather than discussing things ad nauseum?
Invest in some books, read the damn things and make an effort instead of sucking on other people's knowledge for a change.
Cheers,
The parts I was talking about were DGS 10-018A and DGSK 20-018A. I priced the DGSK 20-018A and they are $16.50 each in quantities of 50. Yikes! When using 8 of the single design or 6 of the dual in a dual-bridged design, this is a lot of money for just a portion of the power supply.
I'm trying some MBR20200CT (I trust this identifier is this sufficiently lucid) made by ON-Semi. They are dual Schottkys rated at 200V and 10A per leg. V(F) is about 0.65V at 50 degrees Celsius and 3A of current. They were about $1 each.
I looked into the articles you referenced, Mr. Dieckmann, and I'll give some snubbers a try.
Regards, Robert
I'm trying some MBR20200CT (I trust this identifier is this sufficiently lucid) made by ON-Semi. They are dual Schottkys rated at 200V and 10A per leg. V(F) is about 0.65V at 50 degrees Celsius and 3A of current. They were about $1 each.
I looked into the articles you referenced, Mr. Dieckmann, and I'll give some snubbers a try.
Regards, Robert
fdegrove
Since when did the exchange of information become "sucking on other people's knowledge"? I think you do this forum a great disservice with this attitude and hope you don't really mean to promote it. We are here to share our knowledge and experiences whatever they may be. A good teacher learns just as much from his students "stupid questions, notions and observations" as from his research. Aren't you sucking off someone else's knowledge when you read their books or theorums? Please explain the difference. Ask Fred how much he sucked off Nelson Pass or Pete Goudreau or Steve MacCormack?
Snubs and snubbers
I don't claim to know it all. The reason I put so many references on the forum is to provide access to information written by people who are experts. Yes, I have thoughts I don't want to share yet. I am still doing research, doing simulation, and making measurements. How does one give an answer to such a probing question as:
"Will the heat be an issue in a typical Class A application with sufficient heatsinking?"
For all the Shottky gurus that talk about the lack of reverse recovery effects, why does IXYS refer to the GaAs as having "a soft turn off"? For those who to compare the junction capacitance figures, note how it is specified. 22 pF at a reverse voltage of 150 volts is about 200 pF for the low reverse voltage as the diode first turns off. There is more to all this stuff than reading a few numbers at the top of the data sheet. Like with contracts, it pays to read the fine print. A few application notes wouldn't hurt either.
Dieckmann / does not suffer fools gladly
I don't claim to know it all. The reason I put so many references on the forum is to provide access to information written by people who are experts. Yes, I have thoughts I don't want to share yet. I am still doing research, doing simulation, and making measurements. How does one give an answer to such a probing question as:
"Will the heat be an issue in a typical Class A application with sufficient heatsinking?"
For all the Shottky gurus that talk about the lack of reverse recovery effects, why does IXYS refer to the GaAs as having "a soft turn off"? For those who to compare the junction capacitance figures, note how it is specified. 22 pF at a reverse voltage of 150 volts is about 200 pF for the low reverse voltage as the diode first turns off. There is more to all this stuff than reading a few numbers at the top of the data sheet. Like with contracts, it pays to read the fine print. A few application notes wouldn't hurt either.
Dieckmann / does not suffer fools gladly
Teach And You Will Learn.
Hi,
Seems this is your attitude, not mine...so far I learned very little here.
Maybe you're willing to learn but I fail to see how what Fred said in the xformer thread got him a bashing for his theory in that department?
Allow me to say so but I doubt very much Fred is " sucking " off any member's knowledge in fact I think Fred has added more than you can possibly imagine.
As far as I'm concerned I did pretty much the same ten to fifteen years ago already and I'm still willing to help anyone out, great attitude isn't it?
Nania, I just didn't like your tone against Fred...after all he does nothing but give pearls to the swine.
Pretty noble in my book.
Suck it and see,
Hi,
Seems this is your attitude, not mine...so far I learned very little here.
Maybe you're willing to learn but I fail to see how what Fred said in the xformer thread got him a bashing for his theory in that department?
Allow me to say so but I doubt very much Fred is " sucking " off any member's knowledge in fact I think Fred has added more than you can possibly imagine.
As far as I'm concerned I did pretty much the same ten to fifteen years ago already and I'm still willing to help anyone out, great attitude isn't it?
Nania, I just didn't like your tone against Fred...after all he does nothing but give pearls to the swine.
Pretty noble in my book.
Suck it and see,
of pearls and swine
Fred Dieckmann
fdegrove
Enjoy your sycophancy. As far as my comments to Fred; I don't believe he's as sensitive as you might think and I rather believe he enjoys the row. Fred is like any good oyster and he will give up some beautiful pearls only when exposed to the right irritants. Conversely, handling him will occasionally get you a squirt in the eye.
A god holds no gods in reverence and no one man is a god. Everyone is made in God's image.
Fred Dieckmann
Nice shot Fred. Taken out of context like that the question does look pretty silly but the implication of the question was the possible effectiveness of a premanufactured bridge in comparison to discreet parts.
fdegrove
Enjoy your sycophancy. As far as my comments to Fred; I don't believe he's as sensitive as you might think and I rather believe he enjoys the row. Fred is like any good oyster and he will give up some beautiful pearls only when exposed to the right irritants. Conversely, handling him will occasionally get you a squirt in the eye.
A god holds no gods in reverence and no one man is a god. Everyone is made in God's image.
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