STR5A162D Datasheet, PDF (10/21 Pages) Sanken electric – Off-Line PWM Controllers with Integrated Power MOSFET

STR5A100D Series
VAC
V_DS
CRD clamp snubber
L1
C1 C2
C3 R1
R2
P
D1
4
D/ST
D2 _R6
2
R3
D
U1
V_D
R4
S/GND
5~8
FB
1
R5
PSR circuit
Figure 10-5 FB pin peripheral circuit
D/ST pin current, I_D ^tON
t_OFF
t_ON
I_Dpk
Secondary side
rectifier diode
current, I_DO
I _DOpk
 I _Dpk
 ^NP
N_S
Auxiliary winding
voltage, V_D
  V_D

N_D
N_S

V_OUT  V_F
N_D
N_S
 V_OUT
0
V_Error

N_D
N_S
 V_F
t_FBMS
t_FBD
A
Sampling set point
ΔV_F：Diode Dropped Voltage
Figure 10-6 Detection timing of
auxiliary winding voltage
output voltage when the output load becomes light.
Accordingly, the output voltage of internal error
amplifier (target voltage V_SC) decreases. As a result,
the peak value of V_ROCP is controlled to be lower so
that the peak of the drain current decreases. This
control prevents the output voltage from increasing.
 Heavy Load Conditions
The control circuit performs reverse operations to the
former. The target voltage V_SC of internal comparator
becomes higher and the peak drain current increases.
This control prevents the output voltage from
decreasing.
U1
V_ROCP
PWM
Control
D/ST
4
Feedback
Control
+
VSC
-
VCC 2 ^{D2 R6}
D
FB comp
R_OCP
S/GND
+
E/A_-
S/H
FB
R3
C4
R4
5,6,7
1
R5
Figure 10-7 FB pin peripheral circuit
-
+
FB comparator
V_SC
V_ROCP
Voltage on both side of R_OCP
Drain current, I_D
Figure 10-8 Drain current I_D and FB comparator
in steady operation
10.6 Constant Voltage (CV) Control
The IC achieves the constant voltage (CV) control of
the power supply output by using the peak-current-mode
control method, which enhances the response speed and
provides the stable operation.
The IC controls the peak value of the voltage of build-in
sense resistor (V_ROCP) to be close to target voltage (V_SC),
comparing V_ROCP with V_SC by internal FB comparator.
Feedback Control circuit receives the sampling voltage
which is the reversed auxiliary winding voltage by using
error amplifier (refer to Figure 10-7 and Figure 10-8)
 Light Load Conditions
The FB pin voltage increases with the increase of the
10.7 Constant Current (CC) Control
The IC operates in Constant Current (CC) Control
when output current reaches to constant load and the
state continues for more than the Constant Current
Control Delay Time, t_CCD = 90 ms. In case the IC is in
discontinuous operation, the CV/CC characteristic is as
shown in Figure 10-9.
When output current reaches to constant load,
MOSFET drain current is limited to the Drain Current
Limit I_DLIM(H). When the output voltage becomes low,
the CC Control is maintained by lowering the oscillation
frequency f_OSC. When the output voltage becomes low,
the FB pin voltage becomes low. When FB pin voltage
STR5A100D-DS Rev.1.2
SANKEN ELECTRIC CO.,LTD.
10
Dec. 25, 2013