S-100 power supply transformer

Brent Hilpert hilpert at cs.ubc.ca
Thu May 21 01:30:49 CDT 2009



dwight elvey wrote:
> 
> ----------------------------------------
> > Date: Wed, 20 May 2009 15:07:57 -0700
> > From: hilpert at cs.ubc.ca
> > To: General at invalid.domain
> > Subject: Re: S-100 power supply transformer
> >
> > A slightly different take on this transformer requirements issue..
> > Hammond used to (perhaps they still do) provide a piece of paper with every
> > transformer, listing part numbers and specs. Included on the paper was a table
> > for voltage and current factors for basic rectifier/filter circuits: (extract)
> >
> > Rectifier Filter Voltage Current VA
> > ------------------- ------ ------------------ ---------------- -----------------
> > Half-wave cap in DCV = ACV * 1.16 DCA = ACA * 0.38 DCVA = ACVA*0.44
> > Full-wave center tap cap in DCV = ACV * 1.25/2 DCA = ACA * 1 DCVA = ACVA*0.63
> > Full-wave bridge cap in DCV = ACV * 1.25 DCA = ACA * 0.56 DCVA = ACVA*0.7
> >
> > AC values are RMS; VA figures I added in.
> >
> > They don't say precisely how these figures were arrived at, but reality is a
> > little different than theory (e.g. 1.25 vs 1.414 for the voltage output from
> > the filter, don't know whether that's reduced due to R losses or an average
> > with ripple under load).
> >
> > I take it these values were provided as guidelines, as complete design takes
> > into account C size, tolerable ripple, etc.
> >
> > --
> >
> > TI published "The Voltage Regulator Handbook" in the 70's, which covers a lot
> > of design issues for linear power supplies. Even it references a design
> > procedure from 1943 (Schade graphical techniques) for the rectifier/filter design.
> 
> What voltages were they talking about for these types
> of numbers?
>  The 1.414 number is the best case. allowing some for the diode
> and as you save, expected ripple.
> Dwight

They came in the box with Hammond's low-voltage transformers (3 to 100VAC):
165,166,167 series.
It may be that there is some specificity to Hammond's design characteristics. I
mention them as an example of real-world relationships, and that there is some
derating of the VA capability of the transformer when used in these circuits.



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