Re: LF: How can you tell if a Class D amp output transformer is starting to saturate?

[N1BUG <paul@n1bug.com>]

I am still not sure whether I am using that equation correctly.

Chris, if you will forgive me for tagging along on your post, I'm
trying to get this equation sorted in my head. Put no faith in
anything I say with regard to this! ;-)

Andy, could you please check me out on this?

Let's use the case Chris asks about as an example.

Suppose I want to calculate the maximum RMS voltage to stay out of
saturation.

The manufacturer of the core states its Ae (equivalent cross
sectional area) is 1.58 cm^2. I believe that works out to 0.000158 m^2.

F = 137000

I do not know if I should be using 4 turns or 8 turns for the
primary. It's 4+4. I will assume 8.

Vrms = 4.44 * 137000 * 8 * 0.000158 * 0.1

Vrms = ~77V

Does that look right?

As for practical application I have no idea what this means. The
equation uses Vrms but we're talking about something closer to a
square wave than sine wave. But then it's not really a square wave
either...

Paul



On 05/03/2018 10:00 AM, Andy Talbot wrote:
> By measuring the voltage across the winding using a scope, then
> seeing what Bmax is using teh equation
> 
> Vrms = 4.44.F.N.A.B
> 
> F Hz     N turns   A core cross-sectional area in metres^2    B tesla
> 
> If B works out higher than about 0.1 for a ferrite core, then you
> are approaching saturation
> 
> Andy
> www.g4jnt.com <http://www.g4jnt.com>
> 
> 
> On 3 May 2018 at 14:46, Chris Wilson <dead.fets@gmail.com
> <mailto:dead.fets@gmail.com>> wrote:
> 
> 
> 
>     Hello LF'ers
> 
>     In  say a W1VD power amp, or in general, how can you test if the
>     output transformer is
>     starting to saturate please? Thanks.
> 
>     http://www.w1vd.com/137-500-KWTX.html
>     <http://www.w1vd.com/137-500-KWTX.html>
> 
> 
> 
>     -- 
>     Best regards,
>      Chris                          mailto:dead.fets@gmail.com
>     <mailto:dead.fets@gmail.com>