SSC2016S datasheet(17/22 Pages) SANKEN

17 / 22 page

SSC2016S

SSC2016S - DSJ Rev.1.3

SANKEN ELECTRIC CO.,LTD.

Jul. 22, 2016

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

9.2.7

VCC Pin Peripheral Circuit

< Using External Power Supply >

Figure 9-4 shows the VCC pin peripheral circuit. The

value of capacitor C7 is set approximately 1000 pF, in

order to reduce the switching noise.

COMP

GND

VCC

External

power supply

Figure 9-4.

VCC Pin Peripheral Circuit

(Power supply from external power supply)

< Using Auxiliary Winding D for VCC supply >

Figure 9-5 shows the VCC pin peripheral circuit when

VCC pin is supplied from auxiliary winding.

● R

The value of startup resistor, RST is selected so that

the current more than ICC(OFF) = 100 µA (max.) can be

supplied to VCC pin at startup.RST is expressed as

follows:

RST<√2×VACRMS(MIN)−VCC(ON)max.

ICC(OFF)max. (Ω) (17)

Where, VACRMS(MIN) is Minimum AC input voltage

rms value (V)

When the specification of AC input voltage is 100 V

or Universal, the value of RST is approximately

100 k

Ω to 220 kΩ. When the specification of AC

input voltage is 230 V, the value of RST is

approximately 180 k

Ω to 330 kΩ.

The rating of RST is chosen taking into account the

loss of RST at maximum input voltage. Since the high

voltage is applied to resistor, choose a resistor

designed against electromigration or use a series

combination of resistors.

● C

VCC

The approximate startup time is determined by the

value of CVCC. It is calculated as follows where the

initial voltage of VCC pin is zero.

tSTART≈ C7×VCC(ON)

√2×VACRMS−VCC(ON)

RST −ICC(OFF)(s) (18)

In general, power supply applications, CVCC, is

approximately 22 µF to 47 µF.

● R

Z, CCP and DZVCC

The circuit consists of RZ, CCP and RZ is the boost

circuit of VCC pin.

RZ is the limiting resistor for the breakdown current of

DZVCC. The RZ value is approximately 150

Ω.

CCP is charged when Q1 is in ON state. The CCP value

is approximately 22 nF.

Since the absolute maximum rating value of VCC pin

is 28 V, the zener voltage of DZVCC is chosen to be

less than it.

● C7

If CVCC and the VCC pin are distant from each other,

a capacitor C7 should be placed as close as possible to

the VCC pin. C7 is approximately 1000 pF, in order

to reduce the switching noise.

DVCC

RCS

RST

VCC

GND

CVCC

CCP

DZVCC

DFW

VOUT

LINE

GND

VAC

VCCP

Figure 9-5.

VCC Pin Peripheral Circuit

(Power supply from auxiliary winding)

9.2.8

Power MOSFET, Q1

Choose a power MOSFET having proper margin of

VDSS against output voltage, VOUT. The size of heat sink

is chosen taking into account some loss by switching

and ON resistance of MOSFET.

The loss PRDS(ON) by on-resistance, RDS(ON) of power

MOSFET is calculated using IDRMS of the result of

Equation (12) as follows:

PRDS(ON)=IDRMS2×RDS(ON)125

(W) (19)

Where

RDS(ON)125°C:

resistance

MOSFET

Tch = 125 °C

(Ω)

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