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Registered Member #1497
Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801
Well, I'm building a 7 band spectrum analyzer out of LM3915's and LM358's for bandpass filters. The way the LM3915 performs is that it limits the max current coming out of all 10 LED outputs depending on external resistors, in my case, the most all 10 LEDs will consume is 60ma. The LM3915 also limits the max current a single LED can consume, in my case, 15ma. In order for the circuit to work with 18-20 V input I have to use a resistor to drop the voltage, I'm using a 5W 270ohm ceramic resistor.
Now under typical conditions, about 1 watt of power is dissipated bringing the resistor to about 100degF, or 38degC, and there would be 7 of these resistors in the case in total. My question is whether or not I should heatsink the whole lot of these resistors, or if they can be freestanding without any overheating problems.
Registered Member #15
Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068
aonomus wrote ...
Well, I'm building a 7 band spectrum analyzer out of LM3915's and LM358's for bandpass filters. The way the LM3915 performs is that it limits the max current coming out of all 10 LED outputs depending on external resistors, in my case, the most all 10 LEDs will consume is 60ma. The LM3915 also limits the max current a single LED can consume, in my case, 15ma. In order for the circuit to work with 18-20 V input I have to use a resistor to drop the voltage, I'm using a 5W 270ohm ceramic resistor.
Now under typical conditions, about 1 watt of power is dissipated bringing the resistor to about 100degF, or 38degC, and there would be 7 of these resistors in the case in total. My question is whether or not I should heatsink the whole lot of these resistors, or if they can be freestanding without any overheating problems.
What kind of cooling does the case have? If you have fan cooling, than it probably won't be a problem.
Depends on size of case, type of case, airflow going into and out of the case, etc...
If its a closed case (no airflow), than heatsinks don't do anything.
Registered Member #1497
Joined: Thu May 22 2008, 05:24AM
Location: Toronto, Ontario, Canada
Posts: 801
Since the resistors will generate a fair bit of heat over time, I'm probably going to use a fan to give enough airflow to cool things down. I haven't decided on an enclosure yet,
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Sandstone/Ceramic resistor heat dissipation
