Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Yet Another Soft Start Circuit
Yet Another Soft Start Circuit
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 1st July 2020, 09:40 PM   #91
spookydd is offline spookydd  France
diyAudio Member
 
Join Date: Apr 2012
Location: Florida & France
What's needed are a few cracker jack PIC programmers to help with this.
__________________
"Never trust an Atom!!! They make up everything!!!"
  Reply With Quote
Old 1st July 2020, 10:31 PM   #92
Mark Johnson is offline Mark Johnson  United States
diyAudio Donor
diyAudio Member
 
Mark Johnson's Avatar
 
Join Date: May 2011
Location: Silicon Valley
Yet Another Soft Start Circuit
Bryston did convert over to PIC chips in subsequent generations. Maybe you can find one of their ex-technicians to consult on your project.

_
Attached Images
File Type: png nnnnn.png (194.4 KB, 137 views)
  Reply With Quote
Old 2nd July 2020, 06:02 AM   #93
johnhenryharris is offline johnhenryharris  United States
diyAudio Member
 
Join Date: Nov 2012
Location: San Diego, CA
To answer whether a triac starts when a gate signal is present or does it start at the next zero crossing, from what I have read it starts at the moment the gate voltage is applied. The zero crossing situation is a red herring for a soft start, no matter where the sine wave is when you start, with discharged caps it will still have a large in-rush current. You need something to slow it down whether you PWM the gate of the triac or use NTC varistors, or some other method.

Last edited by johnhenryharris; 2nd July 2020 at 06:07 AM.
  Reply With Quote
Old 2nd July 2020, 06:35 AM   #94
rhythmsandy is offline rhythmsandy
diyAudio Member
 
Join Date: Aug 2012
optocoupler like MOC3049 fires right just above the zero crossing the wave. Hence the inrush will be minimal. I think that can be a better move than complex programmed PIC. Well I dont deny using PIC or any controller but the application is just to start hence even when used with pulse triggering the Triac there will be considerable amount of noise getting modulated isnt it?
  Reply With Quote
Old 2nd July 2020, 08:50 AM   #95
spookydd is offline spookydd  France
diyAudio Member
 
Join Date: Apr 2012
Location: Florida & France
Triggering the Triac right at the zero crossing is unlikely to minimize inrush current, as it's not at zero crossing that the current is low. For a transformer alone it would be more like some 45degrees "after" zero crossing.
Now the transformer being loaded with something having a very different behavior (cap banks), the combined behavior will be different, and there is a sweet spot to find, a certain delay after zero crossing, to use before triggering the Triac, to minimize the inrush current.
Then after that, pwm will keep it going but under control. The pwm can be done in a way to give the transformer less turn on time at first, and then progressively over time to give it more and more, until it's fully on.
That is what would keep inrush current under control.

And one more thing about that opto-coupler detecting zero crossing, it can also be double used as a "loss of mains" sensor, for double duty, handled by the PIC.

Finding ex-techs from bryston is a tall order. I have no idea how I could do such a thing.

But we have a pretty good idea of what's being done. We don't know which time delay would be optimal for first turn on after zero crossing, but I suspect bryston did more than just calculate, they must've done some experimenting to fine tune that delay, which is all part of the PIC programming. Once this is known and properly applied, then it should all be running smoothly and fully controlled by program.
__________________
"Never trust an Atom!!! They make up everything!!!"
  Reply With Quote
Old 2nd July 2020, 01:30 PM   #96
Mark Johnson is offline Mark Johnson  United States
diyAudio Donor
diyAudio Member
 
Mark Johnson's Avatar
 
Join Date: May 2011
Location: Silicon Valley
Yet Another Soft Start Circuit
When you begin to actively experiment with soft start circuits embedded within large audio power amplifiers, complete with heavy power transformers and enormous banks of electrolytic filter capacitors, I think you'll enjoy the work tremendously. The number of possible options to explore is large, with many opportunities for innovation. To name one example: soft start bypass. Bob Cordell's power amp textbook discusses this in section 19.8, and Douglas Self's power amp book discusses it in Chapter 26. Pictured below is an experiment performed using US mains (115 VAC) and a 125 Joule Inrush Current Limiter device (P/N SL22-20007). The bypass event is clearly visible!

