A8437 Просмотр технического описания (PDF) - Allegro MicroSystems

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A8437

Mobile Phone Xenon Photoflash Capacitor Charger with IGBT Driver

Allegro MicroSystems 

A8437

Mobile Phone Xenon Photoflash Capacitor Charger

with IGBT Driver

higher, TRIGGER1 is allowed to activate the IGBT

gate driver (and thereby fire the flash).

The capacitor CTGR1 and resistor RTGR1 form an

integrator for light exposure. When the flash fires,

bright light bounces back from subject and enters the

phototransistor. In example A below, the flash termi-

nates after just 30 μs, without fully discharging the

photoflash capacitor.

If the subject is far away, the reflected light intensity

is lower, so the phototransistor current is also lower.

In example B below, the flash stays on for longer time

(60 μs) and discharges more energy from the photo-

flash capacitor.

Using a larger CTGR1 causes the time constant of the

integrator to increase, so a longer pulse is required

before the flash is terminated.

Example A

VOUT

C1

C2

C3

C1

C4

Common Parameters

Symbol Parameter Units/Division

C1

VOUT

50 V

C2

VTRIGGER2

1V

C3

VTRIGGER1

5V

C4

VGATE

5V

t

time

20 μs

t

Example B

VTRIGGER2

C2

C3

VTRIGGER1

VGATE

C4

VOUT

C1

VTRIGGER2

C2

C2

VTRIGGER1

C3

C3

C1

VGATE

C4

C4

t

Allegro MicroSystems, Inc.

14

115 Northeast Cutoff

Worcester, Massachusetts 01615-0036 U.S.A.

1.508.853.5000; www.allegromicro.com

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