I'm having a look at a flashing led driver circuit to see if I can work out how it works. There are three components that I am having trouble identifying. Other than googling the numbers on the IC, I don't know how to narrow it down. Could you help me identify them (or even better walk me through how to do it myself)?

U1 - looks like a DFN8 3mmx2mm with 4 connections on the short edges. The numbers/letters on it are "BY0 102 6T". I'm pretty sure this is a microcontroller. Appears to have power supplied on pin 1 and ground to pin 8.

Q1 - looks like a SOT-23 with three leg. It is marked "1GW 25". My guess is that this is a fairly simple transistor of some sort.

Q2 - looks like a DFN6 2mm square with three connectors at opposite sides. It is marked on three lines as:
. .
109G (could be 1096)
.. --
My guess is that this is a constant current driver. The LED is permanently connected to +v and this is downstream of the LED (connected to the -ve cathode). The 6 pins appear to be:
1 - connected to LED cathode
2
3 - connected to LED cathode
4 - connected to GND
5 - connected to a pin of U1 (microcontroller control signal?)
6 - connected to LED cathode

Appreciate the help.

 

Please post a photograph.

 

Here we go...

 

it may be a SM version of a Lm3909

http://www.jaycar.co.uk/images_uploaded/LM3909.PDF

 

it may be a SM version of a Lm3909
http://www.jaycar.co.uk/images_uploaded/LM3909.PDF

Looks a close (or exact) match for the pinout. I suspect that it is not quite the right IC.

The circuit alternates between low and high (never off). There are no capacitors on the board. Just the three components I am trying to ID, two resistors and an LED (Cree XP-C).

Based on runtime and battery capacity, I believe the high setting draws about 200mA in high mode and about 80mA in low mode.

 

Could U1 be some sort of PIC? It appears to have three programming pads (in addition to Vcc and Gnd).

I've attached a picture of the circuit. The red line is permanently connected to Vcc and the light blue to Gnd.

 

I agree, it looks to be some type of microcontroller with 3 programming pads.

It could be a PIC 12Fxxx series, the 3 programming pads correspond to MCLR, ICSPC, ICSPD.

Also the top pins 1 and 8 correspond correctly to Vdd and Gnd.

You could probably re-program it to make any flashing operation you want! Like a little PIC LED development board.

Looking at the circuit operation pin 5 PIC output drives the main FET Q3 on, and the 1 ohm resistor sets the current as a linear constant current regulator. If the voltage on the 1 ohm resistor reaches >0.6v it turns Q1 NPN on, which reduces the gate voltage to Q3. So the whole circuit after the PIC is a dumb linear current regulator at 0.6A.

If the PIC sets current at two levels 80mA and 200mA it must PWM control the 600mA constant current LED with two different duty cycles.

 

Ah ha, of course! A MOSFET constant current driver. I didn't realise that FETs could come in DFN packages.

Many thanks. =)