Calculating transformer impedance

[Rusan]

Probably because they’re $25+ per piece.

Ouch!

Cheers

I was recently looking at the BUF634 for a possible upcoming project, and the price for the newer version SOIC-8 package has dropped to less than $4 USD.

 

[ricardo]

It might be higher than that. The OP measured the inductance at 1KHz. If the core material is iron and/or nickel based then its inductance will rise significantly at low frequencies.

Ferrous based transformer inductance varies even more with Level. This has been known from well before Williamson amp days. You might find some stuff in RDH but probably not, as the effect isn't amenable to analysis but may be 2x or more over your operating range.

What CAN be measured and specified reliably is the THD at a particular frequency and level. eg 3% THD @ 20Hz 10V.

Then there is a 'linear' relation at other frequencies & levels. eg the above would have 1.5% THD @ 40Hz 10V or 20Hz 5V etc.

Then you just have to make sure the inductance at a low level (when it is low) is OK for your load and frequency response requirement.

DC resistance of the windings is also a good clue to the designed impedance. A 'good' transformer may have DC = 1% of the winding impedance. But a cheapo one may have DC = 50% of the designed impedance.

 

[ruffrecords]

I was recently looking at the BUF634 for a possible upcoming project, and the price for the newer version SOIC-8 package has dropped to less than $4 USD.

Yes, the newish BUF634A is just £2.84 from Mouser.

Cheers

Ian

 

[amplexus]

Yes, the newish BUF634A is just £2.84 from Mouser.

Cheers

Ian

Much more reasonable!

I can’t imagine justifying $25 for a chip to do a job that a couple $1 op amps and some passives could do!