SSC2016S datasheet(14/22 Pages) SANKEN

14 / 22 page

SSC2016S

SSC2016S - DSJ Rev.1.3

SANKEN ELECTRIC CO.,LTD.

Jul. 22, 2016

http://www.sanken-ele.co.jp/en/

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:

LP=η×VACRMS2×�VOUT−√2×VACRMS�

2×POUT×fSW(SET)×VOUT (H) (4)

where

VACRMS: Maximum or minimum AC input voltage rms

value (V)

POUT: Output Power (W)

fSW(SET): Minimum operational frequency at the peak of

the AC line waveform (kHz)

(The operational frequency becomes lowest at the peak

of the AC line waveform. fSW(SET) should be set above

frequency of 20 kHz.)

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.)

4) Inductor peak current, ILP

ILP is peak current at the minimum of AC input

voltage waveform. ILP calculated as follows:

ILP= 2√2×POUT

η×VACRMS(MIN)(A)

(5)

where,

POUT : Output power (W)

VACRMS(MIN) : Minimum AC input voltage rms value (V)

η : Efficiency of PFC (About 0.90 to 0.97)

5) Maximum On-time, tON(SET)MAX

tON(MAX)_OP is calculated by Equation (6) with results

of Equation (4) and Equation (5). tON(MAX)_OP is the

maximum on time of the peak voltage of the

minimum AC input voltage.

tON(MAX)_OP= LP×IP

√2×VACRMS(MIN) (s) (6)

where,

LP : Inductance value of the result of Equation (4)

VACRMS(MIN) : Minimum AC input voltage rms value (V)

Equation

(7)

shows

the

relationship

between

maximum on time, tON(MAX), and CT pin capacitor, C4

(see Section 8.4). C4 should be set so as tON(MAX) is

larger than tON(MAX)_OP that is calculated by Equation

(6). The value of C4 is about 330 pF to 1500 pF

tON(MAX)=C4×VCT(OFF)

|ICT| (s)

(7)

where

C4: Capacitance of capacitor connected to CT pin

(

μF)

VCT(OFF): CT Pin Threshold Voltage (V)

ICT: CT Pin Source Current (

μA)

9.1.2

Auxiliary Winding, D

Figure 9-1 shows the polarity of boost winding P and

auxiliary winding D.

VOUT

GND

OUT

DFW

ZCD

RCS

Figure 9-1.

ZCD Peripheral Circuit

Given the number of windings of each winding as NP

and ND, the turn ratio ND/NP is set satisfying following

conditions.

The condition of ND/NP making ZCD pin voltage

above VZCD(H) = 1.40 V after power MOSFET turns off

is expressed as follows:

NDNP> VZCD(H)

VOUT−√2×VACRMS(MAX)

(8)

where

NP: The number of turns of boost winding P (turns)

ND: The number of turns of auxiliary winding D (turns)

VOUT: Output voltage (V)

VACRMS(MAX): Maximum AC input voltage rms value

(turns)

When power supply of VCC pin is suplied from

auxiliary winding as shown in Figure 9-2, the condition

of ND/NP is set to larger rate of Equation (8) or Equation

(9).

The maximum VCC pin input voltage is limited by

the zener voltage of DZVCC. The minimum VCC pin

input voltage must be set higher than the maximum

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