Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 28th March 2005, 09:33 AM   #1
diyAudio Moderator Emeritus
 
lumanauw's Avatar
 
Join Date: Oct 2002
Location: Bandung
Send a message via Yahoo to lumanauw
Default Schottky diode as RE?

In EF output stage, usually we use 0.1ohm-0.5ohm/5watt resistor as RE/Rsource degeneration. Has anyone tried to put schottky diode (TO-220pack) in this place?

About diodes....IN4148, is it schottky or what? I cannot read it in its pdf datsheet.
  Reply With Quote
Old 28th March 2005, 09:46 AM   #2
diyAudio Member
 
nemestra's Avatar
 
Join Date: Jul 2002
Location: UK
Hi lumanauw

Douglas Self mentions the use of Schottky diodes for this purpose in his books and also in an article in Electronics World. His conclusions were that it would work but provide no benefit over resistors (if I remember correctly).

1N4148 are not Schottky, they are standard diodes (and not of use for Re replacements as their current handling is very limited)

James
  Reply With Quote
Old 28th March 2005, 09:58 AM   #3
diyAudio Moderator Emeritus
 
lumanauw's Avatar
 
Join Date: Oct 2002
Location: Bandung
Send a message via Yahoo to lumanauw
Hi, James,

I'm thinking about less variation in VBE multiplier if we use schottky in the place of RE.

John Curl writes that in uS time, current flowing in RE can reach more than 20A. If RE is 0.22ohm, it has 4.4V accross it alone (VBE doesn't have that value, the other transistor and its all driver must be off/heavily reversed at the time 20A passed).
If passed 20A , diodes wont give drop as big as 4V4, isn't it?

Inspired by NP who uses ordinary diode in parrarel with RE, so I think why don't just use schottky in this place, without any R? Schottky has very smooth characteristic compared to ordinary diode.

Also thanks about the info about IN4148. If it is ordinary diode (not fast recovery or soft recovery) why is the datashee, the TRR only 25nS, like fast recovery diode? Or is IN4148 is a fast recovery small diode?

Oh one more question. What kind of diode is LED? Is it fast/soft/schottky or ordinary diode?
  Reply With Quote
Old 28th March 2005, 10:00 AM   #4
ilimzn is offline ilimzn  Croatia
diyAudio Member
 
Join Date: Feb 2005
Location: Zagreb
Perhaps the only benefit would be that you could easily cool them if they are TO220 style packages. But I do find the idea interesting - what would be the principle behind it? Reduction in losses compared to resistors? It would certainly make I-V protection difficult to design...
  Reply With Quote
Old 28th March 2005, 10:08 AM   #5
diyAudio Moderator Emeritus
 
lumanauw's Avatar
 
Join Date: Oct 2002
Location: Bandung
Send a message via Yahoo to lumanauw
The main principle is that we have (much) less drop than resistor when big current passing to speaker. Speaker impedance usually written as 8ohm. But if we see the impedance curve, especially in 2 way or 3 way speakers driving real music, the noted 8ohm impedance is not flat. There are frequencies which the impedance is more than 8ohm, but there are also frequencies which impedances drops very low.

But the question : RE with resistor usually needed in parrareled output stages to balance the heat between each transistor (when output to speakers is big, heat needs to be spereaded evenly between each output transistors). If we put schottky in the place of RE, the balancing act is still there or not? If not, then it is dangerous using schottky for parrareled output transistors.
  Reply With Quote
Old 28th March 2005, 10:45 AM   #6
Mr Evil is offline Mr Evil  United Kingdom
diyAudio Member
 
Join Date: Aug 2004
Location: Behind you
Quote:
Originally posted by lumanauw
...Also thanks about the info about IN4148. If it is ordinary diode (not fast recovery or soft recovery) why is the datashee, the TRR only 25nS, like fast recovery diode? Or is IN4148 is a fast recovery small diode?..
It's a small-signal diode, so it's bound to be quite fast compared to big rectifier diodes, if that's what you're thinking. 1N4148 is the standard small-signal diode. If you see a diode somewhere, chances are it's a 1N4148.


Quote:
Originally posted by lumanauw
...Oh one more question. What kind of diode is LED? Is it fast/soft/schottky or ordinary diode?
LEDs are LEDs; they're not quite the same as other types. They aren't intended for rectification, so you'll never see their recovery characteristics specified. I expect Google will reveal information on how the various types of diodes work.
__________________
https://mrevil.asvachin.eu/
  Reply With Quote
Old 28th March 2005, 12:56 PM   #7
Eva is offline Eva  Spain
diyAudio Member
 
Eva's Avatar
 
Join Date: Oct 2003
Location: Near the sea
Send a message via MSN to Eva
According to some datasheet the 1N4148 is a small signal Schottky diode featuring 4pF capacitance and 4ns recovery time. Its only drawbacks are their limited voltage and current capabilities [75V and 300mA] and its high Vf drop [>650mV]

Anyway, I think it's a nice and very useful diode model for low current applications
  Reply With Quote
Old 28th March 2005, 01:27 PM   #8
Mr Evil is offline Mr Evil  United Kingdom
diyAudio Member
 
Join Date: Aug 2004
Location: Behind you
Are you sure? The datasheet(s) I have for 1N4148 call it a silicon switching diode (indicating a normal PN junction diode). The forward voltage drop graph certainly looks like a junction diode.
__________________
https://mrevil.asvachin.eu/
  Reply With Quote
Old 28th March 2005, 01:57 PM   #9
diyAudio Moderator Emeritus
 
lumanauw's Avatar
 
Join Date: Oct 2002
Location: Bandung
Send a message via Yahoo to lumanauw
Hi, James,

I just re-read my Doug Self book. I cannot find where he writes about schottky in the place of RE. Where / in what chapter is it?

Hi, EVA,

In some schematics, the signal are passed through IN4148 or LEDs. But I never see small signal passing thru Schottky. Why is that? ?Is schottky worse than IN4148 or LED in passing small audio signals?

In your opinion, LEDS similiar to what diode? schottky?fast/slow recovery or what?
  Reply With Quote
Old 28th March 2005, 02:07 PM   #10
diyAudio Member
 
nemestra's Avatar
 
Join Date: Jul 2002
Location: UK
Quote:
Originally posted by lumanauw
Hi, James,

I just re-read my Doug Self book. I cannot find where he writes about schottky in the place of RE. Where / in what chapter is it?

Hi lumanauw,

see Audio Power Amplifier Design Handbook, 3rd Edition, pg. 131-132.

James
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
40A 250V Schottky Power Diodes- Has anyone use in Power Amp to replace Diode Bridge? dtm1962 Solid State 10 15th September 2011 07:38 PM
Schottky diode bias pointy Tubes / Valves 10 5th April 2009 03:13 AM
Is SD a Schottky Diode in this schematic? jduffy Tubes / Valves 15 15th March 2007 11:23 AM
HI Voltage & Hi current Schottky diode for sale. ohynot Swap Meet 0 11th June 2004 07:41 PM
Schottky diode bargain dhaen Parts 0 7th November 2003 05:39 PM


New To Site? Need Help?

All times are GMT. The time now is 11:57 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2