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

TL431 Question
TL431 Question
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
Thread Tools Search this Thread
Old 5th March 2006, 04:22 AM   #1
vectorplane is offline vectorplane  United States
diyAudio Member
vectorplane's Avatar
Join Date: Nov 2005
Default TL431 Question

I am using a TL431 for analog control of a 2-switch forward SMPS.
This supply works, and puts out 15V at up to 10 Amps +.

(This is a PC supply on which I removed the --impossible to modify-- analog control circuit and replaced with a 431, then rewound the trafo secondary for 15V.)

The 431 blows once every 20 times or so I turn the SMPS on.

The current into the REF pin is less then 1 mA, and the Cathode current is limited to safe levels by 1K resistors.
Both the REF and the cathode of the 431 are fed from the output filter capacitor node, after the inductor.

But the peak secondary voltage is 60V with a duty cycle of 25%.

I am wondering if, in the first moment during turn-on, the 431 may briefly see the full 60 V on the secondary, until the feedback loop has had a chance to start working??

If that is the case,
it means that the 431 could not be used with peak secondary voltages higher than 36V, without some kind of zener level shifter.

  Reply With Quote
Old 5th March 2006, 05:49 AM   #2
apassgear is offline apassgear  Mexico
diyAudio Member
apassgear's Avatar
Join Date: Nov 2002
Location: Viņa del Mar, Torreon
A schematic would be helpful to give some comments.
  Reply With Quote
Old 5th March 2006, 11:47 AM   #3
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
As you have mentioned, the most probable cause for the TL431 blowing is transient output overvoltage when the SMPS is turned on. This is a serious problem because it may not only blow TL431 references but also output capacitors and whatever load you have connected to the output at power-on.

You have to check output behaviour with oscilloscope (digital storage mode is preferred for slow measurements) and improve your circuit until no overvoltage ocurrs both at turn-on and during the worst case load transient (full load switched abruplty to no load). If the output filter is too peaky, either increasing output capacitance or inductor resistance will help to damp it, altough feedback should be able to correct the effects of peaking to a great extent.
  Reply With Quote


TL431 QuestionHide 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
What's really going on in that TL431 jackinnj Power Supplies 6 1st December 2012 11:53 AM
TL431 and SMPS Question pftrvlr Power Supplies 1 23rd July 2008 10:38 PM
Need help understanding TL431 Archwn Power Supplies 33 21st May 2008 09:57 AM
help understand the TL431 jarthel Parts 6 1st October 2006 10:09 AM
Tl431 sparkle Digital Source 11 22nd February 2004 10:10 PM

New To Site? Need Help?

All times are GMT. The time now is 06:45 PM.

Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 16.67%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.
Copyright ©1999-2017 diyAudio