Ok,
I have an IR LED which is rated at 100mA for a <20ms 'burst'. I plan to check the sensor about 20Hz (perhaps 40) and have the LED on for a matter of 50us or so for the reading to take place.
Problem is i did not think to check the power of the resistor, i am using 0805 SMT package. They are rated at 0.125W and in order to get 100mA with a 3.7V voltage drop (5 - 1.3) i need a 39Ohm (closest value) resistor. Which makes for 0.350W
Too much, but for such a small time period (max of 10ms of a second lets say) would it be acceptable to use just one resistor, or am i going to have to stack a load of values to get a parralel one?
Thanks,
- Martyn
I have an IR LED which is rated at 100mA for a <20ms 'burst'. I plan to check the sensor about 20Hz (perhaps 40) and have the LED on for a matter of 50us or so for the reading to take place.
Problem is i did not think to check the power of the resistor, i am using 0805 SMT package. They are rated at 0.125W and in order to get 100mA with a 3.7V voltage drop (5 - 1.3) i need a 39Ohm (closest value) resistor. Which makes for 0.350W
Too much, but for such a small time period (max of 10ms of a second lets say) would it be acceptable to use just one resistor, or am i going to have to stack a load of values to get a parralel one?
Thanks,
- Martyn