[ARC5] Transformers in low-voltage to B+ supplies

[J Mcvey]

 Why use a trapezoidal wave? Square waves are more efficient, but create more harmonics that need suppressing
The iron core will confine you to lower frequencies The advantage to higher frequencies comes with using a small light weight ferite core.

    On Wednesday, October 26, 2022 at 09:09:28 AM EDT, Bob kb8tq <kb8tq at n1k.org> wrote:  
 
 Hi

The reason you see square waves a lot is the power you dump
in the pass transistors running any other waveform. Dumping 
2/3 of the power into heat tends to get messy in a number of ways.

Matching core material to frequency range is indeed part of this.
A few materials have a “couple of octaves” sort of range for best
performance with square waves. Others are in the “several decades”
range. Working out just what this or that part is without a data sheet 
is tough. 

One saving feature is that a whole lot of surplus comes out of places
that are into 60 KHz as their favorite frequency. Guessing that’s what
this or that eBay part is intended for is often the only rational way
to move the project forward. 

Transformers all have winding inductance. This *can* be measured
and it will give you something to go on in terms of low end. Cores
do saturate so inductance under load …. hmmm …. not quite as 
easy. 

Lots of fun ….

Bob

> On Oct 25, 2022, at 9:09 PM, Leslie Smith <lnsmith99 at gmail.com> wrote:
> 
> 
> Hello all:
> 
> I wish to build a lead-acid battery to B+ inverter using (probably) a conventional iron-core transformer.  Two configurations are generally seen in typical circuits.  I will describe these as "H" bridge and solid-state vibrator replacement.  The "H" bridge uses an untapped low-voltage winding; the vibrator circuits use a transformer with a center-tapped primary winding.
> 
> Since I can choose the switching frequency, and a higher frequency has some advantages, what limits the operating frequency?  Assume a conventional EI (or perhaps toroidal) core using common transformer iron.  (I assume the 'iron' used in most power transformer share a 'common' quality.)
> 
> I intend to feed 'the beast' with a trapezoidal wave-form not a sharp square wave.
> 
> Thanks for observations.
> 
> Leslie
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