9v ac transformer choice

I'm looking for a 9v transformer that I can use as my ac voltage reference that I can wire directly to (I want to put this in a case with other components, and don't want to have to plug the transformer directly into a 13a socket).  Most I see have dual secondaries, either separate or centre tapped. 

If I don't load the secondaries that I'm not using for the the reference, and leave unconnected, will that affect the waveform?  

Also, will a slightly larger transformer than what would be required by just looking at the current requirements give a better shape waveform?

 

Thanks

Lloyd

Robert Wall's picture

Re: 9v ac transformer choice

If I don't load the secondaries that I'm not using for the the reference, and leave unconnected, will that affect the waveform?  

It should not.

Also, will a slightly larger transformer than what would be required by just looking at the current requirements give a better shape waveform?

The current required is to all intents and purposes zero (0.1 uA or so). A larger transformer is likely to have better regulation (the voltage rise when unloaded). But much more importantly, get a transformer whose primary is rated correctly for your mains voltage (i.e. if you are in the UK, a 250 V primary will give you less distortion than a 230 V primary). You can always tweak the calibration or the voltage divider resistors if needs be.

 

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