NCP1203

http://onsemi.com

12

Figure 21. A negative spike takes place on the Bulk capacitor at the switch−off sequence

Simple and inexpensive cures exist to prevent from

internal parasitic SCR activation. One of them consists in

inserting a resistor in series with the high−voltage pin to

keep the negative current to the lowest when the bulk

becomes negative (Figure 22). Please note that the negative

spike is clamped to –2 x Vf due to the diode bridge. Also, the

power dissipation of this resistor is extremely small since it

only heats up during the startup sequence.

Another option (Figure 23) consists in wiring a diode from

sooner and thus stops the switching activity before the bulk

capacitor gets deeply discharged. For security reasons, two

diodes can be connected in series.

Figure 22. A simple resistor in series avoids any

latchup in the controller

D3

1N4007

8

7

6

5

1

2

3

4

+

Cbulk

+

Rbulk

> 4.7 k

8

7

6

5

1

2

3

4

+

Cbulk

+

UVLOlow sooner

ORDERING INFORMATION

Device

Package

NCP1203P40

PDIP−8

50 Units / Tube

NCP1203D40R2

SOIC−8

2500 Units / Tape & Reel

NCP1203P60

PDIP−8

50 Units / Tube

NCP1203D60R2

SOIC−8

2500 Units / Tape & Reel

NCP1203D60R2G

SOIC−8

(Pb−Free)

2500 Units / Tape & Reel

NCP1203P100

PDIP−8

50 Units / Tube

NCP1203D100R2

SOIC−8

2500 Units / Tape & Reel

NCP1203D100R2G

SOIC−8

(Pb−Free)

2500 Units / 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.