Re: High brightness white LEDs damaged by custom switcher


"D from BC" <myrealaddress@xxxxxxxxx> wrote in message
news:v9ll33hit2un763mtr1mkgaqec9j5rsc7i@xxxxxxxxxx
On Fri, 4 May 2007 02:21:33 -0400, "Paul E. Schoen" <pstech@xxxxxxxxx>
wrote:

Some of you may recall my discussions about a 12 VDC powered switching
converter to drive strings of 7 or 13 high power white LEDs, in posts
from
1/5/07 (transients), 2/22/07 (Inductor gaps), and 3/10/07 (TC1410 driver
problems). We built the circuit, found a few problems, then tested it and
it seemed OK. Basically this is a switching boost regulator using a 10 uH
inductor and a PIC with PWM at 100 kHz. I did a lot of LTSpice
simulations
as well.

[snip]

However, someone else was adamant that a PIC would never be as
reliable as a pure analog design, and suggested an off-the shelf Linear
Tech or other part, which would involve a complete redesign and loss of
the
dual brightness feature.

Thanks,

Paul


How about asking Microchip Inc. if PIC's are just as reliable as
dedicated smps PWM controller IC's.
D from BC

I'm sure they would "stand by their chips", but I think the concern was
that the software could go awry and damage could be done before it could
react. That's why I am considering a separate fail-safe mechanism, such as
a fast acting fuse, or an NPN transistor that would turn on, when the
voltage on the 1 ohm sense resistor reached Vbe, and turn off the MOSFET.
Maybe an SCR would be better, requiring a complete power down to reset.

Paul


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