STR5A162D Datasheet, PDF (12/21 Pages) Sanken electric – Off-Line PWM Controllers with Integrated Power MOSFET

STR5A100D Series
When AC input voltage is low (ON Duty is broad),
the Drain Current Limit after compensation increases.
The difference of peak drain current become small
compared with the case where the AC input voltage is
high (ON Duty is narrow).
The compensation signal depends on ON Duty. The
relation between the ON Duty and the drain current limit
after compensation I_DLIM' is expressed as Equation (4).
When ON Duty is broader than 27 %, the drain current
limit becomes a constant value I_DLIM(H).
I_DLIM ' 
I_DLIM(H)  I_DLIM(L)
27(%)
 Duty 
I _{DLIM( L )}
(4)
where,
Duty: MOSFET ON Duty (%)
I_DLIM(H): Drain current limit (ON Duty ≥ 27 %)
I_DLIM(L): Drain current limit (ON Duty = 0 %)
STR5A162D
I_DLIM(H)
0.285 A
I_DLIM(L)
0.242 A
STR5A164D
0.41 A
0.34 A
I_DLIM(H)
I_DLIM(L)
the IC returns to normal operation automatically.
In case the VCC pin voltage is provided by using
auxiliary winding of transformer, the overvoltage
conditions such as FB pin open can be detected because
the VCC pin voltage is proportional to FB pin voltage.
The approximate value of output voltage V_OUT(OVP) in
OVP condition is calculated by using Equation (5).
V_OUT(OVP)
 ^{VOUT NORMAL }  29.3
V_{CCNORMAL }
(5)
where,
V_OUT(NORMAL): Output voltage in normal operation
V_CC(NORMAL): VCC pin voltage in normal operation
10.13 Thermal Shutdown Protection (TSD)
When the temperature of control circuit increases to
Thermal Shutdown Operating Temperature T_j(TSD) = 135
°C (min.) or more, Thermal Shutdown Protection
function is activated and stops switching operation.
In TSD condition, the intermittent operation by
UVLO is repeated by same mechanism as described in
“10.12 Overvoltage protection (OVP)”.
The TSD function of the IC incorporates the
hysteresis. When the temperature of the IC decreases to
T_j(TSD)−T_j(TSDHYS), the IC releases the TSD operation and
restarts.
00%
D_DPC
27%
ON Duty
D_MAX
57%
Figure 10-12 Relationship between ON Duty and Drain
Current Limit after compensation
10.12 Overvoltage Protection (OVP)
When a voltage between VCC pin and S/GND
terminal increases to V_CC(OVP) = 29.3 V or more, OVP
Function is activated and stops switching operation.
When OVP Function is activated, VCC pin voltage
decreases to Operation Stop Voltage V_CC(OFF) = 8.1 V.
After that, the IC reverts to the initial state by UVLO
(Undervoltage Lockout) circuit, and the IC starts
operation when VCC pin voltage increases to
V_CC(ON) = 15.0 V by Startup Current. Thus the
intermittent operation by UVLO is repeated in OVP
condition.
This intermittent operation reduces the stress of parts
such as power MOSFET and secondary side rectifier
diode. In addition, this operation reduces power
consumption because the switching period in this
intermittent operation is short compared with oscillation
stop period. When the abnormal condition is removed,
11.Design Notes
11.1 External Components
Take care to use properly rated, including derating as
necessary and proper type of components.
VAC
L1
CRD clamp snubber
P
D50
S1
VOUT
C1
C2
C3 _R1
R2
4
D/ST
U1
2
VCC
FB ¹
S/GND
5~8
D2
C4
D1
R6
D
R3
R4 ^VD
R5
R51 C51
C52 ^R52
GND
Figure 11-1 Peripheral circuit of FB pin and VCC pin
STR5A100D-DS Rev.1.2
SANKEN ELECTRIC CO.,LTD.
12
Dec. 25, 2013