SSC2016S datasheet(9/22 Pages) SANKEN

9 / 22 page

SSC2016S

SSC2016S - DSJ Rev.1.3

SANKEN ELECTRIC CO.,LTD.

Jul. 22, 2016

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

Operational Description

All of the parameter values used in these descriptions

are typical values, unless they are specified as minimum

or maximum.

Current polarities are defined as follows: a current

flow going into the IC (sinking) is positive current (+);

and a current flow coming out of the IC (sourcing) is

negative current (

−).

8.1

Critical Conduction Mode: CRM

Figure 8-1 and Figure 8-2 show the PFC circuit and

CRM operation waveform. The IC performs the on/off

operation of switching device Q1 in critical mode (the

inductor current is zero). Thus, the low drain current

variation di/dt of power MOSFET is accomplished. Also,

adjusting the turn-on timing at the bottom point of VDS

free oscillation waveform (quasi-resonant operation),

low noise and high efficiency PFC circuit is realized.

DFW

ION

IOFF

VAC

Figure 8-1.

PFC Circuit

IL=ION+IOFF

ION

IOFF

Q1 VDS

OFF

Turn on delay time

Bottom on

Free oscillation

ILPEAK

LPEAK

)

AVG

(

Figure 8-2.

CRM Operation and Bottom On Operation

Figure 8-3 shows the internal CRM control circuit.

The power MOSFET Q1 starts switching operation by

self-oscillation.

The on-time control is as follows: the detection

voltage RVS2 is compared with the Feedback Voltage

Reference VREF = 2.500 V by using error amplifier

(Error AMP) connected to FB pin. The output of the

Error AMP is averaged and the phase is compensated.

This signal VCOMP is compared with the ramp signal

VOSC to achieve the on-time control. The on-time

becomes almost constant in commercial cycle by setting

VCOMP to respond below 20 Hz (Figure 8-4). This is

achieved by tuning the capacitor connected to COMP

pin.

The off-time is set by detecting the zero current signal

of boost winding P. The zero current is detected by

auxiliary winding D and ZCD pin.

VOSC

VSET

OSC

Error AMP

PWM COMP

2.500V

VOUT

RVS1

RVS2

GND

COMP

1.40 V

/0.70 V

OUT

DFW

ZCD

VCOMP

RCS

Figure 8-3.

CRM Control Circuit

ILPEAK

IL(t)

IAC(t)

tON tOFF

VAC(t)

√2×V

ACRMS

√2×I

ACRMS

VCOMP

VOSC

VSET

OUT pin voltage

VAC(t)

ILPEAK(t)

IL(AVG.)(t)

Figure 8-4 CRM Operation Waveforms

The off duty DOFF of boost converter in CRM mode

have the relation of DOFF(t) = VAC(t)/VOUT and is

proportional to input voltage, where VAC(t) is the input

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