C
Clive Mitchell
- Jan 1, 1970
- 0
I just got a cheap Chinese light that operates on three AA cells, an
external adapter or a USB feed. It has eight LEDs and I initially
assumed that it would use either a single resistor for a parallel LED
array or individual resistors per LED.
I popped the lid and noted that the eight white LEDs were in parallel,
so I popped the base and examined the circuit board expecting to see a
big resistor. Nope. It was a small surface mount device with three
pins and a tab, with a capacitor next to it. I noted the device number
and Googled it.
It's a 3.3v regulator with very low drop-out (from about 0.12v to 0.5v
depending on load), built in current limiting (0.6A) and thermal
shutdown.
As many of you will know, white LEDs are usually quite happy to draw
10-20mA at 3.3V so it seems a clever way to drive a parallel array.
Particularly given the generous 0.5W rating of the regulator package.
The regulator is an FS8854.
external adapter or a USB feed. It has eight LEDs and I initially
assumed that it would use either a single resistor for a parallel LED
array or individual resistors per LED.
I popped the lid and noted that the eight white LEDs were in parallel,
so I popped the base and examined the circuit board expecting to see a
big resistor. Nope. It was a small surface mount device with three
pins and a tab, with a capacitor next to it. I noted the device number
and Googled it.
It's a 3.3v regulator with very low drop-out (from about 0.12v to 0.5v
depending on load), built in current limiting (0.6A) and thermal
shutdown.
As many of you will know, white LEDs are usually quite happy to draw
10-20mA at 3.3V so it seems a clever way to drive a parallel array.
Particularly given the generous 0.5W rating of the regulator package.
The regulator is an FS8854.