NCP1200 View Datasheet(PDF) - ON Semiconductor

Part Name

Description

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NCP1200

PWM Current-Mode Controller for Low-Power Universal Off-Line Supplies

ON Semiconductor 

NCP1200

If the leakage inductance is kept low, the MTD1N60E can

withstand accidental avalanche energy, e.g. during a

high−voltage spike superimposed over the mains, without

the help of a clamping network. If this leakage path

permanently forces a drain−source voltage above the

MOSFET BVdss (600 V), a clamping network is mandatory

and must be built around Rclamp and Clamp. Dclamp shall

react extremely fast and can be a MUR160 type. To calculate

the component values, the following formulas will help you:

Rclamp =

2 @ Vclamp @ (Vclamp * (Vout ) Vf sec) @ N)

Lleak @ Ip2 @ Fsw

Cclamp

+

Vripple

Vclamp

@ Fsw @ Rclamp

with:

Vclamp: the desired clamping level, must be selected to be

between 40 V to 80 V above the reflected output voltage

when the supply is heavily loaded.

Vout + Vf: the regulated output voltage level + the secondary

diode voltage drop

Lleak: the primary leakage inductance

N: the Ns:Np conversion ratio

FSW: the switching frequency

Vripple: the clamping ripple, could be around 20 V

Another option lies in implementing a snubber network

which will damp the leakage oscillations but also provide

more capacitance at the MOSFET’s turn−off. The peak

voltage at which the leakage forces the drain is calculated

by:

Ǹ Vmax + Ip @

Lleak

Clump

where Clump represents the total parasitic capacitance seen

at the MOSFET opening. Typical values for Rsnubber and

Csnubber in this 4W application could respectively be 1.5

kW and 47 pF. Further tweaking is nevertheless necessary to

tune the dissipated power versus standby power.

Available Documents

“Implementing the NCP1200 in Low−cost AC−DC

Converters”, AND8023/D.

“Conducted EMI Filter Design for the NCP1200’’,

AND8032/D.

“Ramp Compensation for the NCP1200’’, AND8029/D.

TRANSient and AC models available to download at:

http://onsemi.com/pub/NCP1200

NCP1200 design spreadsheet available to download at:

http://onsemi.com/pub/NCP1200

ORDERING INFORMATION

Device

NCP1200P40

Type

Marking

1200P40

Package

PDIP−8

Shipping†

50 Units / Rail

NCP1200P40G

NCP1200D40R2

FSW = 40 kHz

1200P40

200D4

PDIP−8

(Pb−Free)

SOIC−8

50 Units / Rail

2500 / Tape & Reel

NCP1200D40R2G

200D4

SOIC−8

(Pb−Free)

2500 / Tape & Reel

NCP1200P60

1200P60

PDIP−8

50 Units / Rail

NCP1200P60G

NCP1200D60R2

FSW = 60 kHz

1200P60

200D6

PDIP−8

(Pb−Free)

SOIC−8

50 Units / Rail

2500 / Tape & Reel

NCP1200D60R2G

200D6

SOIC−8

(Pb−Free)

2500 / Tape & Reel

NCP1200P100

1200P100

PDIP−8

50 Units / Rail

NCP1200P100G

NCP1200D100R2

FSW = 100 kHz

1200P100

200D1

PDIP−8

(Pb−Free)

SOIC−8

50 Units / Rail

2500 / Tape & Reel

NCP1200D100R2G

200D1

SOIC−8

(Pb−Free)

2500 / Tape & Reel

†For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging

Specifications Brochure, BRD8011/D.

http://onsemi.com

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