Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

switch mode power supply design

Status
Not open for further replies.
darkstorm said:
is it feasible to switch 240 volts ac first to about 30 volts dc then down from this voltage to 5 volts.

Yes, but why would you want to? - why not just generate the 5V directly, or at least generate something about 9V and then use a 7805 to give 5V.
 
As Nigel said - why? - my guess is that you want two voltages available (30V and 5V). Is this correct?
 
Phasor said:
As Nigel said - why? - my guess is that you want two voltages available (30V and 5V). Is this correct?

That was my guess as well! - but if so, simply have two secondary windings on the transformer, or one tapped winding.
 
Well rectified AC or 240V will give 216V ~DC

IF 5V is wanted from such a high voltage then a duty of

5/216 = 2% which would be very hard to do (to derive a stable DC voltage)

Actually at work we looked into doing something like this. We need to derive a load of aux supplies: 28V, 15V 5V

from a bus of 270V the duty required was far too low (esp since our DC link can flucuate between 216 and 330V)

Our aim was to bring the voltage downto 50V, thus the duty would be alot higher (and thus controlable) the stability of such a rail would not be of too much concern since this crude 50V rail then fed more accurate 28V, 15V DC:DC SMPS

In this instance I would look into finding a XFMR to step the voltage down to give you some more duty headroom. IF the challence is to do a SMPS, have a look into creating the DC (as you have) then AC chopping it at alot higher frequency, thus a smaller XFMR would be needed then tap down to something more manageble in the XFMR

otehrwise yes 2stage converter
 
Its perfectly possible to make a SMPS that steps straight down from 240V ac to two outputs of 30V and 5V without having too small a duty, the duty length will depend upon the design of the inductor. The power supplies used in your computer do just that.

The problem with stepping down from 30V dc to 5V dc is that you will develop 25V across the voltage regulator, even for small currents there will be quite a lot of power dissipated in the regular.

As Nigel and Phasor have already suggested you would be better of using two secondary windings. If this isn't possible maybe you could use a seperate transformer for the 5V output.
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top