Typical bandwidth of 60hz wallwart transformers

Any 60Hz transformer should work well at 400Hz. The reverse is not true, however. This assumes a sine wave without a spray of higher harmonics from switching circuitry.

On Sun, 22 Apr 2007 10:36:13 -0400, Jim Flanagan Gave us:

At a one watt draw? I hardly think you need to worry about your losses in such a circumstance.

On Sun, 22 Apr 2007 10:36:13 -0400, Jim Flanagan Gave us:

Hand wound pot core transformers of about a 25 to 37 mm diameter should be much more efficient at your operating frequency, but at your power level, I hardly think worrying about a custom xfmr is needed.

Small 60 Hz transformers work pretty well to at least a kilohertz, at no more power than their original rating.

No problem, I have used el-cheapo transformers (designed for 50 Hz) several times at 400 Hz (for aircraft test sets) and variable from about 100Hz to 3-4 Khz. They work fine, even though I'm sure the efficiency drops off. At the other end of the scale, they also work OK down to 16 Hz, again I'm sure the efficiency drops off dramatically, but for the power I required (and your 1 Watt) it did not matter.

Barry

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.

--
Tony Williams.

I don't see any problem. I once measured the frequency response of a standard laminated core 12 V filament transformer, and the minimum loss was actually somewhere between 300 and 400 Hz. Also used the 12v center tapped secondary of a Radio Shack transformer as a 16 to 4 Ohm autotransformer for audio. It was quite usable, but sounded a bit mellow.

Tam

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.

I think it is good enough for voice and perhaps an AM radio but not really HiFi.

IIRC, the cutoff frequency on the transformer I used was about 4KHz. It was a 110-220 transformer but I was using the two primaries to make a 1:1 isolation transformer.

"MooseFET"

** Nonsense - a centre tapped or multi-tapped secondary winding ( when used as an auto-transformer) has wide bandwidth, more than the audio band for sure.

The bandwidth of a transformer has little to do with the core and everything to do with the arrangement of the windings - ie side by side on a divided bobbin is the poorest.

....... Phil

The small ones I tested as pretty good as audio output transformers, out to a few kilohertz were the side by side (split bobbin) EI core type.

** Not many consider a few kHz as "pretty good audio".

Even the cheapest 70 volt line transformers for BGM and voice PA are not made that way.

....... Phil

Fair enough. i meant their response was pretty good (amplitude and phase shift) out to that audio frequency.

Yes, of course.

I worked from the measurement I did. I found a bandwidth of about

4KHz on a transformer I used.

Agreed. Have you measured some numbers the OP can use?

Tranformer of unknown make: Numbers 19966624-41965DJ printed on the top. A little larger than typical wall wart xformer about 1.75 by 1.25"

6:1 ratio

Generator resistance: 8.6 Load resistance: 287

Freq Vp-p

100 2.0 1K 2.0 3K 1.80 5K 1.41 7K 1.30

"MooseFET" "Phil Allison"

** Bollocks.

** The OP has no problem with 400Hz.

........ Phil

"MooseFET "Phil Allison"

** Shame that is NOT an auto-transformer.

This is a typical multi-tapped tranny, with divided bobbin construction.

With the 0 volt used as common, the 7.5 volt terminal driven by an audio power amp and the 15 volt terminal loaded with 16 ohms - response tested flat from 15 Hz to 18kHz.

The -3dB point proved to be at 35 kHz.

QED.

Go away.

...... Phil

You said in another post that "The bandwidth of a transformer has little to do with the core...".

Just how little would the bandwidth be affected if your measurement were repeated with the core removed?

"Dr. Polemic Fucking Idiot "

** So go find that other post, read it very carefully & take account of the context.

Then go drop dead - you asinine prick.

........ Phil