[sdiy] IC Temperature

Mike Beauchamp list at mikebeauchamp.com
Tue Aug 4 23:15:59 CEST 2020

On 8/3/20 8:11 AM, Mattias Rickardsson wrote:
> Hi Mike,

> Around 50 degrees is what I'm experiencing as well on TL074s on densely 
> mounted double-sided SMT designs at +/-12 V supplies. At first quite 
> unexpected since we're used to old hole-mount synth circuits not going 
> very warm at all, but when measuring the current draw and summing up the 
> expected supply currents of all circuits it seems to be correct. I guess 
> the density is the main reason here, both having the heat sources much 
> closer to each other AND having much smaller area & less material for 
> dissipating the heat.
> Btw, TL064s are hardly visible in the heat camera - they pull so little 
> current. Applying TL064 op-amps where noise & slewrate aren't critical 
> factors is an important trick in designs where power & heat & cost are.

> It would be very hard to actually measure the temperature on the hottest 
> spot on (or even in) an IC, so from a design perspective I just assume 
> that "Operating Temperature" refers to the surrounding air and PCB - and 
> then the internal IC temperature lands on some reasonably well-known 
> temperature above this, since the delta temperature is given by the 
> expected power draw of the IC. Please do chime in, if someone can 
> correct or clarify this! :-)
> /mr

Thanks Matthias, I appreciate the reply and reassurance. Interesting 
about the TL064, I've never heard of the chip before. It might be useful 
in some CV-summing and other non-audio sections, although taking a squiz 
at the datasheet it can only handle within +/-4V of each rail? (so +/- 
8V on your case with the 12V bipolar supply?). It's easy enough to drop 
in on my PCB to see. I don't need to reduce the current and temperature 
now that I am no longer worried about it, but it would be nice to be a 
bit easier on the power supply. I am using TL074's pretty much 
everywhere to keep my BOM simple, and I have hundreds of them on-hand. 
But clearly they use a lot more power than I expected!


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