_
Attached Images
File Type: png SS_and_bypass.png (52.7 KB, 104 views)

Last edited by Mark Johnson; 2nd July 2020 at 01:33 PM. Reason: bungled the attachment
  Reply With Quote
Old 2nd July 2020, 02:48 PM   #97
rhythmsandy is offline rhythmsandy
diyAudio Member
 
Join Date: Aug 2012
Quote:
Originally Posted by Mark Johnson View Post
When you begin to actively experiment with soft start circuits embedded within large audio power amplifiers, complete with heavy power transformers and enormous banks of electrolytic filter capacitors, I think you'll enjoy the work tremendously. The number of possible options to explore is large, with many opportunities for innovation. To name one example: soft start bypass. Bob Cordell's power amp textbook discusses this in section 19.8, and Douglas Self's power amp book discusses it in Chapter 26. Pictured below is an experiment performed using US mains (115 VAC) and a 125 Joule Inrush Current Limiter device (P/N SL22-20007). The bypass event is clearly visible!

_
Mark what happens when you try to turn on at zero crossing point. Do you have a graph for that?
  Reply With Quote
Old 2nd July 2020, 03:12 PM   #98
spookydd is offline spookydd  France
diyAudio Member
 
Join Date: Apr 2012
Location: Florida & France
A graph would be great to have. But this is highly likely to be different pretty much every time for every situation, with different cap banks, etc...
But if it was the transformer alone, with nothing to load it, it would be about 100% inductive and the core magnetization profile, which would mean turning on at zero crossing would be at the worst time, with maximum current.
Having cap banks at the other end though, changes things quite a bit, so the actual profile would be quite different from a simple transformer's.
A typical graph would still be nice to have to get a rough picture of how it works.
__________________
"Never trust an Atom!!! They make up everything!!!"
  Reply With Quote
Old 2nd July 2020, 03:33 PM   #99
Mark Johnson is offline Mark Johnson  United States
diyAudio Donor
diyAudio Member
 
Mark Johnson's Avatar
 
Join Date: May 2011
Location: Silicon Valley
Yet Another Soft Start Circuit
Emphasis added

Quote:
When you begin to actively experiment with soft start circuits ...
  Reply With Quote
Old 2nd July 2020, 09:29 PM   #100
tomchr is offline tomchr  Canada
diyAudio Member
 
tomchr's Avatar
 
Join Date: Feb 2009
Location: Calgary
Quote:
Originally Posted by spookydd View Post
Triggering the Triac right at the zero crossing is unlikely to minimize inrush current, as it's not at zero crossing that the current is low. For a transformer alone it would be more like some 45degrees "after" zero crossing.
Yeah. The transformer presents an inductive load at inrush when its magnetizing inductance needs to charge. In an inductor, the current is the integral of the applied voltage, so the current and voltage are 90 out of phase. This means that if you turn the current on at the zero crossing, you get the worst case inrush current.

Ametherm has an excellent note on how to design a soft start. Also the HP Journal from December 1982 is informative. I link to both in the References section of my Ultimate Guide to Soft Start Design. You'll likely find my guide useful as well.

Tom
__________________
Modulus-86, 186, 286, & 686: 40-240W (8Ω), <-120dB THD. HP-2 Headphone Amp: 660mW, <-130dB THD. Taming the LM3886.
Neurochrome : : Audio - www.neurochrome.com - Engineering : : Done : : Right
  Reply With Quote

Reply


Yet Another Soft Start CircuitHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
ESP Soft Start Circuit Alcaid Parts 5 29th October 2014 12:11 PM
Soft start circuit Diode Solid State 19 14th January 2013 07:38 PM
ESP soft start circuit 454Casull Power Supplies 19 29th May 2009 02:06 PM
soft start circuit tsearay Swap Meet 0 8th February 2007 01:18 PM
Soft start & Soft Switch circuit: can anybody help? m.parigi Solid State 95 22nd August 2005 03:32 PM


New To Site? Need Help?

All times are GMT. The time now is 02:26 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2020 DragonByte Technologies Ltd.
Copyright ©1999-2020 diyAudio
Wiki