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MC34063A as 28V LED Backlight driver?

Will Constable
Prodigy 10 points
Other Parts Discussed in Thread: MC34063A

I have been thinking about using the MC34063A to drive the white LED backlight system on and LCD.  It only requires 20-30mA but at 28V.  Brightness control via PWM would be a plus.  My questions:

 

1) I didn't find a better part on the LED driver part searcher.  The key problem was that the LED drivers I found topped out at under 20V max Vout.  Is there a better choice than MC34063A which is also relatively simple, small and cheap?

2) With MC34063A set up in boost topology, can I safely apply PWM (of, say, 100Hz) to the VCC pin in order to achieve intensity control?

 

Thanks! 

  • 0
    TI__Guru**** 165146 points

    Hello Will,

    There are few devices less expensive than the MC34063A so it is worth trying.
    The output can be switched from +28V and VCC by raising pin 5 above 1.25V and releasing pin 5 to switch back. Place a diode between the PWM signal and pin 5.
    Alternatively, The backlight can be PWM controlled by a NPN or NMOS transistor between the backlight return pin and ground. The +28V supply is constant, but the backlight current is switched.

    Regards,
    Ron Michallick