diyAudio - Entries for January 3, 2017
Go Back   Home > Forums > Blogs
Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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
Old

Calculating ballast resistor values to to control current hogging in paralleled BJTs

Posted 3rd January 2017 at 07:32 PM by bwaslo
Updated 3rd January 2017 at 07:41 PM by bwaslo

I started a thread at http://www.diyaudio.com/forums/solid...t-hogging.html on this subject, and after some time and many helpful suggestions, here is the calculation I came up with.

The goal is to find out how large the ballast resistors must be to prevent current runaway and to control "current hogging" to a given limit. Current hogging is a phenomenon with bipolar transistors when operated in parallel in which the hotter of the set draws more current than the cooler one(s) and so heats up even further. The fix is to put series resistors ("ballasts") in the emitter circuits (see the drawing), but I've not been able to find anything published that says how to calculate the value of the resistors.

The model is for two BJT transistors, with their collectors and bases commoned and their emitters summed through individual ballast resistors. You need to know what the process-variation-caused...
Attached Thumbnails
Click image for larger version

Name:	Current Hogging Spreadsheet pix.png
Views:	72
Size:	47.3 KB
ID:	2213   Click image for larger version

Name:	Two BJTs in Parallel.png
Views:	64
Size:	7.1 KB
ID:	2214   Click image for larger version

Name:	Current Hogging Prediction.png
Views:	72
Size:	17.4 KB
ID:	2215  
Attached Files
File Type: zip Current Hog Calc v2.zip (27.8 KB, 24 views)
bwaslo's Avatar
diyAudio Member
Posted in Uncategorized
Views 291 Comments 0 bwaslo is offline
Old

Building a DOA SeNNator Headphone Amp

Posted 3rd January 2017 at 03:56 AM by disfunctionalshadow
Updated 3rd January 2017 at 03:26 AM by disfunctionalshadow

In a search to replace a modified SMSL headphone amp that I use at work, I decided to build a DOA SeNNator, a variant of the filtering headphone amp for the Sennheiser HD 650, published by Solderdude over at - diyaudioheaven along with measurements of the HD650's responses.

It's based on the "HD 650 SeNNator" and "SeNNator build tips" pdfs. In adapting the design, DOAs were used. An upgrade to the filtering caps from polyster to polypropylene. To the original circuit, circuits and design ideas from:

  • Sam Groner - +/-30mv DC offset adjust and DC bypass cap.
  • Layout idea lifted from Jeff Steiger's CAPI-2 Line Stage Amp, from Capi-gear.
  • DC filter from Collective Cases, reducing the numerous different electrolytic caps and upgrading the linear regs. from LM217/337 to LT1963/3015.

Minimized mechanical assembly, using the default PWBs available in Kicad, each channel and the DC filter/regulator boards are in a Euro card form factor...
Attached Thumbnails
Click image for larger version

Name:	DOA_SeNNator_HD6500001.png
Views:	79
Size:	638.3 KB
ID:	2197   Click image for larger version

Name:	DOA_SeNNator_97mv_afterCal_02Jan17.png
Views:	63
Size:	55.7 KB
ID:	2211  
Attached Images
File Type: jpg DOA_SeNNator_HD6500003a.jpg (100.4 KB, 51 views)
File Type: jpg DOA_SeNNator_HD6500005a.jpg (105.4 KB, 52 views)
Attached Files
File Type: pdf DOA_SeNNator_V1.5p.pdf (43.5 KB, 59 views)
diyAudio Member
Posted in Headphone Amp
Views 270 Comments 0 disfunctionalshadow is offline
Hide this!Advertise here!

New To Site? Need Help?

All times are GMT. The time now is 09:37 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright 1999-2017 diyAudio

Content Relevant URLs by vBSEO 3.3.2
Wiki