I'd like to replace my 7805 with a 5v out switching regulator. My inputs will likely not be outside of 7-12v and I certainly do not need more than 1 amp any time soon. So I'm wondering if I should go with an IC or use transistors to make the cheapest switching regulator possible. I'm hoping less than 2 or 3 dollars. A specific part number or schematic would really help me out.
Thanks

 

Cheapest would be a 555 timer and discrete driver cranking a cheap buck regulator, but it's not that easy. The easy way would be an LM2575.

 

Find a 5V switching supply used to power consumer electronics. You can find them at electronic surplus stores or second hand stores for less than $5.

 

Ill go with the LM2575... Thanks!

 

The cheapest switch regulator as per me is MC34063A.Its a 1.5 A, Step-Up/Down/Inverting Switching Regulators.

Good Luck

 

MC34063A looks a bit more complicated but Ill keep it in mind for the future... Thanks!

 

The cheapest switching buck regulator is probably this;
http://www.romanblack.com/smps/smps.htm

in quantity you can get the 2 transistors and zener diode down to a few cents each.

 

i like the previous link, but if you prefer ready device, check this one out:
http://canada.newark.com/murata-pow...lar Products&MER=PPSO_N_C_EverywhereElse_None

it is meant to replace 7805, has 1.5A output and it is under $5 (about 3x the cost of discrete version).

 

The cheapest switching buck regulator is probably this;
http://www.romanblack.com/smps/smps.htm

in quantity you can get the 2 transistors and zener diode down to a few cents each.

This is pretty cool, I might give it a try too.. Thanks.

 

Question for THE_RB:

I don't expect LDO but this looks so simple and neat, it got me curious. Did you try it at different supply voltages? What is reasonable range?

regards

PM

 

Yep it works for a wide range, and that is one of its big advantages with the right Q1 transistor you can use it for a higher voltage input like 60v or 70v in 5v out, a range very hard to find in cheap SMPS chips.

Resistor choices are important if you change the input voltage range especially if you want to keep efficiency quite high. For that reason it's not a great SMPS where the input voltage varies within a large range. However that can be fixed easily enough by adding a 3rd transistor to keep Q1 base current constant (when on).

People have built the 2 transistor version to work from 110v mains input (170v DC) with the right resistors and a high voltage Q1. However I won't publish details of a 170v version due to forum regulations and safety issues. If someone is a professional who is allowed to work with mains equipment then they are capable of working out the parts values themselves. AND even then it means that every part of the circuit would be considered live at mains potential and possibly lethal. So don't do it.