Hi,
I'm trying to power my arduino and power leds with 9V 200mAh rechargeable battery.
Arduino reads the value from ultrasonic sensor and writes to the leds. I mean leds brightness changing according to read value from ultrasonic sensor.
Its working properly in low values and i can see the fade fluenlty. But in high values (writing high birightness) my transistor and leds starts to heat up. Then leds gone wild and starts blinking .
How can i fix the heat and blinking in writing high values??
Add a current limit resistor to each LED. MAX continuous current is typically 20 mA.
(9V - (Vce transistor) - (Vf LED))/20mA = resistor value
Vce for Tip120 is ~1V
Vf for a Red LED usually ~2.5V, other colors high, like 3.3V
(9V - 1V - 2.5V)/.02 = 275 ohm. I'd go with 300, 330 as standard values.
You could also wire the LEDs in series instead of parallel, they could then just use 1 resistor and share the 20mA:
(9 - 1V - (2.5 x 2))/.02 = 150 ohm resistor
CrossRoads:
Vf for a Red LED usually ~2.5V, other colors high, like 3.3V
The last batch of red LEDs I bought are rated 1.7V: http://www.dipmicro.com/store/BR5379K
Although contrary to the specs, Vf rises quickly past 5mA. Most other LEDs have a more linear I-V curve.
Some 3mm round red LEDs I've had for years seem to be ~2.1V@20mA, and the red LEDs Tayda has listed all seem to be rated 2.0-2.2 Vf.
CrossRoads:
Add a current limit resistor to each LED. MAX continuous current is typically 20 mA.
(9V - (Vce transistor) - (Vf LED))/20mA = resistor value
Vce for Tip120 is ~1V
Vf for a Red LED usually ~2.5V, other colors high, like 3.3V
(9V - 1V - 2.5V)/.02 = 275 ohm. I'd go with 300, 330 as standard values.
You could also wire the LEDs in series instead of parallel, they could then just use 1 resistor and share the 20mA:
(9 - 1V - (2.5 x 2))/.02 = 150 ohm resistor
I'm really grateful. Thank you so much!!
Problem solved and there is no heat and blinking.
I ve tried 330, 220 and 100 ohm resistors and 100 is better i guess. Their brightness drop too much when i use higher resistors.
Actually i couldn't find any model or name of the leds. I tried couple of leds and I liked their brightness.
These are the leds that I found them from my tool box.
