op amp power supply question

[yougarage]

hello!
Is it bad practice to supply an op-amp trough a resistor?
the circuit is shown in the picture, it's an analog input buffer.
I just want to limit the supply voltage without using a regulator.
could the amplifier behave worse than a direct supply?

resistor = 150 ohm
op amp = tlv2371 (max supply allowed 16 v)
zener = 15 v
vcc = 12 - 16 v
input range = 0 to 12 v

 

[kcyang]

Op-amp supply like to see low impedance voltage source. You can do that by adding one or more capacitor to pin-8 of the op-amp. You can use 0.1uF in parallel with another 10uF capacitor. If the op-amp output load is very larger, there will be voltage drop accross the 150 ohm resistor which will reduce the input supply voltage. This is something to watchout for.

 

[LvW]

For my opinion, this solution makes sense only if the supply voltage exhibits fluctuations.
But don`t forget the modified bias conditions due to single supply!

 

[yougarage]

yes, the supply voltage is usually about 13.5 volt, but it could occasionally reach peaks of 16 - 17 volt.
could you tell me more about the modified bias? I'm a novice so I think I'm missing something...

 

[LvW]

yes, the supply voltage is usually about 13.5 volt, but it could occasionally reach peaks of 16 - 17 volt.
could you tell me more about the modified bias? I'm a novice so I think I'm missing something...

This subject has been discussed several times - also in this forum. And there a lot of papers dealing with single supply in the internet (search for opamp single supply circuits)
Nevertheless, I like to give you some information:
Normally, opamps are designed for double supply - which means: operating point in the middle at 0 volts.
This quiescent voltage at the output (without any input, and forgetting about parasitics like offset) allows the input voltages referenced to zero.
In your case, with single supply, the quiescent dc voltage at the output should be 50% of the opamp supply (at the opamp terminal). Thus, the output voltage can swing to both sides equally.
But this requires that both input dc voltages also at 50% supply. Thus, you need a voltage divider that produces this bias for the non-inv. input. The inv. input gets this bias automatically due to 100% feedback. In order not to disturb this bias, your input signal to be buffered must be coupled through a suitable capacitor.
OK?

 

[yougarage]

perfect, thank you!