diyAudio - Uncategorized
Go Back   Home > Forums > Blogs > bwaslo
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
Uncategorized Entries with no category

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 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:	90
Size:	47.3 KB
ID:	2213   Click image for larger version

Name:	Two BJTs in Parallel.png
Views:	82
Size:	7.1 KB
ID:	2214   Click image for larger version

Name:	Current Hogging Prediction.png
Views:	94
Size:	17.4 KB
ID:	2215  
Attached Files
File Type: zip Current Hog Calc (27.8 KB, 34 views)
bwaslo's Avatar
diyAudio Member
Posted in Uncategorized
Views 456 Comments 0 bwaslo is offline

Ground loop noise, why it is and what you might do about it

Posted 18th January 2016 at 11:37 PM by bwaslo

I recently was motivated to figure out numerically what might be happening when you get hum out of your power amplifier only when connecting other cables to it. And why a fix I sometimes use works so well.

Before you go blowing your budget on expensive audio isolation transformers, please take a look!

Hope someone finds this useful.

bwaslo's Avatar
diyAudio Member
Posted in Uncategorized
Views 1062 Comments 2 bwaslo is offline
Hide this!Advertise here!

New To Site? Need Help?

All times are GMT. The time now is 09:15 AM.

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