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Electronics => Beginners => Topic started by: fonograph on August 26, 2018, 06:22:58 pm

Title: Transformer output impedance
Post by: fonograph on August 26, 2018, 06:22:58 pm

Does 2:1 step up transformer double or quadruple the impedance? I am not sure but I think I read in book that it quadruples for every doubling of voltage,but when I think about it some time later,it seems wrong becose if we send same amount of power through double voltage,we only need to halve the current so just doubling the output impedance should be enough to avoid breaking the law of conservation of energy.

Title: Re: Transformer output impedance
Post by: HB9EVI on August 26, 2018, 06:55:18 pm

Keep Ohms law in mind:

sqrt(P/R)=I
and
sqrt(P*R)=U

resistance/impedance and power are in exponential relation

so a turn ratio of 1:2 leads to an impedance ratio of 1:4

Title: Re: Transformer output impedance
Post by: David Hess on August 26, 2018, 06:56:14 pm

The impedance is the voltage divided by the current.  A 2:1 step up transformer doubles the voltage and halves the current so:

2 / 0.5 = 4

So the impedance is raised by 4 times.

Title: Re: Transformer output impedance
Post by: fonograph on August 26, 2018, 07:00:14 pm

Ahhh yes  :palm:     I am embarrassed that I made such basic mistake,now it seems so obvious.