TL431 and SMPS Question

pftrvlr · 23rd July 2008, 07:57 PM

I have a few DVD SMPS that I want to use in other projects. Don't have much experience on the design of SMPS, just read a few short articles and studied few schematics.

The SMPS that I have has one TL431 - assuming used to regulate the output voltage. It has three outputs with different voltages. My question is like ths . If the 431 is monitoring only one output pin (I might be wrong on this one), how voltage on other pins can be stable if the current loads are all different?

carvinguy · 23rd July 2008, 09:38 PM

The TL431 could be using one or more voltages to set the regulation. It's possible to sum in all of the output voltages with different resistors into the TL431 to get the feedback.

Or... regulation is simply accomplished with the most heavily loaded output (3.3V? 5V? -not sure what the loads of a DVD player are) being sensed by the TL431 and the lightly loaded outputs (12V for example) being close enough due to the coupling of the secondary windings in the SMPS transformer. It's not going to stray much with a properly designed transformer. The key with this scenario is to sense the most heavily loaded output.

23rd July 2008, 07:57 PM	#1
pftrvlr diyAudio Member Join Date: Feb 2007 Location: SoCal	TL431 and SMPS Question I have a few DVD SMPS that I want to use in other projects. Don't have much experience on the design of SMPS, just read a few short articles and studied few schematics. The SMPS that I have has one TL431 - assuming used to regulate the output voltage. It has three outputs with different voltages. My question is like ths . If the 431 is monitoring only one output pin (I might be wrong on this one), how voltage on other pins can be stable if the current loads are all different?

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23rd July 2008, 09:38 PM	#2
carvinguy diyAudio Member Join Date: Jan 2005 Location: So. California, USA	The TL431 could be using one or more voltages to set the regulation. It's possible to sum in all of the output voltages with different resistors into the TL431 to get the feedback. Or... regulation is simply accomplished with the most heavily loaded output (3.3V? 5V? -not sure what the loads of a DVD player are) being sensed by the TL431 and the lightly loaded outputs (12V for example) being close enough due to the coupling of the secondary windings in the SMPS transformer. It's not going to stray much with a properly designed transformer. The key with this scenario is to sense the most heavily loaded output.

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