Re: Typical bandwidth of 60hz wallwart transformers

On Apr 22, 10:50 pm, Tony Williams <t...@xxxxxxxxxxxxxxxxxxx> wrote:
In article <462b72df$0$27027$4c368...@xxxxxxxxxxxxxx>,
Jim Flanagan <j...@xxxxxxxxxxxxxxx> wrote:

Hi -
I am going to be designing a 400hz 3ph test generator
(about 1W max) and want to use some 60Hz transformers
to use in a DC-AC inverter (linear). Would these
show a significant rolloff at 400Hz or is the bandwidth
OK for this application?

Avoid lamination transformers because they can
have a poor output impedance due to their higher
leakage inductance.

Toroidal mains transformers will work ok.

The flux density will be about 1/7th of what it
was designed for, so you can run what was a 115V
primary as a 160V secondary with no trouble.

I assume the OP is making a sine wave with a linear drive to the
transformer. The transformer may be enclosed within a feedback loop.
This would make the output impedance low at the frequencies below the
gain cross over point.

If this is the case, the laminated transformer would not be a big
issue. The gain cross over point could be at several KHz. He is only
drawing 1W from the supply so the load impedance will be quite high.
This would allow Xl to also be fairly high before it started to push
down the practical limit on the gain cross over.

The OP may want to consider placing a modest capacitor across the
secondary windings. This would make the high frequency impedance
lower at the cost of making the circuit resonate with the leakage
inductance. with a good control loop design, this would be a low Q
resonance.


.

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