SPF8201 DATA SHEET

Ver.1

SANKEN ELECTRIC CO.,LTD.

2014 Feb

13 / 19

7-4. S/OCP terminal

S/OCP terminal detects the drain current of the internal MOSFET. The sense resistor is connected between S/OCP and

GND terminal externally. S/OCP terminal detects the drain current at pulse by pulse, and when the S/OCP terminal

voltage exceeds “OCP threshold voltage (Vocp = 0.5V typ.)”, the over-current function operates and the internal

MOSFET is turned off every switching period.

Since the high frequency current flows through the sense resistor, low inductance and high surge tolerance resistor shall

be used.

7-5. COMP terminal

COMP terminal is the output of an error amplifier. The capacitor Ccomp and the resistor Rcomp are connected between

COMP and GND terminals generally. Appropriate capacitance must be chosen by checking the operation.

7-6. FB terminal

FB terminal is the input of an error amplifier. To control output voltage of a converter, the SPF8201 has current mode

control, which is superior transient response and stability. The device has an error amplifier between FB terminal and

COMP terminal. FB terminal adjusts input voltage to equalize VFB, Feedback voltage,=2.5V.

In case that a user does not use an optocoupler to regulate secondary voltage, please use an auxiliary winding and make

combined voltage in primary side from secondary output and an transformer to control operation, as described in Fig.7-9.

When the auxiliary winding circuit is composed as Fig.7-9, a smoothing capacitor, V3, and secondly output VOUT is set

by turn ratio of N2 and N3. The following is the equation.

VOUT=(N2/N3)xV3

The voltage,V3, is divided by resistors and input to FB terminal. Then, IC controls voltage on FB terminal to be

equalized VFB=2.5V.

Therefore,

VOUT=(R1+R2)/R2x2.5

Thus, secondly output will be controlled as follow.

VOUT=N2/N3x(R1+R2)/R2x2.5

Fig.7-9 FB terminal and COMP terminal peripheral circuit