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参数资料
| 型号： | FSEZ1317AMY-F116 |
| 厂商： | FAIRCHILD SEMICONDUCTOR CORP |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHING CONTROLLER, 53 kHz SWITCHING FREQ-MAX, PDSO7 |
| 封装： | GREEN, MS-012AA, SOP-8/7 |
| 文件页数： | 2/16页 |
| 文件大小： | 1031K |
| 代理商： | FSEZ1317AMY-F116 |
2010 Fairchild Semiconductor Corporation
www.fairchildsemi.com
FSEZ1317A Rev. 1.0.1
10
FSEZ1
317
A
—
Primary-Side
-Regulation
PWM
with
P
O
WER
MOSFET
Integrated
Functional Description
Figure 24 shows the basic circuit diagram of primary-
side regulated flyback converter, with typical waveforms
shown
in
Figure
25.
Generally,
discontinuous
conduction mode (DCM) operation is preferred for
primary-side regulation because it allows better output
regulation. The operation principles of DCM flyback
converter are as follows:
During the MOSFET on time (tON), input voltage (VDL) is
applied across the primary-side inductor (Lm). Then
MOSFET current (Ids) increases linearly from zero to the
peak value (Ipk). During this time, the energy is drawn
from the input and stored in the inductor.
When the MOSFET is turned off, the energy stored in
the inductor forces the rectifier diode (D) to be turned
on. While the diode is conducting, the output voltage
(Vo), together with diode forward-voltage drop (VF), is
applied across the secondary-side inductor (LmNs
2/
Np
2) and the diode current (ID) decreases linearly from
the peak value (IpkNp/Ns) to zero. At the end of inductor
current discharge time (tDIS), all the energy stored in the
inductor has been delivered to the output.
When the diode current reaches zero, the transformer
auxiliary winding voltage (Vw) begins to oscillate by the
resonance between the primary-side inductor (Lm) and
the effective capacitor loaded across the MOSFET.
During the inductor current discharge time, the sum of
output voltage and diode forward-voltage drop is
reflected to the auxiliary winding side as (VO+VF)
Na/Ns. Since the diode forward-voltage drop decreases
as current decreases, the auxiliary winding voltage
reflects the output voltage best at the end of diode
conduction time where the diode current diminishes to
zero. Thus, by sampling the winding voltage at the end
of the diode conduction time, the output voltage
information can be obtained. The internal error amplifier
for output voltage regulation (EA_V) compares the
sampled voltage with internal precise reference to
generate error voltage (VCOMV), which determines the
duty cycle of the MOSFET in CV mode.
Meanwhile, the output current can be estimated using
the peak drain current and inductor current discharge
time because output current is same as the average of
the diode current in steady state.
The output current estimator picks up the peak value of
the drain current with a peak detection circuit and
calculates the output current using the inductor
discharge time (tDIS) and switching period (ts). This
output information is compared with internal precise
reference to generate error voltage (VCOMI), which
determines the duty cycle of the MOSFET in CC mode.
With Fairchild’s innovative technique TRUECURRENT
,
constant current (CC) output can be precisely
controlled.
Among the two error voltages, VCOMV and VCOMI, the
smaller one determines the duty cycle. Therefore, during
constant voltage regulation mode, VCOMV determines the
duty cycle while VCOMI is saturated to HIGH. During
constant current regulation mode, VCOMI determines the
duty cycle while VCOMV is saturated to HIGH.
+
V
DL
-
L
m
+
V
O
-
N
p:Ns
I
ds
I
D
Primary-Side Regulation
Controller
+
V
w
-
VDD
VS
CS
+V
F -
N
A
L
O
A
D
I
O
IO
Estimator
VO
Estimator
t
DIS
Detector
PWM
Control
R
CS
VAC
Ref
EA_V
EA_I
V
COMV
V
COMI
R
S1
R
S2
Figure 24. Simplified PSR Flyback Converter Circuit
P
pk
S
N
I
N
pk
I
.
D avg
o
I
A
F
S
N
V
N
A
O
S
N
V
N
Figure 25. Key Waveforms of DCM Flyback
Converter
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