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I’m using the LM7321MAX operational amplifier to supply a 12V digital signal from a 5V source. For the op-amp supply voltage: is it better to use something close/equal to my output value (like 12V) or further away (like 22V)? I know the internals of an op amp are mostly BJTs so am wondering if I’ll draw the same supply current in either case, with the 20V variant therefore using more power. Thinking the 20V->12V will happen across those BJTs
Thanks for your help!
There are a number of curves showing the supply current for different supply voltages and for different temperatures and common-mode voltages, so you can predict the typical supply current. It increases with increasing supply voltage, but fairly gently.
As far your your load current, you'll need enough swing to satisfy your actual requirements, and again the datasheet provides a great number of curves. Once you have enough voltage to (worst-case) supply your required output swing, then additional voltage simply results in more power dissipation in the chip, since the additional output current is drawn directly from the power supply terminals (and possibly a bit more).
The total current drawn is the sum of the two, so it's Is + k\$\cdot\$Iout(Vsupply) where k may be a bit higher than 1, and this the power dissipation in the chip is (Is \$\cdot\$ Vsupply) + k\$\cdot\$Iout(Vsupply-Vout).
This is a Rail-to-Rail output op Amp and hence CMOS, not BJT’s.
It also increases slightly with temperature due to ambient or load current.
Load current is up to you with the max currents specified. VI drop in the output stage determines the self heating power.
