self powered limiter for classD - diyAudio
Go Back   Home > Forums > Amplifiers > Class D

Class D Switching Power Amplifiers and Power D/A conversion

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 15th September 2014, 07:40 PM   #1
diyAudio Member
 
Join Date: Oct 2007
Default self powered limiter for classD

below an idea for a simple limiter consisting of a one-shot and an opto LDR.
the supply is derived from the same PWM stream. the inductor limits the peak current in the diodes and is set to resonate above the max PWM freq.

the oneshot is set at 10usec
Attached Images
File Type: png classD_limiter.png (43.6 KB, 97 views)

Last edited by basreflex; 15th September 2014 at 07:41 PM. Reason: added more detail
  Reply With Quote
Old 15th September 2014, 09:02 PM   #2
diyAudio Member
 
Join Date: Dec 2003
Location: Munich
...promising.
IMHO next relevant step would be a simulation with closed system loop by adding the signal source and power amp and then analysing+tuning of the dynamic behavior of the full system.

And even more promising when you manage to translate it to a solution with the NE555...

Definitely an approach which is worth to examine. Keep on going.
  Reply With Quote
Old 15th September 2014, 09:29 PM   #3
diyAudio Member
 
Join Date: Oct 2007
I don't have a dynamic spice model of the nsl32 yet. I simulated an ucd type pwm using a single digital inverter with delay and vhigh and vlow at +/-80V; the LTC retriggerable timer is just easy , lazy and small. I built it on 1cm2. (w/o the inductor and coupling cap).
pict next time .. need to order the NSL32 (farnell) or the faster one RSL-32 RS2 at rs-components germany; strangely not available at rs-components spain. that faster rs2 may need additional time stabilization. i like the natural release time of the ldr cells.
  Reply With Quote
Old 16th September 2014, 10:00 AM   #4
diyAudio Member
 
Join Date: Oct 2007
found a vactrol VTL52 model that looked OK , only the ac impedance was hosed up by a 100nf cap across the LDR. changed it to 1p. here the sim using a burst with 10% duty and 0.3 amplitude ratio. schematic mostly in behaviourals. the sim time was taking some 6msec for the one-shot to stabilize its output, so I had to trick it not to start in full attenuation. bottom trace is the output saturating at 80V. top trace is the one-shot triggering the opto, and the trace restores undistorted after 1 cycle. this is why we worship ltspice...
I could have simulated this faster by making a one-shot triggering on a threshold set at 95% of the voltage supply on each side. I like the simplified UCD amp behavioural, I found it somewhere on the web.
Attached Files
File Type: pdf ucd_limiter_feedback.pdf (226.1 KB, 12 views)
File Type: pdf ucd_limiter_feedback_schematic.pdf (37.7 KB, 14 views)
  Reply With Quote
Old 16th September 2014, 04:58 PM   #5
diyAudio Member
 
Join Date: Oct 2007
Default 555 version

and here is the 555 version; simulates the same; diodes bat40 or the like.
retrig is done by discharging the cap directly from the trig signal. best seems a slow version like the NSL32 not the SR2 or 3. interestingly the ground reference can be any line , gnd, neg vcc, pos vcc. at neg vcc you can combine it with a comparator and reference to sense the current in the bottom PWM fet for further overload lowZ protection.
Attached Files
File Type: pdf 555_limiter.pdf (28.1 KB, 14 views)
  Reply With Quote
Old 16th September 2014, 06:24 PM   #6
diyAudio Member
 
Join Date: Dec 2003
Location: Munich
Charming simple
From the parameters in your schematic I find a 3kHz signal repeating every 10ms, means you are assuming the DJ to play music with 6000 beeps per minute
That's a panic disco, nothing for old men...

Uncompressed the 3V input would try to chase the poor amp to 96V and the limiter reduces it to 80V. Really nice.
Does it also show such nice behavior at different input levels i.e. 3V and 5V and also different signal frequencies and repetition rates without needing to adjust any component values?
In my solution the challenge was to let the limiter behave well over a wide range of different input levels and finally forced me to settle a PD loop regulation characteristic, while allowing different signal frequencies and repetition rates was simple.

P.S.
Your description of the Vactrol model appeared somehow familiar - I guess I used the same model from the WEB in my limiter simulations.
Spice Component and Circuit Modeling and Simulation
  Reply With Quote
Old 16th September 2014, 07:02 PM   #7
diyAudio Member
 
Join Date: Oct 2007
actually I changed/cheated the recovery time of the vactrol to speed up simulations. I had 17Gb output on a 10ns max timestep total 200msec sim. took a few hours on a 6-core intel. the dynamics could be run simpler by triggering a oneshot or compare on either end of the amplitude. the nice thing is that the one-shot triggers before actual clipping occurs. I'll redo the sims this way ..
  Reply With Quote
Old 16th September 2014, 07:55 PM   #8
diyAudio Member
 
Join Date: Oct 2007
Default tjsak-boom dynamics

this is a behavioural of the vactrol plus the one-shot implemented as a simple . window detector. I don't trust the actual dynamics; especially the attack time is no properly modeled. I found the file on www.fullnet.com/~tomg/VTL5C2.ZIP
remove the 100nf across the ldr ...
anyway feel free to goof around with this schematic .. play with the params ..
Attached Files
File Type: pdf dynamics_limiter555_feedback.pdf (28.8 KB, 16 views)
  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
DIY solar powered-battery powered-mp3-mini boombox thingy thetonywarren Class D 14 21st July 2014 01:25 PM
My first battery powered classD amp Corpius Class D 0 11th September 2012 08:23 AM
Want to build Unusual high powered battery powered headphone amp (and equalizer) bakalorz Headphone Systems 5 10th September 2012 03:17 AM
ClassD using LM311 lumanauw Class D 2 27th August 2007 08:33 PM
New to ClassD DarkOne Class D 2 24th September 2006 04:11 PM


New To Site? Need Help?

All times are GMT. The time now is 08:49 AM.


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