SMPS with controller IC too inefficient
SMPS with controller IC too inefficient
(OP)
Dear Engineers,
I am interested in re-designing an existing SMPS to make it more efficient and hopefully simpler to produce.
The existing SMPS runs off a battery and converts 8-30V DC to 5.6V DC. It is a non-isolated buck converter. There is no controller IC. -The control circuitry is all discrete and this is allegedly because using an SMPS controller IC would be less efficient than the discrete design.
I can't say too much but the power switch is a PNP transistor -again this is said to produce more efficiency than using a MOSFET. I haven't been shown too much but there was certainly a schmitt trigger in there using BJT's and a short circuit protection network using BJT's.
It certainly did not appear to be a quasi-resonant design and was reasonably simple.
Does any reader know of a simple Buck converter SMPS configuration thats very efficient and preferably fairly simple.
Output current is not huge...it just seems to be for some microcontroller chips etc.
I am interested in re-designing an existing SMPS to make it more efficient and hopefully simpler to produce.
The existing SMPS runs off a battery and converts 8-30V DC to 5.6V DC. It is a non-isolated buck converter. There is no controller IC. -The control circuitry is all discrete and this is allegedly because using an SMPS controller IC would be less efficient than the discrete design.
I can't say too much but the power switch is a PNP transistor -again this is said to produce more efficiency than using a MOSFET. I haven't been shown too much but there was certainly a schmitt trigger in there using BJT's and a short circuit protection network using BJT's.
It certainly did not appear to be a quasi-resonant design and was reasonably simple.
Does any reader know of a simple Buck converter SMPS configuration thats very efficient and preferably fairly simple.
Output current is not huge...it just seems to be for some microcontroller chips etc.





RE: SMPS with controller IC too inefficient
Moreover, efficiency at the component level is only marginally relevant. What is important is the OVERALL efficiency. Therefore, having some components being allegedly inefficient may not matter.
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RE: SMPS with controller IC too inefficient
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: SMPS with controller IC too inefficient
You can download their Switcher Cad that has all their switching controllers and run simulations.
You can also buy demonstration boards with most of their switching controllers on them to test or see how they would work in your application.
They have 22 that would probably work.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: SMPS with controller IC too inefficient
http://www.national.com/pf/LM/LM5007.html
This should also work.
http://www.national.com/pf/LM/LM25574.html
How efficient do you need?
What is your current efficiency?
RE: SMPS with controller IC too inefficient
Dan - Owner

http://www.Hi-TecDesigns.com
RE: SMPS with controller IC too inefficient
Linear parts ALWAYS cost more than National parts but Yep, they work really well and are most often in stock.
I recently ordered one of the demo boards from them, (in fact for that battery charger). They were adamant that they check stock since their in-house(linear) sales department has no stock, that they check with the manufacturing stock,(across the street). They had 250 demo boards in stock!! I was impressed.
I think Digikey also really hammers you on low count Linear products.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: SMPS with controller IC too inefficient
Dan - Owner

http://www.Hi-TecDesigns.com
RE: SMPS with controller IC too inefficient
RE: SMPS with controller IC too inefficient
I wanted a white led driver to run from batteries and be as effecient as possible.
I build it and got a solid 90% across wide variation in battery voltage.
That said it isn't cheap.
Use a mosfet instead of bipolar switch. At battery voltages the Vce is a large power loss. The FET with a low Rds on will have significantly lower switch loss.
Then use schottky diodes for free wheeling purposes. And then use an oversize inductor and switch at a low frequency. This reduces power sw loss and magnetic loss.
Just watch the primary loss areas. Power Switch and Magnetics.
RE: SMPS with controller IC too inefficient
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: SMPS with controller IC too inefficient
Cost is not the main issue here....volumes are small and reliability in its (possibly) relatively short life is more important, and of course efficiency.
The temperature in which this SMPS works can rise to above 150 degrees Centigrade. Due to its working environment, there is relatively little that can be done to cool it. I believe 150 degrees C is above most SMPS controller IC manufacturers' test data and so maybe thats another reason for using the discrete controller circuitry. -and sticking year after year with a design that has worked (i believe this SMPS was designed some 20 years ago). -It would be very expensive indeed and inconvenient if this SMPS failed in service.
RE: SMPS with controller IC too inefficient
Dan - Owner

http://www.Hi-TecDesigns.com
RE: SMPS with controller IC too inefficient
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: SMPS with controller IC too inefficient
That will certainly limit options.
You have never stated the important requirement: Current???
The LT1936H is probably your friend.
htt
Buy a reference design and give it a whirl. You may need to replace a few parts for higher temp operation. Or just try it and see if it works. You may need to change some of the other components for the higher temps for your fielded design.
ht
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com