advertisement


Got Fleas?

You can try these two items together:
1) reduce input filter from 10/3u3 to 1K / 47uF electrolytic (reduces voltage drop here)
2) Change 7812 to 7809.

This is very marginal - if the drop-out voltage across the 7805 is less than say 2.5v then you may just need to bypass the input filter. Try a 10ohm resistor instead, so that the input to the 7809 is fed form your available 15v supply by 10ohm/47uF (or larger cap)
 
You can try these two items together:
1) reduce input filter from 10/3u3 to 1K / 47uF electrolytic (reduces voltage drop here)
2) Change 7812 to 7809.

This is very marginal - if the drop-out voltage across the 7805 is less than say 2.5v then you may just need to bypass the input filter. Try a 10ohm resistor instead, so that the input to the 7809 is fed form your available 15v supply by 10ohm/47uF (or larger cap)
Thx for the tips!
I'm not sure where the 7805 came in to the discussion.
 
Sorry, typo! 7809.

AD797 has a datasheet minimum supply of 10v. 7809 + the led reference gives about 10.9v supply to the opamp.
 
Sorry, typo! 7809.
AD797 has a datasheet minimum supply of 10v. 7809 + the led reference gives about 10.9v supply to the opamp.
Gotcha ...
It's been a while since the Flea was updated. During this timespan AD (and other manufs) have released quite a few newer models. For audio ckts, such as I/V or headphone amps, these new devices are quite good. They run on lower pwr (no doubt due to reqs. for portable devices) + they're substantially more economical.
Any thoughts as to using one of the newer OPAs?
 
Another thing I forgot to mention was heat generated by the 797. For certain apps (not clocks) where, say, 50-60mA was what was required, I noted the OPA getting a bit warm. And I've noted this same OPA generally running warm in other ckts apps, like I/V. I'm assuming this is normal.
 
50mA from the 797 alone in this circuit is way too much. It will drive it, but that's a monstrous 600mw dispation in the IC and reduced performance too. You need to use an added pass transistor.

Given your very low supply rail and higher curent requirement, I think a superreg is more suitable. These require about 5v minimum dropout and will obviously deliver rather more current - 300-500mA without a problem.
 


advertisement


Back
Top