More on Fav Designs - switchmode power supplies

[David Halliday (Volt Computer)]

> > What about switching supplies in analog designs? Too much voltage
> and
> > current ripple?
> 
> Voltage ripple, i.e. 100/120Hz ripple, can be reduced to an absolute 
> minimum in switch mode designs. Just a matter of good controlloop 
> design.
> Current ripple can be reduced with proper output filter design 
> containing extreme low ESR capacitors. But there will always be a 
> couple of mV's high frequency ripple on the output.
> 
> For symmetrical power supplies, you have to use hf-transformers with 
> multiple secondary windings, and in general, only one output voltage 
> can be fed back to the PWM. In that case there is usually some kind 
> of post regulation on the outputs necessary too.
> 
> [Dave Halliday]  these are all excellent design ideas!
> 
> 
> So to be short, using a switch mode power supply for DIY projects is 
> just too expensive. Besides that, these things are pretty complex to 
> design.  
> 
> [Dave Halliday]  I think that the question is more one of using
> computer surplus supplies and these have been designed without analog
> considerations.  With PC Clone supplies selling for $20 new, it would
> be tempting to be able to re-work one of them to give +/- 15 volts at
> a couple of amps - maybe a good design project...
> 
> Bye,
> 
> Daniel Schouten
> SMPS designer at TBS Electronics