TASKLED - Smart LED drivers
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V1.01 of the firmware released. This version ships configured for 380mA (or 500mA for uFlex_ovd version) and the user can reconfigure it back and forth from 750mA to 380mA (or 1000mA to 500mA for the uFlex_ovd version). See the manual below for a description of how to reconfigure uFlex.
You can download the instruction manual here (the firmware version number is written on the back of the uFlex PCB):
for V0.05 and V0.06 of the firmware uFlex.pdf (V1.01 of the manual 190kbytes).
for V1.00 and V1.01 of the firmware uFlex.pdf (V2.00 of the manual 190kbytes).
uFlex first prototype (Aug 2003)
Runs from 2.7V to 20V. Below the Vf of the Luxeon the driver goes into direct drive - the only loss is through a low resistance MOSFET and the 4mA or so for the AVR uController. The other contributing loss is the reverse battery protection diode and two EMI reducing ferrite beads (all of which can be bypassed for extremely power sensitive applications).
Can drive a single 1W Luxeon or 2 series connected 1W Luxeons (350mA nominal drive).
Can drive a single 5W Luxeon (with software altered to provide 700mA drive).
Drive current maximum is adjustable (set in the firmware).
Provides a dimming function - prolongs battery life.
Here's a picture of the original prototype in action. The scope shows the PWM gate drive signal, the multimeter the voltage across the Luxeon (the bright thing in the middle of the pic) and the prototype itself (the thing in the panavise with all the crocodile clips connected to it). With a 5V input, no protection diode, no ferrite beads and a 1W Luxeon load, I measured over 95% efficiency - very impressive.
Status Updates:
23 Sep
Efficiency tests.
The following tests was with a
nominal 1W Load Luxeon load. This was on the first prototype with no
series protection diode and no series ferrite beads. So, the efficiency is a bit
better than the production boards.
| Input Voltage (V) | Input Current (A) | Power (W) | Output Power (W) | Efficiency |
| 3.45 | 0.342 | 1.18 | 1.163 | 98.6% |
| 4.98 | 0.242 | 1.21 | 1.163 | 96.1% |
| 7.00 | 0.182 | 1.274 | 1.163 | 91.3% |
| 9.00 | 0.144 | 1.296 | 1.163 | 89.7% |
| 11.00 | 0.120 | 1.32 | 1.163 | 88.1% |
| 12.80 | 0.104 | 1.33 | 1.163 | 87.4% |
The following test was with a nominal 5W
Luxeon load. This was a second prototype board with a series protection diode
and ferrite beads in both the positive and ground input leads. This causes a
0.5V voltage drop in the input and reduces the efficiency a little. For example,
when the input voltage is 7.53V, the actual input voltage after the protection
diode and beads is actually 7.03V, which means the efficiency is actually 93.3%.
The beads and protection diode can be removed for power sensitive situations
that don't require EMI filtering and reverse battery protection.
| Input Voltage (V) | Input Current (A) | Power (W) | Output Power (W) | Efficiency |
| 7.53 | 0.680 | 5.12 | 4.58 | 89.4% |
| 7.9 | 0.656 | 5.18 | 4.64 | 90.5% |
| 8.79 | 0.602 | 5.30 | 4.75 | 89.7% |
| 9.78 | 0.541 | 5.30 | 4.75 | 89.7% |
| 11.98 | 0.443 | 5.31 | 4.75 | 89.1% |
| 13.95 | 0.382 | 5.33 | 4.75 | 88.7% |
| 16.0 | 0.335 | 5.36 | 4.75 | 88.0% |
The dimming function is now working and allows the Luxeon current to be dropped to about 7mA (the lowest output that the PWM driver can attain at 100kHz) - which provides an excellent night-light level of illumination. The current draw from 12.8V is 6mA - pretty well the steady state draw of the circuit when running.
The EEPROM routines are functioning and the current illumination level can be stored and retrieved. This allows the illumination level that was last set prior to powering down to be retrieved on power up.
The
circuit can be totally powered off by switching the input power off or it can be
electronically switched off via the single control switch. Pressing the switch
for less than 1 second puts the circuit into powerdown, pushing it again powers
it up. Pressing the switch for longer than 1 second causes the circuit to either dim
or brighten the output - toggling direction each time. In powerdown the circuit
draws 0.22mA from the 12.8V. That's 189 days to draw 1 A/Hr from the battery.
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