I am planing to design an SMPS using μA 7840 IC.

I have a schamatic from a textbook (Op-Amp and Linear IC - Gaiakwad).

What I understand is that SMPS have an advantage of small size. But the datasheet shows that the SMPS IC requires a DC bias. Where do I get this DB bias from? A simple rectifier or a linear regulator.
Should I have to use a linear regulator, There shall remain no purpose of using an SMPS IC.

How exactly is the SMPS to be designed?

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Bharath Bhushan Lohray.
M.Sc. Electronics.

 

ur datasheet not attached..

ok after going thru the manual of the chip , i think that the 'bias' ur refering is the power supply (Vin) to the IC itself.. and that can be unregulated..many sample ckts are given in the manual itself,and that is self explanatory

 

This part is a switching _regulator_ meaning it efficiently converts the input voltage & regulates it with a switchmode design. The switching tran is built into the device so you have to observe the maximum load current this part can switch. You dont need to supply a regulated DC to this part, so you wont need a linear regulator. IMO, just rectify & smooth the AC with a capacitor.

 

Okay the data sheet is sttached.

But the internal block diagramme shows nothing of internal transformers.(Is that what you ment by "switching trans")

Attached Files

lm78s40_345.pdf (289.8 KB, 28 views)

__________________
Bharath Bhushan Lohray.
M.Sc. Electronics.

 

No, he meant 'transistor'.

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PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

I was told on edaboard that 78S40 is an obsolete device.

I was suggested LM2575, LM2576 and L4978

Hoever I have ordered it... So what can I do about it? Will using this device help me gain some useful bit of knowledge in SMPS design?

My key fascination about SMPS is it's size and DC / DC conversion capability(especially step up) and high efficiency. These are all the features I would like to get hands on experience in designing. How can I proceed?

__________________
Bharath Bhushan Lohray.
M.Sc. Electronics.

 

after viewing the 2576 datasheet i find that the compenent count of this ckt is lower than with the other..

if u have ordered the prev one.. go for it..at least .u may need more debugging (which means more knowledge) and u have more scope of adjusting the components and see the o/p

 

IMO, the best way to get first hand experience with SMPS design is to do one yourself. This does not include using pre-packaged switching regulators. I'm talking discrete parts including your own PWM driver if you desire. At the very least, you will have a new appreciation for what the vendors accomplish with these highly integrated DC/DC modules.