75W SMPS with TEA1507 Quasi- Resonant Flyback controller - NXP ...

Philips Semiconductors
Application Note
AN00047
APPENDIX 2 DETAILED PERIOD DESCRIPTION OF QR WAVEFORMS
The period can be divided into four time intervals, in chronological order:
Interval 1: t0 < t < t1 primary stroke tPRIM = t1 – t0
Interval 2: t1 < t < t2 commutation time tCOM = t2 – t1
Interval 3: t2 < t < t3 secondary stroke tSEC = t3 – t2
Interval 4: t3 < t < t00 dead time tDEAD = t00 – t3
Three situations of VIN with regard to n⋅VOUT has to be distinguished:
1] V IN = n⋅V OUT
Iinductor (A)
Vdrain (V)
I 1 ( t )
I 2 ( t )
I 3 ( t )
I 4x ( t )
I 4 ( t )
__ZERO
t 0
V 1 ( t )
V 2 ( t )
V 3 ( t )
V 4x ( t )
V 4 ( t )
V IN
__ZERO
1.5
0.5
0.5
1
tt0 0
0
tt0 0
0 1 . 10
Situation Drain voltage at switch-on
1] VIN = n⋅VOUT
ZVS
2] VIN < n⋅VOUT
ZVS
3] VIN > n⋅VOUT
LVS
6
2 . 10
6
t1 t t
1
1 t t
2
2
3 . 10
6
4 . 10
t 1 t 2
One period of Inductor Current
6
5 . 10
6
38
6 . 10
t
t (s)
6
7 . 10
6
t 00
t3
t3 t 00
= 0
t 1 = 3.527 μ
t 2 = 4.197 μ t 3 = 7.724 μ t 00x = 11.194 μ T tot = 11.194 μ
600
400
200
0 1 . 0
10
6
2 . 10
6
3 . 10
6
t 1
4 . 10
One period of Drain Voltage
t 2
6
5 . 10
6
6 . 10
t
t (s)
6
7 . 10
Figure 26 Waveforms V IN = n⋅V OUT
Interval 1: t 0 ≤ t < t 1 primary stroke:
During this interval inductive current will be built up in the transformer, which is also called ‘Magnetization’ and/or
primary stroke. End point t00 of the period is the start point of the new period t0. As can be seen in Figure 26 the
MOSFET is switched on at zero drain voltage called ZVS. The inductive current and drain voltage during this
interval can be described by:
I
V
L
D
V
( t)
=
L
( t)
= I
IN
P
L
⋅(
t − t ) + I ( t )
( t)
⋅(
R
0
SENSE
L
0
+ R
DS ( ON )
)
where I ( t ) = 0 and t = 0
L
0
0
6
t 3
t 3
8 . 10
8 . 10
6
6
9 . 10
9 . 10
Equation 17
6
6
1 . 10
1 . 10
5
5
1.1 . 10
1.1 . 10
5
t 00
t 00
5