SSC3S921 datasheet(13/28 Pages) SANKEN

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SSC3S921

SSC3S921 - DSJ Rev.1.7

SANKEN ELECTRIC CO., LTD.

Jan. 17, 2018

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

8.2

Startup Operation

Figure 8-11 shows the VCC pin peripheral circuit.

Figure 8-12 shows the startup operational waveforms.

The power supply starts as follows:

1) The mains input voltage is provided, and the VSEN

pin voltage increases to the on-threshold voltage,

VSEN(ON) = 1.300 V, or more.

2) The startup current, IST, which is a constant current

of 6.0 mA is provided from the IC to capacitor C2

connected to the VCC pin, C2 is charged.

3) CADJ is charged by I

ADJ

= −10µA to increase the ADJ

pin voltage.

4) When the VCC pin voltage increases to the operation

start voltage, VCC(ON) = 17.0 V, the REG pin voltage

is output. At the same time, the ADJ pin outputs the

PFC ON signal, and the PFC control IC is activated.

The VCC pin voltage is decreased by the power

dissipation of the IC.

5) When

the

VCC

voltage

decreases

VCC(BIAS) = 9.8 V, the C9 connected to FB pin starts

to be charged. When the FB pin voltage increases to

the oscillation start threshold voltage, VFB(ON) = 0.30

V, or more, the swiching operation starts.

After that, the startup circuit stops automatically, in

order to eliminate its own power consumption.

During the IC operation, the rectified voltage from the

auxiliary winding voltage, VD, in Figure 8-11 is a power

source to the VCC pin.

The winding turns of the winding D should be

adjusted so that the VCC pin voltage is applied to

equation (7) within the specification of the mains input

voltage range and output load range of the power supply.

The target voltage of the winding D is about 19 V.

⇒9.8 (V) < V

CC < 32.0 (V)

(7)

The startup time, tSTART, is determined by the value of

C2 and C6 connected to the CSS pin. Since the startup

time for C6 is much smaller than that for C2, the startup

time is approximately given as below:

(8)

where:

tSTART is the startup time in s,

VCC(INT) is the initial voltage of the VCC pin in V, and

ICC(ST) is the startup current, 6.0 mA

VCC

GND

VSEN

PC1

VCC

RADJ1

RADJ2

DADJ

VAC

DST1

DST2

SSC2016S

ADJ

RST

REG

CADJ

IADJ

CSS

Figure 8-11.

VCC Pin Peripheral Circuit

VCC Pin Voltage

VCC(ON)

VCC(BIAS)

REG Pin Voltage

FB Pin Voltage

VGL Pin Voltage

VREG

VFB(ON)

VSEN Pin Voltage

VSEN(ON)

ADJ Pin Voltage

Charged by IADJ

PFC on signal output

Figure 8-12.

Startup Operation When PFC ON/OFF

Function is Enabled

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