Why are these LED current limiting resistors so big?
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I'm looking at the charging circuit for a lithium ion battery that was made by Adafruit. Here's an excerpt:
If there's a 5V rail from the USB port and a 470 Ohms resistor, is that limiting the current through the LED to 6 mA just to keep the brightness low? The datasheet for the charger has 470 Ohms resistors in the reference design too. I'm just not sure why.
led battery-charging current-limiting
asked yesterday
D. PatrickD. Patrick
249310
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add a comment |
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I'm looking at the charging circuit for a lithium ion battery that was made by Adafruit. Here's an excerpt:
If there's a 5V rail from the USB port and a 470 Ohms resistor, is that limiting the current through the LED to 6 mA just to keep the brightness low? The datasheet for the charger has 470 Ohms resistors in the reference design too. I'm just not sure why.
led battery-charging current-limiting
asked yesterday
D. PatrickD. Patrick
249310
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3
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Modern LEDs are quite efficient, and the application here is just a status indicator, not trying to light up a room. Why would you waste more power than you need?
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– Dave Tweed♦
yesterday
2
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If it's just an indicator, you only need it to be visibly on, and for most LEDs 5mA or so is more than enough for that.
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– Hearth
yesterday
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You may find some useful details on LED indicators here, electronics.stackexchange.com/q/378129/117785
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– Ale..chenski
yesterday
add a comment |
$begingroup$
I'm looking at the charging circuit for a lithium ion battery that was made by Adafruit. Here's an excerpt:
If there's a 5V rail from the USB port and a 470 Ohms resistor, is that limiting the current through the LED to 6 mA just to keep the brightness low? The datasheet for the charger has 470 Ohms resistors in the reference design too. I'm just not sure why.
led battery-charging current-limiting
asked yesterday
D. PatrickD. Patrick
249310
$endgroup$
I'm looking at the charging circuit for a lithium ion battery that was made by Adafruit. Here's an excerpt:
If there's a 5V rail from the USB port and a 470 Ohms resistor, is that limiting the current through the LED to 6 mA just to keep the brightness low? The datasheet for the charger has 470 Ohms resistors in the reference design too. I'm just not sure why.
led battery-charging current-limiting
led battery-charging current-limiting
asked yesterday
D. PatrickD. Patrick
249310
asked yesterday
D. PatrickD. Patrick
249310
asked yesterday
D. PatrickD. Patrick
249310
asked yesterday
D. PatrickD. Patrick
249310
asked yesterday
D. PatrickD. Patrick
249310
249310
3
$begingroup$
Modern LEDs are quite efficient, and the application here is just a status indicator, not trying to light up a room. Why would you waste more power than you need?
$endgroup$
– Dave Tweed♦
yesterday
2
$begingroup$
If it's just an indicator, you only need it to be visibly on, and for most LEDs 5mA or so is more than enough for that.
$endgroup$
– Hearth
yesterday
$begingroup$
You may find some useful details on LED indicators here, electronics.stackexchange.com/q/378129/117785
$endgroup$
– Ale..chenski
yesterday
add a comment |
3
$begingroup$
Modern LEDs are quite efficient, and the application here is just a status indicator, not trying to light up a room. Why would you waste more power than you need?
$endgroup$
– Dave Tweed♦
yesterday
2
$begingroup$
If it's just an indicator, you only need it to be visibly on, and for most LEDs 5mA or so is more than enough for that.
$endgroup$
– Hearth
yesterday
$begingroup$
You may find some useful details on LED indicators here, electronics.stackexchange.com/q/378129/117785
$endgroup$
– Ale..chenski
yesterday
3
3
$begingroup$
Modern LEDs are quite efficient, and the application here is just a status indicator, not trying to light up a room. Why would you waste more power than you need?
$endgroup$
– Dave Tweed♦
yesterday
$begingroup$
Modern LEDs are quite efficient, and the application here is just a status indicator, not trying to light up a room. Why would you waste more power than you need?
$endgroup$
– Dave Tweed♦
yesterday
2
2
$begingroup$
If it's just an indicator, you only need it to be visibly on, and for most LEDs 5mA or so is more than enough for that.
