Re: DC-DC Flyback magnetics selection (esp, inductance)

On 1 Nov, 18:59, kgll...@xxxxxxxxx wrote:
When choosing magnetics for a flyback type DC-DC converter with
Vin=36-57V Imax=400 mA DC to 3,3V, with a Pmax=12,95W. Is the
inductance of the pulse transformer calculated as below..?
If not, how does one calculate it ..?

L_s = (V_ut*T_s*(1-d_min)) / (2*I_s*I_r)

L_s - Inductance on secondary [H]
V_ut - Output voltage [V]
T_s - Cycle time [s]
d_min - Minimum duty cycle
I_s - Power through secondary [A]
I_r - Allowed ripple [A]

L_p = sqrt(L_s^2 / (N_s/N_p) )

L_p - Inductance primary [H]
L_s - Inductance secondary [H]
N_s - Turns secondary
N_p - Turns primary

If it is a flyback then, by definition, there is no secondary current
whilst the primary is 'charging'.
The primary inductance is give by: L=N^2.AL





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