[Amps] Switching Power Supplies

[Tony King - W4ZT]

I think this was meant for Steve ;)

Will Matney wrote:
> Tony,
> 
> What is the waveform coming out? Is it a square wave, or is it a
> modified sine wave (a stair steeped square wave that supposed to
> mimick a sine wave)? If it were me, I'd want the square wave, rectify
> it, and then filter it well. All older modile tube amps worked this
> way, so did automotive radios that used a vibrator, and later semis
> to switch with. One needs to rectify it first, then filter it
> thoroughly the same as any other supply. In your case you'd probably
> be using a choke instead of a transformer, or will you be switching a
> transformer? There's several ways to set these up. In any instance,
> the weight savings is due to using a higher frequency.
> 
> Best,
> 
> Will
> 
> *********** REPLY SEPARATOR  ***********
> 
> On 7/14/06 at 2:56 PM Tony King - W4ZT wrote:
> 
>> Tom W8JI wrote: <snip>
>>> I can't imagine why an amateur would want to use a switching
>>> supply for a filament. What reason is there to do that?
>>> 
>>> 73 Tom
>> Tom,
>> 
>> The reason I chose a small switcher for my filament supply was to 
>> provide a stable DC filament voltage over changing input line
>> voltages. The switcher I found was a fully shielded commercial
>> variety that appears to be relatively RFI free, weighs less than
>> the transformer normally used and generates none of the heat an
>> analog regulator produces.
>> 
>> My experience with switchers may be limited compared to others but
>> most of the problems I have seen have been noise coupled to and
>> radiated by the incoming power line. The switcher for the amp
>> filament has an output which is very clean on the scope over
>> varying loads and input voltages. At the same time, there was very
>> little detectable RFI from the line cord sniffing across the HF
>> bands.
>> 
>> Well built switchers do exist but it certainly demands a proper 
>> application of that technology as you pointed out with the coupling
>> in the ICOM and MFJ examples.
>> 
>> Thanks for your comments.
>> 
>> 73, Tony W4ZT