$endgroup$
– Hearth
yesterday
$begingroup$
If it's just an indicator, you only need it to be visibly on, and for most LEDs 5mA or so is more than enough for that.
$endgroup$
– Hearth
yesterday
$begingroup$
You may find some useful details on LED indicators here, electronics.stackexchange.com/q/378129/117785
$endgroup$
– Ale..chenski
yesterday
$begingroup$
You may find some useful details on LED indicators here, electronics.stackexchange.com/q/378129/117785
$endgroup$
– Ale..chenski
yesterday
add a comment |
1 Answer
1
active
oldest
votes
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The MCP73831 datasheet specifies a maximum source/sink current on the STAT pin of 35 mA and 25 mA respectively - so if the designer wanted brighter LEDs she could use lower-value resistors without worrying about overloading the output drivers on the charge controller IC. Higher currents would eat into the current available for charging, but not really to a significant extent.
So yes, I think the reason is simply that 6 mA is plenty bright enough for a status LED. Some would even say it's too bright, especially with modern high-efficiency LEDs.
answered yesterday
pericynthionpericynthion
4,253929
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add a comment |
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1 Answer
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1 Answer
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$begingroup$
The MCP73831 datasheet specifies a maximum source/sink current on the STAT pin of 35 mA and 25 mA respectively - so if the designer wanted brighter LEDs she could use lower-value resistors without worrying about overloading the output drivers on the charge controller IC. Higher currents would eat into the current available for charging, but not really to a significant extent.
So yes, I think the reason is simply that 6 mA is plenty bright enough for a status LED. Some would even say it's too bright, especially with modern high-efficiency LEDs.
answered yesterday
pericynthionpericynthion
4,253929
$endgroup$
add a comment |
$begingroup$
The MCP73831 datasheet specifies a maximum source/sink current on the STAT pin of 35 mA and 25 mA respectively - so if the designer wanted brighter LEDs she could use lower-value resistors without worrying about overloading the output drivers on the charge controller IC. Higher currents would eat into the current available for charging, but not really to a significant extent.
So yes, I think the reason is simply that 6 mA is plenty bright enough for a status LED. Some would even say it's too bright, especially with modern high-efficiency LEDs.
answered yesterday
pericynthionpericynthion
4,253929
$endgroup$
add a comment |
$begingroup$
The MCP73831 datasheet specifies a maximum source/sink current on the STAT pin of 35 mA and 25 mA respectively - so if the designer wanted brighter LEDs she could use lower-value resistors without worrying about overloading the output drivers on the charge controller IC. Higher currents would eat into the current available for charging, but not really to a significant extent.
So yes, I think the reason is simply that 6 mA is plenty bright enough for a status LED. Some would even say it's too bright, especially with modern high-efficiency LEDs.
answered yesterday
pericynthionpericynthion
4,253929
$endgroup$
The MCP73831 datasheet specifies a maximum source/sink current on the STAT pin of 35 mA and 25 mA respectively - so if the designer wanted brighter LEDs she could use lower-value resistors without worrying about overloading the output drivers on the charge controller IC. Higher currents would eat into the current available for charging, but not really to a significant extent.
So yes, I think the reason is simply that 6 mA is plenty bright enough for a status LED. Some would even say it's too bright, especially with modern high-efficiency LEDs.
answered yesterday
pericynthionpericynthion
4,253929
answered yesterday
pericynthionpericynthion
4,253929
answered yesterday
pericynthionpericynthion
4,253929
answered yesterday
pericynthionpericynthion
4,253929
4,253929
add a comment |
add a comment |
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$begingroup$
Modern LEDs are quite efficient, and the application here is just a status indicator, not trying to light up a room. Why would you waste more power than you need?
$endgroup$
– Dave Tweed♦
yesterday
2
$begingroup$
If it's just an indicator, you only need it to be visibly on, and for most LEDs 5mA or so is more than enough for that.
$endgroup$
– Hearth
yesterday
$begingroup$
You may find some useful details on LED indicators here, electronics.stackexchange.com/q/378129/117785
$endgroup$
– Ale..chenski
yesterday