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Design of an isolated dc-dc power supply

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Cecemel

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Hi,

I need a 100-150w isolated power rail.

Here’s how I would probably try to achieve this: drive a transformer with a half bridge and a 555 generated high frequency square wave, rectify the output of the transformer, add a capacitor, use a linear or switching converter to get a more stable output.

A few questions:

  • Is this a good way to do it?
  • Should I drive a transformer with a square wave? Won’t this have a negative impact on efficiency?
  • What frequency should I use? I was looking at this transformer but it doesn’t mention a frequency in the datasheet.
  • Is it ok to leave coils unconnected?

Thanks
 

i presume your power source is the mains.
What is your output voltage?
For you i would do a BCM Boost PFC followed by a two transistor forward converter....but it does depend on your vout
...power supplies >75w need power factor correction.
 

Hi,

Is this a good way to do it?
Possible, but no professional designer would do so. There are easy to use dedicated switching regulators ... with lots of additional features, optimized operation, tight specifications..

Every switching regulator manufacturer provides application notes telling you how to do it.
There are many thousands of design examples in the internet.
There are many discussions here in this forum ... and even more in the internet.
And there are ready to but power supplies of almost any configuration, quality and price. I assume there is almost no benefit in designing your own supply.

Klaus
 

Should I drive a transformer with a square wave? Won’t this have a negative impact on efficiency?
..That kind of describes how its done in an LLC resonant converter.....
A full bridge is a bit of a simpler way with square waves.
Try my course, below...the "topologys -hard switched" folder shows you the different ways to do it in simple annotated sims in the free download ltspice

https://drive.google.com/open?id=0B7aRNbu3Fes4TU92Mkw3YlA3ams

- - - Updated - - -

The transformer you show looks like a low power flyback transformer, i doubt it would be good for 150w.
You really need to know the core details from the datasheet....but the core type isnt even spec'd.
At 150w you need to be able to assess if you are in saturation or not...but without the core AL value, how can you find the saturation current..you cant.
....I(sat) = B.A.N/L

....But A = area is not even given

I assume there is almost no benefit in designing your own supply.
You are absolutely correct...theres everything available off the shelf, and mostly from China.......but i wonder....if a country just buys from China....how does it have enough indiginous staff available to design power supplies for its military?
...or supposing Airbus need power supplies designed.......they cant just import stuff from China for that...Airbus must build in-house, with EU citizens working in their EU factorys...but where do they get the power suply engineers from when the whole industry has been farmed oiut to China?
 
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Hi, thanks for your replies. Treez, I’ll look into the files you’ve sent once I’m at my laptop.
Application is a 64 cell li-ion active balancer, my plan is to step down the pack voltage from 190-260v (3-4.1 per cell) to about 5v while isolating it. Then use a buck converter to regulate balancing current before feeding it into the lowest voltage cell through a protection diode with a low forward voltage.

Do you have any recommendations for a transformer? I’m trying to keep the cost down and this seemed like quite good value.
 

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