SSC2016S datasheet(10/22 Pages) SANKEN

10 / 22 page

SSC2016S

SSC2016S - DSJ Rev.1.3

SANKEN ELECTRIC CO.,LTD.

Jul. 22, 2016

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

voltage of AC line as a function of time.

As a result of aforementioned control shown in Figure

8-4, the peak current ILPEAK of the inductance current IL

becomes sinusoidal. Since the averaged input current

become similar to AC input voltage waveform by Low

Pass Filter at input stage, high power factor is achieved.

8.2

Startup Operation

Figure 8-5 and Figure 8-7 show the VCC pin

peripheral circuit. Figure 8-5 shows how to use an

external power supply. Figure 8-7 shows how to use an

auxiliary winding.

8.2.1

To Use an External Power Supply

When an external power supply shown in Figure 8-5

is used, the startup operation is as follows.

As shown in Figure 8-6, when VCC pin voltage rises

to the Operation Start Voltage VCC(ON) = 8.5 V, the

control circuit starts operation and the COMP pin

voltage increases. The COMP pin voltage increases to

the Zero Duty COMP Voltage VCOMP(ZD) = 0.65 V,

switching operation starts.

When

the

VCC

voltage

decreases

VCC(OFF) = 7.5 V, the control circuit stops operation by

Undervoltage Lockout (UVLO) circuit, and reverts to

the state before startup.

Since the COMP pin voltage rises from zero during

startup period, the VCOMP signal shown in Figure 8-3

gradually rises

from low

voltage.

The

on-width

gradually increased to restrict the rise of output power

by the Softstart Function. Thus, the stress of the

peripheral component is reduced.

COMP

GND

VCC

External

power supply

Figure 8-5.

VCC Pin Peripheral Circuit

(Power supply from external power supply)

ICC

VCC（OFF）

VCC（ON）

VCC pin

voltage

Figure 8-6.

Relationship between VCC Pin Voltage

and ICC

8.2.2

To Use an Auxiliary Winding

When an auxiliary winding is used as shown in Figure

8-7, CVCC is charged through RST at startup. When VCC

pin voltage rises to VCC(ON) = 8.5 V, the control circuit

starts operation.

Figure 8-8 shows the VCC pin voltage behavior

during startup period.

When the VCC pin voltage reaches VCC(ON), the

control circuit starts operation. Then the circuit current

increases and the VCC pin voltage decreases. At the

same time, the auxiliary winding voltage VD increases in

proportion to the output voltage. These are all balanced

to produce VCC pin voltage.

The value of CVCC, the turns ratio of boost winding P

and auxiliary winding D should be set so that VCC pin

voltage is maintained higher than VCC(OFF) (See Section

9.1.2).

If the values of RST and CVCC are large, the startup

time becomes longer. Adjustment is necessary in actual

operation.

When the COMP pin voltage increases to the Zero

Duty COMP Voltage VCOMP(ZD) = 0.65 V after the

control circuit starts operation, switching operation starts

and the circuit current is supplied from auxiliary

winding D as follows.

VB and VD are the voltage of auxiliary winding during

Q1 on and off, respectively.

When Q1 is on, CCP is charged by VB. When Q1 is off,

the capacitor connected to VCC pin, CVCC, is charged by

VD + VB (=VCCP).

VB is calculated using Equation (1).

VB=VIN×NDNP (V)

(1)

Where

VIN: C1 voltage (V)

NP: Number of turns of boost winding P (turns)

ND: Number of turns of auxiliary winding D (turns)

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