Re: Canon PowerShot A710 IS backlight

On Mon, 16 Jul 2007 17:08:03 +1000, Franc Zabkar
<fzabkar@xxxxxxxxxxxxxxxxx> put finger to keyboard and composed:

On 15 Jul 2007 23:07:24 GMT, u_1061771155@xxxxxxx (Remove _ for valid
address) put finger to keyboard and composed:

The driver circuit is somewhat hard to trace. (Anyone know of
a source for a schematic... ;-) So far I've traced it back
to a SOT23 sized 5-pin thing:

'large'
_ _____ _ inductor
drive?->--|_| |_|b-------@@@@@-----+------->
| XH |_ _|_ backlight
| 6 |_|GND 'tiny' ___ ?-->
_| G4 |_ cap |
a|_|_____|_|Vcc GND

I think "a" connects to "b" under the chip.

Could "a" connect to the junction of the cap and inductor, in which
case the chip may be a self contained, fixed voltage, PWM regulator
with integrated MOSFET, flywheel diode, oscillator, and error amp. "A"
may be the feedback pin for the error amp, ie this pin may sense the
regulator's output voltage. The "drive" may be an on/off pin.

Do you measure a diode drop between GND and "b" (anode to GND)? If so,
then this could be an internal flywheel diode.

- Franc Zabkar

I believe that the backlight could be a white LED type. This would
make the chip a down-converter which is consistent with the placement
of the inductor and an [internal] flywheel diode. Or maybe it's some
kind of switchmode constant current source ???

I haven't found any info on the A710, but FWIW the PowerShot A200/A100
both have LED backlights:
http://www.canon.com/camera-museum/tech/report/200207/report.html

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
.

Relevant Pages

  • Re: Flash in 72 pin simm package?
    ... put finger to keyboard and composed: ... 72 pin. ... standard board, but I've looked around without finding them anywhere. ...
    (sci.electronics.components)
  • Re: Flash in 72 pin simm package?
    ... put finger to keyboard and composed: ... 72 pin. ... flash ROMs, and one E28F320, which is a 4MB flash ROM. ...
    (sci.electronics.components)
  • Re: Lexmark 3200 MFP DC Power Connector Pin Out
    ... put finger to keyboard and composed: ... Can anyone help me with the pin-out for the connector or point me a ... could someone explain how I might figure out the pin ...
    (sci.electronics.repair)
  • Re: Canon PowerShot A710 IS backlight
    ... with integrated MOSFET, flywheel diode, oscillator, and error amp. ... may be the feedback pin for the error amp, ie this pin may sense the ... Do you measure a diode drop between GND and "b"? ...
    (sci.electronics.repair)