Hi,
I am trying to calculate the resistor value for this diode in attachment, but the calculation gives result in hundreds not in thousand ohms...
I am trying to build a Aleph J and my transfo will gives 20 V. The BOM says the R should be between 3K and 5K so i am puzzled...
any help please ?
I am trying to calculate the resistor value for this diode in attachment, but the calculation gives result in hundreds not in thousand ohms...
I am trying to build a Aleph J and my transfo will gives 20 V. The BOM says the R should be between 3K and 5K so i am puzzled...
any help please ?
Hi. What role this led will perform? Just indication of power is on ? If used just for indication, calculation simple : dc voltage you have - led forward voltage (max 4v) x led current. 20V ac rectified is roughly 28V dc , minus 4 volts led , so 20V for resistor divide by lets say 5ma ( modern leds are very bright ). 20 : 0,005 = 4000 ohms . Datasheet specifies max current , which you should not exceed , but no minimum , so you may have enough brightness event at 1ma with some leds, and 20k resistor in that case.
Thanks,
my diode says 3.4 V and 20mA... so should be around 1230 ohms. But the FirstWatt Pass Aleph J BOM rev D says between 3K and 5K, and the build guide https://diyalephj.blogspot.com/ seems to have chosen 4.75K
How shall i understand it ?
1230 is a min ? and more will decrease the brightness ?
You do NOT want the maximum 20mA on any modern LED as a pilot-light. It will burn your eyes. (Or maybe the resistor...)
3k to 5k is probably fine. In dark rooms even 22k at 28V is "too bright!" for some loud LEDs. Yes, start with a large-number resistor and only change it if too dim (or still too bright).
3k to 5k is probably fine. In dark rooms even 22k at 28V is "too bright!" for some loud LEDs. Yes, start with a large-number resistor and only change it if too dim (or still too bright).