AN296 Silicon_Laboratories, AN296 Datasheet - Page 12

• Manufacturer Part Number: AN296
• Description: Using THE Si3400 AND Si3401 POE PD Controllers IN Isolated AND Non-isolated Designs
• Manufacturer: Silicon_Laboratories

AN296
A transformer with a turns ratio of N:1 is used to help reduce peak currents.
In the discontinuous mode, the output power, I
transformer with some margin for switching losses. If ε is the margin for switching losses (typically 90%), then:
Where P
magnetizing inductance, and operating frequency.
The portion of the switching waveform where the FET is on d
Where V
The time, d
Where V
12
P
d
0
d
2
1
=
=
=
0
o
p
I
, I
0
is the input voltage.
V
is the output voltage (plus diode drop), and N is the transformer turns ratio.
I
2
0
p
×
, where current flows in the secondary is:
p
, and V
×
V
×
L
0
--------------------------------------
(
m
0
N
=
×
0
×
1
-- -
2
V
are output power, current and voltage, and I
----- -
V
(
×
f
V
d1
p
I
0
N*(Vo+Vf)
Isnuber
p
Ipr
Isw
Vs
2
+
×
V
L
f
)
m
)
×
f ε
×
Vin
Figure 9. Typical Waveforms
P=? Vz*Idt
t=Ipeak*Ll/(Vz-N*(Vo+Vf)
0
x V
Rev. 0.8
0
, must be supplied by the ½ x LI
Vin/N
1
is:
N:1
0
p
, L
Vo+Vf
m
, and f are transformer primary peak current,
2
energy stored in the
V