IRS21571D

www.irf.com

© 2008 International Rectifier

21

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

VDC

CPH

RPH

RT

RUN

CT

DT

OC

LO

COM

VCC

VB

VS

HO

SD

CS

+ V

BUS

+ rectified

AC Line

V

C

BS

D

BOOT

R

Supply

C

VCC

R

CS

L

RES

C

RES

R

GHS

R

GLS

C

BLOCK

C

SNUBBER

R4

R3

R5

C2

D1

D2

Figure 12: Lamp presence detection circuit

connection (shaded area)

When the SD pin exceeds 2.0V (approximately 150mV of hysterisis is included to increase noise immunity),

signaling either a lamp fault or lamp removal, the oscillator is disabled, both gate driver outputs are pulled low,

and the chip is put into the micropower mode. Since a lamp fault would normally lead to a lamp exchange, when

a new lamp is inserted into the fixture, the SD pin would be pulled back to near the ground potential. Under these

conditions a reset signal would restart the chip from the beginning of the control sequence, as shown in the timing

diagram in Figure 13.

CT

4

SD

2

CPH

8

LO

15

HO-VS

15

Restart

RUN mode

SD mode

Figure 13: SD pin fault and auto restart

Thus, for a lamp removal and replacement, the ballast automatically restarts the lamp in the proper manner,

maximizing lamp life and minimizing stress on the power MOSFETs or IGBTs.