STR-A6351 SanKen, STR-A6351 Datasheet - Page 14

• Manufacturer Part Number: STR-A6351
• Description: STR-A6300 Series
• Manufacturer: SanKen

7.5 Thermal Shutdown(TSD) Circuit
TSD circuit makes the latch circuit operate when the frame temperature of the IC is above 135 o C(MIN).
Temperature detection is actually made by the control IC.
7.6 Overvoltage Protection(OVP) Circuit
OVP circuit makes the latch circuit operate when the Vin terminal voltage exceeds 25.5V(TYP), and it
In general, the Vin terminal voltage is provided from the drive winding of the transformer and it is proportional
STR-A6300 Application Notes
operation. The cancellation of the latch circuit is made by reducing the Vin terminal voltage below 7.9V, and
generally, it is restarted by AC input switch-off of the power supply.
functions as a protection against the overvoltage at the Vin terminal of the control circuit.
to the output voltage. Therefore, the circuit operates even in the overvoltage output of the secondary side, for
instance, when the voltage detection circuit is open. In this case, the secondary output voltage when the OVP
circuit operates is obtained from;
８ CALCULATION OF PRIMARY INDUCTANCE
Design of the transformer is basically same as that of RCC type power supplies. Assuming D as ON-Duty
decided from the ratio between P winding(Np) and S winding(Ns), the Lp is obtained from the formula below.
Also, due to the fixed OFF-time of the PRC operation, the transformer should be designed in order the drain
current to be un-continuous at the MIN input and MAX load.
9 DESIGN GUIDELINES
9.1 External components
Care needs to be taken in the capacitance, inductance, and allowable dissipation of external components.
For the loss of input/output capacitors to the ripple current and voltage, and for the loss of transformer for
copper and iron, the sufficient margin is to be considered in a power supply. Especially for the OCP resistor,
R5, where high frequency elements flow, a resistor having high internal inductance is likely to cause
malfunctions. Thus a resistor having low internal inductance and high surge energy should be selected.
As switching current contains high frequency elements, the influence of the surface effect is not to be
neglected. Therefore, it is recommended to enlarge the surface area of the transformer winding by using
LP
V
OUT
=
2
(
(OVP)≒--------------------------------------------------------------- × 22.5V (TYP)
VIN
×
Po: Maximum Output Power
fo: Minimum Oscillating Frequency
η：: Power supply efficiency=approx. 0.9(In case of CTV), 0.75~0.85(Low Output Voltage)
D: ON-Duty at Vin(AC)
VIN: C1 voltage at Minimum VIN(AC)
fo
⋅
×
D
Po
)
2
V
×
IN
η
Terminal Voltage at Normal Operation
（Ｈ）
V
OUT
at Normal Operation
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