Saturday, February 20, 2016

Mutual inductance effect on transformer action and impedance matching

For this test I wound a transformer matching the one I posted about earlier. It has 3500T : 500T. I expect it to perform similiar to this one.

For a comparison I wound one with 1000T : 100T.  Then I bread boarded this test jig.

The one thing to remember is that the tail cannot wag the dog!  No matter what the Z load  is the Z input will only go as high as the inductance of the coil at the operating frequency so I establish the base line (start point) but checking the primary with no load. The 3500 : 500 read off the scale so I established the start point fo it at 19H with 490Ohm load. here are the results of the test.

1000 : 100
open circuit          4141mh
5KOhm               4123mh
50Ohm                2146mh
25Ohm                773mh
10Ohm                4.3mh

3500 : 500
490Ohm             19H
372Ohm              15H
261Ohm              10H
153Ohm              5H
45Ohm                1H
0Ohm                  .21H

The math says this is a 36 Henry primary. since my meter only goes to 20 Henry I loaded it to get 19 Henry with 490 Ohms. So the input impedance would be more than 48K for a load above 490 Ohms. The chart above says 25K : 500 Ohm so what's up with that?

 The plate circuit is a voltage divider. The plate resistance in series with the primary will divide the voltage as the current swings. As plate resistance goes down and plate current go up the primary develops a voltage which oposes the change in current and induces an output in the secondary.

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