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If you choose suitable ultrabright LEDs , there is no need to use 40 mA. I have over 10 thousand LEDs all over 16,000 mcd at 20 mA which is painfully bright for close indicator but works well 100 ...
Answer
#3: Post edited
by
TonyStewart
·
2023-10-07T00:25:13Z (7 months ago)
- If you choose suitable ultrabright LEDs , there is no need to use 40 mA. I have over 10 thousand LEDs all over 16,000 mcd at 20 mA which is painfully bright for close indicator but works well 100 m away. They are also all matched brightness and Vf within 10%, but I ordered these special for a high volume user. Otherwise, you can get very wide tolerances from batch to batch from unknown sources.
- Most uC now are using advanced 74ALCxx type CMOS which has a nominal driver impedance of around 22 ohms +/- 50%.Ro= Vol/Io
- This is more than the internal resistance of a small 5mm (15 ohm) or 50 mW SMD LED so that you can drive it directly from the uC with a series R if you know your LDO is 1 or 2% accurate.
- I would choose ultrabright white 5mm LED's 16 Cd @ 20 mA and run them at 5 mA and add a series R something like 50 ohms. But I would do a tolerance stackup calculation.
- Most good 5mm white LEDs these days will be 2.9V at 11 mA, so I don't know what you have. Then 3.0 to 3.1 at 20mA rating.
- If you choose suitable ultrabright LEDs , there is no need to use 40 mA. I have over 10 thousand LEDs all over 16,000 mcd at 20 mA which is painfully bright for close indicator but works well 100 m away. They are also all matched brightness and Vf within 10%, but I ordered these special for a high volume user. Otherwise, you can get very wide tolerances from batch to batch from unknown sources.
- Most uC now are using advanced 74ALCxx type CMOS which has a nominal driver impedance of around 22 ohms +/- 50%.Ro= Vol/Io
- This is more than the internal resistance of a small 5mm (15 ohm) or 50 mW SMD LED so that you can drive it directly from the uC with a series R if you know your LDO is 1 or 2% accurate.
- Using your LED measurement of 3.24@11mA for [ this simulation](https://tinyurl.com/ywplsape).
- I would choose ultrabright white 5mm LED's 16 Cd @ 20 mA and run them at 5 mA and add a series R something like 50 ohms. But I would do a tolerance stackup calculation.
- Most good 5mm white LEDs these days will be 2.9V at 11 mA, so I don't know what you have. Then 3.0 to 3.1 at 20mA rating.
#2: Post edited
by
TonyStewart
·
2023-10-07T00:19:45Z (7 months ago)
- If you choose suitable ultrabright LEDs , there is no need to use 40 mA. I have over 10 thousand LEDs all over 16,000 mcd at 20 mA which is painfully bright for close indicator but works well 100 m away. They are also all matched brightness and Vf within 10%, but I ordered these special for a high volume user. Otherwise, you can get very wide tolerances from batch to batch from unknown sources.
Most uC now are using advanced 74ALCxx type CMOS which has a nominal driver impedance of around 22 ohms +/- 50%. This is more than the internal resistance of a small 5mm or 50 mW SMD LED so that you can drive it directly from the uC if you know your LDO is 1 or 2% accurate.- I would choose ultrabright white 5mm LED's 16 Cd @ 20 mA and run them at 5 mA and add a series R something like 50 ohms. But I would do a tolerance stackup calculation.
- Most good 5mm white LEDs these days will be 2.9V at 11 mA, so I don't know what you have. Then 3.0 to 3.1 at 20mA rating.
- If you choose suitable ultrabright LEDs , there is no need to use 40 mA. I have over 10 thousand LEDs all over 16,000 mcd at 20 mA which is painfully bright for close indicator but works well 100 m away. They are also all matched brightness and Vf within 10%, but I ordered these special for a high volume user. Otherwise, you can get very wide tolerances from batch to batch from unknown sources.
- Most uC now are using advanced 74ALCxx type CMOS which has a nominal driver impedance of around 22 ohms +/- 50%.Ro= Vol/Io
- This is more than the internal resistance of a small 5mm (15 ohm) or 50 mW SMD LED so that you can drive it directly from the uC with a series R if you know your LDO is 1 or 2% accurate.
- I would choose ultrabright white 5mm LED's 16 Cd @ 20 mA and run them at 5 mA and add a series R something like 50 ohms. But I would do a tolerance stackup calculation.
- Most good 5mm white LEDs these days will be 2.9V at 11 mA, so I don't know what you have. Then 3.0 to 3.1 at 20mA rating.
#1: Initial revision
by
TonyStewart
·
2023-10-07T00:18:22Z (7 months ago)
If you choose suitable ultrabright LEDs , there is no need to use 40 mA. I have over 10 thousand LEDs all over 16,000 mcd at 20 mA which is painfully bright for close indicator but works well 100 m away. They are also all matched brightness and Vf within 10%, but I ordered these special for a high volume user. Otherwise, you can get very wide tolerances from batch to batch from unknown sources. Most uC now are using advanced 74ALCxx type CMOS which has a nominal driver impedance of around 22 ohms +/- 50%. This is more than the internal resistance of a small 5mm or 50 mW SMD LED so that you can drive it directly from the uC if you know your LDO is 1 or 2% accurate. I would choose ultrabright white 5mm LED's 16 Cd @ 20 mA and run them at 5 mA and add a series R something like 50 ohms. But I would do a tolerance stackup calculation. Most good 5mm white LEDs these days will be 2.9V at 11 mA, so I don't know what you have. Then 3.0 to 3.1 at 20mA rating.