2 transistor efficient voltage regulator

[fever]

hello all,

i was searching over net for some good and efficient SMPS design.
and i came across this page.
https://www.romanblack.com/smps/smps.htm

my doubts is is this good for some 200-300ma application.
iam building a circuit which uses 10 LED.each will be driven at 20ma so overall required current is 200ma + extra for the circuit to operation.

and how can i make voltage variable? imean for 9v,10v etc.is it the zener that makes it possible?

if u guys have any other ideas for SMPS design, pls do share.

 

[Papabravo]

Why would you be so skeptical? It appears to be a reasonable circuit.

 

[fever]

then how can i get variable voltage for this circuit

 

[Diver300]

The voltage on that circuit is set by the zenner. You can change that.

 

[Sceadwian]

The regulation isn't going to be very good, but it's about as simple a buck converter as you can make, regulation could be dramatically improved using an opamp and some feedback with an accurate voltage refrence.

 

[audioguru]

Why do you need a voltage regulator? LEDs work with current regulation, not voltage regulation.

LEDs in parallel blow up. Connect them in series and in series with a current-limiting resistor. Then the current is only 20mA and each LED has exactly the same amount of current.

Do you want to dim the LEDs? If they are in seies with only 20mA then the dimmer is just a pot and a transistor.

 

[fever]

yes.but my circuit involves some circuit and the LED's.for that circuit i need voltage regulation.

and say if i use parallel LED conection,will the current flowing to the each LED same?
if not this gives me difference in brightness right.

usually what i do is,i connect all the LEDs in parallel with separate resistor for each(using V=IR)

 

[Hero999]

For LEDs use the current limited version and remove the zener or keep it there if you want to limit the open circuit voltage for any reason.
https://www.romanblack.com/smps/a04.htm

What's your input voltage?

You're better off if it's not too high compared to the LEDs' forward voltage, for example if your power supply is 12V and your LEDs' Vf is 3.5V then connect five chains of two in series.