offline SMPS with low "standby" power consumption

[schnell]

Hello,

Please can you tell me, I wish to do an isolated , offline SMPS (85 to 265VAC) , Power output = 34W.



It has one isolated output of 36V (+/-5%), 32W and one isolated output of 5V (+/- 4%) , 2W.

When the SMPS is in “standby” (i.e., its minimum load condition) the 36V rail is completely unloaded, and will be “shut down” completely, to save power.
However, the 5V rail , when the SMPS is in “standby”, will have a load on it of 200mW.

I have to design this SMPS so that it draws no more than 500mW from the mains when in standby.

If you know of a PWM controller which is suitable for this, please can you tell of it....i believe this is a very low requirement for power draw in standby

 

[jimkirk]

Many of the major chip makers have such chips. Here's one example

http://www.st.com/stonline/stappl/st/com/selector/index.html#querycriteria=RNP139=432.0

The 500 mW standby is part of the EU-2013 and future Energy Star requirements.

 

[LionelHutz]

A 2W, 5V converter that is 40% efficient at 10% load doesn't sound that difficult.

I guess if you have no SMPS design experience then I can see it being difficult.

TI sells a lot of interesting SWPS IC's and has a fair number of design notes. But then, look at a few of the main SMPS device players since they all have design notes and reference designs to give you starter ideas.

 

[schnell]

hi

i appreciate that it doesnt sound difficult, but it really is very hard..........because the controller's bias power draw becomes of the same order as the load power.

 

[zappedagain]

It sounds like you need a two stage design. One 5V regulator with low quiescent, and a second regulator for the 36V rail. The second regulator gets "shut down" when you go to standby.

John D

 

[DHambley]

At Apple, we used the Linkswitch PWM IC's from Power Integrations. These little guys did everything, internal 700V MOSFETs, extremely low power draw at idle, etc.
This sounds like what you might need for your 85-265VAC 34W.