SSC2005SC datasheet(12/19 Pages) SANKEN

12 / 19 page

SSC2005SC

SSC2005SC-DS Rev.1.1

SANKEN ELECTRIC CO.,LTD.

Feb. 06, 2015

8.9

Overcurrent Protection (OCP)

Figure 8-14 shows the CS pin peripheral circuit and

internal circuit. The inductor current, IL is detected by

the detection resistor, RCS. The detection voltage, VRCS,

is fed into the CS pin. The OCP COMP compares the

detection voltage, VRCS with Overcurrent Protection

Threshold Voltage, VCS(OCP) = − 0.60 V. When VRCS

increases to absolute value of VCS(OCP) or more, the OUT

pin output is turned-off by pulse-by-pulse.

As shown in Figure 8-14, the CS pin is connected to

capacitor-resistor filter (R4 and C5) and zener diode,

DZCS, for the CS pin overvoltage protection.

VOUT

LINE GND

GND

VCS(ZCD)

= －10mV

OUT

RCS

DZCS

VCS(OCP)

= －0.60V

ZCD

COMP

OCP

COMP

VRCS

Figure 8-14 The CS pin peripheral circuit

and internal circuit.

Design Notes

9.1

Inductor Setup

Apply proper design margin to temperature rise by

core loss and copper loss.

The calculation methods of inductance ,LP,

is as

shown below.

Since

the

following

calculating

formulas

are

approximated, the peak current and the frequency of

operational waveforms may be different from the setting

value at calculating. Eventually, the inductance value

should be adjusted in actual operation.

Apply proper design margin to temperature rise by

core loss and copper loss.

1) Output Voltage, VOUT

The output voltage VOUT of boost-converter should be

set to a higher value than peak value of input voltage,

shown in

the following equation:

DIF

)

MAX

(

ACRMS

OUT







(V)

(4)

where,

VACRMS(MAX) : Maximum AC input voltage rms value (V)

VDIF

: Boost voltage (About 10V) (V)

2) Operational Frequency, fSW(SET)

Determine fSW(SET) that is minimum operational

frequency at the peak of the AC line waveform. The

frequency becomes higher with lowering the input

voltage. The frequency at the peak of the AC line

waveform, fSW(SET) should be set more than the

audible frequency (20 kHz).

3) Inductance, LP

Substituting both minimum and maximum of AC

input voltage to VACRMS, choose a smaller one as LP

value.

LP is calculated as follows:









OUT

)

SET

(

OUT

ACRMS

OUT

ACRMS











(H) (5)

where,

η : Efficiency of PFC (In general, the range of η is

0.90 to 0.97, depending on on-resistance of power

MOSFET RDS(ON) and forward voltage drop of

rectifier diode VF.)

VACRMS : Maximum/Minimum of AC input voltage

rms value (V)

VOUT : Output voltage (V)

POUT : Output power (W)

fSW(SET) : Minimum operational frequency at the peak

of the AC line waveform (kHz)

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