Hi Sir I would Like to get variable voltage starting from 3 V to 9 VDc, With an input of 12V Dc. With 4 Amp Current limit. If you could provide me with schematics with excellent efficiency It would be really helpful to me. Waiting for your reply
Deepak Kamble

 

This was split from 12v to 5v DC high efficiency SMPS buck converter using 34063 IC.

Hijacks are not allowed on AAC, so now you have a thread of you very own.

 

Have you looked at the LM317 datasheet... It will probably work... Looks like figure 47 is just what you need, though it doesn't state the efficiency.

Heat dissipation will be an issue for you.

http://www.ti.com/general/docs/lit/getliterature.tsp?genericPartNumber=lm317-n&fileType=pdf

 

317 can't possibly provide 4A.

I recommend a 5A version of a simple switcher. You can go to TI's website and find there are many to choose from.

Here is one:

http://www.ti.com/lit/ds/symlink/lm2677.pdf

Use the adj version so you can adjust the output voltage.

 

Or if your lazy.

http://www.ebay.com/itm/4-5-30V-to-...675?pt=LH_DefaultDomain_0&hash=item3cda40c173

 

Here's another much like that one, but neither have an amp rating.

http://www.ebay.com/itm/DC-to-DC-co...r-power-supply-power-Converter-/350958556935?

 

317 can't possibly provide 4A.

No, BH, Figure 47 on the datasheet is exactly what the OP was asking for. A very elegant solution to create a switching supply from a LM317.

Figure 47. 4A Switching Regulator with Overload Protection​

 

Or if your lazy.

http://www.ebay.com/itm/4-5-30V-to-...675?pt=LH_DefaultDomain_0&hash=item3cda40c173

Amazing what you can buy for peanuts on ebay.

 

No, BH, Figure 47 on the datasheet is exactly what the OP was asking for. A very elegant solution to create a switching supply from a LM317.

Figure 47. 4A Switching Regulator with Overload Protection​

OK. Looks like something the marketing guy dreamed up after a five beer lunch. I would not use it for a variety of reasons, like there are much cheaper and easier ways that wouldn't be so large with so many parts.

Still can't believe you can buy a 100W DC-DC converter complete for $12 on ebay, but you can.

 

OK. Looks like something the marketing guy dreamed up after a five beer lunch. I would not use it for a variety of reasons, like there are much cheaper and easier ways that wouldn't be so large with so many parts.

Still can't believe you can buy a 100W DC-DC converter complete for $12 on ebay, but you can.

After you questioned the circuit I did some spice analysis... the regulation on this thing sucks... I agree with BH's suggestion to use a dedicated switcher... unless someone can see something that I'm missing. There are many chips available on the market... everyone makes several, and you can buy them on fleabay for a few bucks as already discussed.

I did just suggest it based on simplicity of using a linear regulator... but the circuit is pretty complex. A dedicated buck switcher will work better.

I am curious if anyone can see a way to improve the regulation of this circuit though... maybe I'll learn something.

 

...
I am curious if anyone can see a way to improve the regulation of this circuit though... maybe I'll learn something.

To make it behave better; but still not as good as a modern switcher chip:

Reduce the series resistance of the input supply V1, or reduce the esr of the input capacitor C1.

Reduce the Inductor L1 to 60uH, probably means that it is switching too fast.

Increase the capacitance of C6 to 1uF

Reduce the esr of C4.

 

Hmmm... tried all of those things (with the exception for C6 - I didn't have a C6 in my schematic) - the step load response did not improve to usable levels.

 

Try the circuit of figure 39.