The PA3856.006NL can be used as a flyback transformer. Note 2 in the data sheet states this: -
- For flyback topology applications, it is necessary to ensure that the transformer will not saturate in the application. The peak flux
density (Bpk) should remain below 2700Gauss. To calculate the peak
flux density use the following formula: Bpk (Gauss) = K1_Factor *
Ipk(A)
Given that the peak primary current is calculated as 10 amps on the lowest input volts, Bpk (Gauss) = 41.7 x 10 = 417 gauss and this is well short of 2700 gauss.
Now, is my approach correct ?
Your approach does seem correct but you forgot to mention operating frequency however, i reasoned that the on time is 4.72 us if that helps.
where is the turns ratio specified ?
The turns ratio is 0.47:1 as shown by the little numbers on the picture of the transformer in your question.
Also, what is the actual advantage of have a dual output in the
secondary ? Does it have to do with the current on the output and its
effects on the transformer saturation current.
Dual output means you can wire them in series or in parallel. Saturation of the core is caused by primary current reaching too high a value.
There is a value of 4.33 in the primary of the transformer. Is it the
number of turns in the primary ?
It's the ratio of primary turns to secondary turns (pin 9 and pin 6) - notice the "1" alongside this secondary.
Primary inductance is stated at 21 uH therefore the secondary inductance (should you need to know it) is the square of 4.33 times lower at 1.12 uH. That's how transformer coil inductances are related to turns ratios.
Now, suppose the number of turns of the primary is required to be 1.41
No, you have to stick with integers for number of turns.
Now, suppose the number of turns of the primary is required to be
1.41, is it safe if I use one with 4.33 ?
A winding with more turns can have a massively different inductance and, because you are designing a fly-back power regulator, this is going to be a likely problem. Inductance is proportional to turns squared so if there are 4 times the turns there will be 16 times the inductance (on the same core). You need the primary inductance to be what you have designed it to be.
Also, the datasheet gives only the primary DCR ,saturation current and
inductance. Will these parameters of the secondary have no impact ?
The picture in your question shows the DC resistance of all windings. As for inductance you calculate secondary values based on turns ratio and primary values (as shown above).
Saturation is a primary coil thing and not related to the secondary or its load.
Best Answer
Saturation is a function of the core (there is only one core, and it links primary to secondary winding(s)). In the case of a flyback converter, energy is stored in the core and then released to the secondary. Saturation is thus only a function of the primary current, since there is no secondary current (the rectifier is reverse biased) when the magnetic field reaches the peak value.
In the general case, saturation would be related to the signed sum of the ampere-turns of each winding (each affecting the magnetic flux in the core), but that's not a factor in a flyback.