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 4 hours ago
D. PatrickD. Patrick
237310
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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 4 hours ago
D. PatrickD. Patrick
237310
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1
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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♦
4 hours ago
1
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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
4 hours ago
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 4 hours ago
D. PatrickD. Patrick
237310
$endgroup$
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 4 hours ago
D. PatrickD. Patrick
237310
asked 4 hours ago
D. PatrickD. Patrick
237310
asked 4 hours ago
D. PatrickD. Patrick
237310
asked 4 hours ago
D. PatrickD. Patrick
237310
asked 4 hours ago
D. PatrickD. Patrick
237310
237310
1
$begingroup$
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♦
4 hours ago
1
$begingroup$
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
4 hours ago
add a comment |
1
$begingroup$
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♦
4 hours ago
1
$begingroup$
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
4 hours ago
1
1
$begingroup$
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♦
4 hours ago
$begingroup$
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♦
4 hours ago
1
1
$begingroup$
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
4 hours ago
$begingroup$
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
4 hours ago
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 4 hours ago
pericynthionpericynthion
4,138929
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add a comment |
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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 4 hours ago
pericynthionpericynthion
4,138929
$endgroup$
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 4 hours ago
pericynthionpericynthion
4,138929
$endgroup$
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 4 hours ago
pericynthionpericynthion
4,138929
$endgroup$
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 4 hours ago
pericynthionpericynthion
4,138929
answered 4 hours ago
pericynthionpericynthion
4,138929
answered 4 hours ago
pericynthionpericynthion
4,138929
answered 4 hours ago
pericynthionpericynthion
4,138929
4,138929
add a comment |
add a comment |
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1
$begingroup$
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♦
4 hours ago
1
$begingroup$
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
4 hours ago