transformer size and frequency

Thread Starter

logicman112

Joined Dec 27, 2008
69
I have heard that to have lighter and smaller step-down transformers in a computer switching power supply , the current of 60 HZ converts to much higher.

How the size of a transformer depends on frequency?
 

mik3

Joined Feb 4, 2008
4,843
It can be proved mathematically but think of it logically. You have N primary turns and a core with cross sectional area A with an inductance L. If the transformer is operating at 60 Hz then a flux Ψ will flow through the core. If the frequency increases the current through the primary reduces and so does the flux level. To increase the new flux level to the flux level at 60 Hz, the core is made smaller (smaller A) and thus the inductance reduces. This increases the current and thus the flux level.
 

SgtWookie

Joined Jul 17, 2007
22,230
Current reduces because leakage flux increases , right?
The current is the same. The difference is the physical size of the transformer.

The small toroid is switched at a very high frequency compared to line voltage. That is why the relatively small toroidal transformer can achieve such high efficiency.
 

mik3

Joined Feb 4, 2008
4,843
Current reduces because leakage flux increases , right?
Flux is proportional to current. Imagine a big transformer with a high inductance and small one with low inductance.

To achieve the same current through them, the small transformer has to be operated with a higher frequency than the big one because of its smaller inductance (XL=ω*L).
 
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