a problem...
but perhaps not the only problem...the input offset voltage for the amp is spec'd as a maximum of 10 mV. With the gain of 33.35, that could make for worst case difference in output voltages of about +/- 3.33 Volts, or perhaps a 6.66 volt difference across 0.2 Ohms of resistance. That would be 30 Amps!
So maybe it's only 0.1 that amount, but that's still 3 A of current devoted to the parallel channels fighting each other.
for sure, remove the 0.1 Ohm resistors, as another poster suggested, and try the amp...or...measure the voltage across each 0.1 Ohm resistor...if it is anything more than 0.01 volts, you have a problem!
but perhaps not the only problem...the input offset voltage for the amp is spec'd as a maximum of 10 mV. With the gain of 33.35, that could make for worst case difference in output voltages of about +/- 3.33 Volts, or perhaps a 6.66 volt difference across 0.2 Ohms of resistance. That would be 30 Amps!
So maybe it's only 0.1 that amount, but that's still 3 A of current devoted to the parallel channels fighting each other.
for sure, remove the 0.1 Ohm resistors, as another poster suggested, and try the amp...or...measure the voltage across each 0.1 Ohm resistor...if it is anything more than 0.01 volts, you have a problem!
but perhaps not the only problem...the input offset voltage for the amp is spec'd as a maximum of 10 mV. With the gain of 33.35, that could make for worst case difference in output voltages of about +/- 3.33 Volts
Shouldn't that be 0.33 volts?
You are right...0.33 Volts...so the lower number of 3.3 Amps is really about the worst case.
Even 3.3A is death to a chip amp when sourced at, or very close to, zero volts out. With a 30V supply that's 100W of dissipation in only one of the output transistors.
So, if I understand correctly, the problem seems to be that one side has more gain than the other. I recall seeing close to 0.00V across the 0.1 ohm resistors. I'll check again and report back.
Thanks for the suggestions guys, really appreciate it!
Abraxalito, thanks for the tip on raising just one leg of the resistors. The pcb is tiny and it's very busy around the chip, but I'll give it a try.
Thanks for the suggestions guys, really appreciate it!
Abraxalito, thanks for the tip on raising just one leg of the resistors. The pcb is tiny and it's very busy around the chip, but I'll give it a try.
Not really gain...
The issue we have identified is offset voltage...it will be present all the time...if the issue were a slight gain mismatch, it wouldn't be an issue at small signals.
Remember that just 0.01 Volts across 0.1 Ohms makes 100 mA of current that does nothing useful but warm everything up
The issue we have identified is offset voltage...it will be present all the time...if the issue were a slight gain mismatch, it wouldn't be an issue at small signals.
Remember that just 0.01 Volts across 0.1 Ohms makes 100 mA of current that does nothing useful but warm everything up
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