jkeny wrote:
OK, let me try to understand - the inductance is a measure of the transfer of power across the primary to secondary - the higher the inductance the better the transfer?
No, not quite. The inductance is parasitic - with a perfect transformer the inductance would be infinite and the only load the source would see would be the load impedance, transformed by the square of the turns ratio. With a real world transformer the inductance (its a shunt inductance, in parallel with the primary) isn't infinite so this means even with no load at all the transformer is going to draw current from the source. The current rises as the frequency goes down, in line with the impedance of an inductor. A 1H inductance represents about 300ohms reactance at 50Hz.
I'm trying to get my head around all the various specs of a trafo as regards their effect & significance for design
What have we got with trafos:
- inductance = power transfer?
- turns ratio = gain or reduction or none?
- wire size = current carrying ability
- core size = frequency response??
- core material = frequency response?
I know I've missed many..... copper losses, eddy currents, leakage inductance, more....?
Your equations are more in line with a transformer for power transmission, yet here we're dealing only with signals. So things look a little different
inductance = how heavy a load the source sees, particularly at low frequencies (bass)
turns ratio = how much load impedance transformation occurs
wire size = inversely related to the series resistance presented by the transformer
core size = sensitivity to hum pickup
core material = lots of factors relate to this including inductance and also stray capacitance
Losses are not of much interest in signal transformer applications (eddy currents are part of losses, ferrite doesn't have them because its an insulator but there are other core losses) and leakage inductance tends to be more of an issue in power transformers (where the load impedance is low to maximize power transfer).
And the multitude of effects that trafos bring:
- voltage gain or reduction
- current gain or reduction?
- galvanic isolation
- impedance conversion
Yep those are the key functions which trafos help to implement.
So with the 600:600 trafo with 290mH Vs 1.2H inductance, the second one would better transfer power across the windings resulting in a higher current for a given voltage?
No the second one will be less likely to make the opamp stage driving it run into current limiting (aka heavy distortion) at low frequencies. Or even if current limiting is avoided a lower inductance value is going to impact the driving circuit's power supplies to a greater extent, corrupting the LF (bass) quality of the music.