IR21571 datasheet(13/17 Pages) IRF

13 / 17 page

IR21571(S)

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Figure 11: VDC lead fault and auto restart

Lamp Presence Detection and

Automatic Restart

The second protection lead, SD, is used for both

unlatched shutdown and automatic restart functions.

The SD lead would normally be connected to an

external circuit which senses the presence of the

lamp (or lamps), as shown in Figure 12.

When the SD lead exceeds 2.0V (approximately

150mV of hysteresis 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 lead would be pulled

back to near the ground potential. Under these

Figure 12: Lamp presence detection circuit

connection (shaded area)

conditions a reset signal would restart the chip from

the beginning of the control sequence, as shown in

the timing diagram in Figure 13.

Figure 13: SD lead fault and auto restart

RUN mode

Low VDC

VDC

CPH

HO-VS

Restart

VDC

CPH

RPH

RUN

COM

VCC

+ V

BUS

+ rectified

AC Line

BUS return

BOOT

Supply

VCC

RES

GHS

GLS

BLOCK

SNUBBER

RUN mode

SD mode

CPH

HO-VS

Restart

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