I'm playing around with a flyback DC-DC converter design, and I'd like to know if I'm modeling a stock part correctly.
The part is a Pulse Engineering PA1546NL, which is a small transformer.
Data sheet:
I want to use the winding between pins 4 and 5 as the primary (L1),
1 and 8 as the secondary (L2), and not use the 7-2 feedback winding (not modeled).
The SPICE model I'm using for the transformer is:
L1 Vcc N003 17µ Rser=2.1 L2 0 N001 247µ Rser=0.7 K1 L1 L2 0.95
The data sheet gives the inductance of L2 as 247uH. The data sheet doesn't give the inductance for L1, but it gives the turns ratio as 3.82 : 1. So 247uH / (3.82^2) = 16.9uH, right? DC resistances are from the data sheet.
I have no idea what the efficiency value, K, should be for one of these little things. I'm using 0.95 as a guess. Big iron-core transformers run around 0.98 or so, but I don't know about these little things. This matters; for the circuit I'm trying, for values much below 0.95, the switcher won't oscillate.
John Nagle